MINUTH MARCO (DE)
SAMSON DANIEL (CH)
WO1996003417A1 | 1996-02-08 | |||
WO2022175211A1 | 2022-08-25 | |||
WO1996003417A1 | 1996-02-08 | |||
WO2022195111A1 | 2022-09-22 | |||
WO2016055601A1 | 2016-04-14 | |||
WO2009073809A2 | 2009-06-11 | |||
WO2019075419A1 | 2019-04-18 | |||
WO2000066258A2 | 2000-11-09 | |||
WO2021100773A1 | 2021-05-27 | |||
WO2021094518A1 | 2021-05-20 | |||
WO2017223258A1 | 2017-12-28 |
US20210309690A1 | 2021-10-07 | |||
US7273933B1 | 2007-09-25 | |||
US20080058511A1 | 2008-03-06 | |||
EP2711370A1 | 2014-03-26 | |||
US7202264B2 | 2007-04-10 | |||
US7202264B2 | 2007-04-10 | |||
US6623703B1 | 2003-09-23 | |||
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EP0130739A2 | 1985-01-09 | |||
CN107881102A | 2018-04-06 | |||
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- 1 - Bachem Holding AG BAC74623PC September 18, 2023 Claims 1. A method for the solid-phase synthesis of a target oligonucleotide OT comprising a step (b) of incubating a nucleoside or oligonucleotide, which is covalently linked to a solid support and comprises a backbone hydroxyl moiety protected by a di(p-methoxyphenyl)phenylmethyl protecting group PG-0 with a deprotection mixture M-b, thereby cleaving the protecting group PG-0 from the nucleoside or oligonucleotide, wherein said deprotection mixture M-b is a liquid composition C comprising a solvent, a protic acid having a pKa equal to or smaller than 4, and at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, wherein - said protic acid comprised in the liquid composition C is selected from the group consisting of a carboxylic acid, a sulfonic acid, a mineral acid, a protonated aliphatic, aromatic or heteroaromatic amine, whose protonated form has a pKa in the range of 1−4, and mixtures thereof; and - each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, is independently an alcohol of the following Formula D: (Formula D), wherein in Formula D: RD-1, RD-2, RD-3, RD-4, and RD-5 are independently of each other selected from the group consisting of H, OH, a C1−C6-alkyl group, O(C1−C6-alkyl), C(O)(C1−C6-alkyl), C(O)O(C1−C6-alkyl), F, Cl, Br, I, and CN. 2. The method according to claim 1, wherein the target oligonucleotide OT comprises a first cycle oligonucleotide O-1, and the method comprises the following step (a) and a first coupling cycle comprising the following steps (b) to (e): - 2 - (a) providing a component C-0 selected from the group consisting of a nucleoside and an oligonucleotide, wherein the component C-0 is covalently linked to a solid support and comprises a backbone hydroxyl moiety protected by a di(p-methoxyphenyl)phenylmethyl protecting group PG-0; (b) incubating the component C-0 of step (a) with a deprotection mixture M-b, thereby cleaving the protecting group PG-0 from the component C-0, so as to obtain a component C-0# having a free backbone hydroxyl group; (c) providing a building block B-1 selected from the group consisting of a nucleoside and an oligonucleotide, wherein the building block B-1 comprises a backbone hydroxyl moiety protected by a di(p-methoxyphenyl)phenylmethyl protecting group PG-1 and a phosphorus moiety covalently bonded via its phosphorus atom to an oxygen atom of the backbone of the building block B-1; (d) reacting the component C-0# of step (b) with the building block B-1 of step (c) under conditions suitable to form a covalent bond between said free backbone hydroxyl group of the component C-0# and the phosphorus atom of said phosphorus moiety of the building block B-1, thereby obtaining a first cycle oligonucleotide O-1; (e) optionally, incubating the first cycle oligonucleotide O-1 obtained in step (d) with an oxidizing or sulfurizing agent, thereby converting any P (III) atoms within said first cycle oligonucleotide O-1 to P (V) atoms; wherein in step (b), said deprotection mixture M-b is a liquid composition C as defined in claim 1. 3. The method according to claim 2 wherein the target oligonucleotide OT comprises a n-th cycle oligonucleotide O-n, and the method further comprises performing (n−1) iterations of a coupling cycle comprising the following steps (b’) to (e’), wherein n is an integer in the range of 2 to 99, which denotes the total number of coupling cycles performed to obtain the n-th cycle oligonucleotide O-n, and each individual coupling cycle comprising the following steps (b’) to (e’) is identified by a serial number x, which runs in steps of 1 from 2 to n: (b’) incubating the (x−1)-th cycle oligonucleotide O-(x−1) obtained in the previous coupling cycle with a deprotection mixture M-b’, thereby cleaving the di(p-methoxyphenyl)phenylmethyl protecting group PG- (x−1) from the (x−1)-th cycle oligonucleotide O-(x−1), so as to obtain a - 3 - (x−1)-th cycle oligonucleotide (O-(x−1))# having a free backbone hydroxyl group; (c’) providing a building block B-x selected from the group consisting of a nucleoside and an oligonucleotide, wherein the building block B-x comprises a backbone hydroxyl moiety protected by a di(p-methoxyphenyl)phenylmethyl protecting group PG-x and a phosphorus moiety covalently bonded via its phosphorus atom to an oxygen atom of the backbone of the building block B-x; (d’) reacting the (x−1)-th cycle oligonucleotide (O-(x−1))# obtained in step (b’) with the building block B-x of step (c’) under conditions suitable to form a covalent bond between said free backbone hydroxyl group of the (x−1)-th cycle oligonucleotide (O-(x−1))# and the phosphorus atom of said phosphorus moiety of the building block B-x, thereby obtaining a x-th cycle oligonucleotide O-x; (e’) optionally, incubating the x-th cycle oligonucleotide O-x obtained in step (d’) with an oxidizing or sulfurizing agent, thereby converting any P (III) atoms within said x-th cycle oligonucleotide O-x to P (V) atoms; wherein in at least one iteration of step (b’), said deprotection mixture M-b’ is a liquid composition C as defined in claim 1. 4. The method according to any one of claims 2 and 3, wherein: - the phosphorus moiety of the building block B-1 and each building block B-x is independently selected from the group consisting of a phosphoramidite moiety and a H-phosphonate monoester moiety; - in each coupling cycle, in which said phosphorus moiety of the building block B-1 or the building block B-x is a phosphoramidite moiety, step (e) or (e’) is carried out; and - at least in the final coupling cycle, step (e) or (e’) is carried out. 5. The method according to any one of claims 1 to 4, wherein said nucleoside or oligonucleotide, which is covalently linked to a solid support, of claim 1 and the component C-0 of claim 2 is a compound of the following Formula I: - 4 - wherein in Formula I: each oxygen atom (O) depicted within each nucleoside subunit x-0 to x-m represents the oxygen atom of a hydroxyl moiety of the respective nucleoside subunit; each of the nucleoside subunits x-0 to x-m may be the same or different; PG-0 is a di(p-methoxyphenyl)phenylmethyl protecting group; m is an integer equal to or larger than 0; Y1 is selected independently for each repetitive unit m from the group consisting of O and S; Z1 is selected independently for each repetitive unit m from the group consisting of O-Rz-1 and S-Rz-1; Rz-1 is a protecting group, which may be the same or different for each repetitive unit m; CA is a capping moiety or a covalent chemical bond; L is a linker moiety or a covalent chemical bond; and SM is a solid support. 6. The method according to any one of claims 2 to 5, wherein each of the building blocks B-1 and B-x is a compound of the following Formula II-1: - 5 - (Formula II-1), wherein in Formula II-1: each oxygen atom (O) depicted within each nucleoside subunit y-0 to y-q represents the oxygen atom of a hydroxyl moiety of the respective nucleoside subunit; each nucleoside subunit y-0 to y-q may be the same or different; PG is the protecting group PG-1 or PG-x, and is a di(p-methoxyphenyl)phenylmethyl protecting group; q is an integer equal to or larger than 0; Y2 is selected independently for each repetitive unit q from the group consisting of O and S; Z2 is selected independently for each repetitive unit q from the group consisting of O-Rz-2, S-Rz-2; Rz-2 is a protecting group, which may be the same or different for each repetitive unit q; Z3 is selected from the group consisting of O and S; and Rz-3 is a protecting group; each of Ra and Rb is independently a C1−C6-alkyl group, wherein Ra and Rb may be the same or different and may also bond to each other to form a 5-membered or 6-membered aliphatic cyclic amine moiety together with the nitrogen atom to which Ra and Rb are bonded; and wherein step (e) or step (e’) is carried out in each coupling cycle. 7. The method according to any one of claims 2 to 6, wherein - 6 - - the first coupling cycle further comprises a step (f) of reacting free hydroxyl groups with a blocking agent, wherein step (f) is carried out after step (d) or after step (e); and/or - at least one iteration of the (n−1) iterations of the coupling cycle comprising steps (b’) to (e’) further comprises a step (f’) of reacting free hydroxyl groups with a blocking agent, wherein step (f ’) is carried out after step (d’) or after step (e’). 8. The method according to any one of claims 2 and 4 to 7, wherein - the method further comprises a step (g) of incubating the first cycle oligonucleotide O-1 with a deprotection mixture M-g, thereby cleaving the protecting group PG-1 from the first cycle oligonucleotide O-1, so as to obtain a first cycle oligonucleotide (O-1)# having a free backbone hydroxyl group; and/or - the method further comprises a step (h) of cleaving the first cycle oligonucleotide O-1 or (O-1)# from the solid support; and wherein, if both steps (g) and (h) are performed, they may be performed in any order. 9. The method according to any one of claims 3 to 7, wherein - the method further comprises a step (g’) of incubating the n-th cycle oligonucleotide O-n with a deprotection mixture M-g’, thereby cleaving the protecting group PG-n from the n-th cycle oligonucleotide O-n, so as to obtain a n-th cycle oligonucleotide (O-n)# having a free backbone hydroxyl group; and/or - the method further comprises a step (h’) of cleaving the n-th cycle oligonucleotide O-n or (O-n)# from the solid support; and wherein, if both steps (g’) and (h’) are performed, they may be performed in any order. 10. The method according to any one of claims 1 to 9, wherein at least steps (b) and (b’) are carried out in a batch reactor or wherein at least steps (b) and (b’) are carried out in a column reactor and the flow rate of the liquid composition C through the column reactor is below 300 cm/h. 11. The method according to any one of claims 1 to 10, wherein - the backbone hydroxyl moiety protected by said protecting group PG-0 is part of a nucleoside moiety comprising a purine type nucleobase; and - 7 - - in at least one iteration of the coupling cycle comprising steps (b’) to (e’), in which said protecting group PG-(x−1) is part of a nucleoside moiety comprising a purine type nucleobase, the deprotection mixture M-b’ is a liquid composition C. 12. The method according to any one of claims 1 to 11, wherein the synthesis is carried out on a scale of at least 100 mmol of the target oligonucleotide OT. 13. The method according to any one of claims 1 to 12, wherein the liquid composition C comprises said at least one alcohol according to Formula D in a molar concentration of 0.45−5.60 mol/L. 14. The method according to any one of claims 1 to 13, wherein said solvent comprised in the liquid composition C is a non-halogenated aprotic solvent. 15. A composition comprising - an oligonucleotide which is covalently linked to a solid support and comprises a hydroxyl moiety protected by a di(p-methoxyphenyl)phenylmethyl protecting group, and - a liquid composition C comprising a solvent, a protic acid having a pKa equal to or smaller than 4, and at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, wherein - said protic acid comprised in the liquid composition C is selected from the group consisting of a carboxylic acid, a sulfonic acid, a mineral acid, a protonated aliphatic, aromatic or heteroaromatic amine, whose protonated form has a pKa in the range of 1−4, and mixtures thereof; and - each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, is independently an alcohol of the following Formula D: wherein in Formula D: - 8 - RD-1, RD-2, RD-3, RD-4, and RD-5 are independently of each other selected from the group consisting of H, OH, a C1−C6-alkyl group, O(C1−C6-alkyl), C(O)(C1−C6-alkyl), C(O)O(C1−C6-alkyl), F, Cl, Br, I, and CN; preferably wherein the composition and/or one or more components are defined as in one or more of the preceding claims, in particular wherein the concentration of said at least one alcohol of Formula D is defined as in claim 13, and/or said solvent is defined as in claim 14. |
(Formula II-2), wherein in Formula II-2: each oxygen atom (O) depicted within each nucleoside subunit y-0 to y-q represents the oxygen atom of a hydroxyl moiety of the respective nucleoside subunit; each nucleoside subunit y-0 to y-q may be the same or different (i.e. have the same or a different chemical structure); PG is the protecting group PG-1 (for building block B-1) or PG (for a building block B-x) and comprises an optionally substituted triarylmethyl residue; q is an integer equal to or larger than 0; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S; Z 2 is selected independently for each repetitive unit q from the group consisting of H, O-R z-2 , and S-R z-2 ; and R z-2 is a protecting group, which may be the same or different for each repetitive unit q; and wherein at least in the final coupling cycle, step (e) or step (e’) is carried out. In some embodiments of the method of the invention, the building block B-1 or B-x of Formula II-2 is a compound of the following Formula II-2-a: (Formula II-2-a), wherein in Formula II-2-a: q, PG, Y 2 , Z 2 , and R z-2 are defined as for Formula II-2; B N , R XI , R XII , R XIII , R XIV , and R XV are defined as for Formula II-a; and wherein at least in the final coupling cycle, step (e) or step (e’) is carried out. In some embodiments of the method of the invention, the building block B-1 or B-x of Formula II-2, in particular Formula II-2-a, is a compound of the following Formula II-2-b:
(Formula II-2-b), wherein in Formula II-2-b: q, PG, Y 2 , Z 2 , and R z-2 are defined as for Formula II-2; B N , R XI , R XII , R XIII , R XIV , and R XV are defined as for Formula II-b; and wherein at least in the final coupling cycle, step (e) or step (e’) is carried out. In some embodiments, in the building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1-b, II-2, II-2-a, and II-2-b, the integer q is an integer in the range of 0−150, 0−100, 0−75, 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, 0−5, 0−3, 0−2, 0−1 or q is 0. It will be understood that to state than an integer is in the range of e.g.0−5 means that said integer may be 0, 1, 2, 3, 4, or 5. In some embodiments, in the building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1- b, II-2, II-2-a, and II-2-b, the integer q is 0. It will be understood that, if the integer q in any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1-b, II-2, II-2-a, and II-2-b is 0, the protecting group PG (i.e. PG-1 for B-1 and PG-x for B-x) is bonded to the respective hydroxyl moiety of the then remaining nucleoside subunit carrying the phosphorus moiety (e.g. nucleoside subunit y-0 in Formulae II, II-1 or II-2). In some embodiments, in the building block B-1 or B-x, e.g. of any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1-b, II-2, II-2-a, and II-2-b, the protecting group PG (i.e. PG-1 for B-1 and PG-x for B-x) is selected from the group consisting of the triphenylmethyl group (i.e. the trityl group), the (p-methoxyphenyl)diphenylmethyl group (i.e. the MMT group), and the di(p-methoxyphenyl)phenylmethyl group (i.e. the DMT group). In some preferred embodiments, in the building block B-1 or B-x, e.g. of any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1-b, II-2, II-2-a, and II-2-b, the protecting group PG (i.e. PG-1 for B-1 and PG-x for B-x) is the di(p-methoxyphenyl)phenylmethyl group (i.e. the DMT group). In some embodiments, in the building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1-b, II-2, II-2-a, and II-2-b, Y 2 is for each repetitive unit q O. In some embodiments, in the building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1-b, II-2, II-2-a, and II-2-b, Y 2 is for each repetitive unit q S. In some embodiments, in the building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1-b, II-2, II-2-a, and II-2-b, R z-2 is a protecting group removable under alkaline conditions, wherein R z-2 may be the same or different at each occurrence. In some embodiments, in the building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1-b, II-2, II-2-a, and II-2-b, R z-2 is for each repetitive unit q independently a protecting group of the chemical structure CH 2 -CH 2 -EWG, where EWG is an electron withdrawing group, preferably a cyano group. The electron withdrawing group may for example be selected from the group consisting of a cyano group, a halogen atom such as a chlorine, fluorine, or bromine atom, an aldehyde group, a keto group, a carboxyester group, or a carboxamide group. In some preferred embodiments, in the building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1-b, II-2, II-2-a, and II-2-b, R z-2 is for each repetitive unit q a 2-cyanoethyl group (i.e. CH2-CH2-CN). In some embodiments, in the building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, and II-1-b, Z 2 is selected independently for each repetitive unit q from the group consisting of O-R z-2 and S-R z-2 . In some embodiments, in the the building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, and II-1-b, Z 2 is selected independently for each repetitive unit q from the group consisting of O-R z-2 and S-R z-2 , where R z-2 is for each repetitive unit q a 2-cyanoethyl group (i.e. CH 2 -CH 2 -CN). In such embodiments, Z 2 is selected independently for each repetitive unit q from the group consisting of O-CH 2 -CH 2 -CN and S-CH 2 -CH 2 -CN. In some embodiments, in the building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, and II-1-b, Z 2 is for each repetitive unit q O-R z-2 , where R z-2 is for each repetitive unit q a 2-cyanoethyl group (i.e. CH 2 -CH 2 -CN). In such embodiments, Z 2 is for each repetitive unit q O-CH2-CH2-CN. In some embodiments, in the building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-2, II-2-a, and II-2-b, Z 2 is for each repetitive unit q H. In some embodiments, in the building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-2, II-2-a, and II-2-b, Y 2 is for each repetitive unit q O and Z 2 is for each repetitive unit q H. In some embodiments, in the building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1-b, II-2, II-2-a, and II-2-b, the terminal nucleoside subunit, whose hydroxyl moiety is bonded to the PG (i.e. PG-1 for B-1 and PG-x for B-x) protecting group, is a nucleoside subunit comprising a purine type nucleobase, preferably a nucleobase selected from the group consisting of adenine and guanine, in particular adenine. The skilled person will understand that any kind of nucleobase B N may be present in the building block B-1 or B-x of any one of Formulae II-a, II-b, II-1-a, II-1-b, II-2-a, and II-2-b. In some embodiments, in the building block B-1 or B-x of any one of Formulae II-a, II-b, II-1-a, II-1-b, II-2-a, and II-2-b, B N is a nucleobase and at each occurrence independently selected from the group consisting of adenine, guanine, cytosine, 5-methylcytosine, thymine, and uracil. It will be understood by those skilled in the art, that any nucleobase B N in any one of Formulae II-a, II-b, II-1-a, II-1-b, II- 2-a, and II-2-b may optionally be protected, i.e. carry one or more protecting groups, without this being indicated specifically. Thus, when, for example, stating that B N is adenine, guanine, 5-methylcytosine, cytosine, thymine, or uracil, this embraces the aforementioned nucleobases in protected form and in free form (i.e. with and without any protecting groups). The same rationale applies to nucleobases in general. Nucleobase protecting groups are known to those skilled in the art and have also been explained above, including, for example, the preferred nucleobase protecting groups compiled in Table T-1. In some embodiments, each nucleobase of each building block B-1 or B-x, in particular each nucleobase B N of each building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1-b, II-2, II-2-a, and II-2-b is independently selected from the group consisting of - adenine, in which the exocyclic amino group is protected; - guanine, in which the exocyclic amino group is protected; - cytosine, in which the exocyclic amino group is protected; - 5-methylcytosine, in which the exocyclic amino group is protected; - thymine; and - uracil. In some embodiments, each nucleobase of each building block B-1 or B-x, in particular each nucleobase B N of each building block B-1 or B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1-b, II-2, II-2-a, and II-2-b is independently selected from the group consisting of - adenine, in which the exocyclic amino group is protected by a benzoyl group, an isobutyryl group or a phenoxyacetyl group; - guanine, in which the exocyclic amino group is protected by an isobutyryl group, a 4-isopropylphenoxyacetyl group or a dimethylformamidino group; - cytosine, in which the exocyclic amino group is protected by an acetyl group or a benzoyl group; - 5-methylcytosine, in which the exocyclic amino group is protected by an acetyl group or a benzoyl group; - thymine; and - uracil. In some embodiments, in the building block B-1 or B-x of any one of Formulae II-a, II-b, II-1-a, II-1-b, II-2-a, and II-2-b: R XI is at each occurrence independently selected from the group consisting of H, F, O-(C1-C5-alkyl), O-(C1-C5-alkyl)-O-(C1-C5-alkyl), O-Si(C1-C5-alkyl)3, and O-CH2-O-Si(C1-C5-alkyl)3; R XIII is independently at each occurrence H or R XIII and R XI of the same nucleoside subunit (i.e. bonded to the 4´- and 2´-C atom of the same carbohydrate moiety) together form a structure +–CH2-O−++, +–CH(CH3)-O−++, or +–CH2-CH2-O−++, where + is the point of attachment to the 4´-carbon atom (i.e. the carbon atom to which R XIII is bonded) and ++ is the point of attachment to the 2´-carbon (i.e. the carbon atom to which R XI is bonded); and for each nucleoside subunit independently, R XII , R XIV , and R XV are either all H or they are bonded together so that the respective nucleoside subunit has a structure of the aforementioned Formula II-a-tc (in a building block B-1 or B-x of any one of Formulae II-a, II-1-a, and II-2-a) or Formula II-b-tc (in a building block B-1 or B-x of any one of Formula II-b, II-1-b, and II-2-b). In some embodiments, in the building block B-1 or B-x of any one of Formulae II-a, II-b, II-1-a, II-1-b, II-2-a, and II-2-b: R XI is at each occurrence independently selected from the group consisting of H, F, O-CH3 (i.e. methoxy), O-CH2-CH2-O-CH3 (i.e. 2-methoxyethyl-1-oxy), O-Si(CH 3 ) 3 (i.e. trimethylsilyloxy) , O-Si(CH 3 ) 2 (C(CH 3 ) 3 ) (i.e. tert- butyl(dimethyl)silyloxy), and O-CH2-O-Si(C(CH3)3)3 (i.e. ((triisopropylsilyl)oxy)- methyloxy); R XIII is independently at each occurrence H or R XIII and R XI of the same nucleoside subunit (i.e. bonded to the 4´- and 2´-C atom of the same carbohydrate moiety) together form a structure +–CH2-O−++, +–CH(CH3)-O−++, or +–CH2-CH2-O−++, where + is the point of attachment to the 4´-carbon atom (i.e. the carbon atom to which R XIII is bonded) and ++ is the point of attachment to the 2´-carbon (i.e. the carbon atom to which R XI is bonded); and for each nucleoside subunit independently, R XII , R XIV , and R XV are either all H or they are bonded together so that the respective nucleoside subunit has a structure of the aforementioned Formula II-a-tc (in a building block B-1 or B-x of any one of Formulae II-a, II-1-a, and II-2-a) or Formula II-b-tc (in a building block B-1 or B-x of any one of Formula II-b, II-1-b, and II-2-b). In some embodiments, in the building block B-1 or B-x of any one of Formulae II-a, II-b, II-1-a, II-1-b, II-2-a, and II-2-b: R XI is selected independently at each occurrence from the group consisting of H, F, O-CH 3 (i.e. methoxy), and O-CH 2 -CH 2 -O-CH 3 (i.e.2-methoxyethyl-1-oxy); and each of R XII , R XIII , R XIV , and R XV is H at each occurrence. In some embodiments, in the building block B-1 or B-x of any one of Formulae II-1, II-1-a, and II-1-b, Z 3 is O. In some embodiments, in the building block B-1 or B-x of any one of Formulae II-1, II-1-a, and II-1-b, Z 3 is S. In some embodiments, in the building block B-1 or B-x of any one of Formulae II-1, II-1-a, and II-1-b, R z-3 is a protecting group removable under alkaline conditions. In some embodiments, in the building block B-1 or B-x of any one of Formulae II-1, II-1-a, and II-1-b, R z-3 is a protecting group of the chemical structure CH 2 -CH 2 -EWG, where EWG is an electron withdrawing group, preferably a cyano group. The electron withdrawing group may for example be selected from the group consisting of a cyano group, a halogen atom such as a chlorine, fluorine, or bromine atom, an aldehyde group, a keto group, a carboxyester group, or a carboxamide group. In some preferred embodiments, in the building block B-1 or B-x of any one of Formulae II-1, II-1-a, and II-1-b, R z-3 is a 2-cyanoethyl group (i.e. CH 2 -CH 2 -CN). In some preferred embodiments, in the building block B-1 or B-x of any one of Formulae II-1, II-1-a, and II-1-b, Z 3 is O and R z-3 is a 2-cyanoethyl group (i.e. CH2-CH2-CN). In some embodiments, in the building block B-1 or B-x of any one of Formulae II-1, II-1-a, and II-1-b, each of R a and R b is independently a C1−C6-alkyl group, wherein R a and R b may be the same or different, and wherein R a and R b may not bond to each other. In some embodiments, in the building block B-1 or B-x of any one of Formulae II-1, II-1-a, and II-1-b, each of R a and R b is an isopropyl group (i.e. CH(CH3)2). In some embodiments, in the building block B-1 or B-x of Formula II: PM is a phosphorus moiety, preferably a phosphorus moiety selected from the group consisting of a phosphoramidite moiety and a H-phosphonate monoester moiety; PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−150, 0−100, 0−75, 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, or 0−5, or q is 0; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S; Z 2 is selected independently for each repetitive unit q from the group consisting of O-R z-2 , S-R z-2 , and H; and R z-2 is at each occurrence a 2-cyanoethyl group. In some embodiments, in the building block B-1 or B-x of Formula II: PM is a phosphoramidite moiety; PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, or 0−5, or q is 0; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S; Z 2 is selected independently for each repetitive unit q from the group consisting of O-R z-2 and S-R z-2 ; and R z-2 is at each occurrence a 2-cyanoethyl group. In some embodiments, in the building block B-1 or B-x of Formula II: PM is a phosphoramidite moiety; PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, or 0−5, or q is 0; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S; Z 2 is for each repetitive unit q O-R z-2 ; and R z-2 is at each occurrence a 2-cyanoethyl group. In some embodiments, in the building block B-1 or B-x of Formula II: PM is a H-phosphonate monoester moiety; PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, or 0−5, or q is 0; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S, and preferably is O; and Z 2 is for each repetitive unit q H. In some embodiments, in the building block B-1 or B-x of any one of Formulae II-a and II-b: PM is a phosphorus moiety, preferably a phosphorus moiety selected from the group consisting of a phosphoramidite moiety and a H-phosphonate monoester moiety; PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−150, 0−100, 0−75, 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, 0−5, 0−3, 0−2, 0−1 or q is 0; B N is a nucleobase, which may be the same or different at each occurrence; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S; Z 2 is selected independently for each repetitive unit q from the group consisting of O-R z-2 , S-R z-2 , and H; R z-2 is at each occurrence a 2-cyanoethyl group; R XI is at each occurrence independently selected from the group consisting of H, F, O-(C 1 -C 5 -alkyl), O-(C 1 -C 5 -alkyl)-O-(C 1 -C 5 -alkyl), O-Si(C 1 -C 5 -alkyl) 3 , and O-CH 2 -O-Si(C 1 -C 5 -alkyl) 3 ; R XIII is independently at each occurrence H or R XIII and R XI of the same nucleoside subunit (i.e. bonded to the 4´- and 2´-C atom of the same carbohydrate moiety) together form a structure +–CH 2 -O−++, +–CH(CH 3 )-O−++, or +–CH 2 -CH 2 -O−++, where + is the point of attachment to the 4´-carbon atom (i.e. the carbon atom to which R XIII is bonded) and ++ is the point of attachment to the 2´-carbon (i.e. the carbon atom to which R XI is bonded); and for each nucleoside subunit independently, R XII , R XIV , and R XV are either all H or they are bonded together so that the respective nucleoside subunit has a structure of the aforementioned Formula II-a-tc (in a building block B-1 or B-x of Formula II-a) or Formula II-b-tc (in a building block B-1 or B-x of Formula II-b). In some embodiments, in the building block B-1 or B-x of any one of Formulae II-a and II-b: PM is a phosphorus moiety, preferably a phosphorus moiety selected from the group consisting of a phosphoramidite moiety and a H-phosphonate monoester moiety; PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−150, 0−100, 0−75, 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, 0−5, 0−3, 0−2, 0−1 or q is 0; B N is a nucleobase, which may be the same or different at each occurrence; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S; Z 2 is selected independently for each repetitive unit q from the group consisting of O-R z-2 , S-R z-2 , and H; R z-2 is at each occurrence a 2-cyanoethyl group; R XI is at each occurrence independently selected from the group consisting of H, F, O-CH3 (i.e. methoxy), O-CH2-CH2-O-CH3 (i.e. 2-methoxyethyl-1-oxy), O-Si(CH3)3 (i.e. trimethylsilyloxy), O-Si(CH3)2(C(CH3)3) (i.e. tert- butyl(dimethyl)silyloxy), and O-CH2-O-Si(C(CH3)3)3 (i.e. ((triisopropylsilyl)oxy)- methyloxy); R XIII is independently at each occurrence H or R XIII and R XI of the same nucleoside subunit (i.e. bonded to the 4´- and 2´-C atom of the same carbohydrate moiety) together form a structure +–CH2-O−++, +–CH(CH3)-O−++, or +–CH2-CH2-O−++, where + is the point of attachment to the 4´-carbon atom (i.e. the carbon atom to which R XIII is bonded) and ++ is the point of attachment to the 2´-carbon (i.e. the carbon atom to which R XI is bonded); and for each nucleoside subunit independently, R XII , R XIV , and R XV are either all H or they are bonded together so that the respective nucleoside subunit has a structure of the aforementioned Formula II-a-tc (in a building block B-1 or B-x of Formula II-a) or Formula II-b-tc (in a building block B-1 or B-x of Formula II-b). In some embodiments, in the building block B-1 or B-x of any one of Formulae II-a and II-b: PM is a phosphorus moiety, preferably a phosphorus moiety selected from the group consisting of a phosphoramidite moiety and a H-phosphonate monoester moiety; PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, 0−5, 0−3, 0−2, 0−1 or q is 0; B N is a nucleobase, which may be the same or different at each occurrence; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S; Z 2 is selected independently for each repetitive unit q from the group consisting of O-R z-2 , S-R z-2 , and H; R z-2 is at each occurrence a 2-cyanoethyl group; R XI is selected independently at each occurrence from the group consisting of H, F, O-CH 3 (i.e. methoxy), and O-CH 2 -CH 2 -O-CH 3 (i.e.2-methoxyethyl-1-oxy); and each of R XII , R XIII , R XIV , and R XV is H at each occurrence. In some embodiments, in the building block B-1 or B-x of Formula II-1: PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, or 0−5, or q is 0; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S; Z 2 is selected independently for each repetitive unit q from the group consisting of O-R z-2 and S-R z-2 , and Z 2 preferably is for each repetitive unit q O-R z-2 ; R z-2 is at each occurrence a 2-cyanoethyl group; Z 3 is selected from the group consisting of O and S, and preferably is O; R z-3 is a 2-cyanoethyl group; and each of R a and R b is independently a C 1 −C 6 -alkyl group, preferably an isopropyl group. In some embodiments, in the building block B-1 or B-x of Formula II-1: PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, or 0−5, or q is 0; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S; Z 2 is for each repetitive unit q O-R z-2 ; R z-2 is at each occurrence a 2-cyanoethyl group; Z 3 is O; R z-3 is a 2-cyanoethyl group; and each of R a and R b is an isopropyl group. In some embodiments, in the building block B-1 or B-x of any one of Formula II-1-a and II-1-b: PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, or 0−5, or q is 0; B N is a nucleobase, which may be the same or different at each occurrence; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S; Z 2 is selected independently for each repetitive unit q from the group consisting of O-R z-2 and S-R z-2 , and Z 2 preferably is for each repetitive unit q O-R z-2 ; R z-2 is at each occurrence a 2-cyanoethyl group; Z 3 is selected from the group consisting of O and S, and preferably is O; R z-3 is a 2-cyanoethyl group; each of R a and R b is independently a C1−C6-alkyl group, preferably an isopropyl group; R XI is at each occurrence independently selected from the group consisting of H, F, O-(C1-C5-alkyl), O-(C1-C5-alkyl)-O-(C1-C5-alkyl), O-Si(C1-C5-alkyl)3, and O-CH2-O-Si(C1-C5-alkyl)3; R XIII is independently at each occurrence H or R XIII and R XI of the same nucleoside subunit (i.e. bonded to the 4´- and 2´-C atom of the same carbohydrate moiety) together form a structure +–CH2-O−++, +–CH(CH3)-O−++, or +–CH2-CH2-O−++, where + is the point of attachment to the 4´-carbon atom (i.e. the carbon atom to which R XIII is bonded) and ++ is the point of attachment to the 2´-carbon (i.e. the carbon atom to which R XI is bonded); and for each nucleoside subunit independently, R XII , R XIV , and R XV are either all H or they are bonded together so that the respective nucleoside subunit has a structure of the aforementioned Formula II-a-tc (in a building block B-1 or B-x of Formula II-1-a) or Formula II-b-tc (in a building block B-1 or B-x of Formula II-1-b). In some embodiments, in the building block B-1 or B-x of any one of Formula II-1-a and II-1-b: PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, or 0−5, or q is 0; B N is a nucleobase, which may be the same or different at each occurrence; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S; Z 2 is selected independently for each repetitive unit q from the group consisting of O-R z-2 and S-R z-2 , and Z 2 preferably is for each repetitive unit q O-R z-2 ; R z-2 is at each occurrence a 2-cyanoethyl group; Z 3 is selected from the group consisting of O and S and preferably is O; R z-3 is a 2-cyanoethyl group; each of R a and R b is independently a C1−C6-alkyl group, preferably an isopropyl group; R XI is at each occurrence independently selected from the group consisting of H, F, O-CH 3 (i.e. methoxy), O-CH 2 -CH 2 -O-CH 3 (i.e. 2-methoxyethyl-1-oxy), O-Si(CH 3 ) 3 (i.e. trimethylsilyloxy) , O-Si(CH 3 ) 2 (C(CH 3 ) 3 ) (i.e. tert- butyl(dimethyl)silyloxy), and O-CH 2 -O-Si(C(CH 3 ) 3 ) 3 (i.e. ((triisopropylsilyl)oxy)- methyloxy); R XIII is independently at each occurrence H or R XIII and R XI of the same nucleoside subunit (i.e. bonded to the 4´- and 2´-C atom of the same carbohydrate moiety) together form a structure +–CH2-O−++, +–CH(CH3)-O−++, or +–CH2-CH2-O−++, where + is the point of attachment to the 4´-carbon atom (i.e. the carbon atom to which R XIII is bonded) and ++ is the point of attachment to the 2´-carbon (i.e. the carbon atom to which R XI is bonded); and for each nucleoside subunit independently, R XII , R XIV , and R XV are either all H or they are bonded together so that the respective nucleoside subunit has a structure of the aforementioned Formula II-a-tc (in a building block B-1 or B-x of Formula II-1-a) or Formula II-b-tc (in a building block B-1 or B-x of Formula II-1-b). In some embodiments, in the building block B-1 or B-x of any one of Formula II-1-a and II-1-b: PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, or 0−5, or q is 0; B N is a nucleobase, which may be the same or different at each occurrence; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S; Z 2 is selected independently for each repetitive unit q from the group consisting of O-R z-2 and S-R z-2 , and Z 2 preferably is for each repetitive unit q O-R z-2 ; R z-2 is at each occurrence a 2-cyanoethyl group; Z 3 is selected from the group consisting of O and S and preferably is O; R z-3 is a 2-cyanoethyl group; each of R a and R b is independently a C1−C6-alkyl group, preferably an isopropyl group; R XI is selected independently at each occurrence from the group consisting of H, F, O-CH3 (i.e. methoxy), and O-CH2-CH2-O-CH3 (i.e.2-methoxyethyl-1-oxy); and each of R XII , R XIII , R XIV , and R XV is H at each occurrence. In some embodiments, in the building block B-1 or B-x of Formula II-2: PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, or 0−5, or q is H; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S, and preferably is O; and Z 2 is for each repetitive unit q H. In some embodiments, in the building block B-1 or B-x of any one of Formulae II-2- a and II-2-b: PG (i.e. PG-1 for B-1 and PG-x for B-x) is a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group; q is an integer in the range of 0−50, 0−35, 0−30, 0−25, 0−20, 0−15, 0−10, or 0−5, or q is 0; B N is a nucleobase, which may be the same or different at each occurrence; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S, and preferably is O; Z 2 is for each repetitive unit q H; R XI is at each occurrence independently selected from the group consisting of H, F, O-CH 3 (i.e. methoxy), O-CH 2 -CH 2 -O-CH 3 (i.e. 2-methoxyethyl-1-oxy), O-Si(CH 3 ) 3 (i.e. trimethylsilyloxy) , O-Si(CH 3 ) 2 (C(CH 3 ) 3 ) (i.e. tert- butyl(dimethyl)silyloxy), and O-CH 2 -O-Si(C(CH 3 ) 3 ) 3 (i.e. ((triisopropylsilyl)oxy)- methyloxy); R XIII is independently at each occurrence H or R XIII and R XI of the same nucleoside subunit (i.e. bonded to the 4´- and 2´-C atom of the same carbohydrate moiety) together form a structure +–CH2-O−++, +–CH(CH3)-O−++, or +–CH2-CH2-O−++, where + is the point of attachment to the 4´-carbon atom (i.e. the carbon atom to which R XIII is bonded) and ++ is the point of attachment to the 2´-carbon (i.e. the carbon atom to which R XI is bonded); and for each nucleoside subunit independently, R XII , R XIV , and R XV are either all H or they are bonded together so that the respective nucleoside subunit has a structure of the aforementioned Formula II-a-tc (in a building block B-1 or B-x of Formula II-2-a) or Formula II-b-tc (in a building block B-1 or B-x of Formula II-2-b). In the method of the invention, the building block B-1 or B-x may be the same or different (i.e. have the same or a different chemical structure) for each iteration of the coupling cycle, unless indicated differently in the context of specific embodiments. The term “providing a building block” B-1 or B-x in step (c) or (c’) may be understood in the broadest sense. A building block B-1 or B-x for use in the method of the invention may, for example, be obtained commercially, in particular, if said phosphorus moiety is a phosphoramidite moiety or a H-phosphonate monoester moiety. Alternatively, a building block B-1 or B-x for use in the method of the invention may be obtained by means of chemical synthesis. The person skilled in the art is aware of methods of synthesizing such compounds, wherein the synthesis route will obviously depend on the chemical structure of said phosphorus moiety. Building blocks B-1 or B-x, e.g. of any one of Formulae II, II-a, and II-b, in which said phosphorus moiety, e.g. said phosphorus moiety PM, is a phosphoramidite moiety, in particular building block B-1 or B-x of any one of Formulae II-1, II-1-a, and II-1-b, may, for example, be synthesized as disclosed in, in K.V. Gothelf et al., Nature Communications 2021 and in X. Wei et al., Tetrahedron 2013, 69, 3615−3637. Building blocks B-1 or B-x, e.g. of any one of Formulae II, II-a, and II-b, in which said phosphorus moiety, e.g. said phosphorus moiety PM, is a H-phosphonate monoester moiety, in particular building block B-1 or B-x of any one of Formulae II- 2, II-2-a, and II-2-b, may, for example, be synthesized as disclosed in J. Stawinski and R. Strömberg (2005), Di- and Oligonucleotide Synthesis Using H-Phosphonate Chemistry, in Methods in Molecular Biology, vol. 288: Oligonucleotide Synthesis: Methods and Applications, edited by P. Herdewijn, Humana Press Inc., Totowa NJ, https://doi.org/10.1385/1-59259-823-4:081. Building blocks B-1 or B-x, e.g. of any one of Formulae II, II-a and II-b, in which said phosphorus moiety, e.g. said phosphorus moiety PM, is a P (V) moiety suitable for chiral phosphorothioate synthesis may, for example, be synthesized as disclosed in P.S. Baran et al., Science 2018, 361, 1234−1238 (also see Supplementary Materials for this reference). Step (d) of the method of the invention is: reacting the component C-0 # of step (b) with the building block B-1 of step (c) under conditions suitable to form a covalent bond between said free backbone hydroxyl group of the component C-0 # and the phosphorus atom of said phosphorus moiety of the building block B-1, thereby obtaining a first cycle oligonucleotide O-1. Step (d’) of the method of the invention is: reacting the (x−1)-th cycle oligonucleotide (O-(x−1)) # obtained in step (b’) with the building block B-x of step (c’) under conditions suitable to form a covalent bond between said free backbone hydroxyl group of the (x−1)-th cycle oligonucleotide (O-(x−1)) # and the phosphorus atom of said phosphorus moiety of the building block B-x, thereby obtaining a x-th cycle oligonucleotide O-x. For example, in the fifth coupling cycle (x = 5), step (d’) is: reacting the (5−1)-th cycle (i.e. fourth cycle) oligonucleotide (O-(5−1)) # (i.e. (O-4) # ) obtained in step (b’) with the building block B-5 of step (c’) under conditions suitable to form a covalent bond between said free backbone hydroxyl group of the fourth cycle oligonucleotide (O- (4)) # and the phosphorus atom of said phosphorus moiety of the building block B-x, thereby obtaining a 5-th cycle oligonucleotide O-5. The component C-0 # as well as the (x−1)-th cycle oligonucleotide (O-(x−1)) # have been defined. The term “backbone hydroxyl group” refers to a hydroxyl group which is part of the backbone of the respective nucleoside or oligonucleotide and will be understood based on the above explanations of the terms “hydroxyl group” and “backbone”. The building blocks B-1 and B-x have been defined. The term “reacting” in step (d) may be understood in the broadest sense as any operation during which the component C-0 # and the building block B-1 are present in the same reaction vessel or reactor and engage in the bond forming reaction of step (d). The term “reacting” in step (d’) may be understood in the broadest sense as any operation during which the (x−1)-th cycle oligonucleotide (O-(x−1)) # and the building block B-x are present in the same reaction vessel or reactor and engage in the bond forming reaction of step (d’). Typically, the component C-0 # or the (x−1)-th cycle oligonucleotide (O-(x−1)) # may already be contained in a reaction vessel or reactor, to which the building block B-1 or B-x is then added. Alternatively, the building block B-1 or B-x or a solution thereof may already be contained in a reaction vessel or reactor, to which the component C-0 # or the (x−1)-th cycle oligonucleotide (O-(x−1)) # is then added. During step (d), a covalent (chemical) bond is formed between said free backbone hydroxyl group of the component C-0 # and the phosphorus atom of said phosphorus moiety of the building block B-1. During step (d’), a covalent (chemical) bond is formed between said free backbone hydroxyl group, of the (x−1)-th cycle oligonucleotide (O-(x−1)) # and the phosphorus atom of said phosphorus moiety of the building block B-x. The bond forming reaction of step (d) and (d’) is herein also referred to as coupling or coupling reaction or condensation or condensation reaction, and steps (d) and (d’) are also referred to as coupling steps or condensation steps. The product obtained from the bond forming reaction of step (d) is the first cycle oligonucleotide O-1, which comprises the nucleoside sequence of the component C-0 # and of the building block B-1, wherein these two are now interconnected by an internucleosidic linkage group derived from the phosphorus moiety of the building block B-1. For example, the product obtained from the bond forming reaction of step (d’) of the fifth coupling cycle (x = 5) is the fifth cycle oligonucleotide O-5 which comprises the nucleoside sequence of the fourth cycle oligonucleotide (O-4) # and of the building block B-5, wherein these two are now interconnected by an internucleosidic linkage group derived from the phosphorus moiety of the building block B-5. The “conditions suitable” for the bond forming reactions of steps (d) and (d’) form part of the common knowledge of those skilled in the art. These conditions may, for example, depend on the chemical structure of said phosphorus moiety which is to engage in the bond forming reaction. Any (reaction) conditions suitable to achieve the desired bond forming reaction may be used in the method of the invention. A bond forming reaction of step (d) or (d’), in which the phosphorus moiety engaging in said reaction is a phosphoramidite moiety, as e.g. present in the building block B-1 or B-x of any one of Formulae II-1, II-1-a, and II-1-b, is herein also referred to as phosphoramidite coupling (reaction). Such phosphoramidite couplings may preferably be performed in the presence of an activator. Any activator used in oligonucleotide synthesis by the so-called phosphoramidite method may be used in the method of the invention. The activator may, for example, be selected from the group consisting of: - a tetrazole type activator such as 1H-tetrazole, 5-ethylthio-1H-tetrazole (ETT), 5-benzylthio-1H-tetrazole (BTT), 5-methylthio-1H-tetrazole (MTT), 1-methyl-5-mercaptotetrazole, 1-phenyl-5-mercaptotetrazole, and 5-(4-nitrophenyl)-1H-tetrazole, - an imidazole type activator such as 4,5-dicyanoimidazole (DCI) and 2-bromo- 4,5-dicyanoimidacole (2-Br-DCI), - a 1-hydroxybenzotriazole type activator such as 1-hydroxybenzotriazole, 1-hydroxy-6-trifluorobenzotriazole, and 1-6-trifluoro-4-nitrobenzotriazole, - a pyridinium salt type activator such as pyridinium hydrochloride, pyridinium p-toluenesulfonate, and pyridinium trifluoroacetate, and - a saccharin type activator, i.e. salts obtained from reacting saccharin with an organic base such as pyridine, collidine, lutidine, picoline, N-methylimidazole, and triethylamine. The activators disclosed in X. Wei et al., Tetrahedron 2013, 69, 3615−3637 may, for example, be used in phosphoramidite couplings. 1H-tetrazole, 5-ethylthio-1H- tetrazole (ETT), 5-benzylthio-1H-tetrazole (BTT), and 4,5-dicyanoimidacole (DCI) may be preferred. For example, X. Wei et al., Tetrahedron 2013, 69, 3615−3637 also discloses a range of suitable reaction conditions for these activators. N-methylimidazole (NMI) may be added alongside the activator, which may help to adjust the acidity of the solution. A phosphoramidite coupling of step (d) may preferably be performed in a solvent selected from the group consisting of acetonitrile, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methyl-2-pyrrolidone (NMP), N-methyl-4-piperidone, and mixtures thereof, optionally in combination with a non-polar solvent such as toluene, xylene or mesitylene. Acetonitrile, DMF, and a mixture thereof may be particularly preferred. The solvent (mixture) used for a phosphoramidite coupling is preferably substantially anhydrous, since water might react with phosphoramidites. The solvent for a phosphoramidite coupling may preferably comprise equal to or less than 1000 ppm or 750 ppm or 500 ppm or 250 ppm or 100 ppm or even 50 ppm of water, as determined by means of standard Karl Fischer titration at approximately 20 °C. Phosphoramidite couplings may, for example, be performed at a temperature in the range of 0−90 °C, 10−70 °C, 10−60 °C, 10−50 °C, 10−40 °C, 15−30 °C or 15−25 °C. For convenience, phosphoramidite couplings may simply be performed at room temperature. Increased temperatures may result in shorter reaction times. The reaction time may also depend on the chemical structure of the reactants and will routinely be selected by a skilled person, for example based on reaction monitoring using, e.g., thin-layer chromatography and/or high performance liquid chromatography (HPLC), optionally coupled to mass spectrometry. A bond forming reaction of step (d) or (d’), in which the phosphorus moiety engaging in said reaction is a H-phosphonate monoester moiety, as e.g. present in the building block B-1 or B-x of any one of Formulae II-2, II-2-a, and II-2-b, is herein also referred to as H-phosphonate coupling (reaction). Such H-phosphonate couplings may typically be performed using a condensing agent. Any condensing agent used in oligonucleotide synthesis by the so-called H-phosphonate method may be used in the method of the invention. The condensing agent may, for example, be selected from the group consisting of pivaloyl chloride (PvCl), 1-adamantanecarbonyl chloride (AdCl), 2,2-dimethylbutyryl chloride, isobutyryl chloride, diphenyl chlorophosphate, 2,4,6-triisopropylbenzenesulfonyl chloride, bis(pentafluorophenyl) carbonate, 2-chloro-5,5-dimethyl-1,3,2-dioxaphosphorinane 2-oxide (also referred to as 5,5-dimethyl-2-oxo-2-chloro-1,3,2-dioxaphosphinane, DMOCP), and bis(2-oxo-3-oxazolidinyl)phosphinic chloride (OXP or BOP-Cl). The building block B-1 or B-x comprising said H-phosphonate monoester moiety may be pre-activated with (i.e. incubated with) said condensing agent, and then be combined and reacted with the component C-0 # or the (x−1)-th cycle oligonucleotide (O-(x−1)) # to effect the condensation. The skilled person is familiar with suitable reaction conditions for such H-phosphonate couplings. For example, J. Stawinski and R. Strömberg (2005), Di- and Oligonucleotide Synthesis Using H-Phosphonate Chemistry, in Methods in Molecular Biology, vol.288: Oligonucleotide Synthesis: Methods and Applications, edited by P. Herdewijn, Humana Press Inc., Totowa NJ, https://doi.org/10.1385/1- 59259-823-4:081 discloses such reaction conditions. A H-phosphonate coupling of step (d) or (d’) may preferably be performed in a solvent selected from the group consisting of acetonitrile, pyridine, and a mixture thereof. The solvent (mixture) used for a H-phosphonate coupling is preferably substantially anhydrous. The solvent for a phosphoramidite coupling may preferably comprise equal to or less than 3000 pm, 2000 ppm, 1500 ppm, 1000 ppm or 750 ppm or 500 ppm or 250 ppm or 100 ppm or even 50 ppm of water, as determined by means of standard Karl Fischer titration. H-phosphonate couplings may, for example, be performed at a temperature in the range of 0−90 °C, 10−70 °C, 10−60 °C, 10−50 °C, 10−40 °C, 15−30 °C, 15−25 °C. For convenience, H-phosphonate couplings may simply be performed at room temperature. Increased temperatures may result in shorter reaction times. The reaction time may also depend on the chemical structure of the reactants and will routinely be selected by a skilled person, for example based on reaction monitoring using, e.g., thin-layer chromatography and/or high performance liquid chromatography (HPLC), optionally coupled to mass spectrometry. A bond forming reaction of step (d) or (d’), in which the phosphorus moiety engaging in said reaction is an arylphosphate diester moiety, is herein also referred to as phosphotriester coupling (reaction). Briefly, the arylphosphate diester moieties may typically be activated with an arylsulfonyl chloride activator, such as mesitylene-2- sulfonyl chloride (MsCl), usually in the presence of an auxiliary nucleophile such as 1-methylimidazole. Alternatively, pre-formed or in-situ generated 1-hydroxybenzotriazole-phosphotriesters may, for example, be used as phosphorus moiety instead of an aryl phosphate diester moiety in a phosphotriester coupling, again in the presence of an auxiliary nucleophile such as 1-methylimidazole. A bond forming reaction of step (d) or (d’), in which the phosphorus moiety engaging in said reaction is a P (V) moiety allowing for chiral phosphorothioate synthesis may, for example, be performed as disclosed in Baran et al. (Science 2018, 361, 1234−1238 (see also the Supplementary Materials of said publication) and ACS Central Science 2021, 7, 1473−1485), or in a similar fashion. Step (e) of the method of the invention is: optionally, incubating the first cycle oligonucleotide O-1 obtained in step (d) with an oxidizing or sulfurizing agent, thereby converting any P (III) atoms within said first cycle oligonucleotide O-1 to P (V) atoms. Step (e’) of the method of the invention is: optionally, incubating the x-th cycle oligonucleotide O-x obtained in step (d’) with an oxidizing or sulfurizing agent, thereby converting any P (III) atoms within said x-th cycle oligonucleotide O-x to P (V) atoms. It will be understood that converting any P (III) atoms to P (V) atoms does not change the name by which said first cycle oligonucleotide O-1 or said x-th cycle oligonucleotide O-x is referred to herein, since the terms first cycle oligonucleotide O-1 and x-th cycle oligonucleotide O-x embrace the respective oligonucleotide with any type of backbone structure, in particular with any type of internucleosidic linkage groups. Only the absence of the protecting group PG-0 or PG-(x−1) is indicated specifically by the aforementioned number sign (i.e. hashtag sign) " # " put in superscript. The terms “P (III) atom” and “P (V) atom” have been defined above. As used throughout this text, the term “oxidation state” “equals the charge of an atom after its homonuclear bonds have been divided equally and heteronuclear bonds assigned to the bond partners according to Allen electronegativity, except when the electronegative atom is bonded reversibly as a Lewis-acid ligand, in which case it does not obtain that bond’s electrons", as described in the IUPAC Recommendations 2016 (P. Karen et al., Pure and Applied Chemistry 2016, 88(8), 831−839). The Allen electronegativities given in said reference are to be used and the P−H bond electron pair is assigned to H. As an example, the phosphorus atom of the H-phosphonate monoester moiety in any one of Formulae II-2, II-2-a, and II-2-b has the oxidation state III. As another example, the phosphorus atom of the phosphoramidite moiety in any one of Formulae II-1, II-1-a, and II-1-b has the oxidation state III. As a third example, the phosphorus atoms in the phosphodiester linkage groups of DNA and RNA have the oxidation state V. The term “optionally” in steps (e) and (e’) denotes that the respective step may or may not be carried out in a given iteration of the coupling cycle, unless indicated differently in the context of specific embodiments. As known to those skilled in the art, oligonucleotides comprising one or more P (III) atoms, in particular one or more P (III) linkage groups, are typically less stable than related oligonucleotides comprising only P (V) atoms, in particular only P (V) linkage groups (as e.g. present in DNA and RNA). In some embodiments of the method of the invention, the target oligonucleotide O T comprises only P (V) atoms, in particular only P (V) linkage groups. If the first cycle oligonucleotide O-1 obtained in step (d) does not comprise any P (III) atoms, it may not be necessary to carry out step (e). If the x-th cycle oligonucleotide O-x obtained in step (d’) does not comprise any P (III) atoms, it may not be necessary to carry out step (e’) in the same iteration of the coupling cycle. It is understood by those skilled in the art, that the oxidation state of the phosphorus atom within an internucleosidic linkage group formed in the bond forming reaction of a step (d) or a step (d’) will typically depend on the chemical structure of said phosphorus moiety of said building block B-1 or B-x, which engaged in the respective bond forming reaction. Typically, the oxidation state of the phosphorus atom within such a phosphorus moiety will be preserved in the course of the bond forming reaction of step (d) or (d’). For example, if a phosphotriester coupling as defined herein is carried out in step (d) or (d’) of a coupling cycle, the phosphorus atom of the resulting phosphotriester internucleosidic linkage group will typically be present as P (V) atom, i.e. the phosphotriester linkage group is a P (V) linkage group. The same principle applies to the P (V) chemistry utilized by Baran et al. (Science 2018, 361, 1234−1238 and ACS Central Science 2021, 7, 1473−1485). On the other hand, if the phosphorus moiety of a building block B-1 or B-x engaging in a bond forming reaction of a step (d) or (d’) comprises a P (III) atom, the resulting internucleosidic linkage group will typically also comprise a P (III) atom, i.e. be a P (III) linkage group. Depending on the stability of the so-obtained P (III) linkage group, step (e) or (e’) may need to be carried out in the same coupling cycle x or may optionally be carried out in a later iteration of the coupling cycle, e.g. in the final, i.e. n-th coupling cycle. For example, the bond forming reaction of a step (d) or (d’) may typically give a phosphite triester product (a phosphite triester internucleosidic linkage group, i.e. a P (III) linkage group), if said phosphorus moiety covalently bonded via its phosphorus atom to an oxygen atom of the backbone of the building block B-1 or B-x, e.g. the phosphorus moiety PM in any one of Formulae II, II-a, and II-b, is a phosphoramidite moiety such as, e.g., present in any one of Formulae II-1, II-1-a, and II-1-b, while a H-phosphonate diester product (a H-phosphonate diester internucleosidic linkage group, i.e. a P (III) linkage group) may typically be obtained, if said phosphorus moiety covalently bonded via its phosphorus atom to an oxygen atom of the backbone of the building block B-1 or B-x, e.g. the phosphorus moiety PM in any one of Formulae II, II-a, and II-b, is a H-phosphonate monoester moiety such as, e.g., present in any one of Formulae II-2, II-2-a, and II-2-b. H-phosphonate diester linkage groups may be more stable, e.g. under the conditions of steps (b) and (b’), than phosphite triester linkage groups, so that step (e) or (e’) may not need to be performed in each iteration of the coupling cycle, in which said phosphorus moiety covalently bonded via its phosphorus atom to an oxygen atom of the backbone of the building block B-1 or B-x, e.g. the phosphorus moiety PM in any one of Formulae II, II-a, and II-b, is a H-phosphonate monoester moiety such as, e.g., present in any one of Formulae II-2, II-2-a, and II-2-b. However, at least in the final coupling cycle, step (e) (in case the first coupling cycle is the final coupling cycle) or (e’) is carried out, so that any P (III) atoms are converted to P (V) atoms. In some embodiments of the method of the invention: - the phosphorus moiety of the building block B-1 and each building block B-x is independently selected from the group consisting of a phosphoramidite moiety and a H-phosphonate monoester moiety; - in each coupling cycle, in which said phosphorus moiety of the building block B-1 or the building block B-x is a phosphoramidite moiety, step (e) or (e’) is carried out; and - at least in the final coupling cycle, step (e) or (e’) is carried out. In some embodiments of the method of the invention: - the phosphorus moiety of the building block B-1 and each building block B-x, e.g. the phosphorus moiety PM of any one of Formulae II, II-a, and II-b, is a phosphoramidite moiety; and - in each coupling cycle, step (e) or (e’) is carried out. In some embodiments of the method of the invention: - the phosphorus moiety of the building block B-1 and each building block B-x, e.g. the phosphorus moiety PM of any one of Formulae II, II-a, and II-b, is a H-phosphonate monoester moiety; and - at least in the final coupling cycle, step (e) or (e’) is carried out. In some embodiments of the method of the invention: - in each coupling cycle, the building block B-1 or B-x is independently selected from the group consisting of a compound of Formula II-1 and Formula II-2, preferably from the group consisting of Formula II-1-a and Formula II-2-a, in particular from the group consisting of Formula II-1-b and Formula II-2-b; - in each coupling cycle, in which the building block B-1 or B-x is a compound of any one of Formulae II-1, II-1-a, and II-1-b, step (e) or (e’) is carried out; and - at least in the final coupling cycle, step (e) or (e’) is carried out. In some embodiments of the method of the invention: - in each coupling cycle, the building block B-1 or B-x is a compound of Formula II-1, preferably of Formula II-1-a, in particular of Formula II-1-b; and - in each coupling cycle, step (e) or (e’) is carried out. In some embodiments of the method of the invention: - in each coupling cycle, the building block B-1 or B-x is a compound of Formula II-2, preferably of Formula II-2-a, in particular of Formula II-2-b; and - at least in the final coupling cycle, step (e) or (e’) is carried out. The “oxidizing agent” or the “sulfurizing agent” to be used in step (e) or (e’) are not particularly limited in terms of their chemical structure as long as the respective agent is capable of converting any P (III) atoms within the respective oligonucleotide O-1 or O-x to P (V) atoms. An “oxidizing agent” and a “sulfurizing agent” may differ in the means of how P (III) atoms are converted to P (V) atoms. An “oxidizing agent” may introduce one or more covalent bonds between the phosphorus atom be oxidized and an oxygen atom. A “sulfurizing agent” may introduce one or more covalent bonds between the phosphorus atom to be sulfurized and a sulfur atom. As used herein, the term “oxidizing agent” preferably refers to any agent capable of converting a phosphite triester linkage group to a phosphate triester linkage group and a H-phosphonate diester linkage group to a phosphate diester (i.e. a phosphodiester) linkage group. As used herein, the term “sulfurizing agent” preferably refers to any agent capable of converting a phosphite triester linkage group to a thiophosphate triester linkage group and a H-phosphonate diester linkage group to a thiophosphate diester linkage group (i.e. a phosphorothioate) linkage group. Iodine may be a preferred oxidizing agent. For example, an aqueous solution of iodine may be used, preferably in combination with a base such as pyridine. Optionally, a co-solvent such as tetrahydrofuran (THF) or acetonitrile may be added. As one example, a solution of iodine (e.g.50 mM, i.e.50 mmol/L) in a mixture of water and pyridine (e.g.1:9 v/v) may be used. Alternatively, peroxides such as tert- butyl hydroperoxide, cumene hydroperoxides, bis-trimethylsilyl peroxide, 2- butanone peroxide, and hydrogen peroxide, or peroxy acids such as m-chloroperbenzoic acid (mCPBA) may, for example, be used as oxidizing agents. As another alternative, (1S)-(+)-(10-camphorsulfonyl)-oxaziridine (CSO) may, for example, be used as oxidizing agent, e.g. as a 0.5 M (i.e.0.5 mol/L) solution in, e.g., acetonitrile. The oxidizing agent may, for example, be applied in form of a 0.005−5.0 M solution, preferably a 0.01−1.0 M solution in a suitable solvent, for example, selected from the group consisting of pyridine, acetonitrile, water, tetrahydrofuran, and mixtures thereof. Xanthane hydride (5-amino-3H-1,2,4-dithiazole-3-thione) may be a preferred sulfurizing agent. For example, a solution of xanthane hydride in pyridine may be used, optionally in combination with a co-solvent such as acetonitrile. As one example, a solution of xanthane hydride (e.g.0.2 M) in pyridine may be used. As another example, a solution of xanthane hydride (e.g.0.1 M) in a mixture of pyridine and acetonitrile (e.g.1:1, v/v) may be used. Alternatively, 1,4-dithiothreitol (DTT), phenylacetyl disulfide (PADS), 3H-1,2-benzodithiol-3-one 1,1-dioxide (Beaucage Reagent), 3H-1,2-benzodithiol-3-one, 5-ethoxy-3H-1,2,4-dithiazol-3-one (EDITH), or 3-(N,N-dimethylamino-methylidene)amino)-3H-1,2,4-dithiazole- 5-thione (CAS RN: 1192027-04-5, DDTT) may be used as sulfurizing agents. The sulfurizing agent may, for example, be applied in form of a 0.005−5.0 M solution, preferably a 0.01−1.0 M solution in a suitable solvent, for example, selected from the group consisting of pyridine, acetonitrile, water, tetrahydrofuran, and mixtures thereof. Steps (e) and (e’) may preferably be performed at a temperature in the range of 0−90 °C, 10−70 °C, 10−60 °C, 10−50 °C, 10−40 °C, 15−30 °C, or 15−25 °C. For convenience, step (e) and (e’) may simply be performed at room temperature. Increased temperatures may result in shorter reaction times. The reaction time may also depend on the chemical structure of the reactants and will routinely be selected by a skilled person, for example, based on reaction monitoring using, e.g., thin-layer chromatography and/or high performance liquid chromatography (HPLC), optionally coupled to mass spectrometry. The term “incubating” may in the context of step (e) refer to any process of combining the first cycle oligonucleotide O-1 obtained in step (d) and an oxidizing agent or sulfurizing agent as defined herein in a reaction vessel or reactor (e.g. a batch reactor or a column reactor). The term “incubating” may in the context of step (e’) refer to any process of combining the x-th cycle oligonucleotide O-x obtained in step (d’) of the x-th coupling cycle and an oxidizing agent or sulfurizing agent as defined herein in a reaction vessel or reactor (e.g. a batch reactor or a column reactor). Typically, the reaction vessel or reactor may already contain the respective oligonucleotide, followed by addition of said oxidizing or sulfurizing agent or a solution thereof. In some embodiments of the method of the invention: - the first coupling cycle further comprises a step (f) of reacting free hydroxyl groups with a blocking agent, wherein step (f) is carried out after step (d) or after step (e); and/or - at least one, or each, iteration of the (n−1) iterations of the coupling cycle comprising steps (b’) to (e’) further comprises a step (f’) of reacting free hydroxyl groups with a blocking agent, wherein step (f’) is carried out after step (d’) or after step (e’). In some embodiments of the invention, the first coupling cycle further comprises a step (f) of reacting free hydroxyl groups with a blocking agent, wherein step (f) is carried out after step (d) or after step (e). In some embodiments of the invention, at least one, or each, iteration of the (n−1) iterations of the coupling cycle comprising steps (b’) to (e’) further comprises a step (f’) of reacting free hydroxyl groups with a blocking agent, wherein step (f ’) is carried out after step (d’) or after step (e’). The term “free hydroxyl groups” in steps (f) and (f ’) will be understood from what has been laid out above. A free hydroxyl group formed in the course of step (b) or (b’) is supposed to engage in the condensation reaction of step (d) or (d’), which consumes said free hydroxyl group in the sense of incorporating it into a newly- formed internucleosidic linkage group. However, a (typically quite small, e.g. < 1 %, < 0.5 % or < 0.1 %) fraction of the free hydroxyl groups may not engage in the condensation reaction of step (d) or (d’). Such (unreacted) free hydroxyl groups would be available to participate in the condensation reaction of step (d) or (d’) of the following coupling cycle. This however may not be desirable, since it would give an oligonucleotide product lacking one nucleoside subunit. Such oligonucleotide products may be difficult to remove from the target oligonucleotide O T later on, since they may differ from O T only in the absence of a single nucleoside subunit. Steps (f) and (f’) may serve to prevent the formation of such difficult to remove side products by blocking any (unreacted) free hydroxyl groups before entering a new iteration of the coupling cycle. As used herein, the terms “blocking agent” and “capping agent” are used interchangeably to denote any chemical reagent capable of acylating, preferably acetylating, a free hydroxyl group. Capping agents for oligonucleotide synthesis form part of the common knowledge of those skilled in the art. Any blocking (i.e. capping) agents known from oligonucleotide synthesis may be used in the method of the invention. Preferred examples of such blocking agents comprise anhydrides of carboxylic acids, in particular acetic anhydride. For example, acetylation may be achieved by treating the growing oligonucleotide chains with neat acetic anhydride or a solution thereof, for example, in acetonitrile. An organic base such as N-methylimidazole, pyridine, lutidine (e.g.2,6-lutidine), collidine or a mixture thereof may be used as blocking agent. As one example, a 1:1 mixture (v/v) of a capping mixture A (Cap A: 20% acetic anhydride in acetonitrile, v/v) and a capping mixture B (Cap B: N-methylimidazole, 2,6-lutidine, acetonitrile, 20:30:50 v/v/v) may be used as blocking agent. The term “reacting” in steps (f) and (f’) may be understood in the broadest sense as any operation during which the solid-support bound growing oligonucleotide chains are brought in contact with said blocking agent, so that the blocking/capping (i.e. acylation, preferably acetylation) of the (unreacted) free hydroxyl groups may occur. It will be understood that, since the component C-0 is covalently linked to a solid support, the first cycle oligonucleotide O-1 is also covalently linked to said solid support, unless cleaved from it. It will also be understood that, since the building block B-1 used to prepare the first cycle oligonucleotide O-1 comprises the protecting group PG-1, the first cycle oligonucleotide O-1 will also comprise said protecting group PG-1, unless cleaving the protecting group PG-1. Such cleavage may be performed in step (b’) of the second coupling cycle. If no such second coupling cycle is performed, the protecting group PG-1 and one or more further protecting groups, including the solid support, may still be cleaved from the first cycle oligonucleotide O-1. In some embodiments of the method of the invention: - the method further comprises a step (g) of incubating the first cycle oligonucleotide O-1 with a deprotection mixture M-g, thereby cleaving the protecting group PG-1 from the first cycle oligonucleotide O-1, so as to obtain a first cycle oligonucleotide (O-1) # having a free backbone hydroxyl group; and/or - the method further comprises a step (h) of cleaving the first cycle oligonucleotide O-1 or (O-1) # from the solid support; wherein if both steps (g) and (h) are performed, they may be performed in any order. If step (e) is performed, step (g) and/or step (h) are preferably performed after step (e). If both steps (g) and (h) are performed, step (h) is preferably performed after step (g). It will be understood that if step (g) and/or step (h) is performed, no second coupling cycle is performed. It will be understood that, since the component C-0 is covalently linked to a solid support, the first cycle oligonucleotide O-1, and, if prepared, any (x−1)-th cycle oligonucleotide O-(x−1), (O-(x−1)) # , and any x-th cycle oligonucleotide O-x up to the n-th cycle oligonucleotide O-n is also covalently linked to said solid support, unless cleaving the respective oligonucleotide from said support. It will also be understood that, since the building block B-n used to prepare the n-th cycle oligonucleotide O-n in the final iteration n of the coupling cycle comprises the protecting group PG-n, the n-th cycle oligonucleotide O-n will also comprise said protecting group PG-n, unless cleaving the protecting group PG-n. In some embodiments of the method of the invention: - the method further comprises a step (g’) of incubating the n-th cycle oligonucleotide O-n with a deprotection mixture M-g’, thereby cleaving the protecting group PG-n from the n-th cycle oligonucleotide O-n, so as to obtain a n-th cycle oligonucleotide (O-n) # having a free backbone hydroxyl group; and/or - the method further comprises a step (h’) of cleaving the n-th cycle oligonucleotide O-n or (O-n) # from the solid support; and wherein, if both steps (g’) and (h’) are performed, they may be performed in any order. If step (e’) is performed in the final (i.e. n-th) coupling cycle, step (g’) and/or step (h’) are preferably performed after step (e’). If both steps (g’) and (h’) are performed, step (h’) is preferably performed after step (g’). It will be understood that any explanations and embodiments pertaining to the deprotection mixture M-b may also apply to the deprotection mixture M-g. It will also be understood that any explanations and embodiments pertaining to the deprotection mixture M-b’ may also apply to the deprotection mixture M-g’. In the context of steps (h) and (h’), cleaving an oligonucleotide from the solid support may be understood in the broadest sense as any operation, typically a chemical reaction, leading to the cleavage of the covalent linkage between the respective oligonucleotide and said solid support. If the respective oligonucleotide is covalently linked to a solid support via a direct covalent bond, cleaving an oligonucleotide from the solid support in step (h) and (h’) refers to the cleavage of said direct covalent bond. If the respective oligonucleotide is covalently linked to a solid support via a linker moiety, cleaving an oligonucleotide from the solid support in steps (h) and (h’) refers to the cleavage of the covalent bond between said linker moiety and the respective oligonucleotide. In both cases, the respective oligonucleotide will no longer be covalently linked to the solid support. If a “capping moiety” has been introduced between the terminal nucleoside moiety of component C-0 and the linker moiety or the solid support, as e.g. shown in Formulae I, I-a, and I-b (if CA is not a covalent chemical bond), said capping moiety will not be cleaved from the respective oligonucleotide in the course of step (h) or step (h’), in contrast to a linker moiety. Therefore, as used herein, the expression “capping moiety” may refer to any moiety, which is conjugated to a terminal nucleoside moiety of the oligonucleotide strand. If present in the component C-0, the capping moiety is also comprised in the final oligonucleotide product, i.e. in the target oligonucleotide O T . An example for such a strategy is the insertion of a 3’-GalNAc conjugate as described in, e.g., WO2009073809. A person skilled in the art knows how to cleave an oligonucleotide from a solid support. Typically, such cleavage may be achieved by treating the support-bound oligonucleotide with a base such as an organic amine or alkali hydroxides, wherein concentrated aqueous ammonia (i.e. aqueous ammonium hydroxide solution) is most common and herein preferred. This base (e.g. ammonia) treatment may, for example, be performed at room temperature or under heating, for example to 40−60 °C, e.g. in an autoclave or sealed vessel. Under such alkaline conditions, the typical nucleobase protecting groups will be cleaved as well. As non-limiting, but common examples, any isobutyryl groups from the exocyclic amino group of guanine, any benzoyl groups from the exocyclic amino group of adenine, and any benzoyl or acetyl groups from the exocyclic amino group of cytosine or 5-methylcytosine will typically be cleaved (i.e. removed) under such alkaline conditions. It is understood by those skilled in the art that the protecting groups R z-1 of a component C-0 of any one of Formulae I, I-a, and I-b, as well as the protecting groups R z-2 of each building block B-1 and B-x of any one of Formulae II, II-a, II-b, II-1, II-1-a, II-1-b, II-2, II-2-a, and II-2-b, and the protecting groups R z-3 of each building block B-1 and B-x of any one of Formulae II-1, II-1-a, and II-1-b will typically still be comprised in the n-th cycle oligonucleotide O-n which is to be cleaved from the solid support. Any such protecting groups R z-1 , R z-2 , and R z-3 will typically be selected so that they may be cleaved (i.e. removed) under alkaline conditions, i.e. during the cleavage step (h’). R z-1 , R z-2 , and R z-3 being the 2-cyanoethyl protecting group is a prime example for this strategy. Any 2-cyanoethyl protecting groups may be removed in the course of the base treatment to effect cleavage from the solid support. As known to those skilled in the art, the cleavage step (h) and step (h’) may comprise subsequent treatments with different types of bases. For example, first, a solution of an organic amine such as diethylamine (DEA) or triethylamine (TEA), e.g. in a suitable solvent such as acetonitrile, may be used to remove the 2-cyanoethyl protecting groups, preferably at room temperature, followed by treatment with concentrated aqueous ammonia, preferably at a temperature in the range of 40−60 °C, to effect cleavage from the solid support and removal of base labile permanent protecting groups such as the nucleobase protecting groups. In some embodiments of the method of the invention, said method further comprises a step (i) of modifying the first cycle oligonucleotide O-1 or (O-1) # . In some embodiments of the method of the invention, said method further comprises a step (i’) of modifying the n-th cycle oligonucleotide O-n or (O-n) # . In the context of steps (i) and (i’) of the method of the invention, the term “modifying” may be understood in the broadest sense to embrace “chemically modifying” and/or “biotechnologically modifying” the respective oligonucleotides. In the context of steps (i) and (i’) of the method of the invention, the term “chemically modifying” refers to subjecting the oligonucleotide to be chemically modified to one or more chemical reactions. Such a chemical reaction may, for example, be conjugation with a carbohydrate moiety, the introduction or removal of one or more protecting groups, and intramolecular bond formation to achieve cyclization. In the context of steps (i) and (i’) of the method of the invention, the term “biotechnologically modifying” refers to subjecting the oligonucleotide to be biotechnologically modified to one or more enzymatic reactions. As used herein, the term “enzymatic reaction” refers to any reaction which is enabled by and/or catalyzed by one or more enzymes. For example, the one or more enzymatic reactions of step (i) and (i’) may be used to ligate two or more nucleosides or oligonucleotides. In some embodiments of the method of the invention, said method further comprises a step (k) of isolating the target oligonucleotide O T . The means of isolating oligonucleotides upon oligonucleotide synthesis form part of the common knowledge of those skilled in the art. Typically, such a step of isolating an oligonucleotide comprises one or more purification steps and one or more steps aiming at obtaining the oligonucleotide in solid form. For oligonucleotide purification, chromatographic methods may typically be used, in particular ion exchange (especially anion exchange) chromatography and reversed phase (RP) HPLC, e.g. in form of hydrophobic interaction HPLC. These techniques are known to those skilled in the art. Additionally, a step of isolating an oligonucleotide may comprise ultrafiltration and/or desalting steps. For example, a solution obtained after cleaving oligonucleotides from the solid support may be submitted to ultrafiltration and/or desalting, ion exchange chromatography, and another round of ultrafiltration and/or desalting. Alternatively, the support-cleaved oligonucleotides may be submitted to reversed phase (RP) HPLC, e.g. in form of hydrophobic interaction HPLC. The latter method may preferably be performed, if the oligonucleotides still carry the 5´- terminal hydroxyl protecting group, e.g. the DMT group. Said 5´-protecting group may even be removed on the RP-HPLC column by passing an acidic solution through the column. If the 5´-terminal protecting group has been removed prior to purification, e.g. prior to cleaving the oligonucleotide from the support, ion exchange chromatography may be preferred. Purification is typically followed by one or more steps aiming at obtaining the oligonucleotide in solid form. Lyophilization or spray drying may, for example, be used. In some cases, it may be desirable to obtain the oligonucleotide in form of a salt with certain counter ions. In such cases salt exchange may be performed, typically prior to lyophilization or spray drying. In some embodiments of the method of the invention, the synthesis is carried out at a scale of at least 100 mmol of the target oligonucleotide O T . This means that in such embodiments, the maximum theoretical amount of the target oligonucleotide O T to be obtained from the synthesis by the method of the invention is at least 100 mmol. The maximum theoretical amount of the target oligonucleotide O T equals the total molar amount of the component C-0 provided in step (a), under the assumption that all process steps are 100 % efficient (i.e. proceed with quantitative yield of the desired product). For example, the scale of the synthesis would be 100 mmol, if 100 mmol of component C-0 have been utilized (e.g. provided in step (a)). It will be understood that the scale refers to a single synthesis process (i.e. to a single batch) and not to the sum of several batches handled in parallel or subsequently. This does of course not exclude such parallel or subsequent handling of batches by the method of the invention. Since the component C-0 is covalently linked to a solid support, the molar mass of the component C-0 may not be accessible. In this case, the molar amount of the component C-0 is typically assumed to be identical to the molar amount of functional groups (typically hydroxyl moieties) at the solid support used to synthesize the oligonucleotide. Herein, the term “the synthesis” refers to the synthesis of the target oligonucleotide O T by the method of the invention, unless indicated differently. In some embodiments of the method of the invention, the synthesis is carried out at a scale of at least 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 25, 30, or 35 mol. In one aspect, the present invention provides the use of a liquid composition C comprising a solvent, a protic acid having a pKa equal to or smaller than 4, and at least one alcohol, in which alcohol, one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, for suppressing nucleobase cleavage, in particular depurination, while effecting cleavage of a protecting group comprising an optionally substituted triarylmethyl residue, in particular a di(p-methoxyphenyl)phenylmethyl protecting group, from a hydroxyl moiety during the chemical synthesis of an oligonucleotide. In one aspect, the present invention provides the use of a liquid composition C comprising a solvent, a protic acid having a pKa equal to or smaller than 4, and at least one alcohol, in which alcohol, one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, for suppressing nucleobase cleavage, in particular depurination, while effecting cleavage of a protecting group comprising an optionally substituted triarylmethyl residue, in particular a di(p-methoxyphenyl)phenylmethyl protecting group, from a hydroxyl moiety during the solid-phase synthesis of an oligonucleotide. In one aspect, the present invention provides the use of a liquid composition C comprising a solvent, a protic acid having a pKa equal to or smaller than 4, and at least one alcohol, in which alcohol, one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, for suppressing nucleobase cleavage, in particular depurination, while effecting cleavage of a protecting group comprising an optionally substituted triarylmethyl residue, in particular a di(p-methoxyphenyl)phenylmethyl protecting group, from a hydroxyl moiety during the solid-phase synthesis of an oligonucleotide, wherein said hydroxyl moiety is part of a nucleoside moiety comprising a purine type nucleobase, preferably a nucleobase selected from the group consisting of adenine and guanine, in particular adenine. As used herein, the term “suppressing nucleobase cleavage” may be understood in the broadest sense as reducing the degree of (undesired) nucleobase cleavage. Nucleobase cleavage may be prevented completely or partly upon cleavage of the triarylmethyl type protecting group, e.g. the DMT protecting group. Along the same lines, the term “suppressing depurination” may be understood in the broadest sense as reducing the degree of (undesired) depurination. Depurination may be prevented completely or partly upon cleavage of the triarylmethyl type protecting group, e.g. the DMT protecting group. The degree of nucleobase cleavage / depurination may be used to compare different detritylation protocols with regards to undesired nucleobase cleavage / depurination. Briefly, in a chromatogram (preferred detection wavelength: 260 nm) obtained from HPLC-MS analysis of a synthesized oligonucleotide (cleaved from the support, if support-assisted synthesis was used), the areas of (i.e. underneath) peaks of the nucleobase cleavage-derived / depurination-derived side products may be summed up to obtain the summed up peak area of all identified nucleobase cleavage-derived / depurination-derived side products. The degree of nucleobase cleavage / depurination in percent (%) may then be determined by dividing the summed up peak area of nucleobase cleavage- derived / depurination-derived side products by the area of (i.e. underneath) the peak of the desired product of the respective oligonucleotide synthesis, followed by multiplication with 100 % to arrive at a value in percent (%). Obviously, a low degree of nucleobase cleavage / depurination is desirable. It will be understood that the terms “area of a peak” and “area underneath a peak” are herein used interchangeably. It will be understood that different detritylation protocols may preferably be compared for the synthesis of the same target oligonucleotide (leading to the same nucleobase cleavage-derived / depurination-derived side products). In some embodiments, suppressing nucleobase cleavage is reducing the degree of nucleobase cleavage by at least 5 %, 10 %, 25 %, 50 %, 75 %, or at least 90 % in comparison to a comparable detritylation protocol differing only in that a 1.218 M (i.e.1.218 mol/L) solution of DCA in toluene is used instead of the liquid composition C of the invention. Along the same lines, in some embodiments, suppressing depurination is reducing the degree of depurination by at least 5 %, 10 %, 25 %, 50 %, 75 %, or at least 90 % in comparison to a comparable detritylation protocol differing only in that a 1.218 M (i.e.1.218 mol/L) solution of DCA in toluene is used instead of the liquid composition C of the invention. In this context, the term "comparable detritylation protocol" may refer to a protocol (i.e. procedure or method) of removing a protecting group comprising an optionally substituted triarylmethyl residue, preferably a DMT protecting group, under similar conditions, e.g. same substrate, scale, temperature, time, and volume of the detritylation cocktail, differing only with respect to the composition of the detritylation cocktail, e.g.1.218 M DCA in toluene vs a liquid composition C of the present invention. The meaning of the term "reducing" in the context of the degree of nucleobase cleavage or the degree of depurination will be understood by a person skilled in the art, and may be exemplified as follows: If dividing the degree of depurination of a first synthesis A using the liquid composition C of the invention for detritylation by the degree of depurination of a second synthesis B using 1.218 M DCA in toluene for detritylation gives a quotient of 0.95, the degree of depurination is said to be reduced by 5 %. The terms “effecting cleavage of a protecting group” and “cleaving a protecting group” may be understood in the broadest sense and refer to any process of removing a protecting group from an atom or functional group, e.g. a hydroxyl moiety, so that the latter is again available in free form, e.g. as a hydroxyl group. In one aspect, the present invention provides a composition comprising - an oligonucleotide which is covalently linked to a solid support and comprises a hydroxyl moiety protected by a protecting group comprising an optionally substituted triarylmethyl residue, in particular a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group, and - a liquid composition C comprising a solvent, a protic acid having a pKa equal to or smaller than 4, and at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety. In a preferred embodiment, the composition and/or one or more components are preferably defined as in the context of the method herein. In a preferred embodiment, the protecting group comprising an optionally substituted triarylmethyl residue is defined as in the context of the method herein, the protic acid is defined as in the context of the method herein, the at least one alcohol and/or the concentration thereof are defined as in the context of the method herein, and/or said solvent is defined as in in the context of the method herein. In a preferred embodiment, the protecting group comprising an optionally substituted triarylmethyl residue, the protic acid, the at least one alcohol and/or the concentration thereof, and the solvent are each defined as in in the context of the method herein. In one aspect, the present invention provides a composition comprising - an oligonucleotide which is covalently linked to a solid support and comprises a hydroxyl moiety protected by a protecting group comprising an optionally substituted triarylmethyl residue, in particular a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group, wherein said hydroxyl moiety is part of a nucleoside moiety comprising a purine type nucleobase, preferably a nucleobase selected from the group consisting of adenine and guanine, in particular adenine, and - a liquid composition C comprising a solvent, a protic acid having a pKa equal to or smaller than 4, and at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety. In some embodiments of the method, the use, and the composition of the invention, each protecting group comprising an optionally substituted triarylmethyl residue is at each occurrence a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group. In such embodiments of the method of the invention, the protecting group PG-0, the protecting group PG-1 and each protecting group PG-x and each protecting group PG-(x−1) is a DMT protecting group. In some embodiments of the method, the use, and the composition of the invention, each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety is independently an alcohol of the following Formula D: (Formula D), wherein in Formula D: R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are independently of each other selected from the group consisting of H, OH, a C1−C6-alkyl group, O(C1−C6-alkyl), C(O)(C1−C6-alkyl), C(O)O(C1−C6-alkyl), F, Cl, Br, I, and CN. As used herein, in line with common practice, a carbon-bound oxygen atom may be written in brackets to denote that it is a carbonyl oxygen atom, which does not bear any further substituents. For example: O(C1−C6-alkyl) denotes an alkoxy group, in which the C1−C6-alkyl residue is bonded to the oxygen atom, while C(O)(C1−C6-alkyl) denotes an alkanoyl group, in which the C1−C6-alkyl residue is bonded to a carbonyl carbon atom. In some embodiments, in an alcohol of the aforementioned Formula D, R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are independently of each other selected from the group consisting of H, CH3, OCH3, and OH, with the proviso that at least four of the residues R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are H. In some embodiments, in an alcohol of the aforementioned Formula D, R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are independently of each other selected from the group consisting of H, CH 3 , and OCH 3 , with the proviso that at least four of the residues R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are H. In some embodiments of the method, the use, and the composition of the invention, each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety is independently selected from the group consisting of m-cresol, 4-methoxyphenol, phenol, and resorcinol. In some embodiments of the method, the use, and the composition of the invention, each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety is independently selected from the group consisting of m-cresol, 4-methoxyphenol, and phenol. In some embodiments of the method, the use, and the composition of the invention, each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety is independently selected from the group consisting of m-cresol and 4-methoxyphenol. In some embodiments of the method, the use, and the composition of the invention, said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety is m-cresol. In some embodiments of the method, the use, and the composition of the invention, the liquid composition C comprises said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, in a molar concentration of 0.45−5.6 mol/L, 0.9−5.0 mol/L, 1.0−4.5 mol/L, 1.0−4.0 mol/L, 1.5−4.0 mol/L, 1.5−3.5 mol/L, 2.0−3.5 mol/L, 2.0−3.0 mol/L, or 2.5−3.0 mol/L. Herein, reference is occasionally made to molar concentrations (e.g. in mol/L (i.e. M) or in mmol/L (i.e. mM)). The molar concentration of a component of a solution or liquid composition, e.g. a liquid composition C, is herein determined by dividing the total molar amount of the respective component as added to said solution or liquid composition by the total volume of said solution or liquid composition. The total volume of a solution or liquid composition is herein determined volumetrically directly from said solution or composition after all components have been added. The term “total molar amount of the respective component” is used to highlight that, if the respective component should be added in several portions to said solution or composition, the molar amounts of these distinct portions are to be summed up to arrive at said “total molar amount of the respective component”. Likewise, if the respective component is in fact a mixture of two or more components, the “total molar amount of the respective component” denotes the summed up molar amounts of these two or more components. For example, said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, may be a mixture of, e.g., 4-methoxyphenol and m-cresol, wherein, in this case, the total molar amount of said alcohol would be the sum of the molar amounts of 4-methoxyphenol and m-cresol. Unless indicated differently, volumes are herein determined at 22 °C. In some embodiments of the method, the use, and the composition of the invention, the liquid composition C comprises said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, in a molar concentration of 0.45−5.60 mol/L and/or each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety is independently an alcohol of the following Formula D: (Formula D), wherein in Formula D: R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are independently of each other selected from the group consisting of H, OH, a C1−C6-alkyl group, O(C1−C6-alkyl), C(O)(C1−C6-alkyl), C(O)O(C 1 −C 6 -alkyl), F, Cl, Br, I, and CN. In some embodiments of the method, the use, and the composition of the invention, the liquid composition C comprises a solvent, a protic acid having pKa equal to or smaller than 4, and at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, wherein - said protic acid comprised in the liquid composition C is selected from the group consisting of a carboxylic acid, a sulfonic acid, a mineral acid, a protonated aliphatic, aromatic or heteroaromatic amine, whose protonated form has a pKa in the range of 1−4, and mixtures thereof; - each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, is independently an alcohol of the following Formula D: (Formula D), wherein in Formula D: R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are independently of each other selected from the group consisting of H, OH, a C1−C6-alkyl group, O(C1−C6-alkyl), C(O)(C1−C6-alkyl), C(O)O(C1−C6-alkyl), F, Cl, Br, I, and CN; and - the sum of molar concentrations of alcohols of Formula D in the liquid composition C is within the range of 0.45−5.6 mol/L, 0.9−5.0 mol/L, 1.0−4.5 mol/L, 1.0−4.0 mol/L, 1.5−4.0 mol/L, 1.5−3.5 mol/L, 2.0−3.5 mol/L, 2.0−3.0 mol/L, or 2.5−3.0 mol/L. In some embodiments of the method, the use, and the composition of the invention, the liquid composition C does not contain any of trifluoroethanol (i.e., 2,2,2- trifluoroethanol, TFE), hexafluoroisopropanol, (i.e., 1,1,1,3,3,3-hexafluoro-2- propanol, HFIP), pentafluoropropanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, and nonafluoro tertiary butyl alcohol. In some embodiments of the method, the use, and the composition of the invention, the liquid composition C does not contain any polyfluorinated alcohol. In this context, the term “polyfluorinated alcohol” refers to an alcohol having in its chemical structure two or more fluorine atoms covalently bonded to the same carbon atom. TFE and HFIP are examples of such polyfluorinated alcohols. In some embodiments of the method, the use, and the composition of the invention, the liquid composition C does not contain any fluorinated alcohol. In this context, the term “fluorinated alcohol” refers to an alcohol having in its chemical structure one or more fluorine atoms covalently bonded to a carbon atom. TFE and HFIP are thus also examples of fluorinated alcohols. However, 2-fluoroethanol is a fluorinated alcohol as defined herein but is not a polyfluorinated alcohol as defined herein. In some embodiments of the method, the use, and the composition of the invention, the liquid composition C comprises a solvent, a protic acid having pKa equal to or smaller than 4, and at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, wherein - said protic acid comprised in the liquid composition C is selected from the group consisting of a carboxylic acid, a sulfonic acid, a mineral acid, a protonated aliphatic, aromatic or heteroaromatic amine, whose protonated form has a pKa in the range of 1−4, and mixtures thereof; - each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, is independently an alcohol of the following Formula D: (Formula D), wherein in Formula D: R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are independently of each other selected from the group consisting of H, OH, a C1−C6-alkyl group, O(C1−C6-alkyl), C(O)(C1−C6-alkyl), C(O)O(C1−C6-alkyl), F, Cl, Br, I, and CN; and - the liquid composition C does not contain any of trifluoroethanol (i.e., 2,2,2- trifluoroethanol, TFE), hexafluoroisopropanol, (i.e., 1,1,1,3,3,3-hexafluoro-2- propanol, HFIP), pentafluoropropanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2- propanol, and nonafluoro tertiary butyl alcohol, and does preferably not contain any polyfluorinated alcohol. In some embodiments of the method, the use, and the composition of the invention, the liquid composition C comprises a solvent, a protic acid having pKa equal to or smaller than 4, and at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, wherein - said protic acid comprised in the liquid composition C is selected from the group consisting of a carboxylic acid, a sulfonic acid, a mineral acid, a protonated aliphatic, aromatic or heteroaromatic amine, whose protonated form has a pKa in the range of 1−4, and mixtures thereof; - each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, is independently an alcohol of the following Formula D: (Formula D), wherein in Formula D: R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are independently of each other selected from the group consisting of H, OH, a C 1 −C 6 -alkyl group, O(C 1 −C 6 -alkyl), C(O)(C 1 −C 6 -alkyl), C(O)O(C 1 −C 6 -alkyl), F, Cl, Br, I, and CN; - the sum of molar concentrations of alcohols of Formula D in the liquid composition C is within the range of 0.45−5.6 mol/L, 0.9−5.0 mol/L, 1.0−4.5 mol/L, 1.0−4.0 mol/L, 1.5−4.0 mol/L, 1.5−3.5 mol/L, 2.0−3.5 mol/L, 2.0−3.0 mol/L, or 2.5−3.0 mol/L; and - the liquid composition C does not contain any of trifluoroethanol (i.e., 2,2,2- trifluoroethanol, TFE), hexafluoroisopropanol, (i.e., 1,1,1,3,3,3-hexafluoro-2- propanol, HFIP), pentafluoropropanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2- propanol, and nonafluoro tertiary butyl alcohol, and does preferably not contain any polyfluorinated alcohol. In some embodiments of the method, the use, and the composition of the invention, the total molar amount of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, comprised in the liquid composition C is in the range of 2.0−150.0, 2.0−120.0, 2.0−100.0, 2.0−95.0, 2.5−95.0, 3.0−95.0, 3.0−90.0, 3.0−85.0, 3.0−80.0, 3.0−75.0, 3.0−70.0, or 3.0−65.0 equivalents relative to the total molar amount of nucleobases. The term "total molar amount of nucleobases" may refer to the overall molar amount of all nucleobases present in the respective mixture, e.g. the liquid composition C. It is understood that the nucleobases will essentially all, or at least mostly, be part of nucleoside subunits of the oligonucleotides, from which the protecting group comprising an optionally substituted triarylmethyl residue, preferably the DMT group, is to be cleaved. For example, if the liquid composition C is used to cleave DMT protecting groups from 1.0 mol of an oligonucleotide, whose molecules each comprise 5 nucleobases, the total molar amount of nucleobases is 5.0 mol. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C has a pKa in the range of −10 to 4, −7 to 4, −6 to 4, −5 to 4, −4 to 4, −3 to 4, −2 to 4, −1 to 4, 0 to 4, 0 to 3, or 0 to 2. The term “protic acid” and the conditions for determining the pKa value have been laid out above. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C is selected from the group consisting of a carboxylic acid, a sulfonic acid, a mineral acid, a protonated aliphatic, aromatic or heteroaromatic amine, whose protonated form has a pKa in the range of 1−4, and mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C is selected from the group consisting of a carboxylic acid, a sulfonic acid, a mineral acid, a protonated aliphatic or heteroaromatic amine, whose protonated form has a pKa in the range of 1−4, and mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C is selected from the group consisting of a carboxylic acid, a sulfonic acid, a mineral acid, a protonated heteroaromatic amine, whose protonated form has a pKa in the range of 1−4, and mixtures thereof. Examples of carboxylic acids of the liquid composition C of the invention are halogenated acetic acids such as trifluoroacetic acid (TFA), dichloroacetic acid (DCA), and trichloroacetic acid (TCA), wherein TFA and DCA may be preferred. Examples of sulfonic acids of the liquid composition C of the invention are methanesulfonic acid and p-toluenesuffonic acid. Examples of mineral acids of the liquid composition C of the invention are hydrochloric acid and sulfuric acid. Examples of aliphatic amines of the liquid composition C of the invention are triethylamine (TEA) and diisopropylethylamine (DIPEA). Examples of aromatic amines of the liquid composition C of the invention are diphenylamine and aniline derivatives with electron withdrawing substituents. As used herein, the term “electron withdrawing substituent(s)” may refer to substituents selected from the group consisting of a halogen atom such as a chlorine, fluorine, or bromine, a cyano group, an aldehyde group, a keto group, a carboxyester group, or a carboxamide group, unless indicated differently in the context of specific embodiments. Examples of heteroaromatic amines of the liquid composition C of the invention are pyrimidine, pyridine, pyrazine, thiazole, pyridazine, pyrazole or triazole, all of which may optionally be substituted with electron donating or electron withdrawing substituents. For example, the heteroaromatic amine may be a pyrimidine, a pyridine, a thiazole, a pyridazine, a pyrazole, or a 1,2,4-triazole, substituted with one or more electron withdrawing substituent(s). As another example, the heteroaromatic amine may be a pyrimidine or a pyrazine substituted with one or more electron donating substituent(s). The electron donating substituent(s) may for example be a methoxy group. Preferably, the heteroaromatic amine may be a pyridine, which is substituted with one or more electron withdrawing substituents selected from the group consisting of a halogen atom, a cyano group, an aldehyde group, a keto group, a carboxyester group, and a carboxamide group. Preferably, the heteroaromatic amine may be a pyridine, in which exactly one hydrogen residue is substituted by an electron withdrawing substituent selected from the group consisting of a cyano group and a halogen atom (F, Cl, Br, I). In particular, the heteroaromatic amine may be selected from the group consisting of 4-cyanopyridine, 3-cyanopyridine, 4-chloropyridine, 3-chloropyridine, and a mixture thereof, among which 4-cyanopyridine may be most preferred. For example, the pKa values of diversely substituted pyridinium ions may be taken from or determined according to the procedure disclosed in: A. Fischer et al., Journal of the Chemical Society 1964, 3591-3596. It will be understood by those skilled in the art that a protonated form of an aliphatic, aromatic or heteroaromatic amine is typically obtained by combining said amine with a protic acid, e.g. a carboxylic acid or sulfonic acid or mineral acid, which is capable of protonating the amine. It will be understood that said combination of an acid and an amine may be a preformed salt of the acid and the amine. Alternatively, the acid and the heteroaromatic amine may be added as such (i.e. not as preformed salt). Thus, the amine may be combined with a protic acid, wherein the protic acid has a smaller pKa value than the protonated form of the amine. The combination of said amine and said protic acid may occur beforehand, so as to obtain a salt of a protic acid and an amine. Alternatively, the amine and a protic acid may be combined in the liquid composition C. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C is selected from the group consisting of a (hetero)alkylsulfonic acid, an (hetero)arylsulfonic acid, a hydrogen halide, sulfuric acid, a protonated heteroaromatic amine, whose protonated form has a pKa in the range of 1−4, and mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C is selected from the group consisting of a dihalogenated acetic acid, a trihalogenated actic acid, an alkylsulfonic acid, an arylsulfonic acid, a hydrogen halide, sulfuric acid, a protonated heteroaromatic amine, whose protonated form has a pKa in the range of 1−4, and mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C is selected from the group consisting of a dihalogenated acetic acid, a trihalogenated actic acid, an alkylsulfonic acid, an arylsulfonic acid, a hydrogen halide, a protonated heteroaromatic amine selected from the group consisting of 4-cyanopyridine, 3- cyanopyridine, 4-chloropyridine, and 3-chloropyridine, and mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C is selected from the group consisting of trifluoroacetic acid, dichloroacetic acid, trichloroacetic acid, hydrochloric acid, methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, a combination of any of these acids with a heteroaromatic amine selected from the group consisting of 4-cyanopyridine, 3-cyanopyridine, 4-chloropyridine, and 3-chloropyridine, and mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C is selected from the group consisting of trifluoroacetic acid, dichloroacetic acid, trichloroacetic acid, hydrochloric acid, methanesulfonic acid, p- toluenesulfonic acid, a combination of any of these acids with a heteroaromatic amine selected from the group consisting of 4-cyanopyridine, 3-cyanopyridine, 4- chloropyridine, and 3-chloropyridine, and mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C is selected from the group consisting of trifluoroacetic acid, dichloroacetic acid, hydrochloric acid, methanesulfonic acid, a combination of any of these acids with a heteroaromatic amine selected from the group consisting of 4-cyanopyridine, 3-cyanopyridine, 4-chloropyridine, and 3-chloropyridine, and mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C is selected from the group consisting of trifluoroacetic acid, dichloroacetic acid, 4-chloropyridinium hydrochloride, and 4- cyanopyridiniumtrifluoroacetate. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C is selected from the group consisting of dichloroacetic acid and 4-cyanopyridinium trifluoroacetate. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C is dichloroacetic acid. In some embodiments of the method, the use, and the composition of the invention, said protic acid comprised in the liquid composition C is 4-cyanopyridinium trifluoroacetate. In some embodiments of the method, the use, and the composition of the invention, the liquid composition C comprises said protic acid in a concentration of 0.01−2.0 mol/L, 0.05−1.5 mol/L, 0.05−1.25 mol/L, 0.05−1.0 mol/L, 0.05−0.9 mol/L, 0.05−0.8 mol/L, 0.05−0.7 mol/L, 0.05−0.6 mol/L, 0.05−0.5 mol/L, 0.05−0.4 mol/L, 0.05−0.35 mol/L, 0.06−0.35 mol/L, 0.07−0.35 mol/L, 0.08−0.35 mol/L, 0.09−0.35 mol/L, 0.09−0.3 mol/L, or 0.09−0.25 mol/L. The means of determining the molar concentration of a component of a solution or liquid composition, e.g. a liquid composition C, have been laid out above and apply to said protic acid comprised in the liquid composition C. As laid out above, said protic acid may also be a protonated aliphatic, aromatic or heteroaromatic amine, whose protonated form has a pKa in the range of 1−4. As also laid out above, such a protonated form of an amine may typically be obtained by combining said amine with a protic acid, e.g. a carboxylic acid or sulfonic acid or mineral acid, which is capable of protonating the amine. This combination may either occur by adding the amine and the acid into the respective solution or by preforming a salt of said acid and said amine and adding the preformed salt to the solution. If a preformed salt is used, the molar concentration of the protic acid is to be determined based on the total molar amount of said preformed salt, which was used to prepare the liquid composition, e.g. the liquid composition C, provided that the acid and the amine are present in a 1:1 stoichiometry in said salt, as e.g. in 4-chloropyridinium hydrochloride. Otherwise, the stoichiometry of the acid and the amine in said salt will routinely be taken into account. If, however, a protic acid and a non-protonated amine are added separately and protonation of the amine may occur after addition, the total molar amount of the protic acid added alongside the amine in the first place is to be used for calculating the concentration of the protic acid in the liquid composition, e.g. the liquid composition C. As a first example: If 4-cyanopyridine and trifluoroacetic acid (TFA) are added separately during the preparation of a liquid composition C, the total molar amount of TFA is used for calculating the molar concentration of said protic acid comprised in the liquid composition C. As a second example: If a preformed salt, e.g. 4-chloropyridinium hydrochloride, is added during the preparation of a liquid composition C, the total molar amount of said salt is used for calculating the molar concentration of said protic acid comprised in said liquid composition C. In some embodiments of the method, the use, and the composition of the invention, the total molar amount of said protic acid comprised in the liquid composition C is in the range of 0.80−15.0, 1.0−13.0, or 2.0−12.50 equivalents relative to the total molar amount of protecting groups comprising an optionally substituted triarylmethyl residue, preferably the di(p-methoxyphenyl)phenylmethyl (DMT) groups. The term “total molar amount” when referring to a protecting group such as the DMT group refers to the total molar amount of the compound(s) carrying the respective protecting group multiplied with the amount of said protecting group per molecule of these compound(s). For example, if a composition comprises 1.0 mol of a compound having exactly one DMT group per molecule (and no other compound in said composition comprises any DMT groups), the total molar amount of DMT groups in said composition equals the total molar amount of said compound and would in this example also be 1.0 mol. In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is an aprotic solvent. As used herein, an “aprotic solvent” is a solvent that is not a hydrogen bond donor. Hence, an aprotic solvent may be a solvent without any O−H or N−H bonds. Thus, an alcohol is not an aprotic solvent as defined herein. In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is a non-halogenated aprotic solvent. As used herein, a “non- halogenated solvent” is a solvent which does not comprise any halogen atoms (in particular F, Cl, Br, I) in its chemical structure. In some embodiments of the method, the use, and the composition of the invention, said liquid composition C comprises essentially no halogenated solvents. Examples of such halogenated solvents are dichloromethane (DCM), chloroform, and 1,2- or 1,1-dichloromethane. As used herein, the term “essentially no halogenated solvent” preferably means that any halogenated solvents (i.e. any solvents comprising in their chemical structure at least one halogen atom) together account for equal to or less than 3.0 %, 2.0 %, 1.0 %, 0.1 %, 0.01 %, or 0.001 % of the overall volume of said liquid composition C. If, for example, one or more halogenated solvents should be added during the preparation of a liquid composition C, the summed up volumes of these one or more halogenated solvents as added may be divided by the volumetrically determined total volume of the liquid composition C after all solvents and components have been added, followed by multiplication with 100 % to arrive at a value in % which represents the volume-% for which said one or more halogenated solvents account. The volume of the added solvent(s) and the volume of the liquid composition may be determined at 22 °C. Preferably, no halogenated solvent is added during the preparation of a liquid composition C and any potentially comprised traces of halogenated solvents in the liquid composition C may only be impurities of the solvent(s) or component(s) as obtained (commercially). In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is selected from the group consisting of a halogenated hydrocarbon solvent, a (hetero)aromatic solvent, an alkyl (hetero)aromatic solvent, a (hetero)aromatic ether, an alkyl (hetero)aryl ether, and mixtures thereof. Non-limiting examples of a halogenated hydrocarbon solvent comprise dichloromethane (DCM), dichloroethane, and chloroform. A non-limiting example of a (hetero)aromatic solvent is benzene. Non-limiting examples of an alkyl (hetero)aromatic solvent are toluene, o-xylene, m-xylene, p-xylene, and mesitylene. A non-limiting example of a (hetero)aromatic ether is diphenyl ether. A non-limiting example of an alkyl (hetero)aryl ether is anisole. In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is selected from the group consisting of - benzene, in which one or more hydrogen residues may optionally be substituted by a C1−C3-alkyl group or a O(C1−C3-alkyl) group (e.g. benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene, or anisole); - a halogenated C 1 −C 3 -alkyl solvent (e.g. dichloromethane, 1,1- or 1,2-dichloroethane, or chloroform); - an O(C 1 −C 6 -alkyl) 2 ether with in total not less than 4 carbon atoms (e.g. diethyl ether or cycplopentyl methyl ether); - an aliphatic cyclic ether with 4−6 ring carbon atoms, preferably 4 or 5 ring carbon atoms, in which one or more hydrogen residues may optionally be substituted by a C 1 −C 3 -alkyl group (e.g. tetrahydrofuran, tetrahydropyran or 1,4-dioxane); - a C 5 −C 9 -alkyl solvent (e.g. pentane, hexanes, cyclohexane, heptane, octane or nonane); - a C 1 −C 3 -alkyl solvent in which exactly one hydrogen residue is substituted for a nitrile group (CN) (e.g. acetonitrile or propionitrile); - an ester solvent of the formula (C1−C6-alkyl)-O-C(O)-(C1−C6-alkyl) (e.g. ethyl acetate); and - mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is selected from the group consisting of - benzene, in which one or more hydrogen residues may optionally be substituted by a C1−C3-alkyl group or a O(C1−C3-alkyl) group (e.g. benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene, or anisole); - an O(C1−C6-alkyl)2 ether with in total not less than 4 carbon atoms (e.g. diethyl ether or cycplopentyl methyl ether); - an aliphatic cyclic ether with 4−6 ring carbon atoms, preferably 4 or 5 ring carbon atoms, in which one or more hydrogen residues may optionally be substituted by a C 1 −C 3 -alkyl group (e.g. tetrahydrofuran, tetrahydropyran or 1,4-dioxane); - a C 5 −C 9 -alkyl solvent (e.g. pentane, hexanes, cyclohexane, heptane, octane or nonane); - a C 1 −C 3 -alkyl solvent in which exactly one hydrogen residue is substituted for a nitrile group (CN) (e.g. acetonitrile or propionitrile); - an ester solvent of the formula (C1−C6-alkyl)-O-C(O)-(C1−C6-alkyl) (e.g. ethyl acetate); and - mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is selected from the group consisting of - benzene, in which one or more hydrogen residues may optionally be substituted by a C 1 −C 3 -alkyl group or a O(C 1 −C 3 -alkyl) group (e.g. benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene, or anisole); - an O(C 1 −C 6 -alkyl) 2 ether with in total not less than 4 carbon atoms (e.g. diethyl ether or cycplopentyl methyl ether); - an aliphatic cyclic ether with 4−6 ring carbon atoms, preferably 4 or 5 ring carbon atoms, in which one or more hydrogen residues may optionally be substituted by a C 1 −C 3 -alkyl group (e.g. tetrahydrofuran, tetrahydropyran or 1,4-dioxane); - a C5−C9-alkyl solvent (e.g. pentane, hexanes, cyclohexane, heptane, octane or nonane); and - mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is selected from the group consisting of - benzene, in which one or more hydrogen residues may optionally be substituted by a C1−C3-alkyl group or a O(C1−C3-alkyl) group (e.g. benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene, or anisole); - a halogenated C1−C3-alkyl solvent (e.g. dichloromethane, 1,1- or 1,2-dichloroethane, or chloroform); and - mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is benzene, in which one or more hydrogen residues may optionally be substituted by a C 1 −C 3 -alkyl group or a O(C 1 −C 3 -alkyl) group (e.g. benzene, toluene, o-xylene, m-xylene, p-xylene, mesitylene, or anisole) or a mixture of such solvents. In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is selected from the group consisting of toluene, anisole, o-xylene, m-xylene, p-xylene, mesitylene, dichloromethane, and mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is selected from the group consisting of toluene, anisole, o-xylene, m-xylene, p-xylene, mesitylene, and mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is selected from the group consisting of toluene, anisole, and mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is toluene. In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is anisole. In some embodiments of the method, the use, and the composition of the invention, said solvent comprised in the liquid composition C is selected from the group consisting of toluene, anisole, dichloromethane, and mixtures thereof. In some embodiments of the method, the use, and the composition of the invention, the total volume of said solvent comprised in the liquid composition C accounts for 50−95 %, 50−90 %, 50−85 %, 50−80 %, 50−75 %, 50−70 %, or 60−70 % of the total volume of the liquid composition C. In order to determine the percentage of the total volume for which said solvent accounts, the total volume of said solvent added during the preparation of the liquid composition C is divided by the total volume of the liquid composition C, followed by multiplication with 100 % to arrive at a value in percent (%). The total volume of the liquid composition is herein determined volumetrically directly from said composition after all components have been added. The volume of the added solvent(s) and the volume of the liquid composition are to be determined at 22 °C. In some embodiments of the method, the use, and the composition of the invention, the total volume of the liquid composition C is in the range of 5−100 mL, 10−90 mL, 10−80 mL, 20−75 mL, 10−70 mL, 10−60 mL, 20−60 mL, 30−60 mL or 40−60 mL per 1 millimole (mmol) of the protecting group comprising an optionally substituted triarylmethyl residue, preferably the DMT group, to be cleaved (i.e. removed). The skilled practitioner will routinely adapt the total volume of the liquid composition C, so that the volume of the slurry containing the solid support is minimal while assuring efficient mass transport of reagents to the growing oligonucleotide chains and suitable macroscopic properties of the slurry. In some embodiments of the method, the use, and the composition of the invention: - the total molar amount of said protic acid comprised in the liquid composition C is in the range of 0.80−15.0 equivalents relative to the total molar amount of the protecting groups comprising an optionally substituted triarylmethyl residue; and - the total molar amount of said alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, comprised in the liquid composition C is in the range of the 2.0−210.0 equivalents relative to the total molar amount of nucleobases. In some embodiments of the method, the use, and the composition of the invention, the liquid composition C further comprises a carbocation scavenger. As used herein, the term “carbocation scavenger” relates to a nucleophilic compound, which may be used to bind a carbocation or to consume a carbocation by formal donation of a hydride anion, thereby preventing undesired side reactions of the carbocation. Typical examples of such carbocations are carbocations formed during the cleavage of protecting groups comprising an optionally substituted triarylmethyl residue. For example, the cleavage of a di(p-methoxyphenyl)phenylmethyl (DMT) protecting group may result in a DMT cation (i.e. a di(p-methoxyphenyl)phenylmethyl cation). Examples of carbocation scavengers are aliphatic alcohols (e.g. methanol and ethanol), water, silanes (e.g. triisopropylsilane (TIS) and triethylsilane (TES)), N-heterocycles (e.g. pyrrole, 3-methylpyrrole, 2,4-dimethylpyrrole indole, 2-methylindole, thiols and thiophenols (e.g. 1,2-ethanedithiol (EDT), 1,4- dithioerythrol (DTE), 1,4-dithiothreitol (DTT), 3,6-dioxa-1,8-octanedithiol (DODT), 1,4-benzenedimethanthiol (BDMT), 1,4-butanedithiol, 2-mercaptoethanol, cysteine, thiophenol, p-thiocresol, and thiomalic acid), and polyalkylbenzenes (e.g. 1,3,5- trimethylbenzene and pentamethylbenzene). In some embodiments of the method, the use, and the composition of the invention, the contact time between the liquid composition C and the oligonucleotide from which said protecting group comprising an optionally substituted triarylmethyl residue is to be cleaved is at least 5 min, at least 6 min, at least 7 min, at least 8 min, at least 9 min, at least 10 min, at least 15 min, at least 20 min, at least 30 min, or even more than 1 hour. Such comparably long-time intervals may allow the use of standard pumps having moderate pumping rates for comparably large-size reactors (e.g., column or batch reactors). Such long contacting times would result in undesired cleavage of nucleobases, in particular depurination, when used for detritylation cocktails commonly used in the art such as, e.g., detritylation cocktails containing larger contents of acids such as dichloroacetic acid (DCA) without an alcohol as defined in the present invention. It is a particular advantage of the present invention that the methods of oligonucleotide synthesis can be scaled up without a need to increase the maximum flow rate of the liquid handling system. Furthermore, compared to the standard deprotection protocol using 1.218 M dichloroacetic acid in toluene, the methods of the present invention may allow to increase batch size by a factor of at least 5 fold, preferably as least 10, 20, 30, or 40 fold, while using the same liquid handling system for supplying liquid to and draining liquid from the reaction vessel. For the sake of clarity, it is noted that the reaction vessel may be changed to accommodate the larger amount of reagents. In some embodiments of the method, the use, and the composition of the invention: - each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, comprised in the liquid composition C is an alcohol of the above-mentioned Formula D; - said protic acid comprised in the liquid composition C is selected from the group consisting of a carboxylic acid, a sulfonic acid, a mineral acid, a protonated aliphatic, aromatic or heteroaromatic amine, whose protonated form has a pKa in the range of 1−4, and mixtures thereof; - said solvent comprised in the liquid composition C is an aprotic solvent, preferably a non-halogenated aprotic solvent; and - the liquid composition C comprises said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, in a molar concentration of 0.45−5.6 mol/L. In some embodiments of the method, the use, and the composition of the invention: - each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, comprised in the liquid composition C is an alcohol of the above-mentioned Formula D; - said protic acid comprised in the liquid composition C is selected from the group consisting of a carboxylic acid, a sulfonic acid, a mineral acid, a protonated heteroaromatic amine, whose protonated form has a pKa in the range of 1−4, and mixtures thereof; - said solvent comprised in the liquid composition C is an aprotic solvent, preferably a non-halogenated aprotic solvent; and - the liquid composition C comprises said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, in a molar concentration of 0.45−5.6 mol/L. In some embodiments of method, the use, and the composition of the invention: - each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, comprised in the liquid composition C is an alcohol of the above-mentioned Formula D, wherein R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are independently of each other selected from the group consisting of H, CH3, and OCH3, with the proviso that at least four of the residues R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are H; - said protic acid comprised in the liquid composition C is selected from the group consisting of trifluoroacetic acid, dichloroacetic acid, trichloroacetic acid, hydrochloric acid, methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, a combination of any of these acids with a heteroaromatic amine selected from the group consisting of 4-cyanopyridine, 3-cyanopyridine, 4-chloropyridine, and 3-chloropyridine, and mixtures thereof; - said solvent comprised in the composition C is selected from the group consisting of benzene, in which one or more hydrogen residues may optionally be substituted by a C 1 −C 3 -alkyl group or a O(C 1 −C 3 -alkyl) group, and dichloromethane; and - the liquid composition C comprises said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, in a molar concentration of 0.45−5.6 mol/L. In some embodiments of method, the use, and the composition of the invention: - each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, comprised in the liquid composition C is an alcohol of the above-mentioned Formula D, wherein R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are independently of each other selected from the group consisting of H, CH3, and OCH3, with the proviso that at least four of the residues R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are H; - said protic acid comprised in the liquid composition C is selected from the group consisting of trifluoroacetic acid, dichloroacetic acid, trichloroacetic acid, hydrochloric acid, methanesulfonic acid, p-toluenesulfonic acid, a combination of any of these acids with a heteroaromatic amine selected from the group consisting of 4-cyanopyridine, 3-cyanopyridine, 4-chloropyridine, and 3-chloropyridine, and mixtures thereof; - said solvent comprised in the composition C is benzene, in which one or more hydrogen residues may optionally be substituted by a C 1 −C 3 -alkyl group or a O(C 1 −C 3 -alkyl); and - the liquid composition C comprises said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, in a molar concentration of 0.45−5.6 mol/L. In some embodiments of the method, the use, and the composition of the invention: - each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, comprised in the liquid composition C is selected from the group consisting of m-cresol, 4-methoxyphenol, and phenol; - said protic acid comprised in the liquid composition C is selected from the group consisting of trifluoroacetic acid, dichloroacetic acid, trichloroacetic acid, hydrochloric acid, methanesulfonic acid, p-toluenesulfonic acid, a combination of any of these acids with a heteroaromatic amine selected from the group consisting of 4-cyanopyridine, 3-cyanopyridine, 4-chloropyridine, and 3-chloropyridine, and mixtures thereof; - said solvent comprised in the composition C is selected from the group consisting of toluene, anisole, o-xylene, m-xylene, p-xylene, mesitylene, and mixtures thereof; and - the liquid composition C comprises said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, in a molar concentration of 0.45−5.6 mol/L. In some embodiments of the method, the use, and the composition of the invention: - each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, comprised in the liquid composition C is selected from the group consisting of m-cresol, 4-methoxyphenol, and phenol; - said protic acid comprised in the liquid composition C is selected from the group consisting of trifluoroacetic acid, dichloroacetic acid, hydrochloric acid, methanesulfonic acid, a combination of any of these acids with a heteroaromatic amine selected from the group consisting of 4-cyanopyridine, 3-cyanopyridine, 4-chloropyridine, and 3-chloropyridine, and mixtures thereof; - said solvent comprised in the composition C is selected from the group consisting of toluene, anisole, o-xylene, m-xylene, p-xylene, mesitylene, and mixtures thereof; and - the liquid composition C comprises said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, in a molar concentration of 0.45−5.6 mol/L; - the liquid composition C comprises said protic acid in a molar concentration of 0.01−2.0 mol/L. The present invention also refers to a use of a liquid composition C (deprotection mixture M-b) comprising a solvent, a protic acid having a pKa equal to or smaller than 4, and at least one alcohol, in which one or more hydroxylgroups are covalently bonded directly to an optionally substituted phenyl moiety, for cleaving one or more protecting groups PG-0 form a nucleoside or oligonucleotide. Preferably, the liquid composition C (deprotection mixture M-b) and/or one or more of its components is described as laid out in the context of the method or the composition. The invention, for example, pertains to the following phrases: 1. A method for the solid-phase synthesis of a target oligonucleotide O T comprising a step (b) of incubating a nucleoside or oligonucleotide, which is covalently linked to a solid support and comprises a backbone hydroxyl moiety protected by a protecting group PG-0 comprising an optionally substituted triarylmethyl residue, with a deprotection mixture M-b, thereby cleaving the protecting group PG-0 from the nucleoside or oligonucleotide, wherein said deprotection mixture M-b is a liquid composition C comprising a solvent, a protic acid having a pKa equal to or smaller than 4, and at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety. The method according to phrase 1, wherein the target oligonucleotide O T comprises a first cycle oligonucleotide O-1, and the method comprises the following step (a) and a first coupling cycle comprising the following steps (b) to (e): (a) providing a component C-0 selected from the group consisting of a nucleoside and an oligonucleotide, wherein the component C-0 is covalently linked to a solid support and comprises a backbone hydroxyl moiety protected by a protecting group PG-0 comprising an optionally substituted triarylmethyl residue; (b) incubating the component C-0 of step (a) with a deprotection mixture M-b, thereby cleaving the protecting group PG-0 from the component C-0, so as to obtain a component C-0 # having a free backbone hydroxyl group; (c) providing a building block B-1 selected from the group consisting of a nucleoside and an oligonucleotide, wherein the building block B-1 comprises a backbone hydroxyl moiety protected by a protecting group PG-1 comprising an optionally substituted triarylmethyl residue, and a phosphorus moiety covalently bonded via its phosphorus atom to an oxygen atom of the backbone of the building block B-1; (d) reacting the component C-0 # of step (b) with the building block B-1 of step (c) under conditions suitable to form a covalent bond between said free backbone hydroxyl group of the component C-0 # and the phosphorus atom of said phosphorus moiety of the building block B-1, thereby obtaining a first cycle oligonucleotide O-1; (e) optionally, incubating the first cycle oligonucleotide O-1 obtained in step (d) with an oxidizing or sulfurizing agent, thereby converting any P (III) atoms within said first cycle oligonucleotide O-1 to P (V) atoms; wherein in step (b), said deprotection mixture M-b is a liquid composition C comprising a solvent, a protic acid having a pKa equal to or smaller than 4, and at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety. 3. The method according to phrase 2, wherein the target oligonucleotide O T comprises a n-th cycle oligonucleotide O-n, and the method further comprises performing (n−1) iterations of a coupling cycle comprising the following steps (b’) to (e’), wherein n is an integer in the range of 2 to 99, which denotes the total number of coupling cycles performed to obtain the n-th cycle oligonucleotide O-n, and each individual coupling cycle comprising the following steps (b’) to (e’) is identified by a serial number x, which runs in steps of 1 from 2 to n: (b’) incubating the (x−1)-th cycle oligonucleotide O-(x−1) obtained in the previous coupling cycle with a deprotection mixture M-b’, thereby cleaving the protecting group PG-(x−1) from the (x−1)-th cycle oligonucleotide O-(x−1), so as to obtain a (x−1)-th cycle oligonucleotide (O-(x−1)) # having a free backbone hydroxyl group; (c’) providing a building block B-x selected from the group consisting of a nucleoside and an oligonucleotide, wherein the building block B-x comprises a backbone hydroxyl moiety protected by a protecting group PG-x comprising an optionally substituted triarylmethyl residue, and a phosphorus moiety covalently bonded via its phosphorus atom to an oxygen atom of the backbone of the building block B-x; (d’) reacting the (x−1)-th cycle oligonucleotide (O-(x−1)) # obtained in step (b’) with the building block B-x of step (c’) under conditions suitable to form a covalent bond between said free backbone hydroxyl group of the (x−1)-th cycle oligonucleotide (O-(x−1)) # and the phosphorus atom of said phosphorus moiety of the building block B-x, thereby obtaining a x-th cycle oligonucleotide O-x; (e’) optionally, incubating the x-th cycle oligonucleotide O-x obtained in step (d’) with an oxidizing or sulfurizing agent, thereby converting any P (III) atoms within said x-th cycle oligonucleotide O-x to P (V) atoms; wherein in at least one iteration of step (b’), said deprotection mixture M-b’ is a liquid composition C comprising a solvent, a protic acid having a pKa equal to or smaller than 4, and at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety. 4. The method according to any one of phrases 2 and 3, wherein: - the phosphorus moiety of the building block B-1 and each building block B-x is independently selected from the group consisting of a phosphoramidite moiety and a H-phosphonate monoester moiety; - in each coupling cycle, in which said phosphorus moiety of the building block B-1 or the building block B-x is a phosphoramidite moiety, step (e) or (e’) is carried out; and - at least in the final coupling cycle, step (e) or (e’) is carried out. The method according to any one of phrases 1 to 4, wherein said nucleoside or oligonucleotide, which is covalently linked to a solid support, of phrase 1 and the component C-0 of phrase 2 is a compound of the following Formula I: (Formula I), wherein in in Formula I: each oxygen atom (O) depicted within each nucleoside subunit x-0 to x-m represents the oxygen atom of a hydroxyl moiety of the respective nucleoside subunit; each of the nucleoside subunits x-0 to x-m may be the same or different; PG-0 is a protecting group comprising an optionally substituted triarylmethyl residue; m is an integer equal to or larger than 0; Y 1 is selected independently for each repetitive unit m from the group consisting of O and S; Z 1 is selected independently for each repetitive unit m from the group consisting of O-R z-1 and S-R z-1 ; R z-1 is a protecting group, which may be the same or different for each repetitive unit m; CA is a capping moiety or a covalent chemical bond; L is a linker moiety or a covalent chemical bond; and SM is a solid support. The method according to any one of phrases 2 to 5, wherein each of the building blocks B-1 and B-x is a compound of the following Formula II-1: (Formula II-1), wherein in Formula II-1: each oxygen atom (O) depicted within each nucleoside subunit y-0 to y-q represents the oxygen atom of a hydroxyl moiety of the respective nucleoside subunit; each nucleoside subunit y-0 to y-q may be the same or different; PG is the protecting group PG-1 or PG-x, and comprises an optionally substituted triarylmethyl residue; q is an integer equal to or larger than 0; Y 2 is selected independently for each repetitive unit q from the group consisting of O and S; Z 2 is selected independently for each repetitive unit q from the group consisting of O-R z-2 and S-R z-2 ; R z-2 is a protecting group, which may be the same or different for each repetitive unit q; Z 3 is selected from the group consisting of O and S; and R z-3 is a protecting group; each of R a and R b is independently a C 1 −C 6 -alkyl group, wherein R a and R b may be the same or different and may also bond to each other to form a 5-membered or 6-membered aliphatic cyclic amine moiety together with the nitrogen atom to which R a and R b are bonded; and wherein step (e) or step (e’) is carried out in each coupling cycle. 7. The method according to any one of phrases 2 to 6, wherein - the first coupling cycle further comprises a step (f) of reacting free hydroxyl groups with a blocking agent, wherein step (f) is carried out after step (d) or after step (e); and/or - at least one iteration of the (n−1) iterations of the coupling cycle comprising steps (b’) to (e’) further comprises a step (f’) of reacting free hydroxyl groups with a blocking agent, wherein step (f ’) is carried out after step (d’) or after step (e’). 8. The method according to any one of phrases 2 and 4 to 7, wherein - the method further comprises a step (g) of incubating the first cycle oligonucleotide O-1 with a deprotection mixture M-g, thereby cleaving the protecting group PG-1 from the first cycle oligonucleotide O-1, so as to obtain a first cycle oligonucleotide (O-1) # having a free backbone hydroxyl group; and/or - the method further comprises a step (h) of cleaving the first cycle oligonucleotide O-1 or (O-1) # from the solid support; and wherein, if both steps (g) and (h) are performed, they may be performed in any order. 9. The method according to any one of phrases 3 to 7, wherein - the method further comprises a step (g’) of incubating the n-th cycle oligonucleotide O-n with a deprotection mixture M-g’, thereby cleaving the protecting group PG-n from the n-th cycle oligonucleotide O-n, so as to obtain a n-th cycle oligonucleotide (O-n) # having a free backbone hydroxyl group; and/or - the method further comprises a step (h’) of cleaving the n-th cycle oligonucleotide O-n or (O-n) # from the solid support; and wherein, if both steps (g’) and (h’) are performed, they may be performed in any order. 10. The method according to any one of phrases 1 to 9, wherein at least steps (b) and (b’) are carried out in a batch reactor or wherein at least steps (b) and (b’) are carried out in a column reactor and the flow rate of the liquid composition C through the column reactor is below 300 cm/h. 11. The method according to any one of phrases 1 to 10, wherein - the backbone hydroxyl moiety protected by said protecting group PG-0 is part of a nucleoside moiety comprising a purine type nucleobase; and - in at least one iteration of the coupling cycle comprising steps (b’) to (e’), in which said protecting group PG-(x−1) is part of a nucleoside moiety comprising a purine type nucleobase, the deprotection mixture M-b’ is a liquid composition C. The method according to any one of phrases 1 to 11, wherein each protecting group comprising an optionally substituted triarylmethyl residue is a di(p-methoxyphenyl)phenylmethyl protecting group. The method according to any one of phrases 1 to 12, wherein the liquid composition C comprises said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, in a molar concentration of 0.45−5.60 mol/L and/or wherein each of said at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety is independently an alcohol of the following Formula D: (Formula D), wherein in Formula D: R D-1 , R D-2 , R D-3 , R D-4 , and R D-5 are independently of each other selected from the group consisting of H, OH, a C1−C6-alkyl group, O(C1−C6-alkyl), C(O)(C1−C6-alkyl), C(O)O(C1−C6-alkyl), F, Cl, Br, I, and CN. The method according to any one of phrases 1 to 13, wherein said protic acid comprised in the liquid composition C is selected from the group consisting of a carboxylic acid, a sulfonic acid, a mineral acid, a protonated aliphatic, aromatic or heteroaromatic amine, whose protonated form has a pKa in the range of 1−4, and mixtures thereof. The method according to any one of phrases 1 to 14, wherein said solvent comprised in the liquid composition C is a non-halogenated aprotic solvent. 16. A composition comprising - an oligonucleotide which is covalently linked to a solid support and comprises a hydroxyl moiety protected by a protecting group comprising an optionally substituted triarylmethyl residue, and - a liquid composition C comprising a solvent, a protic acid having a pKa equal to or smaller than 4, and at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, preferably wherein the composition and/or one or more components are defined as in one or more of the preceding phrases, in particular wherein said protecting group comprising an optionally substituted triarylmethyl residue is defined as in phrase 12, said protic acid is defined as in phrase 14, said at least one alcohol and/or the concentration thereof are defined as in phrase 13, and/or said solvent is defined as in phrase 15. The following Figures and Examples, including the experiments conducted and the results achieved, are provided for illustrative purposes only and are not to be construed as limiting the scope of the claims.
Description of the Figure Figure 1 illustrates the one or more coupling cycles which may be performed as part of the method of the invention. The method of the invention may comprise a first coupling cycle comprising steps (b) to (e), wherein step (e) is optional which is indicated in Figure 1 by embracing step (e) in brackets. Prior to the first coupling cycle, a component C-0 is provided [step (a)]. In the first coupling cycle, the protecting group PG-0 is removed from said component C-0 [step (b)], and the resulting component C-0 # is reacted with a provided first building block B-1 [steps (c), (d)] to yield a first cycle oligonucleotide O-1. Optionally, any P (III) atoms within O-1 may be converted to P (V) atoms by incubation with an oxidizing or sulfurizing agent [step (e)]. The method of the invention may further comprise one or more coupling cycles comprising steps (b’) to (e’), wherein step (e’) is optional which is indicated in Figure 1 by embracing step (e’) in brackets. The first cycle oligonucleotide O-1 will then be used as an educt O-(x−1), of the second coupling cycle (x=2). The protecting group PG-(x−1), i.e. PG-1, is removed [step (b’)], and the resulting oligonucleotide (O-(x−1)) # , i.e. (O-1) # , is reacted with a provided building block B-x, i.e. B-2 [steps (c’), (d’)] to yield a x-th cycle oligonucleotide O-x, i.e. a second cycle oligonucleotide O-2. Optionally, any P (III) atoms within O-x, i.e. O-2, may be converted to P (V) atoms by use of an oxidizing or sulfurizing agent [step (e’)]. Up to (n−1) further coupling cycles comprising steps (b’) to (e’) may be performed, in each of which the oligonucleotide O-x of the previous coupling cycle is used as educt O-(x−1). The fact that the first cycle oligonucleotide O-1 need not be subjected to the second coupling cycle and the fact that each x-th cycle oligonucleotide O-x need not be subjected to another coupling cycle are indicated in Figure 1 by the dashed "exit" arrows. Examples General methods and information 1. Determination of weight gain and yield The experimental weight gain was determined by subtracting the mass of the solid support from the mass of the dried support-bound oligonucleotides after completion of all coupling cycles, the final dimethoxytrityl removal step (i.e. after the additional step (g) or (g’) was carried out), and the diethylamine treatment to remove the 2- cyanoethyl protecting groups from the internucleosidic linkage groups. To determine the mass of the solid support, the mass of the dimethoxytrityl groups (i.e. the di(p-methoxyphenyl)phenylmethyl groups or DMT groups) was subtracted from the mass of the starting resin (which consisted of the solid support, optionally carrying the starting nucleoside, with dimethoxytrityl groups) according to the scale of the synthesis and the molecular weight of the dimethoxytrityl group. The theoretical maximum weight gain was determined by multiplying the molecular weight of the assembled oligonucleotide strand after removal of any 2-cyanoethyl protecting groups from the internucleosidic linkage groups (without taking the molecular weight of the solid support into account) with the molar amount of the DMT-protected hydroxyl moieties originally available at the staring resin (assuming that all of these hydroxyl moieties now carry the desired oligonucleotide strand). Unless indicated differently, yields are given in percent (%) and were obtained by dividing the experimental weight gain by the theoretical maximum weight gain, followed by multiplication with 100 % to arrive at a value in percent. 2. Determination of purity Unless indicated differently, oligonucleotide purity was determined by analytical reversed phase HPLC using a C18 stationary phase, and elution was effected by a gradient (eluent A: HFIP/TEA/H 2 O; eluent B: methanol). The detection wavelength was 260 nm. Unless specified otherwise, the reported oligonucleotide purities in percent (%) were obtained by dividing the area of (i.e. underneath) the peak of the target oligonucleotide by the sum of areas of (i.e. underneath) all significant peaks (including the peak of the target oligonucleotide), followed by multiplication with 100 % to arrive at a value in percent (%). Unless indicated differently, the UV trace was integrated applying a minimal relative area threshold of 0.05 %. Unless indicated differently, the determination of purity was performed using support-cleaved oligonucleotides. Such support-cleaved oligonucleotides were obtained as stated in section "4. Synthesis of oligonucleotides", unless indicated differently. 3. Determination of the degree of depurination Unless indicated differently, the degree of depurination was determined from the UV-trace of the respective HPLC-MS measurements via the following steps (i)−(iii): (i) The area of (i.e. underneath) the peak(s) of the one or more identified depurination-derived side products was determined. If more than one such peak was identified, the peak areas were summed up to obtain the summed up peak area of all identified depurination-derived side products. (ii) The area of the peak of the target oligonucleotide was determined. (iii) The peak area or summed up peak area determined in step (i) was divided by the peak area determined in step (ii), followed by multiplication with 100 % to arrive at a value in percent (%). Unless indicated differently, the determination of the degree of depurination was performed using the support-cleaved oligonucleotides. Such support-cleaved oligonucleotides were obtained as stated in section "4. Synthesis of oligonucleotides", unless indicated differently. 4. Synthesis of oligonucleotides Reactors Unless indicated differently, all syntheses were carried out in form of automated oligonucleotide synthesis. In such automated syntheses, all reactions were performed in 25 mL sparged-bed reactors (herein also referred to as R-1), in which agitation was achieved by bubbling N2 gas through the reactor. Alternatively, if indicated specifically, oligonucleotide syntheses were performed manually, in a 1 L stirred-bed reactor equipped with a mechanical stirrer (herein also referred to as R-2). All reactor types were equipped with filters, frits, or membranes of appropriate pore sizes for retaining the resin in the reactor and draining solvents and reagents. Starting resins (solid supports) Two sorts of commercially available DMT-protected polystyrene starting resins were used, unless indicated differently: - resins to which the 5´-O-DMT-protected starting nucleoside moieties (i.e. the 3´- terminal nucleoside subunits of the oligonucleotide strands to be synthesized) were linked via a succinate-type linker (ester bond with the 3´-hydroxyl moiety of a nucleoside moiety and amide bond with an amine moiety at the resin); or - resins carrying DMT-protected UnyLinker TM moieties (i.e. not already carrying the 3´-terminal nucleoside subunits). In these cases, the 3´-terminal nucleoside subunits were added via a coupling cycle as summarized in Table 1 below. Preparation of specific solutions General Protocol A (GP-A): Preparation of phosphoramidite solutions The 5'-O-DMT protected nucleoside phosphoramidite derivatives with optional 2'-modifications (e.g. 2'-deoxy, 2'-fluoro or 2'-O-methyl, i.e. 2´-methoxy) of the benzoyl protected adenosine (A Bz ), benzoyl protected cytidine (C Bz ) [or acetyl protected cytidine (C Ac ), if indicated specifically], isobutyryl protected guanosine (G iBu ), thymidine (T), and uridine (U), were typically dissolved at a concentration of 0.2 M in dry acetonitrile or in a mixture of dry acetonitrile and N,N-dimethylformamide. Molecular sieves (3 Å) were added and the headspace was flushed with nitrogen. The solution was then dried for a minimum of 12 h. General Protocol B (GP-B): Preparation of a liquid composition C The liquid compositions C were typically prepared by dissolving the protic acid in a mixture of the indicated solvent, the at least one alcohol, in which one or more hydroxyl groups are covalently bonded directly to an optionally substituted phenyl moiety, and, where applicable, an additional carbocation scavenger. Standard coupling cycle Unless indicated differently, all syntheses were performed using 3'-phosphoramidite nucleosides according to the desired sequence from 3' to 5' direction. The syntheses were typically executed at a scale of 0.1 mmol based on the resin weight and substitution (approx.0.25−0.35 mmol/g). Prior to the first coupling cycle, the desired amount (according to the desired scale of the synthesis) of the starting resin was transferred to the reactor and washed with acetonitrile (ACN, 5−10 mL/g) for 2 min. For each of the nucleoside phosphoramidites to be added, one coupling cycle according to the following Table 1 was carried out, unless indicated differently. Table 1: Typical coupling cycle for the synthesis of oligonucleotides. a) volume time per step repetitions per mass resinb) repetitionc) detritylation 1−8 6.28−25.1 mL/g 5−20 min wash 1−7 21.1−221 mL/g 1 min 1 8.6−13.1 mL/g 2−3 min coupling 1 3.14 mL/g 15 min wash 1 21.1−31.6 mL/g 1 min oxidation d) 1 12.6 mL/g 5 min wash d) 2 21.1−94.9 mL/g 1 min or sulfurization e) 1 12.6 mL/g 5 min wash e) 2 21.1 − 94.9 mL/g 1 min capping 1 3.1−7.9 mL/g 2 min wash 3-6 21.1−94.9 mL/g 1 min a) Each repetition equals one treatment of the support-bound growing oligonucleotide chains with the respective solution; a value of "1" indicates a single treatment; for each treatment a new batch of the respective solution was used; prior to each repetition, the solution of the previous repetition was drained. b) The mass of the starting resin was used as point of reference for all coupling cycles. The given volume refers to the summed up volume of all repetitions. c) Contact time between the growing oligonucleotide chains and the respective solution during each repetition. d) and e) Each coupling cycle comprised either the oxidation and wash step denoted with d) or the sulfurization and wash step denoted with e), but not both. The detritylation step was performed using a liquid composition C prepared according to GP-B or a comparative detritylation cocktail, e.g. a detritylation cocktail from the prior art. Prior to detritylation, the resin was typically washed with the solvent of the respective detritylation cocktail, e.g. DCM or toluene. The coupling step was typically performed using a phosphoramidite solution prepared according to GP-A, to which 5-(ethylthio)-1H-tetrazole activator (ETT, 0.5 M) had been added. The oxidation step was typically performed using a solution of iodine (50 mM) in a mixture of water and pyridine (1:9, v/v). The sulfurization step was typically performed using a solution of xanthane hydride (0.2 M) in pyridine or using a solution of xanthane hydride (0.1 M) in a mixture of acetonitrile and pyridine (2:3, v/v). The capping step was typically performed using a mixture (1:1, v/v) of Cap A (20 vol-% acetic anhydride in acetonitrile) and Cap B (N-methylimidazole, 2,6-lutidine, acetonitrile, 20:30:50, v/v/v). The wash steps were typically performed using acetonitrile. Only prior to detritylation, DCM (e.g. when using DCM as solvent of the detritylation cocktail) or toluene (e.g. when using toluene or anisole as solvent for the detritylation cocktail) were used for the wash steps. Unless indicated differently, each repetition of each step of a typical coupling cycle comprised contacting the solid support carrying the growing oligonucleotide chains with the respective solution (e.g. a detritylation cocktail for detritylation steps or neat solvent for wash steps) for the indicated time under stirring (stirred-bed reactor) or shaking (syringe reactor) or agitating by nitrogen bubbling (sparged-bed reactor), followed by draining of the respective solution through a filter or frit or membrane of appropriate pore size, so as to retain the support-bound growing oligonucleotides inside the reactor. In the following Examples, the number of repetitions of each detritylation step as well as the contact time with the detritylation cocktail per repetition is indicated specifically in tabular form. For example, two repetitions with 10 min contact time each would be referred to as 2 × 10 min or 10 + 10 min. Unless indicated differently, syntheses were performed at 22°C. The coupling cycles were repeated according to the sequence using the appropriate nucleoside phosphoramidites, unless indicated differently. After completion of all coupling cycles, the final 5'-O-DMT detritylation was performed using the same procedure that was used in the previous cycles including the wash step. Subsequently the cyanoethyl-protected phosphate triester or thiophosphate triester linkage groups were deprotected by treatment with diethylamine (DEA) in acetonitrile, unless indicated differently. Alternatively, the cyanoethyl protecting groups could be removed during resin cleavage by treatment with aqueous ammonium hydroxide solution. The resin was then dried under reduced pressure for a minimum of 16 h. The resin carrying the fully-assembled oligonucleotides was weighed, and a trial cleavage and deprotection of the sample was performed. For this purpose, typically, 10−50 mg dried resin was weighed into a suitable reaction vessel (e.g. a 2 mL PP- tube). Aqueous ammonium hydroxide solution (i.e. aqueous ammonia solution, 25−28 wt-%, 1-2 mL) was added. The tube was closed, sealed, shaken, and heated to 45−55°C for 2−20 h, depending on length and sequence of the oligonucleotide. The supernatant was typically removed using a syringe and transferred to a second tube (2−5 mL). The ammonia was typically removed using a vacuum centrifuge or with a slight stream of nitrogen gas. The solution (containing the support-cleaved oligonucleotides) was then diluted with H2O to the desired concentration, followed by analysis via reversed phase HPLC or HPLC-MS. 5. Target oligonucleotides Example 1: 5´-mUmUmUmUfA-3´ Example 2: 5'-mAsfCsmAfAfAfAmGfCmAfAmAmAmCfAmGfGmUfCmUmAmGsmAsmA-3' The following notation was used to denote the nucleoside subunits: A = adenosine, dA = 2´-deoxyadenosine, G = guanosine, dG = 2´-deoxyguanosine, C = cytidine, dC = 2´-deoxycytidine, T = thymidine (2´-deoxy and not ribothymidine), U = uridine, "f" indicates that the respective nucleoside moiety (denoted to the right of the letter "f") bears a 2´-fluoro (i.e. 2´-F) substituent (e.g. fA for adenosine with 2´-F modification), "m" indicates that the respective nucleoside moiety (denoted to the right of the letter "m") bears a 2´-methoxy (i.e.2´-OMe) substituent (e.g. mU for uridine with 2´-OMe modification). Unless indicated differently, all internucleosidic linkage groups are phosphodiester linkage groups. The letter "s" to the right of a nucleoside symbol indicates that the internucleosidic linkage group in 3´-position of the respective nucleoside-subunit is a phosphorothioate linkage group instead of a phosphodiester linkage group (e.g. fAsmC for a phosphorothioate linkage group interconnecting the 3´-hydroxyl moiety of 2´fluoroadenosine and the 5´-hydroxyl moiety of 2´-methoxycytidine). Herein, unless indicated differently, all oligonucleotides are denoted in 5´ to 3´ direction (i.e. the nucleoside subunit denoted to the very left is the 5´-terminal nucleoside subunit). Example 1: Synthesis of 5´-mUmUmUmUfA-3´ using different detritylation conditions The target oligonucleotide 5´-mUmUmUmUfA-3´ was synthesized according to the general methods laid out above with an oxidation step in each coupling cycle, and with varying detritylation conditions. The syntheses and the results are compiled in the following Table E-1. Table E-1: Synthesis of 5´-mUmUmUmUfA-3´ using different detritylation conditions Abbreviations: DCA = dichloroacetic acid, MSA = methanesulfonic acid, 4-ClPy-HCl = 4-chloropyridinium hydrochloride (preformed salt), TFA = trifluoroacetic acid, 4-CYP = 4-cyanopyridine. a) Starting resin: polystyrene resin carrying DMT- protected UnyLinker TM moieties; Scale: 0.10 mmol (i.e.0.10 mmol of 3´-nucleoside subunits at resin); Reactor: automated synthesis in a sparged-bed reactor (R-1). b) Detritylation volume: 5.0 mL / 0.10 mmol starting material (i.e.0.10 mmol of DMT- protected OH-groups on the starting resin) per detritylation repetition. c) n.d. = not determined, since no product formation was observed at all. d) According to the invention. e) Comparative. Due to the stability of abasic sites in 2’-F / 2’-OMe oligonucleotides during ammonia treatment, the only noteworthy depurination-derived side product was a compound differing from the target oligonucleotide 5´-mUmUmUmUfA-3´ only in that an abasic site was located at the 3´-terminal fA-nucleoside subunit (i.e. the adenine nucleobase was substituted for a hydroxyl group). Thus, the degree of depurination was determined by dividing the area of (i.e. underneath) the peak of said single depurination-derived side product by the area of (i.e. underneath) the peak of the target oligonucleotide, followed by multiplication with 100 %, to arrive at a value in percent (%). The syntheses summarized in Table E-1 differ only with regards to the detritylation cocktail that was utilized. Synthesis 1.1 of Table E-1 utilized a 1.218 M solution of DCA in toluene (i.e. 10 vol-% DCA in toluene) which is a standard detritylation cocktail for industrial synthesis. When reducing the concentration of DCA to 0.243 M (i.e.2 vol-%, synthesis 1.2), a decrease of the degree of depurination from 0.38 % to 0.11 % was observed, which was, however, accompanied by a reduction of the yield from 96 % to 43 % (cf. syntheses 1.1. and 1.2). The degree of depurination could be further reduced to 0.10 % by addition of m-cresol (2.867 M, synthesis 1.3), which also led to an increase of the yield from 43 % to 75 % (cf. syntheses 1.2 and 1.3). Replacing m-cresol for the same concentration of ethanol (synthesis 1.4) completely prevented product formation. Thus, in terms of reducing the degree of depurination while achieving an acceptable yield, synthesis 1.3 according to the invention outperformed the comparative syntheses 1.1, 1.2, and 1.4. The detritylation cocktail of synthesis 1.5 differs from the detritylation cocktail of synthesis 1.3 in that a combination of TFA and 4-cyanopyridine was used as protic acid instead of DCA and in that the solvent was anisole instead of toluene. The degree of depurination (0.09 %) was again lower than for the industrial standard protocol of synthesis 1.1 (0.38 %) (cf. entries 1.5 and 1.1). In the absence of m-cresol (synthesis 1.6) an unacceptably low yield of 36 % instead of 84 % was obtained (cf. syntheses 1.5 and 1.6). The detritylation cocktail of synthesis 1.7 differs from the detritylation cocktail of synthesis 1.5 in that 4-methoxyphenol was used as the alcohol instead of m-cresol. The detritylation cocktail of synthesis 1.8 differs from the detritylation cocktail of synthesis 1.5 in that toluene was used as solvent instead of anisole. The detritylation cocktail of synthesis 1.9 differs from the detritylation cocktail of synthesis 1.8 in that phenol was used as the alcohol instead of m-cresol. In syntheses 1.7, 1.8, and 1.9, the degree of depurination was lower than for the industrial standard protocol (cf. syntheses 1.1, 1,7, 1.8, and 1.9) showing that the method of the invention allows for variation with regards to the alcohol and the solvent. Besides DCA (an exemplary carboxylic acid, synthesis 1.3) and the combination of TFA (an exemplary carboxylic acid) and 4-cyanopyridine (syntheses 1.5, 1.7, 1.8, and 1.9), methanesulfonic acid (MSA, an exemplary sulfonic acid) and a preformed salt of hydrochloric acid (an exemplary mineral acid) and 4-chloropyridine were used as protic acids of the detritylation cocktail (syntheses 1.10 and 1.11). In both cases, the degree of depurination was reduced as compared to the industrial standard protocol (cf. syntheses 1.1, 1.10, and 1.11). These results show that the method of the invention allows for variation with regards to the protic acid. Example 2: Synthesis of 5'-mAsfCsmAfAfAfAmGfCmAfAmAmAmCfAmGfGmUfCmUmAmGsmAsmA-3' 5'-mAsfCsmAfAfAfAmGfCmAfAmAmAmCfAmGfGmUfCmUmAmGsmAsmA-3' (target oligonucleotide) was synthesized according to the general methods laid out above. When the nucleoside moiety to be added should be interconnected to the growing oligonucleotide via a phosphodiester linkage group, an oxidation step was performed. When the nucleoside moiety to be added should be interconnected to the growing oligonucleotide via a phosphorothioate linkage group, a sulfurization step was performed. Starting resin: polystyrene resin with 5´-O-DMT protected 3´-terminal nucleoside subunit (i.e.5´-O-DMT-A) bonded via succinate-type linker; Scale: 0.10 mmol (i.e.0.10 mmol of 3´-nucleoside subunits at resin); Reactor: automated synthesis in a sparged-bed reactor (R-1); Detritylation cocktail: TFA (0.7 vol-%, 0.092 M) and 4-CYP (0.9 wt-%, 0.096 M) in toluene + m-cresol (30 vol-%, 2.87 M) Detritylation volume: 5.0 mL / 0.10 mmol starting material (i.e.0.10 mmol of DMT- protected OH-groups on the starting resin) per detritylation repetition. The target oligonucleotide was obtained in a yield of 87 % and with a purity of 76 %, indicating that the method of the invention is suited for the synthesis of longer oligonucleotides.
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