The present invention relates to a process for the purification of analogues of human glucagon-like peptide-1 (GLP-1 ), particularly to a process for the purification of the GLP-1 analogue (Aib ^8,35 )GLP-1 (7-36)NH ₂ with the amino acid sequence:

His-Aib-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Val-Ser-Ser-Tyr-Leu-G lu-Gly-Gln-Ala-Ala-Lys-Glu- Phe-lle-Ala-Trp-Leu-Val-Lys-Aib-Arg-NH ₂ .

The synthesis of GLP-1 analogues can follow a hybrid approach encompassing both solid phase peptide synthesis (SPPS) and fragment couplings in solution. The peptide (Aib ^8,35 )GLP-1 (7-36)NH ₂ designates an analogue formally derived from natural human GLP-1 (7-36)NH ₂ by substituting the naturally occurring amino acid residues in positions 8 (Ala) and 35 (Gly) with a-aminoisobutyric acid (Aib).

This peptide and its therapeutical use as well as its preparation by SPPS are known from the PCT patent application WO 2000/34331 . However, the process of this peptide as described in WO 2000/34331 is not suitable for commercial scale production.

The PCT Publication WO 2007/147816 describes a preparation of this particular analogue of GLP-1 by preparing three fragments and coupling these fragments in solution whereas the PCT patent application WO 2010/033254 describes a preparation comprising a stepwise solid-phase Fmoc-chemistry. However, whatever the preparation process used, the purity is in general less than 95 %.

Purification for human glucagon-like peptide-1 using chromatography has been widely described in the art.

For instance, according to the PCT Publication WO 2007/147816, the GLP-1 analogue is subjected to a two-step reversed phase process using tetrahydrofuran. However, the use of this eluent is detrimental for performing RP-HPLC on a large scale since it can form peroxides.

The PCT patent application WO 201 1 /161007 proposes to employ an acidic RP-HPLC step followed by a RP-H PLC performed at high pH of the mobile phase. However, the high pH conditions make the peptide less stable and generate new impurities, resulting in inconsistancy of purities between batches. There is thus a real need to develop a process to obtain a highly pure (Aib ' )GLP-1 (7- 36)NH ₂ on a commercial scale, aiming to reduce impurities and thus side effects and to increase the tolerance of the treatment.

The Applicant has now discovered that by incorporating ion-exchange chromatography as an orthogonal step for the purification of (Aib ^8,35 )GLP-1 (7-36)NH ₂ , it was possible to obtain a higher purity of this product at levels of production suitable for commercial scale production.

In particular, this approach produces better separation of the closely related impurities with similar hydrophobicity that might not be efficiently purified by solely RP-HPLC. Indeed, the purity of the final product in one preferred embodiment of this invention is required to be higher than 99.3 % with an individual impurity not larger than 0.3 %. For example, the purity of the final product is about 99.3 %, about 99.4 %, about 99.5%, about 99.6%, about 99.7%, about 99.8%, about 99.9%, and the individual impurity is about 0.3 %, about 0.2 %, about 0.1 %. In another preferred embodiment, the purity of the final product is at least 99.9 % and the individual impurity is less than 0.1 %. The availability of highly pure (Aib ^8,35 )GLP-1 (7-36)NH ₂ is critical for its clinical evaluation.

Moreover, the loading capacity of the ion-exchange column is approximately 3 times higher than the reversed phase one, which significantly reduces purification time. In one preferred embodiment of the invention, the acetate content is not larger than 0.3%. Additional advantage of ion-exchange method is elimination of eluent such as acetonitrile in the mobile phase during first step purification, such as the one described in PCT patent applications WO 2007/147816 and WO 201 1 /161007, thus further decreasing cost of goods.

Finally, the purification process according to the invention leads to a good overall yield. For example, the inventive process results in at least 15 % yield, at least 16 % yield, at least 17 % yield, at least 18 % yield, at least 19 % yield, or at least 20 % yield. Preferably, the process results in about 21 % yield.

One subject of the present invention is thus a purification process of (Aib ^8,35 )GLP-1 (7- 36)NH ₂ comprising 2 steps: a) an ion-exchange chromatography purification step, and

b) a reversed phase HPLC purification step. ln the text herein below, unless otherwise indicated, the limits of a range of values are included in that range, especially in the expression "ranging from".

An acidic buffer is an acidic solution containing a buffer agent which prevents a change in the pH value. The term "an individual impurity" defines a peptide that is not (Aib ^8,35 )GLP-1 (7-36)NH ₂ .

The term "RP-HPLC" is understood to mean reversed phase HPLC.

Unless otherwise indicated, the following definitions are set forth to illustrate and define the meaning and scope of the various terms used to describe the invention herein.

For the purposes of the present invention, the term "orthogonal" means that two complementary but different forms of chromatographic purification are used to separate compounds.

According to the present invention, the orthogonal chromatographic process is composed of two steps: a) ion-exchange purification, which is a chromatographic separation based on charge differences of the components, and b) RP-HPLC purification, which is a chromatographic separation based on differences in hydrophobicity of the components.

Preferably, step a) is performed before step b). However, step a) and step b) may be performed concurrently. According to the present invention, step a) is performed with an acidic buffer.

The mobile phase of step a) may be one acidic buffer or a mixture thereof. Thus, the acidic buffer used as mobile phase of step a) may preferably comprise two eluents, eluent A and eluent B, and wherein the total amount of eluent A and eluent B is always 100 %. Eluents A and B may be selected from acidic buffers known by a skilled in the art such as acetic acid or its salts thereof, in particular ammonium and sodium salts; formic acid or its salts thereof, in particular ammonium and sodium salts; and phosphoric acid or its salts thereof in particular ammonium and sodium salts.

Preferably eluents A and B are acetic acid and one of its salts, respectively. More preferably eluents A and B are acetic acid and ammonium acetate, respectively. ln another embodiment, step a) is performed with an acidic buffer at a pH ranging from 1 .0 to 6.0, 1 .25 to 5.0, and more preferably at a pH ranging from 1 .5 to 4.6.

In another embodiment, step a) is performed with two eluents, eluent A and eluent B. Preferably, step a) is performed with ammonium acetate as eluent A and acetic acid as eluent B. More preferably, the step a) is performed before step b) with ammonium acetate as eluent A and acetic acid as eluent B.

In a preferred embodiment, step a) is performed with ammonium acetate as eluent A and acetic acid as eluent B, at a pH ranging from 1 .0 to 6.0, 1 .25 to 5.0, and more preferably at a pH ranging from 1.5 to 4.6. More preferably, step a) is performed with gradient increase of acetic acid content in ammonium acetate mobile phase.

Advantageously, the gradient of step a) is ranging from 0 to 60 % (v/v) of acetic acid as eluent B and from 100 to 40 % (v/v) of ammonium acetate as eluent A. More preferably, the gradient of step a) is ranging from 0 to 50 % (v/v) of acetic acid as eluent B and from 100 to 50 % (v/v) of ammonium acetate as eluent A.

In a particular embodiment of the present invention, step a) is performed with ammonium acetate at a pH ranging from 4.0 to 5.0, 4.1 to 4.9, 4.2 to 4.8, 4.3 to 4.7, or 4.4 to 4.6, etc.. More preferably, step a) is performed with ammonium acetate at a pH ranging from 4.2 to 4.8, even more preferably from 4.4 to 4.5. According to the present invention, ammonium acetate is used in step a) in a concentration ranging from 0.1 to 50 mM, 0.25 to 40 mM, 0.5 to 30 mM, or 0.75 to 25 mM, etc . In a preferred embodiment, ammonium acetate is used in step a) in a concentration ranging from 1 to 20 mM, more preferably from 8 to 12 mM and in particular in a concentration of about 10 mM (10 ± 0.5 mM). In another particular embodiment of the present invention, step a) is performed with acetic acid at a pH ranging from 0.5 to 3.0, 0.75 to 2.75, 0.8 to 2.5, or 0.9 to 2.25, etc. More preferably, step a) is performed with acetic acid at a pH ranging from 1 .0 to 2.0, even more preferably from 1 .5 to 1 .7.

Acetic acid used in step a) may be diluted acetic acid, in particular in water such as HPLC grade water. Preferably, acetic acid used in step a) is from 40 to 60 % of acetic acid in water, more preferably from 45 to 55 % of acetic acid in water, and in a preferred embodiment from 49 to 51 % of acetic acid in water.

According to the present invention, step b) corresponds to a reverse phase chromatography with a gradient elution.

Preferably, step b) is performed with an acidic buffer. In a preferred embodiment, step b) is performed with an acidic buffer at a pH ranging from 1 .0 to 6.0, 1 .25 to 5.75, 1.5 to 5.5, or 1 .75 to 5.25, etc. More preferably at a pH ranging from 2.0 to 4.5, even more preferentially at a pH ranging from 2.5 to 3. According to the present invention, in step b), the gradient elution may be performed with one or more acidic eluent, and more particularly with two acidic eluents, eluent C and eluent D. In such a case, the total amount of eluent C and eluent D is always 100 %. Eluents C and D may be an acidic aqueous or organic solution. Such solution may be a solution of acid such as acetic acid, in water or in an organic solvent such as acetonitrile or alcohol, in particular methanol, ethanol and propyl alcohol.

In a preferred embodiment, the gradient elution of step b) is performed with an acidic eluent C and an acidic eluent D, and more preferably with acetic acid in water as eluent C and with acetic acid in acetonitrile as eluent D.

Advantageously, the gradient of step b) is ranging from 0 to 70 % (v/v) of acidic eluent D and from 100 to 30 % (v/v) of acidic eluent C. More preferably, the gradient of step b) is ranging from 0 to 60 % (v/v) of acidic eluent D and from 100 to 40 % (v/v) of acidic eluent C.

Advantageously, the gradient of step b) is ranging from 0 to 70 % (v/v) of acetonitrile, containing acetic acid, as eluent D, and from 100 to 30 % (v/v) of water, containing acetic acid, as eluent C. More preferably, the gradient of step b) is ranging from 0 to 60 % (v/v) of acetonitrile, containing acetic acid, as eluent D, and from 100 to 40 % (v/v) of water, containing acetic acid, as eluent C.

In another preferred embodiment, the concentration of acetic acid in eluent C and in eluent D used as mobile phases in step b) is ranging from 0.1 to 0.5 N. More preferably, the concentration of acetic acid in eluent C and in eluent D used as mobile phases in step b) is ranging from 0.2 to 0.3 N.

Advantageously, the GLP-1 analogue (Aib ^8,35 )GLP-1 (7-36)NH ₂ thus obtained by the process according to the present invention contains less than 10 % (w/w) of acetic acid. ln a preferred embodiment, the GLP-1 analogue (Aib ' )GLP-1 (7-36)NH ₂ thus obtained contains less than 7 % (w/w) of acetic acid and more preferentially less than 6.5 % (w/w) of acetic acid. In another preferred embodiment, the content of acetic acid in (Aib ⁸ ' ³⁵ )GLP-1 (7-36)NH ₂ is less than 6 % (w/w). By way of example, the GLP-1 analogue (Aib ^B,35 )GLP-1 (7-36)NH ₂ obtained by the process of the present invention contains 6 % ± 1 % (w/w) acetic acid, 5 % ± 1 % (w/w) acetic acid, 4 % ± 1 % (w/w) acetic acid, 3 % ± 1 % (w/w) acetic acid, 2 % ± 1 % (w/w) acetic acid, 1 % ± 0.5 % (w/w) acetic acid, or 0.5 % ± 0.1 % (w/w) acetic acid.

The ion-exchange is expediently performed using ion-exchange resin as stationary phase. Suitable resin types used in ion-exchange can be selected from any weak cation- exchange resin. The weak cation-exchange resin may be selected from the following resins: PolyCAT A® 1000-5, Agilent Bio ^® WCX, or ProPac ^® WCX-10. The PolyCAT A ^® resin type is particularly suitable.

The RP-HPLC is expediently performed using a silica gel sorbent as stationary phase. Suitable silica gel types used in RP-HPLC can be selected from the following silica gel sorbents: Kromasil® 100-16-C18, Kromasil® 100-10-C18, Kromasil® 100-16-C8, Kromasil® 100-16-C4, Kromasil® 100-10-Phenyl, Kromasil® Eternity-5-C18, Kromasil® 100- 5-C4, Chromatorex® C18 SMB 100-15 HE, Chromatorex® C8 SMB 100-15 HE, Chromatorex® C4 SMB 100-15 HE, Daisogel ^® SP-120-15-ODS-AP, Daisogel ^® SP-120-10- C4-Bio, Daisogel ^® SP-200-10-C4-Bio, Zeosphere ^® 100 C18, Zeosphere ^® 100 C8, Zeosphere® 100 C4, SepTech® ST 150-10-C18, Luna® 100-1 0-C18, Gemini 1 10-10-C18, YMC-Triart 120-5-C18 and YMC-Triart 200-10-C8. The Kromasil® silica gel types as listed above are particularly suitable.

Alternatively the RP-HPLC can be performed by using polymeric based stationary phases. Suitable polymeric phases can be selected from PLRP-S 100-10 or Amberchrom ^{(T >}

Profile XT20.

According to the present invention, the purity of the peptide product is higher than 99 %. For example, the purity of the final product is about 99.3 %, about 99.4 %, about 99.5%, about 99.6%, about 99.7%, about 99.8%, about 99.9%. In a preferred embodiment, the purity of the peptide product is higher than 99.3 %, and more preferably higher than 99.4 %. In another preferred embodiment, the purity is higher than 99.5 %.

In another particular embodiment of the present invention, individual impurities are not larger than 0.5 %. For example, the individual impurity is about 0.3 %, about 0.2 %, about 0.1 %. More preferably, individual impurities are not larger than 0.3 %. Advantageously, the combined yield of the steps a) and b) is higher than 15 %, 16 %, 17 %, 18 %, 19 %, or 20 %. More preferably, the combined yield of the steps a) and b) is higher than 21 %.

In order to obtain a dry final product which is suitable for the drug formulation, the solution obtained after purification as described above can be subjected to precipitation, lyophilisation or spray-drying techniques.

The following examples are presented to illustrate the above procedures without limiting the scope of the invention.

Experimental part Example 1 : Preparation of the GLP-1 compound

The crude peptide (Aib ^8,35 )GLP-1 (7-36)NH ₂ can be prepared according to the methods described in WO 2007/147816 and WO 2009/074483 by producing three fragments and coupling these fragments in solution.

The chromatographic purification involves an ion-exchange step purification followed by a reversed phase purification at a pH of 2.75.

Example 2: Purification process a) Ion-exchange chromatography

Specifications of the process used for the ion-exchange step are given in Table 1 .

Table 1

100 mg of crude (Aib ' )GLP-1 (7-36)NH ₂ being a mass concentration of 6.67 mg/mL was dissolved in 10 mM ammonium acetate at a pH of 4.42 and loaded onto a weak cation ion- exchange column.

Positively charged peptide retained by the ion-exchange column was eluted by gradient increase of acetic acid content in the mobile phase due to protonation of weak acid ion- exchange resins. Parameters and purification program of the above-mentioned ion-exchange step are respectively shown in Tables 2 and 3:

Table 2

Table 3

Fractions were then collected and the ones with purity above 95 % were combined and lyophilized.

The lyophilized product had purity of about 97 % and yield of approximately 38 %. The pooled fractions are further purified by the reverse phase chromatographic (RP-HPLC) purification. b) Step-two RP-HPLC

Specifications of the process used for the RP-HPLC step are given in Table 4.

Table 4

Kromasil 100-10-C18 (21 .2 mm I .D. x 250 mm, 10 μιη

Column

particle diameter, 100 A pore size) sold by Akzo Nobel

Detection UV (280 nm) The pooled fractions from ion-exchange step are loaded onto the HPLC column and the purification program is continued by a gradient elution reverse phase chromatography.

Parameters and purification program of the above-mentioned RP-HPLC step are respectively shown in Tables 5 and 6:

Table 5

Fractions were collected. Only fractions having purity above 99.3 % were pooled and lyophilized.

Fractions not having the required purity were pooled, evaporated under reduced pressure and re-purified under the same conditions performed in step b).

The yield of the RP-HPLC step purification was 70 %. The combined yield of the ion- exchange purification and the reversed phase HPLC purification steps was 21 %. The purity of the GLP-1 analogue (Aib ⁸ ' ³⁵ )GLP-1 (7-36)NH ₂ obtained was 99.9 %. This peptide product purity corresponds to a high level for purification process standard.

Moreover the GLP-1 analogue (Aib ^8,35 )GLP-1 (7-36)NH ₂ obtained contains less than 7 % (w/w) of acetic acid. Other embodiments and uses of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. All references cited herein, including all patents and patent applications and patent publications, are specifically and entirely hereby incorporated herein by reference. It is intended that the specification and examples be considered exemplary only, with the true scope and spirit of the invention indicated by the following claims.