Technical Field

The invention belongs to the field of drug synthesis, and particularly relates to a intermediates and methods for preparing (S)-2-(3S,8S)-3-(4-(3,4-dichlorobenzyloxy)phenyl-7-((S)- 1-pheny I propyl)- 2,3,6,7,8,9-hexahydro-[l,4]-dioxino[2,3-g]isoquinolin-8-ylfo rmylamino)-3-(4- (2,3-dimethylpyridin-4-yl) phenyl) propanoic acid dihydrochloride.

Background of the Invention

(S)-2-(3S,8S)-3-(4-(3,4-dichlorobenzyloxy)phenyl-7-((S)-l -phenylpropyl)-2,3,6,7,8,9- hexahydro-[l,4]-dioxino[2,3-g]isoquinolin-8-ylformylamino)-3 -(4-(2,3-dimethylpyridin-4- yl)phenyl)propanoic acid dihydrochloride ("OAD2 dihydrochloride"), is an oral, non-peptide glucagon-like peptide 1 (GLP-1) receptor agonist. OAD2 dihydrochloride has a molecular formula of C50H49CI4N3O6, a molecular weight of 929.76, and the following chemical structure:

A patent for invention CN102378574B (and related international publication WO 2010/114824) discloses a method for preparing OAD2 (summarized in Scheme 1), which utilizes 4-hydroxyacetophenone as the starting material and comprises 14 steps including nucleophilic substitution, bromination, asymmetric reduction, condensation, hydrolysis, etc.

Scheme 1

However, the preparation method in Scheme 1 includes many steps, requires multiple column chromatographic separations, and has a total yield of only 5%, which makes it difficult to apply to industrial production. Thus, it is necessary to redevelop a synthetic route suitable for industrial production.

Summary of the Invention

The present invention provides a method for preparing OAD2 dihydrochloride. Compared with the prior art, the method has less steps and increased yield, and adopts multi-step continuous feeding reaction, which does not require column chromatographic separation and is suitable for industrial production. Further, the method installs a chiral center using a different route than previously disclosed. In a first aspect, the present invention provides a process for preparing a compound of

Formula 13, or salt thereof: wherein the process comprises reacting a compound of Formula 1: with a compound of Formula 12: to give a compound of Formula 13, or salt thereof, wherein R ^a and R ^b are independently selected from C _1-6 a Ikyl, R ¹ is C _1-6 alkyl, and R ² is a C _1-6 alkyl, C _1-6 haloalkyl, C _1-6 alkoxy, C _1-6 haloalkoxy or an arylmethoxy group.

In a second aspect, the present invention provides a process for preparing a compound of Formula 14, or a salt thereof: wherein the process comprises treating a compound of Formula 13, or salt thereof, to hydrolysis conditions to give a compound of Formula 14, or salt thereof, wherein R ¹ is C _1-6 alkyl and R ² is a C _1-6 alkyl, C _1-6 haloalkyl, C _1-6 alkoxy, C _1-6 haloalkoxy or an arylmethoxy group.

In a third aspect, the present invention provides a process for preparing a compound of Formula 15, or a salt thereof: wherein the process comprises (a) reacting a compound of Formula 14, or salt thereof, with (S)-phenylpropyl amine and a reducing agent to give a compound of Formula 15, and (b) optionally forming a salt of the compound of Formula 15.

In a fourth aspect, the present invention provides a process for preparing a compound of Formula 8, or salt thereof: wherein the process comprises (a) reacting a compound of Formula 15, or salt thereof, with a formaldehyde equivalent to give a compound of Formula 8 and (b) optionally forming an alkali metal or an earth alkali metal salt of compound of Formula 8.

In a fifth aspect, the present invention provides a process for preparing a compound of Formula 10, or salt thereof: wherein the process comprises reacting a compound of Formula 8-M: , wherein M is an alkali metal or earth alkali metal, with the compound of Formula 9 to give the compound of Formula 10, or salt thereof

In a sixth aspect, the present invention provides a process for preparing the mono HCI salt of OAD2 (compound of Formula 11), wherein the process comprises a first step of hydrolyzing the methyl ester of the compound of Formula 10 acid so as to produce the mono HCI salt of OAD2 (compound of Formula 11):

In a seventh aspect, the present invention provides a process for preparing the di-HCI salt of

OAD2, wherein the process comprises reacting the mono HCI salt of OAD2 (compound 11) with HCl, so as to produce the di-HCl salt of OAD2. According to the invention, the specific preparation method may comprise one or more of the steps in Aspects 1 to 7 as shown below in Scheme 2. In an eighth aspect, the present invention provides compounds of Formula 13 and 14. Detailed Description of the Invention Definitions The term "alkyl" as used herein means a monovalent saturated hydrocarbon group which may be linear or branched or combinations thereof. Unless otherwise defined, such alkyl groups typically contain from 1 to 12 carbon atoms. Representative alkyl groups include, by way of example, methyl (Me), ethyl (Et), n-propyl (n-Pr) or (nPr), isopropyl (i-Pr) or (iPr), n-butyl (n-Bu) or (nBu), sec-butyl, isobutyl, tert-butyl (t-Bu) or (tBu), n-pentyl, n-hexyl, 2,2-dimethylpropyl, 2- methylbutyl, 3-methylbutyl, 2-ethylbutyl, 2,2-dimethylpentyl, 2-propylpentyl, and the like. When a specific number of carbon atoms are intended for a particular term, the number of carbon atoms is shown preceding the term. For example, the term "C _1-3 alkyl" means an alkyl group having from 1 to 3 carbon atoms wherein the carbon atoms are in any chemically-acceptable configuration, including linear or branched configurations. The term "haloalkyl" as used herein refers to straight-chain or branched alkyl groups having 1 to 12 carbon atoms (as mentioned above), where some or all of the hydrogen atoms in these groups are replaced by halogen atoms. Examples of C _1-2 -haloalkyl groups include chloromethyl, bromomethyl, dichloromethyl, trichloromethyl, fluoromethyl, difluoromethyl, trifluoromethyl, chlorofluoromethyl, dichlorofluoromethyl, 1-chloroethyl, 2-fluoroethyl, 2,2-difluoroethyl, and 2,2,2-trifluoroethyl groups. The term “alkoxy” as used herein refers to an alkyl group attached via an oxygen atom. The term "C _1-2 -alkoxy" is a C _1-2 -alkyl group, as defined above, attached via an oxygen atom. Examples of C _1-3 -Alkoxy include methoxy, ethoxy, n-propoxy and 1-methylethoxy (isopropoxy). The term "haloalkoxy" as used herein refers to a haloalkyl group attached via an oxygen atom. Examples of C _1-3 haloalkoxy groups include OCH ₂ F, OCHF ₂ , OCF ₃ , OCH ₂ Cl, OCHCl ₂ , OCCl ₃ , 2- fluoroethoxy, 2-chloroethoxy, 2,2-difluoroethoxy, 2,2,2-trifluoroethoxy, 2-chloro-2-fluoroethoxy, 2-chloro-2,2-difluoroethoxy, 2,2,2-trichloroethoxy, and 2-fluoropropoxy. The term “aryl” as used herein refers to an aryl group with 6 to 14 carbon atoms as ring members. Aryl is a mono-, bi- or polycyclic carbocyclic (i.e. without heteroatoms as ring members) ring system where one or more rings are aromatic. One example for a monocyclic aryl radical is phenyl. In bicyclic rings, two rings maybe condensed, i.e. they share two vicinal C atoms as ring members. One example for a bicyclic aryl group is naphthyl. In polycyclic aryl rings, three or more rings may be condensed. Examples for polycyclic aryl radicals are fluorenyl (9H-fluorenyl), phenanthrenyl and anthracenyl. One or more of the hydrogens of the aryl group may be independently substituted with a substituent independently selected from the group consisting of halogen, nitro, C1-3 alkyl, C1-3 haloalkyl, C1-3 alkoxy, and C1-3 haloalkoxy. The term “arylmethoxy” group as used herein is aryl as defined above bound by a methoxy group to the remainder of the molecule. Examples of arylmethoxy groups include benzyloxy, 9- fluorenylmethoxy, p-nitrobenzyloxy, 2,4-dichlorobenzyloxy, and 5-benzisoxazolylmethoxy. A suitable "coupling agent" for the formation of an amide bond between a compound of Formula 14 with a compound of Formula 9 may be selected from the group consisting of N,N'- carbonyldiimidazole (CDI), N,N'-dicyclohexylcarbodiimide (DCC), 1-(3-dimethylaminopropyl)-3- ethylcarbodiimide hydrochloride (EDCI), 1-hydroxy-1,2,3-benzotriazole (HOBT), benzotriazole-1- yloxy-tris(dimethylamino)-phosphonium hexafluorophosphate (BOP), benzotriazole-1-yloxy- tripyrrolidino-phosphonium hexafluorophosphate (PyBOP), 1-[bis(dimethylamino)-methylene]- 1H-1,2,3-triazolo[4,5-b]pyridinium-3-oxi-de hexafluorophosphate (HATU), O-benzotriazole- N,N,N',N'-tetramethyl-uronium- hexafluoro-phosphate (HBTU), (2-(6-Chloro-1H-benzotriazol-1- yl)-N,N,N’,N’-tetramethylaminium hexafluoro-phosphate (HCTU), and O-benzotriazol-1-yl- N,N,N',N'-tetramethyluronium tetrafluoroborate (TBTU). The term “formaldehyde equivalent” as used herein refers to formaldehyde or its chemical equivalent such as, but not limited to, metaformaldehyde, paraformaldehyde, or polyformaldehyde. The term “non-polar organic solvent” as used herein includes aliphatic hydrocarbons, such as alkanes, e.g. pentane, hexane, heptane, octane, mixtures thereof and technical mixtures, such as petrol ether; cycloaliphatic hydrocarbons, such as cycloalkanes, e.g. cyclohexane, cycloheptane, or cyclooctane; chlorinated aliphatic hydrocarbons, such as halogenalkanes, e.g. dichloromethane, trichloromethane, tetrachloromethane, dichloroethane or tetrachloroethane, aromatic hydrocarbons, such as benzene, toluene, the xylenes, ethylbenzene, cumene (isopropylbenzene), chlorobenzene, o-dichlorobenzene or nitrobenzene, or open-chained ethers, such as diethylether, dipropylether, methyl-tert-butylether or methyl-isobutylether. In certain embodiments, a non-polar organic solvent is selected from the group consisting of benzene, toluene, the xylenes, ethylbenzene, cumene (isopropylbenzene), chlorobenzene, o- dichlorobenzene and nitrobenzene. In other embodiments, a non-polar organic solvent is selected from the group consisting of toluene, xylenes, and chlorobenzene. The term “polar aprotic solvent” as used herein includes solvents which are water-miscible in a desired ratio of water/polar aprotic solvent to be used in a reaction. A polar aprotic solvent are solvents without a functional group from which a proton can dissociate. "Miscible" means that a homogenous solution is formed. Examples for suitable polar aprotic solvents are amides, such as N,N-dimethylformamide (DMF) and N,N-dimethylacetamide; sulfoxides, such as dimethylsulfoxide (DMSO); lactams, such as N-methylpyrrolidone (NMP); cyclic ethers, such as tetrahydrofuran, 1,3-dioxane and 1,4-dioxane; ketones, such as acetone and methylethylketone; nitriles, such as acetonitrile; lactones, such as gamma-butyrolactone; nitro compounds, such as nitromethane; ureas, such as tetramethyl urea or dimethylpropylene urea (DMPU); sulfones, such as sulfolan; and carbonic acid esters, such as dimethylcarbonate or ethylenecarbonate. In certain embodiments, the polar aprotic co-solvent is a cyclic ether, such as tetrahydrofuran, or 1,4- dioxane. The term “polar protic solvent” as used herein includes solvents such as water, acetic acid, formic acid, methanol, ethanol, n-butanol, 1-butanol, 2-butanol, isobutanol, sec-butanol, tert- butanol, n-propanol, isopropanol, 1,2 propan-diol, and glycerol. The term “base” as used herein refers to inorganic and organic bases. Suitable inorganic bases may include for example alkali metal carbonates, e.g. Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ or Cs ₂ CO ₃ , earth alkaline metal carbonates, e.g. MgCC or CaCC , alkali metal phosphates, e.g. U ₃ PO ₄ , Na ₃ P0 ₄ , K ₃ PO ₄ or CS ₃ PO ₄ , earth alkaline metal phosphates, e.g. Mg ₃ (P0 ₄ or CasiPC , alkali metal hydrogenphosphates, e.g. Li ₂ HPO ₄ , Na ₂ HPO ₄ , K ₂ HPO ₄ or CS ₂ HPO ₄ , earth alkaline metal hydrogenphosphates, e.g. MgHPO ₄ or CaHPO ₄ , alkali metal hydroxides, LiOH, NaOFI or KOH, and earth alkaline metal hydroxides, e.g. Mg(OH)2 or Ca(OH)2. Suitable organic bases may include open-chained amines, e.g. trimethylamine, triethylamine, tripropylamine, ethyldiisopropylamine and the like, or basic N-heterocycles, such as morpholine, pyridine, lutidine, DMAP, DABCO, DBU or DBN.

Aspects of Invention

First Aspect

In a first aspect, the present invention provides a process for preparing a compound of Formula 13, or salt thereof: wherein the process comprises reacting a compound of Formula 1: with a compound of Formula 12: to give a compound of Formula 13, or salt thereof, wherein R ^a and R ^b are independently selected from C _1-6 a Ikyl, R ¹ is C _1-6 alkyl, and R ² is a C _1-6 alkyl, C _1-6 haloalkyl, C _1-6 alkoxy, C _1-6 haloalkoxy or an arylmethoxy group.

In an embodiment, the reaction is conducted in a solvent comprising one or more solvents selected from the group consisting of dichloromethane, toluene, tetrahydrofuran, and 2- methyltetrahydrofuran. In another embodiment, the reaction is conducted in a non-polar organic solvent. In anotherembodiment, the reaction is conducted in toluene. In anotherembodiment, the reaction is conducted in 2-methyltetrahydrofuran.

In an embodiment, R ¹ , R ² , R ^a and R ^b are methyl or ethyl

In another embodiment, the reaction is carried out under alkaline conditions. In a further embodiment, a base is added to the reaction to create alkaline conditions. In a further embodiment, the base is an organic base. In another embodiment, the organic base is one, two or more bases selected from the group consisting of DBU, DMAP, triethylamine, isopropylamine, dibutylamine, piperazine, piperidine, and morpholine. In a further embodiment, the base is dimethylaminopyridine (DMAP).

In another embodiment, the compounds of Formula 1 and Formula 12 and the alkaline reagent (base) are fed at a molar ratio in the range of 1:1.05:1.5 to 1:2:3.

In another embodiment, Compound 1 and acetylamino-(dimethoxy-phosphoryl)-acetic acid ethyl ester (1.1 eq) may be suspended in dry dichloromethane (DCM). To this stirring solution, DBU (2 eq) may be added. During the addition, the internal temperature may be raised to BO- 34 °C and progress of the reaction monitored by TLC (50:50 hexanes:EtOAc). After reaction does not progress further, 4 angstrom molecular sieves may be added, and mixture was stirred overnight at room temperature. The solvent is evaporated, and the residue suspended in MeOFI and water added while stirring. After a period of at least 1 to 3 hrs, the mixture is filtered, and the cake washed with MeOFhwater (2:1) with agitation. Further purification to remove the molecular sieves and other impurities may be needed before the product (Compound 13, where R ¹ is ethyl and R ² is methyl) is optimal for use in subsequent steps.

In another embodiment, the workup mode of is as follows: after the completion of the reaction, an aqueous solution of ammonium chloride is added to the reaction, and the reaction mixture is stirred and washed; the aqueous layer is separated and removed out, and the organic layer is washed with saturated brine and then concentrated; methanol/water is added to the concentrated solution and stirred to crystalize, and the precipitated crystals are filtered and dried to give the compound of Formula 13.

Second Aspect

In a second aspect, the present invention provides a process for preparing a compound of Formula 14, or a salt thereof: wherein the process comprises treating a compound of Formula 13, or salt thereof, to hydrolysis conditions to give a compound of Formula 14, or salt thereof, wherein R ¹ is C _1-6 alkyl and R ² is a C _1-6 alkyl, C _1-6 haloalkyl, C _1-6 alkoxy, C _1-6 haloalkoxy or an arylmethoxy group.

In an embodiment, the reaction is conducted in a solvent. In an embodiment, the solvent is a polar aprotic solvent. In a further embodiment, the solvent is one, two or more selected from the group consisting of 1,4-dioxane, N-methylpyrrolidone, dimethyl sulfoxide, dimethylacetamide, and dimethylformamide. In a further embodiment, the solvent is N-methylpyrrolidone.

In another embodiment, the reaction is carried out under acidic condition. In a further embodiment, an acid is added to the reaction to create acidic conditions. In a further embodiment, the acid is an aqueous solution, wherein the acid is one, two or more selected from the group consisting of hydrochloric acid, sulfuric acid, and phosphoric acid. In a further embodiment, the acid is an aqueous solution of hydrochloric acid.

In another embodiment, the compound of Formula 13 and the acidic aqueous solution are fed at a molar ratio in the range of 1:10 to 1:13, and the concentration of the acidic aqueous solution is between 2 mol/L and 6 mol/L.

In anotherembodiment, the workup mode is as follows: afterthe completion ofthe reaction, the temperature is lowered and water is added and stirred to crystalize; wet product is obtained after filtration, and then the wet product is slurried with methanol/dichloromethane; and compound 14 is obtained after filtration and drying.

Third Aspect

In a third aspect, the present invention provides a process for preparing a compound of Formula 15, or a salt thereof: wherein the process comprises (a) reacting a compound of Formula 14, or salt thereof, with (S)-phenylpropyl amine and a reducing agent to give a compound of Formula 15, and (b) optionally forming a salt of the compound of Formula 15.

In an embodiment, the reaction is conducted in a solvent, wherein the solvent is one, two or more solvents selected from the group consisting of dioxane, N-methylpyrrolidone, dimethyl sulfoxide, toluene, dimethylformamide, and dimethylacetamide. In another embodiment, the solvent is a mixture of toluene and dimethylacetamide. In another embodiment, the solvent is a mixture of a polar aprotic solvent and a non-polar organic solvent.

In another embodiment, the reaction is carried out under alkaline condition. In a further embodiment, the alkaline reaction condition is created by adding an organic base. In a further embodiment, the organic base is one, two or more selected from the group consisting of triethylamine, isopropylamine, diethylamine, n-butylamine, DBU, DMAP, and N,N- diisopropylethylamine. In another embodiment, the organic base is isopropylamine.

The reducing agent used in this reaction may be any reducing agent suitable to reduce an imine formed between the compound of Formula 14 and (S)-phenylpropyl amine without substantially reacting with the other portions of the compound. In an embodiment, the reducing agent may be a borohydride reagent such as sodium borohydride, sodium cyanoborohydride, sodium triacetoxyborohydride, sodium tris[2-(ethylhexanoic)]borohydride, and the like can be used. In another embodiment, the reducing agent may be formed in situ. In another embodiment, the reducing agent is sodium tris[2-(ethylhexanoic)]borohydride. In another embodiment, the reducing agent is NaBFI(OCOR ^c ) ₃ , with R ^c being C ₁ -C ₁₂ alkyl, and preferably C ₇ -C ₉ alkyl. The molar amount of the reducing agent may be between 1 to 3 times to that of compound 14, and preferably 1.5 to 2 times.

In an embodiment, the reaction is worked up as follows: after the completion of the reaction, partial solvent is removed out by concentration, and then methanol is added and stirred to crystalize.

Fourth Aspect

In a fourth aspect, the present invention provides a process for preparing a compound of Formula 8, or salt thereof: wherein the process comprises (a) reacting a compound of Formula 15, or salt thereof, with a formaldehyde equivalent to give a compound of Formula 8 and (b) optionally forming an alkali metal or an earth alkali metal salt of compound of Formula 8.

In an embodiment, the reaction forms a sodium salt of the compound of Formula 8.

In an embodiment, the reaction solvent is a mixture of a polar aprotic solvent and a non polar organic solvent. In another embodiment, the solvent is one, two or more selected from the group consisting of toluene, xylene, chlorobenzene, ethyl acetate, isopropyl acetate, propyl acetate, and butyl acetate. In another embodiment, the solvent is a mixture of chlorobenzene and isopropyl acetate.

In another embodiment, an acid catalyst is added to the reaction. In a further embodiment, the acid catalyst is one, two or more selected from the group consisting of trifluoroacetic acid, concentrated sulfuric acid, hydrochloric acid, and trifluoromethanesulfonic acid. In another embodiment, the acid catalyst is trifluoromethanesulfonic acid.

In another embodiment, the reaction is carried out at a temperature in the range of 20 to 50°C, and preferably in the range of 30 to 40°C.

In another embodiment, the workup mode of the reaction is as follows: the temperature is lowered, and a sodium hydroxide solution of 1 to 4 mol/L is added at a weight amount of 8 to 11 times to that of compound 15; after stirring and extraction, organic layer is separated and then washed with saturated brine; a high boiling solvent is added, and then low boiling solvent is removed out by stirring and concentration; the concentrating is stopped till the remaining concentrated solution is approximately 4 times to that of compound 15 by weight; and the remaining concentrated solution is directly used in the next step of the reaction. The high boiling solvent is one, two or more selected from the group consisting of N,N-dimethylformamide, N,N- dimethylacetamide, and dimethyl sulfoxide, and preferably N,N-dimethylacetamide. Fifth Aspect

In a fifth aspect, the present invention provides a process for preparing a compound of Formula 10, or salt thereof: wherein the process comprises reacting a compound of Formula 8-M: , wherein M is an alkali metal or earth alkali metal, with the compound of Formula 9 to give the compound of Formula 10, or salt thereof

In an embodiment, the reaction solvent is a polar aprotic solvent. In another embodiment, the reaction solvent is one, two or more selected from the group consisting of N,N- dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. In another embodiment, the reaction solvent is N,N-dimethylacetamide.

In another embodiment, M is an alkali metal. In a further embodiment, M is sodium.

In another embodiment, the reaction is carried out at a temperature in the range of 10 to 40°C, and preferably in the range of 20 to 30°C.

In another embodiment, a coupling agent is added to the reaction. In another embodiment, the coupling agent is selected from the group consisting of HATU, HBTU, HCTU, PyBOP, and TBTU. In another embodiment, the coupling agent is PyBOP.

In another embodiment, the reaction is conduction under alkaline conditions. In another embodiment, the alkaline condition is achieved by adding a base is added to the reaction. In an embodiment, the base is an organic base. In a further embodiment, the base is selected from the group consisting of triethylamine, N-methylmorpholine, diisopropylethylamine, and 4- methylaminopyridine. In another embodiment, the base is N-methylmorpholine.

In another embodiment, compound 8-M and coupling agent are fed at a molar ratio in the range of 1:1.1 to 1:3. In another embodiment, compound 8-M, compound 9 and an organic base are fed at a molar ratio in the range of 1:1.05:1 to 1:1.1:3.

In another embodiment, the workup mode of the reaction is as follows: after the completion of the reaction, ethyl acetate and water are added under stirring to extract, aqueous layer is separated and removed out, and the organic layer is poured into the reaction solvent that is used in the next step and then concentrated till the remaining concentrated solution is approximated 2 times to that of compound 8-M by weight; and the remaining concentrated solution is directly used in the next step of the reaction without separation.

Sixth Aspect

In a sixth aspect, the present invention provides a process for preparing the mono HCI salt of OAD2 (compound of Formula 11), wherein the process comprises a first step of hydrolyzing the methyl ester of the compound of Formula 10

acid so as to produce the mono HCI salt of OAD2 (compound of Formula 11):

In an embodiment, the reaction solvent is a polar aprotic solvent. In another embodiment, the reaction solvent is selected from the group consisting of 2-methyltetrahydrofuran, tetrahydrofuran, 1,4-dioxane, acetone, and acetonitrile, and preferably tetrahydrofuran. In another embodiment, the weight amount of the solvent is 4 to 8 times to that of OAD2.

In another embodiment, the reaction is carried out at a temperature in the range of 10 to 40°C, and preferably in the range of 15 to 25°C.

In an embodiment, an alkaline solution is added to the reaction. In a further embodiment, the alkaline solution is a sodium hydroxide solution of 2 to 4 mol/L, and compound 10 and sodium hydroxide are fed at a molar ratio in the range of 1:4 to 1:6.

In another embodiment, the process of adding a hydrochloric acid solution of 1 to 2 mol/L; and the pH is adjusted to the range of 1 to 4, and preferably to the range of 2 to 3.

In another embodiment, the workup mode of the reaction is as follows: after adjusting the pH to between 1 to 4, the reaction mixture is stirred to crystalize or stood to crystalize, and preferably stood to crystalize. Seventh Aspect

In a seventh aspect, the present invention provides a process for preparing the di-HCI salt of OAD2, wherein the process comprises reacting the mono HCI salt of OAD2 (compound 11) with HCI, so as to produce the di-HCI salt of OAD2.

In an embodiment, the reaction is conducted in a solvent mixture comprising water and a polar aprotic solvent. In another embodiment, the reaction is conducted in a solvent mixture comprising water and a solvent selected from the group consisting of acetic acid, tetrahydrofuran, and acetone. In another embodiment, the reaction is conducted in a solvent mixture comprising water and tetrahydrofuran, and the weight amount of the reaction solvent is 15 to 20 times to that of mono HCI salt of OAD2.

In another embodiment, during the reaction, a hydrochloric acid solution A is first added and stirred, and subsequently water is added and further stirred, and then a hydrochloric acid solution B is added and stirred to crystalize. The weight amount of hydrochloric acid solution A is 2 to 3 times to that of the mono HCI salt of OAD2, and the weight amount of hydrochloric acid solution B is 6 to 8 times to that of compound mono HCI salt of OAD2. The concentrations of hydrochloric acid solutions A and B are 3 to 6 mol/L, and preferably 4 to 5 mol/L.

According to the invention, the specific preparation method may comprise one or more of the steps in Aspects 1 to 7 as shown below in Scheme 2.

Scheme 2

Eighth Aspect

In an eighth aspect, the present invention provides intermediate compounds of Formula 13 and 14. In an embodiment, the present invention provides a compound of Formula 13, or salt thereof: , wherein R ¹ is Ci-6 alkyl, and R ² is a Ci-6 alkyl or arylmethoxy group. In another embodiment of the compound of Formula 13, or salt thereof, R ¹ is methyl. In another embodiment of the compound of Formula 13, or salt thereof, R ² is methyl. In another embodiment of the compound of Formula 13, or salt thereof, R ¹ is methyl and R ² is methyl.

In another embodiment, the present invention provides a compound of Formula 14, or a salt thereof:

The invention may achieve the following beneficial effects: compared with the prior art methods, the method of the invention for preparing OAD2 dihydrochloride has fewer steps, does not require separation and purification by column chromatography, and is suitable for industrial scale production. Moreover, in the method of the invention, the steps for preparing the mono HCI salt of OAD2 from compound 15 can be carried out in a continuous feeding mode, may not require purification process; the workup is simplified and the loss of the product is minimized; solid product may be precipitated from a certain solvent by the salt forming mode of acid and alkaline, to achieve purification effect and meanwhile obtain mono HCI salt of OAD2 having high purity, and then target compound OAD2 di HCI is obtained via further salt forming step. The preparation method of the invention may have a total yield of more than 35% from compound 1 to the final product compound OAD2 dihydrochloride, and the purity of the final product may be more than 98%. Compared with the prior art, the method of the invention may have a significantly improved yield and is suitable for large-scale industrial production. The certain embodiments of the current method have reached a batch size of 50 kg and showed good process stability and controllable product quality.

Examples

The invention will be further illustrated by combining the following specific examples. The following examples are used to explain the method of the invention and the core concept thereof, and for those skilled in the art, any possible change or substitution without departing from the inventive concept falls within the protection scope of the invention. In the following examples, where the specific conditions of the experimental methods are not indicated, they are typically the conventional conditions, or are those recommended by the raw material or commodity manufactures; and the solvents without indicating the source are typically conventional solvents that are commercially available. Compounds 1, 12 and 9 may be prepared according to the methods described in CN102378574B and W02007093013 Al, hereby incorporated by reference in their entirety.

Example 1: Process for preparation of compound 13 (where R ¹ is -ethyl and R ² is -methyl)

To a DCM solution of Compound 1 (30 kg) was added acetylamino-(dimethoxy-phosphoryl) - acetic acid ethyl ester (19.2 kg). The mixture was cooled to 16.8 °C and DBU (22.17 kg) was added over 2 h, maintaining the internal temperature below 34 °C. The reaction mixture was agitated at 25 °C - 30 °C overnight. Saturated aqueous NH4CI (250 L) was added, the mixture was agitated for 1.5 h, and then allowed to settle for 1 h. The organic layer was separated and DCM (199.3 kg) was added and the mixture was agitated for 1 h. Brine (300 L) was added, the mixture was agitated for 30 min, and allowed to stand overnight. The organic layer was separated. The aqueous phase was agitated with DCM (150.4 kg) for 1 h and the organic layer was separated. The combined organic phases were filtered and the filtrate was concentrated to a volume of 170 L. MeOH (199.4 kg) was added and the mixture was concentrated to 165 L. volume. MeOH (199.7 kg) was added, the mixture was concentrated to 180 L volume. MeOH (68.4 kg) and Water (150.2 kg) were added and the mixture was agitated at room temperature overnight and filtered. The filtered solid was treated with MeOH (159.6 kg) and water (100.0 kg) and agitated overnight.

Approximately one-half of this mixture was filtered and the collected solid was washed with water (10.0 kg) and MeOH (16.0 kg). The solid was dried to afford 14.18 kg of 13 as gray solid.

The remaining one-half of the aforementioned mixture was filtered and the collected solid was washed with water (15.0 kg) and MeOH (24.0 kg). The solid was dried to afford 19.45 kg 13 as gray solid, total yield 33.63 kg.

Example 2: Preparation of compound 14

Compound 13 (31.3 kg) (where R ¹ is ethyl and R ² is methyl) was treated with dioxane (242.8 kg) and stirred at ambient temperature. The mixture was treated with 6N hydrochloric acid (prepared from 58.7 kg water and 70.4 kg of concentrated aqueous HCI). The mixture was heated at reflux (84-94.3 °C) with stirring for 19.5 h. The mixture was allowed to cool to 25 °C and treated with water (782.5 kg). After stirring for 1.5 h at 20 °C, the mixture was filtered and the collected solid was washed with two 30-kg portions of water. The solid was triturated with water (300 kg) with agitation at 17-19 °C for 1 h. The solids were collected by filtration, and the collected solid was washed with two 30-kg portions of water. The solid was triturated with 86.7 kg methanol with agitation at 20 °C for 2 h. The solid was collected by filtration and washed with 12.4 kg of methanol. The solid was collected and dried at 39 °C under reduced pressure. The solid was triturated at 20 °C with dichloromethane (165.9 kg) with agitation for 2 h. The solid was collected by filtration, washed with 20.8 kg of dichloromethane, and dried at 40 °C under reduced pressure to afford 20.76 kg of Compound 14 as a beige/off-white solid. Example 3: Preparation of compound 15

Into a reaction vessel were added anhydrous dioxane (2.4 L), sodium borohydride (278 g) and toluene (2.4 L). The mixture was stirred at 25 °C for 15-20 min. The mixture was cooled to - 7 °C, and 2-ethylhexanoic acid (1.56 L) was added over 90 min the while keeping the temperature at -5±2 °C . The temperature was increased to 10 °C to initiate the exothermic reaction, whereupon external cooling was applied to maintain internal temperature at 15 °C. The reaction mixture was stirred at 15 °C for 18 h. The solution of reducing agent was used in the next step without further modification.

Toluene (22.0 L) and 14 (2.2 kg) were combined and tri-n-butylamine (1.22 L) was added to the stirred suspension while temperature was kept below 25 °C. Stirring was continued at 25 °C for 30 min until all starting material dissolved. (S)-l-Phenylpropan-l-amine (810 mL) was added to the mixture, and the mixture stirred for 1.5 h at 25 °C. The mixture was cooled to 10 °C, and the reducing agent (prepared above) was added dropwise keeping the temperature below 15 °C . The resulting mixture was stirred at 15 °C for 18 h. The reaction mixture was quenched via addition of MeOH (600 mL) and mixture stirred at 25 °C for 1 h. The quenched reaction mixture was concentrated to dryness, and the residue was treated with DMF (8.1 L). The suspension was heated at 75-80 °C for 30 min. The clear solution was cooled to 25 °C and was seeded with a sample of 15 (5 g). The mixture was cooled to 15 °C and stirred for 30 min. The solid product was collected by filtration and was washed with three 2 L - portions of methanol. The product was dried to afford 1.98 kg of Compound 15. Example 4A: Preparation of compound 8-M (where M is Na)

Dioxane (1.93 L), TFA (6.43 L), toluene (10 L), and paraformaldehyde (324 g, 10.8 mol) were mixed and cooled to 27 °C. Compound 15 (1606 g, 2.713 mol) was added along with additional toluene (7.4 L). The reaction mixture was stirred at 27 °C for 20 h until the reaction was complete. The mixture was cooled to 22 °C and diluted with EtOAc (22 L) and washed with brine (20 L). Brine (8 L) was added to the organic layer, and the pH of the mixture was adjusted to 6.5 with 2 M sodium carbonate (19 L added over 3 h). The organic and aqueous layers were separated, and the organic layer was washed with brine (15 L). The organic layer was dried over sodium sulfate, filtered through diatomaceous earth and concentrated under reduced pressure. The residue was taken up in 10 L EtOAc and stirred with saturated sodium carbonate (10 L) for 15 min. Brine (10 L) was added, and the mixture was stirred for 10 min. The organic and aqueous layers were separated, and the organic layer was filtered through a pad of sodium sulfate. The pad was washed with EtOAc. Methyl tert-butyl ether (MTBE)

(110 L) was added to the filtrate with stirring for 1 h. The resulting solid was filtered under gravity and the collected solid was washed with MTBE (2 L). Vacuum was then applied to remove solvents, and the material was air dried overnight. The resulting solid was dried with agitation rotary evaporator for 6 h to provide 1406 g of product 8-M.

Example 4B: Alternate preparation of compound 8-M (where M is Na)

Paraformaldehyde (1176.0 g), TFA (26.0 kg), toluene (48.4 kg) and iPrOAc (12.1 kg) were combined. The temperature of the mixture was adjusted to 22.0 °C and Compound 15 (5.9 kg) was added along with an additional 6.0 kg of toluene. The mixture was stirred at 25.7-30.8 °C for approximately 3.5 h. Isopropyl acetate (10.2 kg) was added, and the resulting mixture was cooled to 5.9 °C. A solution of 4N NaOH (68 kg) was added over 26 min while maintaining a temperature below 25 °C. The temperature of the mixture was adjusted to 20.4°C, and the resulting mixture was agitated at 20.4-21.1°C for 10 min. The layers were separated, and the organic layer was washed with brine (2 x 14.6 kg). The organic layer was diluted with DMF (10.8 kg), and the mixture was concentrated under reduced pressure to 12 L volume. DMF (10.8 kg) was added, and the mixture stirred at 22.4-25.0 °C for 10 min. The DMF solution of 8-M was used as starting material in Example 5B.

Example 5A: Preparation of compound 10

Under nitrogen, Compound 9 ((S)-2-amino-3-[4-(2,3-dimethyl-pyridin-4-yl)-phenyl]- propionic acid methyl ester) (702.4 g) was dissolved in DMF (4.75 L), and the temperature brought to 20 °C. Compound 8-M (1406 g, 2.246 mol), HBTU (937 g, 2.47 mol), and DMF (2.75 L) was added. NMM (4-methylmorpholine) (493 mL) was added, and the temperature rose to 28 °C. The mixture was immediately brought to 23-25 °C and stirred for 1 h. The mixture was poured onto vigorously stirring water (35 L), and the resulting suspension stirred for 1 h. The solid was filtered and washed with water (10 L) and hexanes (10 L). The solid was dissolved in EtOAc (12 L) and washed with brine. The organic layer was dried over sodium sulfate, filtered, and concentrated. The resulting solid was dissolved in MTBE-DCM (3.1 L, 30:1) and chromatographed over silica gel (6 kg) using MTBE as the eluant to afford Compound 10 (1851 g).

Example 5B: Alternate preparation of compound 10

A solution of Compound 9 (3.1 kg) in 8 L of DMF was treated with 4-methylmorpholine (2001.2 g). The Compound 8-M solution in DMF (from Example 4B) was added, along with additional DMF (3.5 kg). The temperature of the mixture was adjusted to 0 °C. HBTU (4.1 kg) was added while maintaining a temperature below 15 °C. The mixture was warmed to 17.9 °C and stirred at 17.9 °C to 22.6 °C for 3 h. The reaction mixture was diluted with EtOAc (42.1 kg), and the temperature was adjusted to 12.3 °C. Water (69.6 kg) was added and the resulting mixture stirred at 19.1 °C to 20.4 °C for 30 min. The separated organic layer was concentrated under reduced pressure to 6 L volume. 2-Methyltetrahydrofuran (two portions of 9.9 kg) was added, and the mixture was concentrated under reduced pressure to 6 L volume. The resulting solution of Compound 10 was held at -10 ± 5°C and used in the next step, Example 6.

Example 6: Preparation of OAD2 dihydrochloride.

OAD2 dihydrochloride

The solution of Compound 10 from Example 5B was diluted with 2-methyltetrahydrofuran (29.9 kg). The mixture was warmed to 17.9 °C and stirred at 17.9- 21.3 °C for 1 h. The mixture was cooled to 9.5 °C. 2N NaOH (prepared from NaOH 1568.9 g, water 19.4 kg) was added while maintaining a temperature below 20 °C. The mixture was allowed to come to 15.3 °C and was held between 15.3-22.9 °C for 21 h. The reaction mixture was cooled to 4.6 °C and the pH of the mixture was adjusted to 3.94 with 1 N HCI. The temperature of the reaction mixture was adjusted to 8.8 °C. The mixture was stirred at 5.7-8.8 °C for 2.5 h which resulted in formation of a slurry. The slurry was warmed to 16.5°C and stirred at 16.5-18.7°C for 1 h. The solids were collected by filtration and then washed with water (5.8 kg) and 2-methyltetrahydrofuran (5.1 kg). The solid product was dried at 39 °C under reduced pressure to afford 6.4 kg of crude OAD2-HCI as a white solid.

The crude OAD2-HCI (6.4 kg), 2-methyltetrahydrofuran (110.2 kg) and water (12.8 kg) were combined. The mixture was heated to 55.0 °C and agitated at 55.0-65.0°C for 2 h. The mixture was cooled to 25.0 °C over 1 h and stirred at 19.8-25.0°C for 1 h. The solids were filtered, washed with 2-methyltetrahydrofuran (4.1 kg) and dried at 39 °C under reduced pressure to afford 4.2 kg OAD2-HCI as white solid.

OAD2-HCI (4.1 kg) was treated with AcOH (8.9 kg), the temperature of the mixture was adjusted to 19.7 °C, and the mixture was stirred at 19.4-19.7 °C for 30 min. 5N HCI (prepared from water 5.0 kg, 37% HCI 4.2 kg) was added over 10 min while maintaining a temperature below 25 °C. The mixture was stirred at 19.1 - 21.2 °C for 1 h. Water (84.0 kg) was added over 1 h while maintaining a temperature below 25 °C. The mixture was stirred at 19.7-22.4 °C for 1.5 h to provide a clear solution which was transferred to a second reaction vessel along with AcOH (4.1 kg) and water (8.5 kg). 5N HCI (prepared from water 14.6 kg, HCI 37% 12.6 kg) was added while maintaining a temperature below 25 °C. The mixture was stirred at 19.4 -

20.2 °C for 1 h. The resulting solids were collected by filtration and washed with 1 N HCI (4.5 kg). The collected solids were treated with IN HCI (42.8 kg) . The mixture was stirred at 19.2 -

19.3 °C for 30 min, filtered, and the collected solid was washed with 1 N HCI (5.3 kg). The collected solid was treated withl N HCI (42.8 kg). The mixture was stirred at 19.2-19.6 °C for 40 min, filtered, and the collected solid was washed with 1 N HCI (6.1 kg). The solid product was dried at 40 °C under reduced pressure to afford 4.1 kg of OAD2-2HCI as a white solid.