DESC:Related Patent Application
This application claims the priority to and benefit of Indian Provisional Patent Application No. 202141031278 filed on July 12, 2021; the disclosure of which are incorporated herein by reference.
Filed of the Invention
The present invention relates to an improved process for the preparation of migalastat or its pharmaceutical acceptable salts and its intermediates thereof, particularly related to a chemoenzymatic process for the preparation of amine intermediate of migalastat from keto intermediate of migalastat by using transaminase enzyme during the preparation of migalastat or its pharmaceutically acceptable salts thereof.
Background of the Invention
Migalastat hydrochloride is low molecular weight imino sugar, having chemical name (+)-(2R,3S,4R,5S)-2-(hydroxymethyl) piperidine-3,4,5-triol hydrochloride. Migalastat is an active pharmaceutical ingredient used in the treatment of Fabry disease and having the formula-I as mentioned below.

Migalast is prepared from a microbiological process and a synthetic process. Synthetically migalastat may be prepared from the D-glucofuranose, D-galactofuranose, D-galactose, 1-dexoynojirimycin or their derivatives.
The Publication Heterocycles 1988, Vol-27, N0-1, pages 63 to 66 discloses a process for the preparation of Miglastat from 1,2-isopropylidine-D-glucofuranose involving the steps of: oxidizing glucofuranose to a 5-oxo-derivative in excess molecular sieves and purified the resultant derivative in a column of silica gel; treating the 5-oxo-derivative with methylhydroxylamine hydrochloride in the presence of sodium bicarbonate to give mixture of methyloximes and the mixture of methyloximes is passed to silica gel column to remove inorganic materials; treating the mixture of methyloximes with toluene sulfonic acid in methanol followed by the treatment with lithium aluminum hydride to give 5-amino derivative; and the 5-amino derivative is then converted to migalstat as mentioned below.

The Publication Carbohydrate Research 1986, 155, pages 119-129 discloses the preparation of miglastat from 3-O-acetyl-1,2:5,6-di-O-isopropylidene-D-galactofuranose as disclosed below. As 3-O-acetyl-1,2:5,6-di-O-isopropylidene-D-galactofuranose was not easily accessible, it was prepared from 1,2:5,6-di-O-isopropylidine-D-glucose via the D-gulo-epimer.

The Publication Synlett 1999, No-5, Pages 593-595 discloses the preparation of migalastat from the D-galactose as mentioned below.

The Publication Carbohydrate Research 1990, 203, pages 314 to 318 discloses the preparation of the migalastat from 1-dexoynojirimycin (miglitol) as mentioned below.

The Patent US10077458 discloses the microbial synthesis of migalastat involving the steps of culturing a microorganism under conditions such that at least one imino sugar is produced; then detecting and isolating the imino sugar.
The carry over impurities formed during each stages of chemical conversion of the synthetic processes are to be controlled in the final active substance. The reduction or control of these impurities at different stages of the process is difficult and challenging.
Besides different processes for the preparation of migalastat, there is a need to develop a process for the preparation of migalastat at commercial scale.

Summary of the Invention
The main aspect of the present invention is to provide a chemoenzymatic process comprising the steps of: converting compound of formula-IV as mentioned below,

wherein said Prot refers to the protecting groups, to compound of formula-III as mentioned below

using enzyme transaminase.
In one embodiment of the present invention, the compound of formula-IV is converted to the compound of formula-III in the presence of transaminase enzyme (GB 71) under nitrogen atmosphere.
In one embodiment, the protecting groups include benzyl group, pivaloyl group, and hydroxy groups.
Another aspect of the present invention is to provide a process for the preparation of Migalastat of formula-I or its pharmaceutical acceptable salts, comprising the steps of:
(i) converting compound of formula-V as mentioned below,

wherein said Prot refers to the protecting groups, to compound of formula-IV as mentioned below,

(ii) converting the compound of formula-IV to compound of formula-III as mentioned below.

using enzyme transaminase;
(iii) deprotecting the compound of formula-III to compound of formula-II as mentioned below,

(iv) converting the compound of formula-II to migalastat of formula I.
In one embodiment, the compound of formula-V is prepared by reacting D-galactose with pivaloyl imidazole in dimethylformamide. In one embodiment, the compound of formula-V is an altrofuranoside. In one embodiment, the compound of formula-V is converted to the compound of formula-IV by an oxidizing agent in an organic solvent. In one embodiment, the oxidizing agent is pyridinium chlorochromate and the organic solvent is dichloromethane.
In one embodiment, the step (iii) is carried out in the presence of sodium methoxide in methanol.
In one embodiment, the step (iv) is carried out with palladium on carbon catalyst in methanol.

Detailed Description of Invention
One embodiment of the present invention is to provide a chemoenzymatic process, comprising the step of: converting compound of formula-IV as mentioned below,

wherein said Prot refers to the protecting groups, to compound of formula-III as mentioned below

using enzyme.
Another embodiment of the present invention is to provide a process for the preparation of Migalastat of formula-I or its pharmaceutical acceptable salts, comprising the steps of:
(i) converting compound of formula-V as mentioned below,

wherein said Prot refers to the protecting groups, to compound of formula-IV as mentioned below,

(ii) converting the compound of formula-IV to compound of formula-III as mentioned below.

using enzyme transaminase;
(iii) deprotecting the compound of formula-III to compound of formula-II as mentioned below,

(iv) converting the compound of formula-II to migalastat of formula I.
The compound of formula-V employed in the step (i) of the present invention is prepared from the D-galactose involving the protection of the hydroxy groups by the protection groups suitable for the process by forming galactofuranose and the conversion of galactofuranose to the compound having the formula-V. The compound having the formula-V is an altrofuranoside. The term “Prot” refers to the suitable protecting groups employed in the state of art. Protecting groups include, but not limited to, benzyl group or pivaloyl group. Protecting groups may also include the protecting adjacent hydroxy groups of D-galactose by the formation methylenedioxyl group.
Preferably the compound of formula-V of the present invention is prepared from D-galactose involves the steps of: (a) reacting D-galactose with pivaloyl imidazole in a suitable solvent such as dimethylformamide.
The compound of formula-V is converted to the compound of formula-IV according to the step (i) of the present invention with oxidizing agents in the state of art. Preferably the compound of formula-V is converted to the compound of formula-IV by the oxidizing agent such as pyridinium chlorochromate in an organic solvent or its mixtures such as dichloromethane.
The compound of formula-IV is converted to the compound of formula-III according to the step (ii) of the present invention in enzyme, particularly transaminase enzyme or aminotransferase. Preferably, the the compound of formula-IV is converted to the compound of formula-III in the presence of transaminase enzyme (GB 71) under nitrogen atmosphere.
The conversion of the compound of formula-III to the compound of formula-II according to the step (iii) of the present invention is a deprotection step involving suitable reagents for deprotection of the protected groups in the compound of formula-III. Preferably the deprotection step may be carried out in the presence of sodium methoxide in methanol.
The compound of formula-II is converted to the migalast of formula-I according to the step (iv) of the present invention with suitable reducing agents in a suitable solvent. Preferably the conversion of the compound of formula-II to the migalast of formula-I may be carried out with palladium on carbon catalyst in methanol.
The migalastat prepared by the process of the present invention may be converted to its pharmaceutically acceptable salts for pharmaceutical purposes.
The inventors of the present invention found an improved process for the preparation of migalastat from galactose derivative by avoiding hazardous azidation chemistry. The prior art process for the preparation of migalastat from galactose involves hazardous azidation chemistry.
The process of the present invention for the preparation of migalastat from D-galactose or its derivative is mentioned below.

Certain specific aspect and embodiment of the present invention will be explained in detail with reference to the following examples, which are provided only for purposes of illustration and should not be construed as limiting the scope of the invention in any manner.

Examples
Example-1: Preparation of pivaloyl imidazole
To a solution of imidazole (1129.2 g, 2.0 eq moles) in chloroform (10000 ml) under nitrogen atmosphere, pivaloyl chloride (1000.0 g, 1.0 moles) was added in drops at a temperature of 0±5 °C and stirred for 2-3 hours at a temperature between 25°C-30°C. The progress of the reaction was monitored by TLC. After completion of the reaction, the reaction mass was quenched by water (5000 ml) to form a biphasic mixture. The organic layer was separated and washed with water (2 x 5000 ml), dried over sodium sulphate and concentrated under vacuum. The residue was co-distilled with hexane (1000 ml) to obtain a crude. The crude material thus obtained was crystallized with hexane (1000 ml). %Yield: 73.67%
Example-2: Protecting hydroxy groups in D-galactose

To a solution of D-galactose (220.0 g, 1.0 eq) in dimethyl formamide (2200 ml), the pivaloyl imidazole (929.2 g, 5.0 eq) obtained in the example-1 was added at a temperature between 20°C-30°C and stirred at a temperature 65°C-70°C for 4-6 hours. The progress of the reaction was monitored by TLC. After completion of the reaction, the reaction mass was cooled to room temperature followed by the addition of water (2200 ml). The contents in the reaction mass was then extracted two times with methyl-tert-butyl ether (3300 ml). The combined extracts were washed with water (3 x 2200 ml), dried over sodium sulphate and concentrated under vacuum to obtain a residue. The residue was co-distilled twice with n-heptane (2x 220 ml) and crystallized with n-heptane. %Yield: 36.2%

Example-3: Oxidation of secondary alcohol

To a solution of pyridinium chlorochromate (20.8 g, 5.0 eq) in dichloromethane (300.0 ml) under nitrogen atmosphere, 4Å molecular sieves (15.0 g) was added and stirred for 10-15 minutes at room temperature. To the stirred reaction mixture, a solution of tetrapivaloyl protected D-galactose (10.0 g, 1.0 eq) obtained in example-2, in dichloromethane (30.0 ml) was added in drops at a temperature between 20°C to 30°C and stirred for 16-24 hours at a temperature between 25°C-35°C. The progress of the reaction was monitored by TLC. After the completion of the reaction, the reaction mass was passed through celite bed, filtrate was washed with 10% aqueous hydrochloric acid (100ml) and concentrated under vacuum to obtain a residue. The obtained residue was purified by column chromatography using silica gel (60-120) and hexane-ethyl acetate (3000ml) as an eluent. % Yield: 60.24%
Example-4: Enzymatic preparation of amine intermediate from transaminase

To a solution of secondary alcohol obtained from the example-3 (0.5 g, 1.0 eq) in ethanol (10 ml), L-alanine (0.103 g, 1.2 eq) and Transaminase enzyme (GB 71, Obtained Iosynth Private Lab Limited, Bangalore) (0.05 g, 10% w/w) were added under nitrogen atmosphere at room temperature and stirred for 16-18 hours at a temperature between 20°C-30°C. The progress of the reaction was monitored by TLC. After completion of the reaction, the inorganic material was filtered off from the reaction mass and the filtrate was concentrated under vacuum to obtain a residue. The obtained residue was purified by column chromatography using silica gel (60-120) and hexane-ethyl acetate (500 ml) as an eluent. Yield: 60%.
,CLAIMS:1. A chemoenzymatic process comprising the step of:
converting compound of formula-IV as mentioned below,

wherein said Prot refers to protecting groups, to compound of formula-III as mentioned below

using enzyme transaminase.
2. The process as claimed in Claim 1, wherein the compound of formula-IV is converted to the compound of formula-III in the presence of transaminase enzyme (GB 71) under nitrogen atmosphere.
3. The process as claimed in Claim 1, wherein the protecting groups include benzyl group and pivaloyl group, and hydroxy groups.
4. A process for the preparation of Migalastat of formula-I or its pharmaceutical acceptable salts comprising the steps of:
(i) converting compound of formula-V as mentioned below,

wherein said Prot refers to protecting groups, to compound of formula IV as mentioned below,

(ii) converting the compound of formula-IV to compound of formula-III as mentioned below.

using enzyme transaminase;
(iii) deprotecting the compound of formula-III to compound of formula-II as mentioned below,

(iv) converting the compound of formula-II to migalastat of formula I.

5. The process as claimed in Claim 4, wherein the compound of formula-V is an altrofuranoside.
6. The process as claimed in Claim 4, wherein the compound of formula-V is prepared by reacting D-galactose with pivaloyl imidazole in dimethylformamide.
7. The process as claimed in Claim 4, wherein the protecting groups include benzyl group, pivaloyl group, and hydroxy groups.
8. The process as claimed in Claim 4, wherein the step (i) is carried out by an oxidizing agent in an organic solvent.
9. The process as claimed in Claim 8, wherein the oxidizing agent is pyridinium chlorochromate.
10. The process as claimed in Claim 8, wherein the organic solvent is dichloromethane.
11. The process as claimed in Claim 4, wherein the step (iii) is carried out in the presence of sodium methoxide in methanol.
12. The process as claimed in Claim 4, wherein the step (iv) is carried out with palladium on carbon catalyst in methanol.