DESC:Field of the invention:
The present invention relates to a process for the preparation of Imeglimin or pharmaceutically acceptable salts thereof, particularly Imeglimin hydrochloride.

Background of invention:
Imeglimin, is a tetrahydrotriazine compound or a dihydro-1,3,5-triazine, with a chemical name as (6R)-(+)-4-dimethylamino-2-imino-6-methyl-1,2,5,6-tetrahydro-1,3,5-triazine or (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine, represented by formula (I) below,

Formula (I)

Imeglimin is the first in a new class of drugs, the glimins and is being developed for the treatment of type 2 diabetes. Imeglimin, developed by Poxel SA, exhibits a dual mechanism of action that is designed both to increase insulin secretion in response to glucose and to reduce insulin resistance. Due to its dual mechanism of action, it targets mitochondrial bioenergetics. The mitochondrion is the power station of the cell and its dysfunction is implicated in the pathophysiology of type 2 diabetes.

Imeglimin acts on all three key organs which play an important role in the treatment of type 2 diabetes: the pancreas, muscles, and the liver. It has demonstrated glucose lowering benefits by increasing insulin secretion in response to glucose, improving insulin sensitivity and suppressing gluconeogenesis. Imeglimin has the potential to prevent endothelial and diastolic dysfunction, which can provide protective effects on micro- and macro-vascular defects induced by diabetes. It also has the potential for protective effect on beta-cell survival and function.

The galenic or immediate release formulation of Imeglimin is a coated, oblong-shaped tablet with immediate release. Three different dose strengths, namely 250 mg, 500 mg and 750 mg have been developed.

US7034021 discloses dihydro-1,3,5-triazine amine derivatives and process for preparation thereof.

US8461331 discloses a process for preparation of 3,6-Dihydro-1,3,5-triazine derivatives using meformin and paraldehyde derivatives.

US7501511 discloses a process for resolving amines derived from dihydro-1,3,5- triazines from the corresponding racemic mixture.

WO2007079914 discloses that polymorphic form A1 of (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride is obtained from Example 1 of WO2004089917. This document further discloses the process for preparation of Form H1 of (+)-2-amino-3,6—dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride.

US8742102 discloses a process for enantiomeric separation of racemic dihydro-1,3,5-triazines via preferential crystallization.

US8742103 discloses a process of separation of triazine derivatives enantiomers involving tartaric acid.

WO2009141040 discloses a process for preparation of 3,6-dihydro-1,3,5-triazine derivatives by treating Metformin hydrochloride with a suitable aldehyde in a polar solvent or solvent mixture in presence or absence of an inorganic and/or organic base.

US8703940 discloses a process for preparation of 3,6-dihydro-1,3,5-triazine derivatives wherein a biguanide is reacted with acetaldehyde in the presence of an inorganic and/or organic base.
There still exists a need to develop a simple, economical, reproducible, commercially viable and industrially feasible process for preparation of Imeglimin or pharmaceutically acceptable salts thereof. The present invention provides a simple, economical, reproducible, commercially viable and industrially feasible process for preparation of Imeglimin or pharmaceutically acceptable salts thereof.

Object of the invention:
An object of the present invention is to provide a simple, economical, reproducible, commercially viable and industrially feasible process for preparation of Imeglimin or pharmaceutically acceptable salts thereof.

Another object of the present invention is to provide an analytical method to determine the chiral purity of Imeglimin or pharmaceutically acceptable salts thereof.

Yet another object of the present invention is to provide a pharmaceutical composition comprising Imeglimin or pharmaceutically acceptable salts thereof.

Summary of invention:
An aspect of the present invention is to provide a process for preparation of (R)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine (Imeglimin) or a pharmaceutically acceptable salt thereof, comprising the steps of,
a) treating Metformin or a salt thereof with acetaldehyde or a cyclic derivative thereof in an amount of 0.5 - 5 equivalents with respect to Metformin or a salt thereof to obtain racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or a salt thereof;
b) subjecting racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or a salt thereof to resolution using a chiral acid to obtain (R)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine (Imeglimin) or a pharmaceutically acceptable salt thereof; and
c) optionally purifying said (R)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or a pharmaceutically acceptable salt thereof.
Preferably said cyclic derivative of acetaldehyde is selected from paraldehyde or metaldehyde and said treatment of metformin or a salt thereof with said cyclic derivative of acetaldehyde is carried out in the presence of an acid catalyst at a temperature of 75-85 ºC.
Preferably said treatment of metformin or a salt thereof with acetaldehyde is carried out at a temperature below 35 ºC.
Preferably said Metformin or a salt thereof is treated with acetaldehyde or a cyclic derivative thereof in an amount of 0.5 – 1.5 equivalents with respect to Metformin or a salt thereof.
Preferably said resolution comprises the steps of:
a) treating racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or a salt thereof with a chiral acid to obtain the R-isomer of 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine; and
b) isolation of the R-isomer of 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine from the mother liquor.
Preferably the mother liquor obtained after isolation of the R-isomer of 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine is subjected to racemization to obtain racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine.
Preferably said pharmaceutically acceptable salt is (R)-2-amino- 3,6-dihydro- 4-dimethylamino- 6-methyl- 1,3,5-triazine hydrochloride and said (R)-2-amino- 3,6-dihydro- 4-dimethylamino- 6-methyl- 1,3,5-triazine hydrochloride is subjected to slurry wash with ethanol for removal /reduction of the dihydrochloride impurities.
Preferably said chiral purity of Imeglimin or a salt thereof is determined by a method comprising the steps of:
a) dissolving a sample of Imeglimin or its salt or a dosage form comprising Imeglimin or its salt in a solvent to produce a sample solution;
b) dissolving the reference standard for the S-isomer in a solvent to produce a reference marker solution;
c) subjecting the sample solution and the reference marker solution to a suitable chromatographic technique; and
d) determining the presence and quantity of said S-isomer in the sample solution.

Another aspect of the present invention is to provide a method for determining the chiral purity of Imeglimin or a salt thereof comprising the steps of:
a) dissolving a sample of Imeglimin or its salt or a dosage form comprising Imeglimin or its salt in a solvent to produce a sample solution;
b) dissolving the reference standard for the S-isomer in a solvent to produce a reference marker solution;
c) subjecting the sample solution and the reference marker solution to a suitable chromatographic technique; and
d) determining the presence and quantity of said S-isomer in the sample solution.
Preferably, said chromatographic technique is a HPLC method or a gradient HPLC method; stationary phase is a normal phase chiral column; and mobile phase comprises a combination of hexane, 2-propanol, diethylamine and trifluoroacetic acid.

Brief description of the Drawings:
Fig. 1: XRPD of Imeglimin hydrochloride obtained by the process of the present invention.
Fig. 2: XRPD of Imeglimin hydrochloride obtained by the process of the present invention.

Detailed Description of the invention:
The present invention relates to a simple, economical, reproducible, commercially viable and industrially feasible process for the preparation of Imeglimin or its pharmaceutically acceptable salt, in particular Imeglimin hydrochloride.

According to one embodiment of the present invention, there is provided a process for preparation of (R)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine (Imeglimin) or a pharmaceutically acceptable salt thereof, comprising the steps of:
a) treating Metformin or a salt thereof with acetaldehyde or a cyclic derivative thereof to obtain racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or a salt thereof;
b) subjecting racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or a salt thereof to resolution to obtain the R-isomer of 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine (Imeglimin); and
c) optionally, treating Imeglimin with a suitable reagent to obtain Imeglimin salt.

Cyclic derivative of acetaldehyde is selected from paraldehyde or metaldehyde.
Metformin or a salt thereof is treated with acetaldehyde or a cyclic derivative thereof in an amount of 0.5 - 5 equivalents with respect to Metformin or a salt thereof
Said treatment of Metformin or a salt thereof with acetaldehyde or a cyclic derivative thereof is carried out in the presence or absence of a catalyst, preferably an acid catalyst.

One embodiment provides a process for preparation of (R)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine (Imeglimin) or a pharmaceutically acceptable salt thereof, comprising the steps of,
a) treating Metformin or a salt thereof with acetaldehyde or a cyclic derivative thereof in an amount of 0.5 - 5 equivalents with respect to Metformin or a salt thereof to obtain racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or a salt thereof;
b) subjecting racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or a salt thereof to resolution using a chiral acid to obtain (R)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine (Imeglimin) or a pharmaceutically acceptable salt thereof; and
c) optionally purifying said (R)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or a pharmaceutically acceptable salt thereof.
Preferably, acetaldehyde or a cyclic derivative thereof in an amount of 0.5 - 5 equivalents with respect to Metformin or a salt thereof is used.
In a preferred embodiment, the process for preparation of Imeglimin or its pharmaceutically acceptable salt, in particular Imeglimin hydrochloride comprises the steps of:
Step 1: Metformin hydrochloride and an acid catalyst are taken in an alcoholic solvent under nitrogen atmosphere to obtain a reaction mixture. Metaldehyde is charged to the reaction mixture to obtain a suspension and the obtained suspension is heated to 75-85ºC, preferably 77 - 82ºC. The suspension is maintained under stirring for about 2-5 hours, preferably 3 hours at the same temperature. Another lot of metaldehyde is added and the mixture is maintained under stirring for about 5-10 hours, preferably 6 hours. The completion of reaction is monitored using thin layer chromatography (TLC). The solvent is distilled under vacuum and the resulting solid is charged with a polar aprotic solvent to obtain a slurry. The slurry is cooled to about 10ºC and the white precipitate obtained is filtered. The solid obtained after filtration is washed with a polar aprotic solvent, dried under vacuum at 50-55ºC to obtain racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride.
Alcoholic solvent is a C1-C4 alcohol selected from isopropanol, n-propanol, n-butanol, isobutanol, tert-butanol, methanol or ethanol, preferably isopropanol. Polar aprotic solvent is selected from acetonitrile, ethyl acetate, dichloromethane, tetrahydrofuran, acetone, DMF or DMSO, preferably ethyl acetate or acetonitrile.
Acid catalyst is selected from sulphuric acid, nitric acid, hydrochloric acid, hydrobromic acid, phosphoric acid, orthophosphoric acid, p-toluenesulfonic acid, formic acid, acetic acid, propionic acid, pivalic acid, diethylacetic acid, malonic acid, succinic acid, pimelic acid, fumaric acid, maleic acid, lactic acid, tartaric acid, malic acid, citric acid, gluconic acid, ascorbic acid, nicotinic acid, isonicotinic acid, methanesulfonic acid or benzenesulfonic acid, preferably para toluenesulfonic acid.

Metformin or salt thereof, particularly Metformin hydrochloride is prepared by the processes known in the art.

Racemic 2-amino-3,6-dihydro- 4-dimethylamino- 6-methyl- 1,3,5-triazine hydrochloride, obtained by the present invention, has a purity of more than about 80%, preferably more than about 90%, more preferably more than about 95%, as determined by HPLC.
Step 2 involves resolution of racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine to obtain the R-isomer of 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine.
Racemic 2-amino-3,6-dihydro- 4-dimethylamino- 6-methyl- 1,3,5-triazine hydrochloride is suspended in a suitable solvent to obtain a mixture. The obtained mixture is heated to about 40-50ºC to obtain a suspension. The resulting suspension is treated with a suitable base and further heated to about 70-75ºC to obtain a solution. The solution is treated with a chiral acid at the same temperature to obtain a clear solution which is further maintained under stirring at the same temperature for about an hour. This solution is then cooled to about 25-35ºC and maintained under stirring at the same temperature for about 4 hours. The diastereomeric salt thus obtained is filtered, washed with a suitable solvent and dried under vacuum.

Suitable solvent is selected from ethanol, methanol, isopropanol, ethyl acetate, acetonitrile, water or mixture thereof.
Suitable base is selected from sodium hydroxide, potassium hydroxide, triethylamine, diisopropyl ethyl amine, diethylamine, pyridine, ethanolamine, diethanolamine or triethanolamine, preferably triethylamine.
Chiral acid is selected from L-(+)-tartaric acid, D-(-)-tartaric acid, (D)-(+)-Camphorsulfonic acid, (L)-(-)-Camphorsulfonic acid, D-(+)-di-O-benzoyltartaric acid, L-(-)-di-O-benzoyltartaric acid, (-)-di-O,O'-p-tolyl-L-tartaric acid, (+)-di-O, O'-p-tolyl-D-tartaric acid, R(+)-malic acid, S-(-)-malic acid, D(-)-mandelic acid, or L(+)-mandelic acid.

The diastereomeric salt thus obtained is subjected to purification using a suitable solvent selected from ethanol, methanol, isopropanol, n-propanol, n-butanol, isobutanol, tert-butanol, ethyl acetate, acetonitrile, dimethylformamide, dimethylacetamide, dimethylsulfoxide, acetone, tetahydrofuran, acetonitrile, diisopropyl ether, water or mixture thereof.

Preferably, an aqueous alcoholic solution of the diastereomeric salt is heated to 60 to 90ºC, preferably 75 to 80ºC to obtain a mixture. The mixture is maintained under stirring at the same temperature for about an hour. The mixture is cooled to about 25 to 35ºC and maintained under stirring at the same temperature for about 4 hours. The solid obtained is filtered, washed and dried under vacuum to obtain the diastereomeric salt having chiral purity of more than 80%, preferably more than
90 %, more preferably more than 95%.
The diastereomeric salt is further purified to obtain a chiral purity of more than 99.5%.

Another embodiment of the present invention provides a process for conversion of (+)-2-amino- 3,6-dihydro-4-dimethylamino- 6-methyl- 1,3,5-triazine tartarate to (+)-2-amino- 3,6-dihydro-4-dimethylamino- 6-methyl- 1,3,5-triazine or (+)-2-amino- 3,6-dihydro-4-dimethylamino- 6-methyl- 1,3,5-triazine hydrochloride
Preferably, (+)-2-amino- 3,6-dihydro-4-dimethylamino- 6-methyl- 1,3,5-triazine tartarate is taken in isopropanol followed by the addition of conc. HCl to obtain a suspension. The obtained suspension is heated to reflux and then maintained at the same temperature for about 2 hours. The solvent is distilled under vacuum and the residue obtained is treated with isopropanol to obtain a solution. The solution is cooled to 25-35ºC and further maintained under stirring for 2 hours at the same temperature to obtain a solid. The solid obtained is filtered, washed and dried under vacuum at 50-55ºC to obtain pure (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride, having purity greater than 99%.
Alternatively, Isopropanol can be replaced with any other suitable solvent.
In another embodiment of the present invention, (+)-2-amino- 3,6-dihydro-4-dimethylamino- 6-methyl- 1,3,5-triazine hydrochloride is subjected to slurry wash with ethanol or any other alcoholic solvent to remove or reduce the dihydrochloride contamination

In a preferred embodiment, the process for preparation of Imeglimin or a pharmaceutically acceptable salt thereof is as shown below, in Scheme I:
Scheme 1
The reaction with acetaldehyde can carried out either as a neat reaction or in the presence of a solvent, preferably in an aqueous medium.
In a preferred embodiment, the process for preparation of Imeglimin or its pharmaceutically acceptable salt, in particular Imeglimin hydrochloride comprises the steps of:
Step 1:
To an alcoholic solution of sodium hydroxide is charged metformin hydrochloride and the solution is stirred for about 1.5 hours. The solution is filtered followed by addition of about 1-1.5 equivalent(s) of acetaldehyde to the filtrate at a temperature below 35°C. After completion of reaction, the solvent is distilled under vacuum and the resulting residue is treated with water followed by treatment with 1.1 equivalent of L-(+)-tartaric acid to obtain a mixture. The mixture is heated to about 70 -75°C and maintained under stirring for about half an hour. The mixture is then cooled to about 25 to 35°C followed by further cooling the mixture to 10-15°C. The mixture is maintained under stirring for about 3 hours and then filtered. The solid obtained after filtration is dried under vacuum at 50-55°C to yield crude Imeglimin tartarate.
In this step, the reaction of metformin with acetaldehyde is carried out without addition of an external base.
Preferably, Metformin is treated with 1-1.2 equivalents of 30% acetaldehyde.

Step 2:
Crude Imeglimin tartarate is taken in 90% aqueous ethanol to obtain a mixture which is heated to about 70 -75°C. The reaction mixture is maintained under stirring for about an hour at the same temperature. The reaction mixture is further cooled to about 15°C and maintained at the same temperature for about 4 hours. The solid obtained is filtered, washed with 90% aqueous ethanol and dried under vacuum to obtain pure tartarate salt of Imeglimin, having chiral purity of more than 96%.
The above process is repeated to obtain Imeglimin tartarate having chiral purity of more than 99.5%.
The filtrate obtained in the purification process can be recycled to isolate the desired isomer.

Step 3:
To an aqueous or aqueous alcoholic solution of Imeglimin tartarate is added sodium hydroxide solution (5.12 gm of sodium hydroxide was dissolved in 50ml water) to obtain a mixture. The mixture is maintained under stirring. The solvent is then distilled out under vacuum and the solid obtained is extracted with ethanol. The ethanolic extract is filtered and the filtrate is treated with conc. hydrochloric acid. The resulting mixture is maintained under stirring for about half an hour. The solvent is distilled under vacuum to reduce the volume of the mixture, which is then filtered to obtain a solid. The solid thus obtained is filtered, washed and dried at 50-55ºC to yield Imeglimin hydrochloride, having chiral purity of more than 99.5%.

Imeglimin hydrochloride obtained according to present invention is substantially pure and has chemical purity of more than 99.5% with all known impurities below 0.15% and unknown impurities below 0.1%.
Imeglimin hydrochloride obtained according to the present invention has ROI content below 0.2%, preferably below 0.1%. Further the tartaric acid content is below 0.15%.

In a preferred embodiment, the process for preparation of Imeglimin or a pharmaceutically acceptable salt thereof is as shown below, in Scheme 2,
Scheme 2

Another embodiment of the present invention provides the conversion of the unwanted (S)-isomer to the (R)-isomer by racemization.
In a preferred embodiment, the process for conversion of the unwanted (S)-isomer to the (R)-isomer comprises the steps of:
a) subjecting a solution enriched with the (S)-isomer of 2-amino- 3,6-dihydro-4-dimethylamino- 6-methyl- 1,3,5-triazine or salt thereof to heat treatment or treatment with a base to obtain racemic 2-amino- 3,6-dihydro-4-dimethylamino- 6-methyl- 1,3,5-triazine;
b) subjecting racemic 2-amino- 3,6-dihydro-4-dimethylamino- 6-methyl- 1,3,5-triazine to resolution to obtain the R-isomer of 2-amino- 3,6-dihydro-4-dimethylamino- 6-methyl- 1,3,5-triazine.

In a preferred embodiment, the process comprises:
Step 1: The filtrate obtained in the resolution stage after isolation of the R-isomer of 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine tartarate is concentrated to obtain a residue. This residue is then treated with a base in the presence of a suitable solvent to obtain a solution. This solution is heated to reflux for 8 to 12 hours, preferably 9 hours followed by cooling to obtain a solid. The solid obtained was filtered, washed and dried to obtain racemic Imeglimin base.

Suitable solvent is selected from water, methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol or tert-butanol, preferably methanol.
Base is selected from sodium hydroxide, potassium hydroxide or calcium hydroxide, preferably sodium hydroxide.

Step 2 involves resolution of racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or salt thereof to obtain the R-isomer.
Resolution of the racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or salt thereof is carried out by techniques known in the art or by process of the presnt invention.

Another embodiment of the present invention provides a process for conversion of (R)- Imeglimin tartarate to (R)- Imeglimin or (R)- Imeglimin hydrochloride.

Preferably, (R)- Imeglimin tartarate is taken in isopropanol followed by the addition of conc. HCl to obtain a suspension. The obtained suspension is heated to reflux and then maintained at the same temperature for about 2 hours. The solvent is distilled under vacuum and the residue obtained is treated with isopropanol to obtain a solution. The solution is cooled to 25-35ºC and further maintained under stirring for 2 hours at the same temperature to obtain a solid. The solid obtained is filtered, washed and dried under vacuum at 50-55ºC to obtain pure (R)- Imeglimin hydrochloride, having purity greater than 99%.

(+) 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride (Imeglimin hydrochloride) obtained according to the present invention is characterized by X-ray powder diffraction pattern as shown in Fig. 1 and / or Fig. 2. (+) 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride (Imeglimin hydrochloride) is characterized by X-ray powder diffraction pattern having peaks at 2-theta values of about 14.74, 16.82, 24.85, 25.40 and 26.99 degrees. 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride (Imeglimin hydrochloride) is characterized by X-ray powder diffraction pattern having peaks at 2-theta values of about 10.72, 10.99, 11.69, 12.12, 14.74, 15.28, 15.47, 16.82, 24.37, 24.85, 25.40, and 26.99 degrees.

In a preferred embodiment, (+) 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride (Imeglimin hydrochloride) obtained according to the present invention is anhydrous with chemical purity of more than 99.5%.

The KF value of (+) 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride (Imeglimin hydrochloride) obtained according to the present invention is found to be below 1%, preferably below 0.5%, more preferably below 0.15%. In a preferred embodiment, (+) 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride (Imeglimin hydrochloride) obtained according to the present invention has a KF value of 0.12%.
Another embodiment of the present invention provides an analytical method to determine the chiral purity of Imeglimin or salt thereof by a method comprising:
a) dissolving a sample of Imeglimin or its salt or a dosage form comprising Imeglimin or its salt in a solvent to produce a sample solution;
b) dissolving the reference standard for the S-isomer in a solvent to produce a reference marker solution;
c) subjecting the sample solution and the reference marker solution to a suitable chromatographic technique; and
d) determining the presence and quantity of said S-isomer in the sample solution.

In a preferred embodiment, the chromatographic method comprises
Column: Chiralpak AD-H (250 x 4.6) mm, 5µ
Mobile phase: n-Hexane: 2-propanol: Diethylamine: Trifluoroacetic acid (90:10:0.1:0.1) v/v/v/v or (93:07:0.1:0.1) v/v/v/v
Flow rate: 0.7 mL/min or 0.8 mL/min
Diluent: Mobile phase
Wavelength: 240nm
Injection volume: 10µL
Column Temperature: 30°C
Seal wash: n-Hexane:2-propanol (90:10) v/v
Needle wash solvent: Methanol

Imeglimin hydrochloride obtained in accordance with the present invention, exhibits a chiral purity of more than about 99.5%, with the S-isomer content less than about 0.5%, preferably less than about 0.2%.

Another embodiment of the present invention provides a pharmaceutical composition comprising Imeglimin or pharmaceutically acceptable salt thereof, obtained by the process of the present invention. Imeglimin or pharmaceutically acceptable salt thereof may be combined with pharmaceutically acceptable excipients such as glidant, disintegrant, lubricant and binder to obtain a pharmaceutical composition.

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.
The term “substantially pure” means Imeglimin or a pharmaceutically acceptable salt thereof having less than about 1%, preferably less than about 0.5%, more preferably less than about 0.3%, most preferably less than about 0.15% of undesired compounds.

The term “reflux” means the temperature at which the solvent or solvent system refluxes or boils at atmospheric pressure.

The term “pharmaceutically acceptable” means that which is acceptable in preparing a pharmaceutical composition, which is generally non-toxic and not biologically undesirable and includes that which is acceptable for human pharmaceutical use.

The following examples are for illustrative purposes only and are not intended to limit the scope of the invention in any way.
Examples
Example 1
Preparation of racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride.
A) In a four necked RB flask equipped with a mechanical stirrer and a reflux condenser over an oil bath, were taken isopropanol (1400ml), metformin hydrochloride (200 g, 1.2075 moles) and para toluenesulfonic acid monohydrate (18 g) under nitrogen atmosphere to obtain a reaction mixture. Metaldehyde (60 g, 0.340 mole) was charged to the reaction mixture to obtain a suspension and the obtained suspension was heated to 77 to 82ºC. The reaction mixture was maintained under stirring for 3 hours at the same temperature. Another lot of metaldehyde (60 g, 0.340 mole) was added and the mixture was maintained under stirring for another 6 hours. The completion of reaction was monitored using thin layer chromatography (TLC). The solvent was distilled under vacuum and the resulting solid was charged with ethyl acetate (600 ml) to obtain a slurry. The slurry was cooled to 10ºC and the white precipitate obtained was filtered. The solid obtained after filtration was washed with ethyl acetate and then dried at 50-55ºC. Yield: 220 g (94.8%) ; Purity: 98%

B) In a four necked RB flask equipped with a mechanical stirrer and a reflux condenser over an oil bath, were taken isopropanol (1400ml), metformin hydrochloride (200 g, 1.2075 moles) and para toluenesulfonic acid monohydrate (18 g) under nitrogen atmosphere to obtain a reaction mixture. Metaldehyde (60 g, 0.340 mole) was charged to the reaction mixture to obtain a suspension and the obtained suspension was heated at 77 to 82ºC. The reaction mixture was maintained under stirring for 3 hours at the same temperature. Another lot of metaldehyde (60 g, 0.340 mole) was added and the mixture was maintained under stirring for another 6 hours. The completion of reaction was monitored using thin layer chromatography (TLC). The solvent was distilled under vacuum and the resulting solid was charged with acetonitrile (1000 ml) to obtain a slurry. The slurry was cooled to 10ºC and the white precipitate obtained was filtered. The solid obtained after filtration was washed with acetonitrile and dried at 50-55ºC. Yield: 150 gm (65%); Purity: 84%

C) In a four necked RB flask equipped with a mechanical stirrer and a reflux condenser over an oil bath, were taken isobutanol (800 ml), metformin hydrochloride (200 g, 1.2075 moles) and para toluenesulfonic acid monohydrate (18 g) under nitrogen atmosphere to obtain a reaction mixture. Metaldehyde (60 g, 0.340 mole) was charged to the reaction mixture to obtain a suspension. The obtained suspension was heated at 77 to 82ºC. The reaction mixture was maintained under stirring for 3 hours at the same temperature. Another lot of metaldehyde (60 g, 0.340 mole) was added and the mixture was maintained under stirring for another 6 hours. The completion of reaction was monitored using thin layer chromatography (TLC). The solvent was distilled under vacuum and the resulting solid was charged with ethyl acetate (800 ml) to obtain a slurry. The slurry was cooled to 10ºC and the white precipitate obtained was filtered. The solid obtained after filtration was washed with ethyl acetate and dried at 50-55ºC.Yield: 180 gm (78%) ; Purity: 88%.

Example 2:
Preparation of (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine tartarate
A) Racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride (200 gm, 1.044 moles) was suspended in ethyl acetate (1000 ml) and ethanol (1000 ml) to obtain a reaction mixture. The obtained reaction mixture was heated to 40-50ºC. Triethylamine (105.6 g, 1.044 moles) was charged to the reaction mixture and the mixture was heated to 70-75ºC to obtain a suspension. The suspension was charged with L(+) Tartaric acid (185 g, 1.233 moles) at the same temperature to obtain a solution which was maintained under stirring for 1 hour at the same temperature. The solution was then cooled to 25 - 35ºC and maintained under stirring at the same temperature for 4 hours. The solid obtained was filtered, washed with chilled ethanol: ethyl acetate and dried under vacuum. Yield: 137.4 gm (43 %); Chiral Purity: 85.0%

B) Racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride (200 gm, 1.044 moles) was suspended in 90% ethanol (1000 ml) to obtain a reaction mixture. The obtained reaction mixture was heated to 40 - 50ºC. Triethylamine (105.6 g, 1.044 moles) was charged to the reaction mixture and the mixture was heated to 70-75ºC to obtain a suspension. The suspension was charged with L(+) Tartaric acid (185 g, 1.233 moles) at the same temperature to obtain a solution which was maintained under stirring for 1 hour at same temperature. The solution was then cooled to 25 – 35ºC and maintained under stirring at the same temperature for 4 hours. The solid obtained was filtered, washed with chilled 90% ethanol and dried under vacuum. Yield: 137.4 gm (43 %); Chiral Purity: 85.0%

Example 3:
Purification of (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine tartarate
To (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine tartarate (10gm) was charged 90 % ethanol (50 ml) to obtain a reaction mixture. The obtained reaction mixture was heated to 75-80ºC. The reaction mixture was maintained at the same temperature for 1 hour. The reaction mixture was cooled to 25 – 35ºC and maintained under stirring for 4 hours at the same temperature to obtain a solid. The solid obtained was washed with chilled ethanol and dried under vacuum at 50-55ºC to obtain pure (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine tartarate. Yield: 6.5 gm (65.0%); Chiral Purity: > 96.0%

Example 4:
Preparation of (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine di-p-toluyl tartarate
Racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride (5 gm) was suspended in methanol (25 ml) followed by addition of di-O,O’-p-toluyl tartaric acid (8.71 gm) to obtain a reaction mixture. The obtained reaction mixture was maintained under stirring for 12 hours. Triethylamine (2.64 gm) was charged to the reaction mixture and the mixture was maintained under stirring for 2 hours at 25-30ºC to obtain a solid. The solid obtained was filtered, washed with methanol (5 ml) and dried under vacuum at 50-55ºC to obtain the titled product. Yield: 6.2 gm (45%); Chiral Purity: 60.0%

Example 5:
Purification of (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine di-p-toluyl tartarate salt
To (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine tartarate (2 gm) were charged DMF (10 ml) and 90 % ethanol (10 ml) to obtain a reaction mixture. The obtained reaction mixture was heated to 75-80ºC and the reaction mixture was maintained at the same temperature for 1 hour. The reaction mixture was cooled to 25 – 35ºC and the reaction mixture was maintained under stirring for 4 hours at the same temperature to obtain a solid. The solid obtained was washed with chilled DMF: Ethanol (2 ml) and dried under vacuum at 50-55ºC to obtain pure (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine tartarate. Yield: 0.8 gm (40%); Chiral Purity: 85%

Example 6:
Preparation of (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride
To (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine tartarate (8.0 gm) were added isopropanol (16 ml) and conc. HCl (2.62 ml) to obtain a suspension. The obtained suspension was heated to reflux and then maintained at the same temperature for 2 hours. The solvent was distilled under vacuum and the residue obtained was treated with isopropanol (16 ml) to obtain a solution. The solution was cooled to 25 – 35ºC and further maintained under stirring for 2 hours at the same temperature to obtain a solid. The solid obtained was filtered, washed and dried under vacuum at 50-55ºC to obtain pure (+)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine hydrochloride. Yield: 1.38 gm (34%); Chiral Purity: >99%;

Example 7: Preparation of Imeglimin hydrochloride
I) Preparation of crude Imeglimin tartarate
A) In a four necked RB flask equipped with a mechanical stirrer and a reflux condenser were taken methanol (10L) and sodium hydroxide (0.485 Kg) to obtain a mixture. To this mixture was charged metformin hydrochloride (2 Kg) and stirred for 2.0 hr to obtain a solution. The solution was filtered followed by addition of acetaldehyde (1.0 L) to the filtrate at a temperature below 35°C. After completion of reaction, the solvent was distilled under vacuum and the resulting residue was treated with water (0.740 L) and L-(+)-tartaric acid (1.9 Kg) to obtain a mixture. The mixture was heated to 75°C and maintained under stirring for 30 min. The mixture was then cooled to 25 to 35°C. The mixture was further cooled to 10-15°C followed by stirring for 3 hr. The mixture was filtered and the solid obtained after filtration was dried under vacuum at 50-55°C to yield crude Imeglimin tartarate. Yield: 0.986 Kg (29 %); Chiral Purity:85.0%

B) In a four necked RB flask equipped with a mechanical stirrer and a reflux condenser were taken Methanol (10L) and sodium hydroxide (0.485 Kg) to obtain a mixture. To this mixture was charged metformin hydrochloride (2 Kg) and stirred for 2.0 hr to obtain a solution. The solution was filtered followed by addition of 30% acetaldehyde solution (2.2 L) to the filtrate at a temperature below 35°C. After completion of reaction, the solvent was distilled under vacuum and the resulting residue was treated with L-(+)-tartaric acid (1.9 Kg) to obtain a mixture. The mixture was heated to 75°C and maintained under stirring for 30 min. The mixture was then cooled to 25 to 35°C. The mixture was further cooled to 0-10°C followed by stirring for 3 hr. The mixture was filtered and the solid obtained after filtration was dried under vacuum at 50-55°C to yield crude Imeglimin tartarate. Yield: 0.986 Kg (29 %); Chiral Purity:85.0%

II) Purification of crude Imeglimin tartrate
The mixture of crude Imeglimin tartarate (500 gm) and 90% aqueous ethanol (5 L) was heated to 75°C to obtain a reaction mixture. The reaction mixture was maintained under stirring for 1 hour at the same temperature. The reaction mixture was further cooled to 15°C and maintained at the same temperature for 4 hours. The solid obtained was filtered, washed with 90% aqueous ethanol and dried under vacuum to obtain pure tartarate salt of Imeglimin. Yield: 375 Kg(75%); Chiral purity: >96%
The above process was repeated to obtain Imeglimin tartarate with the desired chiral purity of more than 99.5%.

III) Preparation of Imeglimin hydrochloride
To a mixture of Imeglimin tartarate (20 gm) and water (2.0ml) was added sodium hydroxide solution (5.12 gm of Sodium hydroxide was dissolved in 140.0 ml Methanol) to obtain a mixture. The mixture was maintained under stirring. The solvent was then distilled out under vacuum and the solid obtained was extracted with ethanol (150ml).The ethanol extract was filtered and the filtrate was treated with Conc. hydrochloric acid (5.80 ml). The resulting mixture was maintained under stirring for 30 min. The solvent was distilled under vacuum to concentrate the mixture, which was then filtered to obtain a solid. The solid thus obtained was filtered, washed and dried at 50-55ºC to yield Imeglimin hydrochloride. Yield: 8.9 gm (71%) ; Chiral purity: >99.5%

Example 8: Racemization of (S)- Imeglimin tartarate
The filtrate/mother liquor from example 7(1) was concentrated to obtain a residue (50gm). The obtained residue was dissolved in 200ml of methanol to obtain a solution. A solution of 16.2 gm sodium hydroxide in 100ml of methanol and 10 ml of water was charged to the above residue to obtain a reaction mixture. The reaction mixture was heated to reflux for 9 hours followed by cooling to obtain a solid. The solid obtained was filtered, washed and dried to obtain racemic Imeglimin base. Yield: 35gm (70%).
The racemic Imeglimin base can be converted to (R) - Imeglimin hydrochloride. ,CLAIMS:We Claim,
1. A process for preparation of (R)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine (Imeglimin) or a pharmaceutically acceptable salt thereof, comprising the steps of,
a) treating Metformin or a salt thereof with acetaldehyde or a cyclic derivative thereof in an amount of 0.5 - 5 equivalents with respect to Metformin or a salt thereof to obtain racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or a salt thereof;
b) subjecting racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or a salt thereof to resolution using a chiral acid to obtain (R)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine (Imeglimin) or a pharmaceutically acceptable salt thereof; and
c) optionally purifying said (R)-2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or a pharmaceutically acceptable salt thereof.

2. The process as claimed in claim 1, wherein the cyclic derivative of acetaldehyde is selected from paraldehyde or metaldehyde and said treatment of metformin or a salt thereof with said cyclic derivative of acetaldehyde is carried out in the presence of an acid catalyst at a temperature of 75-85 ºC.

3. The process as claimed in claim 1, wherein the treatment of metformin or a salt thereof with acetaldehyde is carried out at a temperature below 35 ºC.

4. The process as claimed in claim 1, wherein said Metformin or a salt thereof is treated with acetaldehyde or a cyclic derivative thereof in an amount of 0.5 – 1.5 equivalents with respect to Metformin or a salt thereof.

5. The process as claimed in claim 1, wherein said resolution comprises the steps of:
a) treating racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine or a salt thereof with a chiral acid to obtain the R-isomer of 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine; and
b) isolation of the R-isomer of 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine from the mother liquor.

6. The process as claimed in claim 5 wherein the mother liquor obtained after isolation of the R-isomer of 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine is subjected to racemization to obtain racemic 2-amino-3,6-dihydro-4-dimethylamino-6-methyl-1,3,5-triazine.

7. The process as claimed in claim 1 wherein said pharmaceutically acceptable salt is (R)-2-amino- 3,6-dihydro- 4-dimethylamino- 6-methyl- 1,3,5-triazine hydrochloride and said (R)-2-amino- 3,6-dihydro- 4-dimethylamino- 6-methyl- 1,3,5-triazine hydrochloride is subjected to slurry wash with ethanol for removal /reduction of the dihydrochloride impurities.

8. The process as claimed in claim 1 wherein said chiral purity of Imeglimin or a salt thereof is determined by a method comprising the steps of:
a) dissolving a sample of Imeglimin or its salt or a dosage form comprising Imeglimin or its salt in a solvent to produce a sample solution;
b) dissolving the reference standard for the S-isomer in a solvent to produce a reference marker solution;
c) subjecting the sample solution and the reference marker solution to a suitable chromatographic technique; and
d) determining the presence and quantity of said S-isomer in the sample solution.

9. A method for determining the chiral purity of Imeglimin or a salt thereof comprising the steps of:
a) dissolving a sample of Imeglimin or its salt or a dosage form comprising Imeglimin or its salt in a solvent to produce a sample solution;
b) dissolving the reference standard for the S-isomer in a solvent to produce a reference marker solution;
c) subjecting the sample solution and the reference marker solution to a suitable chromatographic technique; and
d) determining the presence and quantity of said S-isomer in the sample solution.

10. The method as claimed in claim 9, wherein said chromatographic technique is a HPLC method or a gradient HPLC method; stationary phase is a normal phase chiral column; and mobile phase comprises a combination of hexane, 2-propanol, diethylamine and trifluoroacetic acid.

Dated this 08th day of February 2022

Saija C. Menon
Deputy General Manager
USV Private Limited