Technical Field

The invention relates to diastereomeric salts of the compound of formula I with D-(-)- mandelic and R-(-)-3-chloromandelic acid, a method for the preparation thereof and their use in the synthesis of the drug ticagrelor.

Background Art

The application WO 2009/064249 describes preparation of a salt of the compound I with dibenzoyl-L-tartaric acid by crystallization from a water - ethanol mixture. Several methods are mentioned, either with isolation of a racemic intermediate which is a mixture of the compound I and the undesired stereoisomer la

or without isolation of this intermediate. A racemic mixture of the compounds I and la is obtained by hydrogenation of a racemate consisting of the two antipodes with the corresponding configuration of asymmetrical centres:

The patent EP 1 289 992 B l describes preparation of the hydrochloride of the compound I, consisting in depfotection of the imidocarbonate group in the environment of hydrochloric acid. The same method of preparation is also mentioned in the applications WO 00/34283 and WO 99/05142.

Preparation of salts of the compound I in these documents starts with the compound II.

The compound II is prepared from the compound III

(III)

in such a way that the O-acetate group is replaced with a substituted amino group by the Tsuji- Trost reaction under catalysis of tetrakis triphenyl phosphine palladium, followed by hydroxylation of the double bond.

Disclosure of Invention

The invention provides diastereomeric salts of the compound I with D-(-)-mandelic and R-(-)- 3-chloromandelic acid, a method for the preparation thereof and their use for the preparation of the compound I with high purity, serving as an intermediate for the production of the drug ticagrelor. The invention further provides a method for the preparation of ticagrelor, comprising preparation of a diastereomeric salt of the compound I with D-(-)-mandelic or R- -)-3 -chloromandelic acid in accordance with the invention,

wherein R is H or CI.

Detailed description of the invention

The method according to the invention comprises mixing of a solution of the racemic mixture of the compounds I and la with a solution of D-(-)-mandelic or R-(-)-3 -chloromandelic acid at a temperature from 0 °C to the boiling point of the solvent used, preferably while hot, and isolation of the solid salt. The term "while hot" is to be understood as meaning the same or higher temperature as compared to the boiling point of the selected solvent at the normal pressure, reduced by 15 K. An especially preferable approach is mixing a solution of the racemic mixture of the compounds I and la with a solution of D-(-)-mandelic or R-(-)-3- chloromandelic acid at a temperature which is the same or higher as compared to the value of the boiling point of the selected solvent at the normal pressure, reduced by 5 K. Isolation of the solid salt from the mother liquor is done in usual ways, e.g. by means of pressure filtration, aspiration, or centrifugation, while the isolated solid phase may be freed from residues of the mother liquor by washing with a suitable solvent if necessary. A preferable embodiment of the invention consists in isolation of the solid salt according to the invention in a crystalline state. A suitable temperature for crystallization of the salt is a temperature lower than 35 °C with most solvents; a preferable temperature is a temperature lower than 25°C.

Solvents for the preparation of salts according to the invention include organic solvents not containing strong acidic or basic groups, able to dissolve the two constituents forming the resulting salt at least while hot. Suitable solvents include aliphatic or cyclic ketones with three to six carbon atoms such as acetone, butanone or cyclohexanone, esters with two to six carbon atoms such as methyl acetate, ethyl acetate or butyl acetate, nitriles with two to six carbon atoms such as acetonitrile or propionitrile. Especially suitable solvents are Ci-C ₆ aliphatic alcohols, e.g. methanol, ethanol, n-propanol, 2-propanol, n-butanol. For crystallization or precipitation of the solid salt according to the invention a mixture of two solvents can also be used, such that, e.g., the racemic mixture of compounds I and la can be dissolved in a different solvent than the acid. The method according to the invention makes it possible to obtain the compound I in a purity comparable to hitherto findings, but in a higher yield. This especially relates to the salt of D-(-)-mandelic acid. In the case of R-(-)-3-chloromandelic acid the result is comparable to the hitherto findings as regards the optical quality of the product and slightly better as regards the yield.

Working Examples

Example 1

Method for the preparation of D-(-)-mandelate of compound I

10.3 g of the racemic mixture of the compounds I and la were dissolved in 25 ml of ethanol and D-(-)-mandelic acid was dissolved in 15 ml of ethanol, both at the boil. The resulting solutions were mixed in the molar ratio of the base to the corresponding acid of 1 : 1 while warm. The mixture was cooled to the room temperature, at which a crystalline product precipitated.

The precipitated solid substance was aspirated and washed with 2 x 5 ml of ethanol. The product was first dried at the room temperature and then in a vacuum drier at 50 °C.

9.5 g of a product (49 %) was obtained with a purity characterized by the enantiomeric excess (ee) of 97 %, m. p.: 190 to 193 °C, which was further used for the synthesis of ticagrelor. The purity was determined by the gas chromatography (GC) method with the standardized quality evaluation procedure. Example 2

Method for the preparation of R-(-)-3-chloromandelate of compound I

12.3 g of the racemic mixture of the compounds I and la were dissolved in 25 ml of ethanol at the boil. R-(-)-3-chloromandelice acid (11.8 g) was dissolved in 15 ml of ethanol at the boil. The prepared hot solutions were mixed in the molar ratio of the base to the acid of 1 : 1 . The mixture was cooled to the room temperature under stirring, at which the crystalline product precipitated.

This solid substance was aspirated and washed with 3 x 5 ml of ethanol. The product was first dried at the room temperature and then in a vacuum drier at 50 °C.

9.1 g of a product (40 %) was obtained with a purity characterized by the enantiomeric excess (ee) of 98.6 %, m. p.: 186 to 188 °C, which was further used for the synthesis of ticagrelor. The purity was determined by the gas chromatography (GC) method with the standardized quality evaluation procedure.

It has been verified that using the salts according to the invention with the purity of at least 96 % ee makes it possible to obtain, in any of the further steps of the synthesis of ticagrelor, the final product containing less than 0.15 % of the isomeric impurity IV with a configuration derived from the undesired diastereoiso ier la, without the necessity to use chromatographic purification.

The salts of compound I with D-(-)-mandelic and R-(-)-3-chloromandelic acid in the purities mentioned in Examples 1 and 2 were used for the preparation of ticagrelor, which is illustrated in Scheme 1. The salts of the compound I with the said acids are marked I * HA therein.

ticagrelor

SCHEME 1

Abbreviations used:

CBz = benzyloxycarbonyl,

MIBK methyl isobutyl ketone,

DIPEA diisopropylethylamine.

The total yield of the method described in Scheme 1 was 16 %. The quality of the obtained product was determined using the liquid chromatography method and amounted to 99.5 % with the content of impurity IV lower than 0.1 %. The method of preparation of ticagrelor according to Scheme 1 did not require the use of chromatographic purification in any of the steps of its synthesis.