Patent ID: 7754883

Claim:
A method of preparation of the S(+) isomer of the (2-chlorophenyl)-6,7-dihydro-thieno[3,2-c]pyridine-5(4H)-acetic acid methyl ester of formula I wherein a mixture of R and S isomers of clopidogrel is dissolved in an ester of formula Ra(O)ORb, wherein Ra and Rb independently represent a C1-C5 aliphatic substituent or a C5-C8 aromatic substituent, and a solution of R-camphorsulfonic acid in a solvent of formula RaOH is added to the solution, from the mixed solution the camphorsulfonic salt of the substance of formula I is crystallized, which is converted to S(+) isomer of the (2-chlorophenyl)-6,7-dihydro-thieno[3,2-c]pyridine-5(4H)-acetic acid methyl ester of formula I in the next step; further a base of formula R 1 R 2 R 3 R 4 N + OH − wherein R 1 , R 2 , R 3 and R 4 are identical or different substituents selected from C1-C5 alkyls or C5, C6 cycloalkyls or aryls, C7-C9 alkyl-cycloalkyls or alkyl-aryls in a solution in a substance of formula RaOH is added to the mother liquors after crystallization, thus resulting in a mixture of R and S isomers of clopidogrel, that are used for preparation of S(+) isomer of the (2-chlorophenyl)-6,7-dihydro-thieno[3,2-c]pyridine-5(4H)-acetic acid methyl ester of formula I.