| abstract |
A process for the preparation of a mixture of compounds of ** formula ** enriched in the compound of formula, and pharmaceutically acceptable salts thereof, wherein R1 is C1-C6 alkyl; R2 is C1-C6 alkyl, C1-C6 haloalkyl or substituted phenyl or phenyl; R3 is hydrogen or halo; m is zero, one or two; comprising the steps of (a1) reacting a mixture of compounds of ** formula ** with an acid of formula HX, HX being selected from the group consisting of (S) - (+) - mandelic acid, D - (- ) -tartaric acid, di-p-toluoyl-D-tartaric acid, ((1R) - endo, anti) - (+) - 3-bromocanfo-8-sulfonic acid, quinic acid, acetic acid and hydrobromic acid, to form a mixture of diastereomeric compounds of formulas Va and Vb, respectively: 49 (b1) allowing the HX salt of the mixture of the diasteromeric product of step (a1) to crystallize in a solution thereof in an appropriate solvent; (c1) treating the resulting mixture of the compounds obtained from step (b1) with a base to obtain a mixture of compounds Ia and Ib, which is enriched in the compound of formula. |