Crystallization of optical isomers of leukotriene antagonists using (R)-4-nitro-.alpha.-methylbenezenemethonamine

A process for separating a single isomer from a racemic mixture of a compound of formula II ##STR15## where:

• R.sub.1 is C.sub.8 to C.sub.13 alkyl, C.sub.7 to C.sub.12 alkoxy, C.sub.7 to C.sub.12 alkylthio, C.sub.10 to C.sub.12 1-alkynyl, 10-undecynyloxy, 11-dodecynyl, phenyl-C.sub.4 to C.sub.10 alkyl, phenyl-C.sub.3 to C.sub.9 alkoxy, phenylthio-C.sub.3 to C.sub.9 alkyl with the phenyl optionally mono substituted with bromo, chloro, trifluoromethyl, C.sub.1 to C.sub.4 alkoxy, methylthio or trifluoromethylthio, furyl-C.sub.4 to C.sub.10 alkyl, trifluoromethyl-C.sub.7 to C.sub.12 alkyl or cyclohexyl-C.sub.4 to C.sub.10 alkyl;
• q is 0, 1 or 2, with the proviso that R.sub.1 is not alkylthio or phenylthioalkyl when q is 1 or 2;
• Y is COR.sub.3', C(R.sub.4)H(CH.sub.2).sub.m COR.sub.3', or (CH.sub.2).sub.0-1 -C-tetrazolyl;
• R.sub.3' is OH, amino, or C.sub.1 to C.sub.6 alkoxy,
• R.sub.4 is hydrogen, methyl, C.sub.1 to C.sub.4 -alkoxy, fluoro or hydroxy;
• m is 0, 1, or 2;
• R is (CH.sub.2).sub.n COR.sub.6' ;
• n is 0 to 6;
• R.sub.6' is OH, amino, or C.sub.1 to C.sub.6 -alkoxy;
• with the proviso that at least one of R.sub.3' or R.sub.6' is --OH or a salt thereof, which process comprises:
• (i). treating a racemic mixture of formula II with between about 0.5 to 2.5 equivalents, relative to the number of carboxylic acid groups in formula (II), of (R)-4-nitro-.alpha.-methylbenzenemethanamine;
• (ii). recovering a crystalline salt, and
• (iii). converting the salt to an acid or a pharmaceutically acceptable salt.