branched chain groups those groups having 2 to 10 carbon atoms are preferred the term 34 aryl 34 refers to phenyl and substituted phenyl exemplary substituted phenyl groups are phenyl groups substituted with 1 2 or 3 amino nh 2 alkylamino dialkylamino nitro halogen hydroxyl trifluoromethyl lower alkyl lower alkoxy alkylthio of 1 to 4 carbon atoms alkanoyloxy of 2 to 4 carbon atoms carbonyl or carboxyl groups the term 34 cycloalkyl 34 refers to groups having 3 4 5 6 or 7 carbon atoms the process of the present invention begins with a racemic mixture of compound ii disclosed in european patent application no 154 838 filed feb 15 1985 compound ii is treated with a chiral acid such as tartaric acid in an organic solvent at a temperature of about 50 u00b0 to 80 u00b0 c in molar ratios from about 1 0 1 1 to about 1 0 1 5 compound ii chiral acid and about 1 10 compound ii organic solvent to resolve the threo isomer of compound ii which may be recovered from the mixture other chiral acids are useful for this process including camphoric and camphorsulfonic acid see newman optical resolution procedures volume i amines and related compounds pp 7 to 24 1978 the organic solvent may be ethanol isopropyl alcohol aqueous ethanol methanol acetone ethyl acetate butanol and the like alcohol solvents particularly ethanol and 95 ethanol are preferred the moieties oy 1 and oy 2 in.