PURPOSE: To provide novel alkyl substituted nitroimidazole acetic acids useful as intermediates for the substantially pure (R) enantiomer of angiotensin II antagonists.

CONSTITUTION: A compound represented by formula I (wherein R1 is a 4-9C straight chain alkyl) whose configuration is substantially (R) enantiomer or (-)-cinchonidine salt thereof, for example (-)-cinchonidine salt of (R) α-hexyl-4- nitro-1H-imidazole-1-acetic acid, is provided by reacting racemic mixture of compound of formula II with (-)-cinchonidine in the presence of or free from alkylamine in an alcoholic solvent to obtain crystalline salt, separating the crystalline salt and optionally convert it into free acid, and a compound of formula IV (wherein Ar represents a group of formula V or VI; X represents CONH; R2 represents a group of formula VII; R5 represents H, alkyl or the like; X' represents O or the like; m is of 0 or 1) is obtained from a compound of formula I without a resolution reagent.