Interaction of L-histidine methyl ester (2) with N,N'-carbonyldiimidazole gave nearquantitative ring closure between the N' and the N" function to form (7S)-5,6,7.8-tetrahydro-7-(methoxycarbonyl)-5-oxoimidazo[l,5-c~]pyrimidine (3). Alkylation of 3, c.g. with an alkyl halide. trialkyloxonium tetrafluoroborate or dialkyl sulfate, is then only possible at the "N' function" to form (7S)-2-alkyl-5,6,7,8-tetrahydro-7-(methoxycarbonyl)-5-oxoimidazo[ I ,5-r,]pyrimidinium salt (4).Hydrolysis of 4, aided by hydrochloric acid, afforded L-W-alkylhistidines in high yield. The L-Wmethylhistidine (523) was found to be identical with the costly natural amino acid and,optically purc. introductionA method for preparing L-W-methylhistidine was discovered in this Laboratory'. We now wish to report a convenient method for the regioselective synthesis of L-Walkylhistidines in general and of L-N'-methylhistidine (5), a costly natural amino acid, in particular.

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(‐)‐(S)‐2‐Chloro‐3‐(5‐imidazolyl)propanol (4) was synthesized by reduction of both the acid chloride and the methyl ester of (‐)‐(S)‐2‐chloro‐3‐(5‐imidazolyl)propionic acid. The optical rotatory dispersion and circular dichroism spectra are discussed.