Notes plate) by using chloroform-methanol (9: 1, v/v) as the eluent. Compounds la and lb were prepared from imidazole and N*-benzoyl-L-histidine methyl ester,'respectively. The synthesis of compounds IC and le has been published in an earlier paper. 8 That of compounds Id and If will be described elsewhere! A typical procedure for the introduction and removal of the N"-tosyl group will be given.