The homologation of histidine

(S)-3-Amino-4-[(1H)imidazol-4-yl]butanoic acid (1), a β-amino acid which is a homologue of l-histidine, has been synthesised in five steps from l-histidine methyl ester. The presence of N(α)- and N(Im)-2,4,6-trimethylbenzenesulfonyl protecting groups was crucial to the success of the route, the key step of which involved the ring opening of an aziridine intermediate by sodium cyanide.