Amino-acids and peptides. Part 45. The protection of the thiol function of cysteine and the imidazole-N of histidine by the diphenyl-4-pyridylmethyl group

Abstract

S-(Diphenyl-4-pyridylmethyl)-L-cysteine (1) and its derivatives (2)–(7) have been prepared and used in peptide synthesis. In contrast to the analogous S-trityl group, this protection is stable in acid but it is cleaved readily by zinc–acetic acid, by mercury(II) acetate, by iodine, and by electrolytic reduction. N(lm)-Diphenyl-4-pyridylmethyl-L-histidine derivatives (9)–(13) are also reported; the protecting group is again stable to acid but cleaved by hydrogenolysis, by zinc–acetic acid, and by electrolytic reduction, and it has been used in the synthesis of L-histidyl-L-leucine, -L-phenylalanine, and -glycine.