S-tert-Butylcysteine was obtained by a new method. A number of its N-protected derivatives and esters were synthesized. Syntheses of several peptides containing tert-butyl and acetamidomethyl or benzyl thioethers of cysteine were carried out. The tert-butyl group was removed from the thiol group of peptides by treatment with (2-nitropheny1) sulfenyl chloride (NpsC1). The S-(2-nitrophenyl) sulfenyl derivatives so obtained were converted either into ...