Thiolysis of the 3-nitro-2-pyridinesulfenyl (Npys) protecting group. An approach towards a general deprotection scheme in peptide synthesis.

The hydroxylic side-chain functional groups of serine, threonine, hydroxproline and tyrosine, the alpha and epsilon-amino moieties of lysine and the thiol group of cysteine were masked by the 3-nitro-2-pyridinesulfenyl (Npys) protecting group. Deprotection was mildly affected by thiolysis with either 2-mercaptopyridine and 2-mercaptomethyl imidazole (O- and N-Npys) or with 3-mercaptoacetic acid and 2-mercaptoethanol (S-Npys). Thiolysis was monitored spectrophotometrically and was completed in a rather short time. Incorporation of the Npys group into a whole and single thiolyzable deprotection scheme is suggested.