Facile thiolytic removal of the o-nitrophenylsulphenyl amino-protecting group

2-Mercaptopyridine was used to effect the selective, mild and efficient cleavage of the o-nitrophenylsulphenyl amino-protecting group from several amino acids and peptides. By utilization of this reagent a stepwise synthesis of the tetrapeptide Thr-Lys-Leu-Arg([Leu3]tuftsin) was successfully achieved. The potential use of 2-mercaptopyridine in mechanized peptide synthesis via the polymeric reagents approach is discussed.