Amines and other N-functions can be protected as 4-methoxybenzenesufonyl (PMBS, Mps) derivatives: Chem. Pharm. Bull., 29, 2592 (1981), useful for the imidazole in histidines, stable to TFA and HBr/AcOH: Bull. Chem. Soc. Jpn., 47, 3146 (1974); J. Org. Chem