Selective deprotection of N-Boc group was achieved in excellent yields using bismuth (III) trichloride in a mixed solvent of acetonitrile and water (50: 1, v/v) at 55° C. Acid-labile groups such as Pmc and tert-butyl ester were not affected and no alkylation of tryptophan, methionine, and cysteine residues was observed under the deprotection conditions.
