An N-protection free ligation of the peptide thioester and the peptide with an N-alkoxy- or N-aryloxyamino group at its N-terminus

•An N-alkoxy or N-aryloxyamino group at the N-terminus of a peptide is selectively acylated under acidic condition.•As an acylating agent, peptide thioester with silver ion activation can be used.•N-Methoxy group can be cleaved by samarium(II) iodide treatment.•Using this method, human atrial natriuretic peptide was successfully synthesized.