Identification of a sequence‐dependent reversible acylation of tosylarginine in a peptidyl‐resin reacted with isonicotinyl p‐nitrophenylcarbonate

In this paper, we report on the identification of an unexpected acylation that occurred on the solid phase when a peptide containing an unprotected lysyl and a tosyl-protected arginyl residue was treated with a large excess of isonicotinyl p-nitrophenylcarbonate. NMR and matrix-assisted laser desorption/ionisation -post-source decay analysis of the purified peptide demonstrated the presence of one extra isonicotinyloxycarbonyl (iNoc) group located on the ω nitrogen atom of the arginine which was adjacent to the Lys(iNoc). The desired peptide was obtained by quantitative removal of the unwanted iNoc group during a brief treatment with diluted aqueous hydrazine.