Side reactions in peptide synthesis. X. Prevention of O-acylation during coupling with active esters

Acylation of the hydroxyl groups in the side chains of serine, threonine or tyrosine occurs in coupling with active esters. This side reaction, which is quite pronounced in histidine-containing peptides, can be prevented with additives. From a series of compounds tested, 2,4-dinitrophenol and pentachlorophenol were the most effective.