Phenolic Ester Mediated Oligopeptide Synthesis Promoted by HOBt

Although substituted phenolic ester mediated peptide synthesis is an efficient and well established method, the same via totally unsubstituted phenyl ester is not preferred due to the extremely slow rate of aminolysis. We have investigated the scope of the unsubstituted phenyl ester as an intermediate in peptide bond formation and found that it may be useful for the design of chemoselective peptide ligation when HOBt is used as an acyl transfer catalyst. The scope of HOBt catalyzed, oxo ester mediated ligation is explored for the synthesis of oligopeptides containing a cysteine, serine and threonine at the N-terminus of the ligating peptide.