3-(Diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one(DEPBT) condensation developed by our group is an effective organophosphorus condensation reagent for the synthesis of protected peptides containing Tyr,Ser and Thr with unprotected hydroxyl group on their side chain.Thus,DEPBT is useful for the synthesis of peptide alcohols,which have attracted much attention not only as the ligands but also as the enzyme inhibitors.A side reaction of DEPBT was found in the synthesis of Boc-β-Ala-HisOMe with unprotected imidazolyl group.In this paper,the discovery of this side reaction and the confirmation of the structure of this side product were reported.In addition,the influence of different reaction conditions on the side reaction were studied.Imidazolyl group was a key factor to cause the side reaction,excess DEPBT and high reaction temperature promoted the side reaction.
