DEPBT as an efficient coupling reagent for amide bond formation with remarkable resistance to racemization.

3-(Diethoxyphosphoryloxy)-1, 2, 3-benzotriazin-4(3H)-one (DEPBT) is an effective coupling reagent for synthesis of linear and cyclic peptides by both solution and solid-phase peptide synthesis. DEPBT mediates amide bond formation with remarkable resistance to racemization. When DEPBT is used as a coupling reagent, it is not necessary to protect the hydroxy group of the amino component (such as tyrosine, serine, and threonine) and the imidazole group in the case of histidine. The high efficiency of DEPBT and its utility have been demonstrated in the syntheses of complex natural products such as ramoplanin A2, ramoplanose aglycon, ustiloxin, and teicoplanin aglycon.