Studies of racemization in peptide synthesis for a phosphoryloxy-benzotriazin-one coupling reagent (DEPBT)

Racemization during peptide syntheses has been a major concern for all peptide chemists [1]. Much research has been carried out to develop new coupling reagents which allow rapid amide bond formation and inhibit racemization. The reagent, 3-(diethoxyphosphoryloxy)-1,2,3-benzotrazin-4(3H)-one (DEPBT), has been recently developed [2] (Figure 1). It has been shown that this new coupling reagent, as with BOP and HBTU, is efficient both in solid phase peptide synthesis and peptide synthesis in solution. It can also be used for cyclization reactions. Analysis of DEPBT by X-ray diffraction confirms its chemical structure (Figure 1). In our laboratories, we have established a protocol to measure intrinsic rates of racemization employing the separation and quantitative analyses of enantiomeric N-protected amino acid derivatives by chiral HPLC [3]. In this presentation, we carried out racemization studies to compare DEPBT with commonly used coupling reagents such as BOP, HATU and HBTU.