Amino acids and peptides. XXIV. Phosphorus in organic synthesis. XIII. Application of diphenyl phosphorazidate (DPPA) to the synthesis of the protected N-terminal hexapeptide of secretin.

The diphenyl phosphorazidate (DPPA) method, a new coupling procedure in the peptide synthesis, was successfully applied to the synthesis of Z-His(Z)-Ser-Asp(OBut)-Gly-Thr-Phe-OBut (I) corresponding to sequence 1-6 of secretin. Comparison of the DPPA method with the classical azide method was made by the fragment coupling of Ser-Asp with Gly-Thr-Phe, revealing that the former may be as good as the latter.