Synthesis of Casein-Related Peptides and Phosphopeptides. XVI. The Efficient Synthesis of the Casein-Related O-Phosphoseryl-Containing Peptide Ac-Glu-Ser(P)-Leu-Ser(P)-Ser(P)-Ser(P)-Glu-Glu-NHMe

Abstract

The multiple-O-phosphoseryl-containing peptide, Ac-Glu-Ser (P)-Leu-Ser (P)-Ser (P)-Ser (P)-Glu-Glu-NHMe, was prepared in high yield by the use of Boc-Ser(PO₃Ph₂)-OH in the Boc mode of peptide synthesis for the preparation of the protected Ser(PO₃Ph₂)-octapeptide followed by its one-step hydrogenolytic deprotection with platinum oxide. Peptide synthesis was performed by the repetitive excess mixed-anhydride coupling procedure and 40% CF₃CO₂H/CH₂Cl₂ for removal of the Boc group from intermediate peptides. The phosphopeptide was found to be greater than 99% pure by C₈ r.p.-h.p.1.c. analysis, and was readily characterized by amino acid analysis, ¹³C n.m.r. spectroscopy and f.a.b. mass spectrometry.