Dehydroalanine-containing peptides: preparation from phenylselenocysteine and utility in convergent ligation strategies.

This protocol describes the methodology for the synthesis of dehydroalanine (Dha)-containing peptides and illustrates their use in convergent ligation strategies for the preparation of peptide conjugates. A nonproteinogenic amino acid, Fmoc-Se-phenylselenocysteine (SecPh), can be prepared in high yield over four synthetic steps and be conveniently incorporated into peptides by standard solid-phase peptide synthesis techniques. Globally deprotected peptides containing phenylselenocysteine can be converted to dehydrated peptides following a chemoselective, mild oxidation with hydrogen peroxide or sodium periodate (i.e., the phenylselenocysteine side chain is converted to that of Dha). Dha residues are electrophilic handles for the preparation of glycopeptides, lipopeptides or other peptide conjugates; one such transformation will be outlined here. The preparation of Dha-containing peptides, including the synthesis of SecPh, peptide elongation and oxidative treatment of phenylselenocysteine-containing peptides can be completed by one person in approximately 3-5 weeks. However, once SecPh is in hand, the time required for the preparation of peptides is significantly shorter and comparable to that for any peptide synthesis.