Simultaneous Lipidation of a Characterized Peptide Mixture by Chemoselective Ligation

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Abstract
The modification of a peptide antigen by a fatty acid such as palmitic acid is now recognized as a mean to induce cellular responses. Mixtures of lipopeptides, obtained by combining individually synthesized compounds, were shown to be promising synthetic vaccine candidates. Usually, in lipopeptide synthesis, the fatty acyl moiety is introduced on the crude peptide chain using solid-phase methods. The separation of the target compound from impurities by RP-HPLC is often complicated by the amphiphilic properties of lipopeptides and results in low overall yields. To overcome the difficulties associated with lipopeptide synthesis and mixture preparation, we have developed a method where the fatty acyl moiety is site-specifically and collectively introduced in solution onto a mixture of individually prepurified peptides. The lipidation is based on the quasistoichiometric and high-yielding ligation of a glyoxylyl lipid with hydrazinoacetyl peptides. The hydrazone constructs were prepared in a salt-free medium and could be isolated by direct lyophilization of the reaction mixture. This process is compatible with cysteinyl peptides, and no aggregation nor degradation could be observed.