Chemical Modification of Peptides Containing γ-Carboxyglutamic Acid

At acidic pH the γ-proton of the γ-carboxyglutamic acid (Gla) side chain undergoes rapid exchange. We have utilized the reactivity of the resulting enol form to develop a method for the chemical modification of peptide-bound Gla residues. Reaction of Gla peptides with a morpholine-formaldehyde mixture at pH 4.5 yields the Mannich base adduct. Fragmentation of the Mannich base occurs rapidly in 50% aqueous DMF to yield carbon dioxide, morpholine, and the corresponding γ-methyleneglutamyl residue.