A new approach to the chemical synthesis of keto-proteins

To increase the versatility of protein-conjugation, an orthogonal protection strategy is described, which enables the efficient synthesis of keto-proteins bearing a reactive ketone functionality using Boc, Fmoc, and chemical ligation methodologies. A 1,3-dithiolane group was used to protect the ketone function of levulinate- and pyruvate-derivatized peptides during solid-phase synthesis, acidolytic cleavage, and purification. When required, the 1,3-dithiolane group could be cleanly removed using aqueous silver or mercuric solutions to regenerate the reactive keto-protein at ambient temperature. The liberated keto-protein was chemoselectively conjugated in situ to an aminooxy-derivatized monodisperse polymer.