A convenient and rapid method for the selective oxygen-17 enrichment of aspartyl peptides during solid-phase synthesis

In this work we describe, for the first time, a rapid and efficient method for 17O selective labeling on the β-carboxyl group of an aspartic acid residue already incorporated into a peptide sequence anchored on a solid-phase support. The β-O-benzyl ester of the Asp residue of the Ac-RGD-benzydrylamine resin was successfully saponified using Na17OH in a methanol/dichloromethane mixture. The 17O selective enriched peptide was then released from the solid support by acidic cleavage. The 17O NMR spectrum confirmed the 17O labeling of the Asp β-carboxylate.