Solid-phase glycosylation of peptide templates and on-bead MAS-NMR analysis: Perspectives for glycopeptide libraries

The efficient solid-phase glycosylation of amino acid side chains (serine (Ser), threonine (Thr), and tyrosine (Tyr)) in peptides was demonstrated with a variety of glycosyl trichloroacetimidate donors in high yields and purities. A novel photolabile linker, with no chiral centre, was introduced to facilitate analysis by both matrix-assisted laser desorption ionisation time of flight (MALDI-TOF) mass spectrometry and nanoprobe magic angle spinning (MAS) NMR spectroscopy. Product analysis by nanoprobe MAS NMR spectroscopy, LC-MS and MALDI-TOF mass spectrometry of the glycosylation reactions indicated that the reactivity order of the hydroxy side-chain functions of amino acids in peptides on the solid-phase was Tyr > Ser > Thr. The nearly quantitative glycosylation yields and the efficient on-bead product analysis by nanoprobe MAS NMR spectroscopy have made a truly solid-phase approach for the synthesis and analysis of glycopeptide libraries possible.