Efficient synthesis of O-glycosylated amino acids

Abstract

Protein glycosylation is one of the most abundant and complex post-translational modifications, necessitating many different approaches to fully understand the biological effects. Investigation using synthetic glycopeptides is limited by the high cost of building blocks; typically >100x more than other modified amino acids e.g. phosphorylation. We report a simple, low cost route to O-glycosylated amino acids suitable for Fmoc-SPPS in two or three steps starting from peracetylated sugars. One set of reagents can furnish either the α- or β-anomer through adjusting the equivalents and reaction time. Depending on the derivative, the cost of our route is 25-60× less than commercial alternatives and offers scope for producing modified analogues. Overall, this is a convenient and user-friendly approach to access O-glycosylated amino acids, urgently required for continued investigation of the manifold roles of glycosylation in biology.

Fig. 1. Glycopeptides are useful reagents for understanding protein glycosylation but require compatible building blocks for Fmoc-SPPS. Reported syntheses of α1 were recently reviewed by Liu et al.

Fig. 2. Product distribution over time following treatment of a 7 : 1 β7/α7 mixture to 1 equiv. Cu(OTf)₂ in refluxing DCE as determined by LCMS (UV absorbance at 280 nm).