Preprint: Expedient Synthesis of O-Glycosylated amino acids
This is a working paper in which we report a simple, short (2-step), low cost route to Fmoc-SPPS compatible building blocks of threonine and serine modified with N-acetylgalactosamine or N-acetylglucosamine. Using peracetylated sugars directly, the amino acids could be glycosylated via Cu(OTf)2 catalysis. The β-anomer is formed initially and can be isolated in reasonable yields with short reactions times. Prolonged reaction (overnight) leads to formation of the α-anomer, which could be isolated in moderate yields. The high cost of glycosylated amino acids can be a barrier to researchers beginning investigations in this area; our route is conservatively 100x cheaper, straightforward and allows formation of α- or β- stereochemistry by altering the reaction time. We hope this will facilitate entry to new researchers in glycoscience.