A large-scale chemoenzymatic method was developed to synthesize natural and modified analogues of the Glycophorin A tetrasaccharide with either C9 or C5 terminal α-2,3-sialic acid variants. Selective α-2,6-sialylation of galactosamine was achieved by maintaining acetylation of the galactose during the course of enzymatic reactions. The products can aid protein binding studies or serve as MS analytical standards for glycomics research.

Abstract

A large-scale chemoenzymatic methodology has been developed to prepare a natural and substituted analogues of the Glycophorin A tetrasaccharide, in which the α-2,3-sialic acid is modified at either C5 or C9 either as F, OMe, CH₃, glycolyl or N₃. The strategy involved a chemical synthesis of a Gal-β-1,3-GalNAc disaccharide in which the galactose remains acetylated to first enable selective α-2,6-sialylation using a one-pot aldolase-NmCSS-Pd2,6-ST enzyme system. Finally, C5 or C9 modifed α-2,3 sialosides were placed at the galactoside moiety using C2 or C6 modified MaNAc derivatives catalyzed by aldolase NmCSS-Pd2,3-ST enzyme combination. The synthesised molecules can be useful in binding studies with a protein of interest or as an entry point to establish a library of analytical samples for mass-spectrometric studies.