Stereoselective synthesis of a 9-O-sulfo Neu5Gc-capped O-linked oligosaccharide found on the sea urchin egg receptor

Abstract

A straightforward synthesis of the (25)-linked 9-O-sulfated Neu5Gc-capped O-linked tetrasaccharide (1) identified in the egg cell surface glycoproteins of the sea urchin Strongylocentrotus purpuratus receptor for sperm is reported. The construction of the (25)Neu5Gc trimer by the formation of an amide linkage rather than a glycosidic bond avoids the requirement for -stereoselective glycosylation. To highlight this amide bond formation strategy as a relatively facile method for synthesizing oligo-Neu5Gc containing O-linked glycans, its versatility is demonstrated by application to the coupling of SO3H-9Neu5Gc(25)Neu5Gc glycolic acid and a sialyl-Tn-derived amine for achieving the target tetrasaccharide. This synthetic strategy may be implemented in the generation of other structurally similar O-sulfo Neu5Gc-capped 25-O-glycolyl-linked oligo-Neu5Gc chains, enabling additional biological and chemical investigations.