Ganglioside analog synthesis via late-stage sialylation and fatty acid introduction

Abstract

Gangliosides are sialylated glycosphingolipids comprising various chemical forms of glycans and ceramides. They perform various biological functions in cell plasma membranes. Differences in the sialic acid forms (Neu5Ac and Neu5Gc) and ceramide species (lengths and degrees of unsaturation) result in variations in ganglioside's functions, even though their core glycan structures are common. However, ganglioside research requires considerable effort due to complications in their chemical synthesis. Further, a facile supply of ganglioside samples with variations in substructures is required for comprehensive research. We recently reported a chemical synthesis method for gangliosides via the late-stage sialylation of oligosaccharyl ceramide acceptors. Based on this method, we developed a synthetic method via late-stage incorporation of sialic acids and fatty acids. An oligosaccharyl sphingosine acceptor was efficiently sialylated using a minimally protected design to enhance the reactivity of the acceptor hydroxyl group. Subsequently, the azide group at the sphingosine C2 position was reduced for fatty acid incorporation. Further several steps of Neu C5-modification (N-Ac or N-Gc), global deprotection, and fluorescent dye incorporation enabled neolacto-series ganglioside (sialyl-neolactotetraosylceramide, Neu nLc₄Cer) probe synthesis. These results indicate the applicability of this method for the systematic synthesis of ganglioside analogs with modifications to the sialic acid or lipid structure.