Chemoenzymatic Total Synthesis of GM3 Gangliosides Containing Different Sialic Acid Forms and Various Fatty Acyl Chains

Abstract

Gangliosides are sialic acid-containing glycosphingolipids that have been found in the cell membranes of all vertebrates. Their important biological functions are contributed by both the glycan and the ceramide lipid components. GM3 is a major ganglioside and a precursor for many other more complex gangliosides. To obtain structurally diverse GM3 gangliosides containing various sialic acid forms and different fatty acyl chains in low cost, an improved process was developed to chemically synthesize lactosyl sphingosine from an inexpensive l-serine derivative. It was then used to obtain GM3 sphingosines from diverse modified sialic acid precursors by an efficient one-pot multienzyme sialylation system containing Pasteurella multocida sialyltransferase 3 (PmST3) with in situ generation of sugar nucleotides. A highly effective chemical acylation and facile C18-cartridge purification process was then used to install fatty acyl chains of varying lengths and different modifications. The chemoenzymatic method represents a powerful total synthetic strategy to access a library of structurally defined GM3 gangliosides to explore their functions.

Scheme 1.

Efficient chemical synthesis of LacβSph (10) from commercially available inexpensive N-Boc L-serine methyl ester (1) with purification of the desired D-erythro isomer 6 by crystallization.

Scheme 2.

Synthesis of GM3 gangliosides with different fatty acyl chains.