An efficient convergent synthesis of GP1c ganglioside epitope

In this report, we describe an efficient convergent synthesis of the GP1c glycolipid epitope, which is one of the most complex c-series gangliosides. The alpha(2,3) and alpha(2,8) sialylations were accomplished by use of 5N,4O-carbonyl and 7,8-O-isopropyliden as well as 5N,4O-carbonyl- and 7,8-di-O-chloroacetyl-protected sialyl donors in good yields with excellent alpha-selectivity, respectively. The two sialyl donors enable synthesis of the di- and trisialylgalactosides by simple glycosylation and deprotection. We synthesized the protected GP1c glycolipid epitope, which is a compact, rigid, branched structure, via direct coupling of tetarasaccharide and pentasaccharide units.