Synthesis of a pseudo tetrasaccharide mimic of ganglioside GM1

The pseudo tetrasaccharide 2 was designed to mimic ganglioside GM1, the membrane receptor of both the cholera toxin and of the heat-labile toxin of E. coli. Compound 2 retains the Gal and Neu5Ac recognition determinant of GM1 and uses as the scaffold element a new, conformationally restricted cyclohexanediol (DCCHD 3), with the same relative and absolute configuration of natural galactose; The diol 3 was enantioselectively synthesized by an asymmetric Diels-Alder reaction, followed by dihydroxylation of the resulting cyclohexene. Glycosylation of 3 with the sialyl donor 17 and the Gal beta(l-3)GalNAc donor 15, followed by removal of the protecting groups, completed the synthesis of 2.