Synthesis of a pseudo tetrasaccharide mimic of ganglioside GM1

The pseudo tetrasaccharide 2 was designed to mimic ganglioside GM1, the mem brane 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 cycloh exanediol (DCCHD 3), with the same relative and absolute configuration of n atural galactose; The diol 3 was enantioselectively synthesized by an asymm etric Diels-Alder reaction, followed by dihydroxylation of the resulting cy clohexene. 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 t he synthesis of 2.