Synthesis and NMR characterisation of methyl mono- and di-O-alpha-L-rhamnopyranosyl-alpha-D-glucopyranosiduronic acids

The synthesis and NMR characterisation of methyl mono- and di-O-alpha-L-rha mnopyranosyl-alpha-D-glucopyranosiduronic acids 1-6 are described. Two comm ercial starting products were used: methyl alpha-D-glucopyranoside 7 for th e preparation of 1 and 2, and methyl (R)-4,6-O-benzylidene-alpha-D-glucopyr anoside 8 for 3-6. Oxidation reaction of the hydroxymethyl group of glucose to a carboxylic acid group was performed by sodium hypochlorite 2,2,6,6-te tramethyl-1-piperidinyloxy (TEMPO)-mediated procedure after the coupling re action. Glycosylation was can-led out using the trichloroacetimidate approa ch with trimethylsilyl trifluoromethanesulfonate (TMSOTf) as promoter, resu lting in a completely stereoselective formation of the a glycosyl linkage.