Synthesis and NMR Characterisation of Methyl Mono- and Di-O-α-L-Rhamnopyranosyl-α-D-Glucopyranosiduronic Acids

Abstract

ABSTRACT The synthesis and NMR characterisation of methyl mono- and di-O-α-L-rhamnopyranosyl-α-D-glucopyranosiduronic acids 1-6 are described. Two commercial starting products were used: methyl α-D-glucopyranoside 7 for the preparation of 1 and 2, and methyl (R)-4,6-O-benzylidene-α-D-glucopyranoside 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-tetramethyl-1-piperidinyloxy (TEMPO)-mediated procedure after the coupling reaction. Glycosylation was carried out using the trichloroacetimidate approach with trimethylsilyl trifluoromethanesulfonate (TMSOTf) as promoter, resulting in a completely stereoselective formation of the α glycosyl linkage.