H-1 NMR chemical shifts of hydroxy protons in conformational analysis of disaccharides in aqueous solution

In a continuing study on the use of hydroxy protons in conformational analy sis of saccharides in aqueous solution by NMR spectroscopy, a number of dis accharides with 1,3-, 1,4- and 1,6-linkages have been investigated. The H-1 -NMR chemical shifts, vicinal coupling constants ((3)J(CH,OH)), temperature coefficients and rates of exchange with the solvent have been measured for the hydroxy protons. Most of the hydroxy proton signals in the disaccharid es have chemical shifts similar (\Delta delta\ less than or equal to 0.3 pp m) to those in the corresponding methyl monosaccharides. Three hydroxy prot ons, however, O(2)H in beta-L-Fucp-(1-->3)-alpha-D-Glcp-OMe, O(3)H in beta- L-Fucp-(1-->4)-alpha-D-Galp-OMe and O(6)H in beta-L-Fucp-(1-->4)-alpha-D-Gl cp-OMe show a large upfield shift (Delta delta less than or equal to -0.3 p pm) attributed to the proximity of the hydroxy proton to the ring oxygen of the neighbouring sugar. In beta-L-Fucp-(1-->4)-alpha-D-Galp- OMe, the chem ical shift, (3)J(CH,OH) and temperature coefficient of the O(3)H signal ind icate that a weak hydrogen bond interaction exists between O(3)H and O(5'). In beta-L-Fucp-(1-->4)-alpha-D-Glcp-OMe, the chemical shift and the NOEs i nvolving the O(6)H signal suggest a preference for the trans-gauche conform ation around the C5-C6 bond.