ONE-BOND CARBON PROTON COUPLING-CONSTANTS - ANGULAR-DEPENDENCE IN BETA-LINKED OLIGOSACCHARIDES

The angular dependence of 1J(C,H) in model compounds related to beta-linked oligosaccharides has been established by FPT INDO quantum chemical calculations. Values calculated for models of (1 --> 1)-, (1 --> 2)-, (1 --> 3)- and (1 --> 4)-linked disaccharides were compared, and the effect of the orientation of HO-2 elucidated. The angular dependence of 1J(C,H) on the torsional angles PHI(H) and PSI(H) and the solvent dielectric constant (epsilon) was characterized in the form: 1J(C,H) = A cos2phi + B cosphi + C sin2phi + D sinphi + E + Fepsilon. The 1J(C,H) values, measured by DEPT methods for C-1-H-1 and C-X'-H-X' in cellobiose, cyclic trisaccharide and hexopyranoses were used to adjust the calculated angular dependences. Based on the occurrence of the conformers for agarobiose, neoagarobiose, mannobiose and methyl beta-xylobioside, the thermodynamically averaged <1J(C,H) > values were calculated. The results obtained (< 1J(C-1,H-1) > 162.4, < 1J(C-4',H-4') > 147.6 Hz for methyl beta-xylobioside; < 1J(C-1,H-1) > 162.4 and < 1J(C-4',H-4' > 147.6 Hz for mannobiose; < 1J(C-1,H-1 > 162.8 Hz for neoagarobiose and < 1J(C-1,H-1 > 163.2 Hz for agarobiose) agree well with the experimental values of 162.7, 147.5, 160.4 147.2 160.9 and 165.7 Hz, respectively.