One-bond carbon-proton coupling constants: Angular dependence in β-linked oligosaccharides

Summary

The angular dependence of¹J_C,H in model compounds related to β-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 of¹J_C,H on the torsional angles Φ^H and Ψ^H and the solvent dielectric constant (s) was characterized in the form:¹J_C,H = A cos2ϖ+B cosϖ + C sin2ϖ + D since + E + Fe. The¹J_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 β-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 β-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 neo agarobiose 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.