An NMR investigation of putative interresidue H-bonding in methyl α-cellobioside in solution

Methyl α-cellobioside (methyl β-d-glucopyranosyl-(1→4)-α-d-glucopyranoside) was labeled with 13C at C4′ for use in NMR studies in DMSO-d6 solvent to attempt the detection of a trans-H-bond J-coupling (3hJCCOH) between C4′ and OH3. Analysis of the OH3 signal at 600 MHz revealed only the presence of two homonuclear J-couplings: 3JH3,OH3 and a smaller, longer range JHH. No evidence for 3hJC4′,OH3 was found. The longer range JHH was traced to 4JH4,OH3 based on 2D 1H–1H COSY data and inspection of the H2 and H4 signal lineshapes. A limited set of DFT calculations was performed on a methyl cellobioside mimic to evaluate the structural dependencies of 4JH2,O3H and 4JH4,O3H on the H3–C3–O3–H torsion angle. Computed couplings range from about −0.7 to about +1.1 Hz, with maximal values observed when the C–H and O–H bonds are roughly diaxial.

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