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

Abstract

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- d 6 solvent to attempt the detection of a trans-H-bond J-coupling ( 3h J CCOH) between C4′ and OH3. Analysis of the OH3 signal at 600 MHz revealed only the presence of two homonuclear J-couplings: 3 J H3,OH3 and a smaller, longer range J HH. No evidence for 3h J C4′,OH3 was found. The longer range J HH was traced to 4 J H4,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 4 J H2,O3H and 4 J H4,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.