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

摘要

Methyl alpha-cellobioside (methyl beta-D-glucopyranosyl-(1 -> 4)-alpha-D-glucopyranoside) was labeled with C-13 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 JHH was traced to (4)J(H4.OH3) based on 2D H-1-H-1 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 CH and O-H bonds are roughly diaxial.