Elsevier, Carbohydrate Research, (403), p. 149-156, 2015
DOI: 10.1016/j.carres.2014.05.011
Full text: Unavailable
(1)H and (13)C NMR chemical shifts were accurately determined by consistent referencing for an extensive set of chemically synthesized branched α-glucan model compounds. The model compounds include anomerically fixed and reducing oligosaccharides ranging in size from isomaltose to a doubly branched decasaccharide. Both the (13)C1 chemical shift and the (13)C6 chemical shifts in α-(1→6) glycosidic bonds are strongly dependent on the chemical structure in the vicinity of the branch point, especially on the addition of glucopyranosyl units towards the non-reducing end of the backbone chain. The conformational sampling at the branch point of the branched α-glucan model compounds was experimentally probed with homo-nuclear scalar couplings. Substitution at O6 consistently increases the fraction of C6-O6 trans conformations, but to a lesser extent, if the attachment occurs at the reducing end residue. Increasingly complex structures in the vicinity of the branch point increase the population of the gauche-trans conformation of the C5-C6 bond. This population change is found to correlate with the (13)C6 chemical shift.