Pullulan nonaacetate: Assignment of chemical shifts of the acetyl protons and acetyl carbonyl carbons by 2D-NMR spectroscopy

Pullulan nonaacetate, a homogulucan having an α-(1 → 6)-linked maltotriosyl repeating-unit, was studied by 1H and 13C NMR spectroscopy. Nine resolved signals were observed for both the methyl protons and for the carbonyl carbons of the acetyl substituents. A series of 2D-NMR experiments was used to assign fully the proton and carbon chemical shifts of pullulan nonaacetate. The determination of long-range correlations between acetyl protons and maltotriosyl carbons, and between acetyl carbonyl carbons and maltotriosyl protons, by a field-gradient HMBC (heteronuclear multibond coherence) experiment was of particular utility for assigning the protons and the carbons of the acetyl groups. A series of 2D-NMR experiments was performed to fully assign the proton and carbon chemical shifts of pullulan nonaacetate. The determination of long-range correlations between acetyl protons and maltotriosyl carbons, and between acetyl carbonyl carbons and maltotriosyl protons by a field-gradient HMBC experiment was of particular utility.