Determination of acid dissociation constants of anomers of amino sugars by 1H NMR spectroscopy

Abstract Acid dissociation constants of α- and β- d -glucos-, mannos-, and galactos-ammonium ions have been determined from 1 H NMR chemical shifts of the individual anomers in D 2 O. Values of p K a (D) for the α- and β-ammonium ions are, respectively: glucosamine, 8.12 and 7.87, mannosamine, 7.78 and 8.50, galactosamine, 8.49 and 8.02. The differences are ascribed largely to differences in the hydration requirements of ammonium and amino groups in the axial and equatorial positions and hydration at upper and lower faces of the sugars. Acid dissociation constants of the 1-hydroxyl group of nonionic d -glucosamine and d -glucose are higher for the β than the α anomer.