Formulation of anomerization and protonation in d-glucosamine, based on H NMR.

The major anomer of non-protonated neutral d-glucosamine GlcN is the β-form, while the α-anomer is dominant for protonated cationic glucosamine GlcNH. The present work confirmed correlation between the anomerization and the protonation by simultaneous determination of signal intensity and chemical shift in pD-variation H NMR, and formulated the equilibrium constants between subspecies α-GlcN, β-GlcN, α-GlcND, and β-GlcND to interpret the correlation. The individual anomerization constants, K = [βGlcN]/[αGlcN] and K = [βGlcND]/[αGlcND], are linked to each other through the relation K∙K = K∙K with the deuteration constants K and K of the anomers. The anomer populations are stimulated by OD and D ions in the dose-response form. The acidic deuteron in α-GlcND is populated mostly at the nitrogen atom, whereas the population in β-GlcND is comparable at nitrogen and anomeric oxygen; this difference is consistent with the basicity of the nitrogen and the anomerization process of glucosamine.