Formulation of anomerization and protonation in D-glucosamine, based on ¹H NMR

© 2020 Elsevier Ltd The major anomer of non-protonated neutral D-glucosamine GlcN0 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 1H NMR, and formulated the equilibrium constants between subspecies α-GlcN0, β-GlcN0, α-GlcND+, and β-GlcND+ to interpret the correlation. The individual anomerization constants, Kan = [βGlcN]/[αGlcN] and KanD = [βGlcND+]/[αGlcND+], are linked to each other through the relation KDα∙KanD = KDβ∙Kan with the deuteration constants KDα and KDβ 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.