Heterocyclic derivatives of sugars: an NMR study of the formation of 1-glycosyl-3,5-dimethyl-1 H-pyrazoles from hydrazones

Hydrazones were prepared by treatment of monosaccharides and disaccharides with hydrazine hydrate and converted in high yield to mixtures of 1-glycosyl-3,5-dimethyl-1 1H-pyrazoles by reaction with pentan-2,4-dione (acetylacetone). The isomeric products were separated by HPLC and characterized by NMR spectroscopy. This represents a new approach to the introduction of a heteroaromatic label into sugars under nonacidic and nonreducing conditions, and it is a process likely to be especially useful for glycan hydrazones obtained from glycoproteins by hydrazinolysis or beta elimination in the presence of hydrazine.