Structural elucidation of a novel transglycosylated compound α-glucosyl rhoifolin and of α-glucosyl rutin by NMR spectroscopy.

We report the full assignment of H and C NMR signals belonging to α-glucosyl rhoifolin (Rhf-G), a novel transglycosylated compound synthesized from a flavone glycoside, rhoifolin, as well as its chemical structure. Furthermore, we report the complete NMR signal assignment for another transglycosylated compound, α-glucosyl rutin (Rutin-G), as the signals corresponding to its sugar moieties had not been identified. Electrospray ionization-mass spectrometry along with multiple NMR methods revealed that Rhf-G possesses three sugar moieties in its chemical structure. The additional glucose was bound directly via a transglycosylation to rhoifolin at position 3a of the sugar moiety. Interestingly, intramolecular hydrogen bonds in the basic Rhf-G and Rutin-G skeletons were confirmed by HMBC experiments. These findings will be helpful for comprehensive NMR studies on transglycosylated compounds in food, cosmetic, and pharmaceutical fields.