Glycosylation of 6-gingerol and unusual spontaneous deglucosylation of two novel intermediates to form 6-shogaol-4′- O-β -glucoside by bacterial glycosyltransferase

ABSTRACT 6-Gingerol is a major phenolic compound within ginger ( Zingiber officinale ), often used in healthcare; however, its lower bioavailability is partly due to its poor solubility. Four bacterial glycosyltransferases (GTs) were tested to glycosylate 6-gingerol into soluble gingerol glucosides. Bs UGT489 was a suitable GT to biotransform 6-gingerol into five significant products, which could be identified via nucleic magnetic resonance and mass spectrometry as 6-gingerol-4′,5- O - β -diglucoside ( 1 ), 6-gingerol-4′- O - β -glucoside ( 2 ), 6-gingerol-5- O - β -glucoside ( 3 ), 6-shogaol-4′- O - β -glucoside ( 4 ), and 6-shogaol ( 5 ). The enzyme kinetics of Bs UGT489 showed substrate inhibition toward 6-gingerol for producing two glucosides. The kinetic parameters were determined as K M (110 µM), k cat (862 min −1 ), and K I (571 µM) for the production of 6-gingerol-4′- O-β -glucoside ( 2 ) and K M (104 µM), k cat (889 min −1 ), and K I (545 µM) for the production of 6-gingerol-5- O-β -glucoside ( 3 ). The aqueous solubility of the three 6-gingerol glucosides, compound ( 1 ) to ( 3 ), was greatly improved. However, 6-shogaol-4′- O - β -glucoside ( 4 ) was found to be a product biotransformed from 6-shogaol ( 5 ). This study first confirmed that the glucose moiety at the C-5 position of both 6-gingerol-4′,5- O - β -diglucoside ( 1 ) and 6-gingerol-5- O - β -glucoside ( 3 ) caused spontaneous deglucosylation through β -elimination to form 6-shogaol-4′- O - β -glucoside ( 4 ) and 6-shogaol ( 5 ), respectively. Moreover, the GTs could glycosylate 6-shogaol to form 6-shogaol-4′- O - β -glucoside ( 4 ). The assays showed 6-shogaol-4′- O - β -glucoside ( 4 ) had higher anti-inflammatory activity (IC 50 value of 10.3 ± 0.2 µM) than 6-gingerol. The 6-gingerol-5- O - β -glucoside ( 3 ) possessed 346-fold higher solubility than 6-shogaol, in which the highly soluble glucoside is a potential prodrug of 6-shogaol via spontaneous deglucosylation. This unusual deglucosylation plays a vital role in influencing the anti-inflammatory activity. IMPORTANCE Both 6-gingerols and 6-shogaol possess multiple bioactivities. However, their poor solubility limits their application. The present study used bacterial GTs to catalyze the glycosylation of 6-gingerol, and the resulting gingerol glycosides were found to be new compounds with improved solubility and anti-inflammatory activity. In addition, two of the 6-gingerol glucosides were found to undergo spontaneous deglucosylation to form 6-shogaol or 6-shogaol glucosides. The unique spontaneous deglucosylation property of the new 6-gingerol glucosides makes them a good candidate for the prodrug of 6-shogaol.