Plant polyphenols, including dietary polyphenols such as resveratrol, are important components in the plant antioxidant and defence systems. They are also known to exert beneficial effects on human health through diet. As they are produced, these polyphenols may be subjected to deleterious enzymic oxidation by the plant polyphenol oxidases. They are generally synthesized as glycosides like 5,4′-dihydroxystilbene-3-O-β-d-glucopyranoside, the 3-glucoside of resveratrol. The effects of the glycosylation and methylation of the parent resveratrol on its enzymic oxidation were studied. Methyl and glucosyl derivatives were synthesized using simple one-step methodologies. The kinetics of their enzymic oxidation by tyrosinases were defined. Substitution at the p-hydroxy group, by either glucose or methyl, abolished enzymic oxidation by both mushroom and grape tyrosinases. Substitution at the m-hydroxy group with methyl had a small effect, but substitution with glucose resulted in a much lower affinity of the enzymes for the glycoside. We suggest that glycosylation of polyphenols in nature helps to protect these vital molecules from enzymic oxidation, extending their half-life in the cell and maintaining their beneficial antioxidant capacity and biological properties.
Abbreviations used: AUC, area under the curve; BSTFA, N,O-bis(trimethylsilyl)trifluoroacetamide; piceid, 5,4′-dihydroxystilbene-3-O-β-d-glucopyranoside; PPO, polyphenol oxidase; trans-resveratrol, trans-3,5,4′-trihydroxystilbene.