Microbial glucuronidation of polyphenols

In a typical series of experiments, several polyphenol O-β-d-glucuronides (including human metabolites) deriving from two flavonoids (naringenin, quercetin) and several stilbenoids (trans-resveratrol, rhapontigenin, deoxyrhapontigenin) have been obtained from the aglycones or their natural glycosides (Naringenin-7-O-glucoside, rutin, piceid, rhapontin or deoxyrhapontin), in a one step biotransformation and in moderate to high yields by incubation with a Streptomyces sp. strain M52104. Regioselectively glucuronidated products have been separated by chromatographic methods, then extensively characterized by MS and NMR. In all cases glucuronidation is β-stereospecific, but not completely regioselective. When present, the 4′(para)-hydroxyl group is generally favoured, then the 7-OH-group of flavonoids (corresponding to the 3-OH of stilbenoids). Several pure O-β-d-glucuronidated derivatives, commercially not available, have been prepared in high purity by this method.

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► A number of polyphenolic compounds, including biologically active flavanols and stilbenoids or their corresponding glycoside derivatives, have been converted by a microbial transformation into the corresponding O-β-d-glucuronide derivatives, which are known as the circulating form of these compounds.
► The glucuronidation reaction is carried out stereospecifically in high yield, but several regioisomers are produced, necessitating chromatographic separations.
► All products have been completely characterized by MS and NMR techniques.
► This method advantageously compares with the current chemical approach for the preparation of glucuronide conjugates.