Polyphenols in lahpet-so and two new catechin metabolites produced by anaerobic microbial fermentation of green tea

The phenolic constituents of lahpet-so, a traditional postfermented tea of Myanmar produced under anaerobic conditions, were examined. The major polyphenols were identified to be pyrogallol and 4′-hydroxyphenyl-3- (2′′,4′′,6′′-trihydroxyphenyl)-propan-2-ol, 3′,4′-dihydroxyphenyl-3-(2′′,4′′, 6′′-trihydroxyphenyl)-propan-2-ol, and 3′,4′,5′- trihydroxyphenyl-3-(2′′,4′′,6′′- trihydroxyphenyl)-propan-2-ol. The hydroxydiphenylpropan-2-ols were identical to the initial metabolites produced from green tea catechins by mammalian intestinal bacteria. In addition, an anaerobic mixed-fermentation experiment using lahpet-so and Japanese commercial green tea afforded two new catechin degradation products together with known compound bruguierol B and the above-mentioned catechin metabolites. Based on spectroscopic evidence, the structures of the new compounds were concluded to be 4-(2,5-dihydroxyhexyl) benzene-1,2-diol and (5S,8R)-6,7,8,9-tetrahydro-5-methyl-5・8-epoxy-5H- benzocycloheptene-2,3,4-triol. Interestingly, the production mechanism was deduced to be the inverse of the biosynthesis of the flavan-3-ol A ring

Selective oxidation of pyrogallol-type catechins with unripe fruit homogenate of Citrus unshiu and structural revision of oolongtheanins

In our previous chemical study of the production mechanism of black tea polyphenols, we demonstrated that Japanese pear fruit homogenate oxidizes green tea catechins bearing pyrogallol-type and catechol-type B-rings to produce theaflavins and dehydrotheasinensins. In contrast, unripe fruit homogenate of Citrus unshiu selectively oxidizes pyrogallol-type catechins to yield only dehydrotheasinensins. The difference in the selectivity of the two homogenates is probably related to the lower redox potential of pyrogallol-type catechins. The oxidation of epigallocatechin with C. unshiu homogenate gave two new compounds, including an ethanol adduct of an oolongtheanin precursor and epigallocatechin 4′-O-rutinoside, together with theasinensin C, dehydrotheasinensin E, and desgalloyl oolongtheanin. The structure of desgalloyl oolongtheanin should be revised based on the spectroscopic and computational data collected in the current study, and a mechanism responsible for the production of oolongtheanins is also proposed

A new catechin oxidation product and polymeric polyphenols of post-fermented tea

A new epicatechin oxidation product with a 3,6-dihydro-6-oxo-2H-pyran-2- carboxylic acid moiety was isolated from a commercially available post-fermented tea that is produced by microbial fermentation of green tea. The structure of this product was determined by spectroscopic methods. A production mechanism that includes the oxygenative cleavage of the catechol B-ring of (-)-epicatechin is proposed. In addition, polymeric polyphenols were separated from the post-fermented tea and partially characterised by 13C NMR spectroscopy and gel-permeation chromatography. The polymers appear to be primarily composed of epigalloacetechin-3-O-gallate and the molecular weight (Mn) of the acetylated form was estimated to be ∼3500

Transformation of tea catechins and flavonoid glycosides by treatment with Japanese post-fermented tea acetone powder

Japanese post-fermented teas are produced by a combination of aerobic and anaerobic microbial fermentation of the leaves of tea plant. Recently, it was revealed that tea products contain characteristic polyphenols identical to the tea catechin metabolites produced by mammalian intestinal bacteria, such as (2S)-1-(3′,4′,5′-trihydroxyphenyl)-3-(2″,4″,6″-trihydroxyphenyl)-propan-2-ol (EGC-M1). In the present study, degradation of epigallocatechin-3-O-gallate (EGCg) and epigallocatechin (EGC) with acetone powder prepared from Japanese post-fermented tea was examined. Under aerobic conditions, EGCg was hydrolysed to EGC and gallic acid, which were further converted to gallocatechin (GC) and pyrogallol, respectively. Under anaerobic conditions, EGCg was hydrolysed to EGC, which was further metabolised to GC, EGC-M1 and (4R)-5-(3,4,5-trihydroxyphenyl)-4-hydroxypentanoic acid (EGC-M2). Gallic acid was degraded to pyrogallol and then further decomposed. Anaerobic treatment of EGC with the acetone powder yielded EGC-M1, EGC-M2, (4R)-5-(3,4,5-trihydroxyphenyl)-γ-valerolactone, and (4R)-5-(3,4 -dihydroxyphenyl)-γ-valerolactone. Furthermore, similar anaerobic treatment of rutin and hesperidin yielded 3,4-dihydroxyphenylacetic acid and 3-(3,4-dihydroxyphenyl)propanoic acid, respectively

Biomimetic One-Pot Preparation of a Black Tea Polyphenol Theasinensin A from Epigallocatechin Gallate by Treatment with Copper(II) Chloride and Ascorbic Acid

Chromatographic separation of black tea polyphenols is too difficult to supply sufficient quantities of pure compounds for biological experiments. Thus, facile methods to prepare black tea constituents were desired. Treatment of epigallocatechin gallate with copper(II) chloride efficiently afforded an unstable quinone dimer, dehydrotheasinensin A, and subsequent treatment with ascorbic acid stereoselectively yielded theasinensin A. The latter is a dimer with an R-biphenyl bond, one of the major polyphenols found in black tea. The method is simpler and more effective than enzymatic preparation

Diastereomeric Ellagitannin Isomers from Penthorum chinense

From the dried stem of Penthorum chinense (Penthoraceae), 1-<i>O</i>-galloyl-4,6-(<i>R</i>)-hexahydroxydiphenoyl (HHDP)-β-d-glucose and 2′,4′,6′-trihydroxyacetophenone 4′-<i>O-</i>[4,6-(<i>R</i>)-HHDP]-β-d-glucoside were isolated together with their (<i>S</i>)-HHDP isomers. Ellagitannins with a 4,6-(<i>S</i>)-HHDP-glucose moiety are widely distributed in the plant kingdom; however, 4,6-(<i>R</i>)-HHDP glucoses are extremely rare. Lowest-energy conformers of 1-<i>O</i>-galloyl-(<i>S</i>)- and (<i>R</i>)-HHDP-glucopyranoses were derived by density functional theory calculations, and the calculated ¹H and ¹³C NMR chemical shifts and the ¹H–¹H coupling constants were in agreement with the experimental values. The results revealed a conformational difference of the diastereomeric macrocyclic ester rings. In addition, a new compound, 1′,3′,5′-trihydroxybenzene 1′-<i>O</i>-[4,6-(<i>S</i>)-HHDP]-β-d-glucoside, was also isolated