AbstractGoupiolones A and B are unique phenolic compounds with significant DNA-damaging activity. In this study, the structure of goupiolone B was revised on the basis of DFT calculations of the 13C NMR chemical shifts and biosynthetic considerations. The dibenzobicyclo[3.2.2]nonane skeleton of the revised structure suggested that goupiolone B was produced by oxidative coupling between catechol and goupiolone A, which was strongly supported by biomimetic synthesis. Furthermore, racemization of goupiolone B was observed during the attempted resolution of its racemic mixture. A plausible racemization mechanism involving α-ketol rearrangement is proposed.

AbstractGoupiolones A and B are unique phenolic compounds with significant DNA-damaging activity. In this study, the structure of goupiolone B was revised on the basis of DFT calculations of the 13C NMR chemical shifts and biosynthetic considerations. The dibenzobicyclo[3.2.2]nonane skeleton of the revised structure suggested that goupiolone B was produced by oxidative coupling between catechol and goupiolone A, which was strongly supported by biomimetic synthesis. Furthermore, racemization of goupiolone B was observed during the attempted resolution of its racemic mixture. A plausible racemization mechanism involving α-ketol rearrangement is proposed.

Polyphenols in the leaves of Camellia japonica L. at different stages of growth were analyzed by HPLC. Pedunculagin [2,3; 4,6-bis-(S)-hexahydroxydiphenoyl-d-glucose] was the major polyphenol in the youngest leaves. The levels of this compound and (+)-catechin decreased as the leaves matured. The level of (−)-epicatechin did not change with leaf maturity. Enzymatic oxidation of pedunculagin was examined to investigate the mechanism of the decrease. Pedunculagin was not directly oxidized by treatment with oxidative enzymes. However, when (+)-catechin was added to the reaction mixture, the pyrogallol rings of the 4,6-hexahydroxydiphenoyl group was oxidatively cleaved to give 2H-2-oxo-pyran-6-carboxylic acid. The in vitro oxidation products were not detected in fresh leaves, but two pedunculagin oxidation products conjugated with flavan-3-ol were isolated. A new metabolite, camelliatannin I, was isolated and characterized by spectroscopic and density functional theory calculation of NMR chemical shifts.

Theacitrins A–C are yellow pigments of black tea that are produced by oxidative coupling of gallocatechins, i.e., flavan-3-ols with pyrogallol-type B-rings. However, their stereostructures have not yet been determined. In this study, DFT calculations of NMR chemical shifts of theacitrin C (1) and TDDFT calculations of the ECD spectra of theacitrinin A (5), a degradation product of theacitrin C (1), were used to determine the stereostructure of the theacitrins. Furthermore, the preparation of theacitrins A (4) and C (1) by enzymatic oxidation of an epigallocatechin (7) and epigallocatechin-3-O-gallate (2) mixture confirmed their structural relationship.

The stereochemistry of the C-glycosidic ellagitannins, vescalagin and castalagin, has been reinvestigated using computational methods. DFT calculations of their 1H and 13C NMR spectra, as well as TDDFT calculations of the ECD spectra of their des-hexahydroxydiphenoyl analogues, revealed that the structure of the triphenoyl moiety of vescalagin and castalagin should be revised.

From the dried stem of Penthorum chinense (Penthoraceae), 1-O-galloyl-4,6-(R)-hexahydroxydiphenoyl (HHDP)-β-d-glucose and 2′,4′,6′-trihydroxyacetophenone 4′-O-[4,6-(R)-HHDP]-β-d-glucoside were isolated together with their (S)-HHDP isomers. Ellagitannins with a 4,6-(S)-HHDP-glucose moiety are widely distributed in the plant kingdom; however, 4,6-(R)-HHDP glucoses are extremely rare. Lowest-energy conformers of 1-O-galloyl-(S)- and (R)-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′-O-[4,6-(S)-HHDP]-β-d-glucoside, was also isolated.

A large number of black tea polyphenols remain uncharacterized because of the complexity of catechin oxidation reactions that occur during tea fermentation. In the course of our studies on black tea polyphenols, we examined the enzymatic degradation of theaflavins, which are black tea pigments having a benzotropolone chromophore. Oxidation of theaflavin with peroxidase afforded a new product named theacoumarin A together with known pigment theanaphthoquinone. The structure of the new compound was determined by spectroscopic examination and a production mechanism via theanaphthoquinone is proposed.

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.

•Chinese Dragon’s Blood produced from Dracaena cochinchinensis was investigated.•Chalcane–stilbene conjugates were isolated from Chinese Dragon’s Blood.•Twenty-five known compounds were also isolated.•The major constituents were oligomeric flavonoids.•Oligomeric flavonoids were mainly composed of chalcane units.A detailed chemical investigation of Chinese Dragon’s Blood, which is a traditional medicine produced form the red resin of Dracaena cochinchinensis, yielded two chalcane–stilbene conjugates, named cochinchinenenes G and H, together with 25 known compounds. The structures of these compounds were determined by spectroscopic examination. HPLC analysis of the resin indicated that the major constituents were a complex mixture of oligomeric polyphenols, which were detected as a broad hump on the base line of a HPLC chromatogram. 13C NMR analysis indicated that the oligomers were mainly composed of oxygenated chalcane units. This suggestion was supported by the results of a thiol degradation experiment with mercaptoethanol, which yielded a thioether of 4-[(4-hydroxyphenyl)propyl]-3-methoxyphenol. Furthermore, methylation followed by electrospray ionization mass spectroscopic analysis of the resulting fractions established the presence of at least one heptamer of chalcane units.Chalcane–stilbene conjugates were isolated from Chinese Dragon’s Blood produced from Dracaena cochinchinensis together with 25 known compounds. The major constituents were oligomeric flavonoids composed of chalcane units, which were characterized by spectroscopic and chemical methods.

Two unusual ellagitannin metabolites, quercusnins A (3) and B (4), have been isolated from the sapwood of Quercus crispula, and their structures determined by spectroscopic methods, as well as DFT calculations of 1H and 13C NMR chemical shifts of the possible four diastereomers. Treatment of the major ellagitannin species, vescalagin, with Shiitake mushroom (Lentinula edodes) gave 3, which indicated that these unique ellagitannins were the fungal metabolites of ellagitannins.

•Polyphenols in sapwood of Quercus mongolica var. crispula were investigated.•A new oxidation metabolite of vescalagin was isolated.•New galloyl esters of a phenol glycoside and a lignan glycoside were obtained.•The structures were determined chemical and spectroscopic methods.•Nineteen known compounds were identified.Two novel glycosides, 4,5-dimethoxy-3-hydroxyphenol 1-O-β-(6′-O-galloyl)-glucopyranoside (1) and (+)-2α-O-galloyl lyoniresinol 3α-O-β-d-xylopyranoside (2), as well as a novel ellagitannin named epiquisqualin B (3), were isolated from sapwood of Quercus mongolica var. crispula along with 19 known phenolic compounds. The structures of the novel compounds were elucidated on the basis of chemical and spectroscopic investigation. Compound 2 is the first example of a lignan galloyl ester, and 3 is the oxidation product of vescalagin, which is the major ellagitannin of this plant.

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.Highlights► Constituents of Japanese post-fermented tea were examined. ► The post-fermented tea contained tea catechin metabolites. ► The metabolites were identical to those produced by intestinal bacteria. ► The acetone powder of the tea converted tea catechins to the catechin metabolites. ► The acetone powder converted rutin and hesperidin to phenol carboxylic acids.

In the course of a chemotaxonomical study of Castanopsis species (Fagaceae), detailed investigation of the leaves of C. sclerophylla led to isolation of three new phenolic compounds together with 62 known compounds. The structures of the new compounds were elucidated as 2-O-galloyl-O-4,6-(S)-valoneoyl-d-glucose (1), 6-O-galloyl-1-O-vanilloyl-β-d-glucose (2), and 4″-O-galloylchestanin (3) by means of spectroscopic analyses and enzymatic hydrolysis with tannase. Comparison with other Castanopsis species indicated that C. sclerophylla characteristically accumulates chlorogenic acid and a dimeric ellagitannin, rugosin E. Triterpene hexahydroxydiphenoyl esters, which are major constituents of C. cuspidata var. sieboldii, C. hystrix, and C. fissa were not detected.Graphical abstractPhenolic constituents of the leaves of Castanopsis sclerophylla were investigated and chemotaxonomically compared with other Castanopsis species.Highlights► A new ellagitannin was isolated from Castanopsis sclerophylla. ► A galloyl ester of chestanin was isolated from C. sclerophylla. ► A galloyl vanilloyl glucose was isolated from C. sclerophylla. ► Sixty-two known compounds were isolated together with the new compounds. ► The constituents were chemotaxonomically compared with other Castanopsis species.

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.Highlights► A new catechin oxidation product was isolated from a post-fermented tea. ► The structure was determined by spectroscopic methods. ► Polymeric polyphenols of the post-fermented tea were partially characterised by NMR and gel-permeation chromatography.

The bark extract of Acacia mearnsii showed strong lipase and α-amylase inhibition activities. Fractionation of the extract by column chromatography and subsequent 13C NMR and MALDI-TOF-MS analysis revealed that the active substances are proanthocyanidin oligomers mainly composed of 5-deoxyflavan-3-ol units. In addition, 4′-O-methylrobinetinidol 3′-O-β-d-glucopyranoside, fisetinidol-(4α,6)-gallocatechin, and epirobinetinidol-(4β,8)-catechin were isolated as new compounds, and their structures were determined from spectroscopic data. Furthermore, a modified thiol degradation method using strongly acidic conditions was applied to the extract to yield three thiol degradation products derived from robinetinidol units. This method is useful for characterizing acacia proanthocyanidins (wattle tannins).

Phenolic constituents of a new functional fermented tea produced by tea-rolling processing of a mixture (9:1) of tea leaves and loquat leaves were examined in detail. The similarity of the phenolic composition to that of black tea was indicated by high-performance liquid chromatography comparison with other tea products. Twenty-five compounds, including three new catechin oxidation products, were isolated, and the structures of the new compounds were determined to be (2R)-2-hydroxy-3-(2,4,6-trihydroxyphenyl)-1-(3,4,5-trihydroxyphenyl)-1-propanone 2-O-gallate, dehydrotheasinensin H, and acetonyl theacitrin A by spectroscopic methods. In addition, theacitrinin A and theasinensin H were obtained for the first time from commercial tea products. Isolation of these new and known compounds confirms that reactions previously demonstrated by in vitro model experiments actually occur when fresh tea leaves are mechanically distorted and bruised during the production process.

Triterpene hexahydroxydiphenoyl (HHDP) esters have only been isolated from Castanopsis species, and the distribution of these esters in nature is of chemotaxonomical interest. In this study, the chemical constituents of the leaves of Castanopsis fissa were examined in detail to identify and isolate potential HHDP esters. Together with 53 known compounds, 3,4-di-O-galloyl-1-O-purpurogallin carbonyl quinic acid (1) and 3,24-(S)-HHDP-2α,3β,23,24-tetrahydroxytaraxastan-28,20β-olide (2) were isolated and their structures were elucidated by spectroscopic and chemical methods. The polyphenols of the leaves were mainly composed of galloyl quinic acids, triterpenes HHDP esters, ellagitannins and flavonol glycosides. In particular, the isolation yields of 1,3,4-trigalloyl quinic acid and compound 2 were 1.53% and 0.27%, respectively, from the fresh leaves. The presence of lipid soluble HHDP esters of oleanane-type triterpenes as one of the major metabolites is an important chemotaxonomical discovery. Lipase inhibition activities and ORAC values of the major constituents were compared. The triterpene HHDP ester showed moderate lipase inhibition activity and myricitrin gave the largest ORAC value.Graphical abstractChemotaxonomically important hexahydroxydiphenoyl ester of triterpenes and a phenolic pigment were isolated from the leaves of Castanopsis fissa..Highlights► Fifty five compounds were isolated from the leaves of Castanopsis fissa. ► Chemotaxonomically important hexahydroxydiphenoyl ester of triterpenes and a phenolic pigment were isolated. ► C. fissa is a rich source of galloyl quinic acids and triterpene hexahydroxydiphenoyl esters. ► Lipase inhibition activities and ORAC values of the major constituents were compared.

ent-Eudesmane sesquiterpenoids, 8,11-dihydroxy-2,4-cycloeudesmane, 11-hydroxy-2,4-cycloeudesman-8-one and 2,4-cyclo-7(11)-eudesmen-8-one, were isolated from the wood of Platycarya strobilacea, which has been used as an aromatic tree since at least the 18th century. On charring the wood, 2,4-cyclo-7(11)-eudesmen-8-one was detected in the smoke. In the charred wood, the concentrations of ellagitannins, such as galloyl pedunculagin, dramatically decreased, whereas concentrations of pentagalloyl glucose, and other gallotannins were relatively stable. In addition, two other compounds, the 6′-O-m- and p-digalloyl oak lactone precursor and the 3-O-methylellagic acid 4′-O-(4″-O-galloyl)-xylopyranoside, were isolated from the charred wood along with m- and p-digallic acid.Graphical abstractThree ent-eudesmane sesquiterpenoids with cyclopropane rings were isolated from the wood of Platycarya strobilacea.Highlights► Three sesquiterpenes were isolated from the wood of Platycarya strobilacea. ► 2,4-Cyclo-7(11)-eudesmen-8-one was important as an aroma on charring of the incense. ► 6′-O-m- and p-digalloyl oak lactone precursor was isolated from the charred wood. ► Ellagitannins were decomposed on charring but gallotannins were relatively stable.

Chemical constituents of the leaves of rabbiteye blueberry (Vaccinium ashei READE) were investigated in detail. The major phenolic components were caffeoyl quinic acids, flavonol glycosides, flavan-3-ols and proanthocyanidins. Catechins and proanthocyanidins having additional phenylpropanoid units, such as cinchonains, kandelins and mururins, characterised the polyphenols of this plant. Among them, vaccinin A, an isomer of mururin A, was found to be a new compound, and the structure was characterised by spectroscopic methods. The most abundant polyphenols (11.3% of freeze-dried leaves) were oligomeric proanthocyanidins. Thiol degradation with mercaptoethanol indicated that the polymer was constituted of (+)-catechin and (−)-epicatechin as the terminal units and (−)-epicatechin, procyanidin A-2, and cinchonains Ia and Ib as the extension units. Mass spectral analysis suggested the presence of at least dodecamers with A-type linkages and phenylpropanoid moieties.

Degradation of the black tea pigment theaflavin was examined in detail. Enzymatic oxidation of a mixture of epigallocatechin and epicatechin initially produced theaflavin, while prolonged reaction decreased the product. Addition of ethanol to the reaction mixture at the point when theaflavin began to decrease afforded four new products, together with theanaphthoquinone, a known oxidation product of theaflavin. The structures of the new products were determined by spectroscopic methods. One of the products was an ethanol adduct of a theanaphthoquinone precursor, and this reacted with theaflavin to give two further products. A product generated by coupling of theaflavin with epicatechin quinone was also obtained. The structures of the products indicate that oxidation and coupling with quinones are key reactions in the degradation of theaflavins. The degradation of theaflavin probably contributes to production of thearubigins.

Hydrophobic catechin derivatives were produced by heating with natural aldehydes or allyl alcohols. (+)-Catechin or (−)-epigallocatechin-3-O-gallate was heated with trans-2-hexenal, citral, (+)-citronellal, geraniol, or phytol. Although each reaction generated complex mixtures of products, 11 compounds were isolated and characterized by spectroscopic methods. The unsaturated aldehydes were found to attach to the flavan A-ring. Besides C−C linkage between aldehyde and the C-8 and/or C-6 of the catechin A-ring, formation of ether linkages between unsaturated carbons of the aldehydes and phenolic hydroxyl groups was observed. The allyl alcohols, geraniol and phytols, reacted at the galloyl group as well as the A-ring. After partitioning between triglyceride and water, the lipid layer of the reaction products showed strong 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. In contrast, epigallocatechin-3-O-gallate was not transferred to the lipid layer.

In a project to produce a new fermented tea product from non-used tea leaves harvested in the summer, we found that kneading tea leaves (Camellia sinensis) with fresh loquat leaves (Eriobotrya japonica) accelerated the enzymatic oxidation of tea catechins. The fermented tea obtained by tea-rolling processing of tea and loquat leaves had a strong, distinctive flavor and a plain aftertaste, which differed from usual black, green, and oolong teas. The phenolic constituents were similar to those of black tea. However, the concentrations of theaflavin 3-O-gallate, theaflavin 3,3′-di-O-gallate, and thearubigins were higher in the tea leaves kneaded with loquat leaves than in tea leaves kneaded without loquat leaves. The results from in vitro experiments suggested that acceleration of catechin oxidation was caused by the strong oxidation activity of loquat leaf enzymes and a coupled oxidation mechanism with caffeoyl quinic acids, which are the major phenolic constituents of loquat leaves.

Structures of two condensation products obtained by the reaction of cinnamaldehyde with (+)-catechin were determined by spectroscopic methods. One had two phenylpropanoid units at the C-6 and C-8 positions of the catechin skeleton. The other product had a dimeric structure with two catechin and two phenylpropanoid units. Matrix-assisted laser desorption time-of-flight mass spectrometric analysis of the reaction products of cinnamaldehyde with procyanidin B1 suggested that procyanidins were oligomerized in a manner similar to the reaction with catechin. Furthermore, 13C NMR spectral comparison of the condensation products with the polymeric procyanidins obtained from commercial cinnamon bark strongly suggested that the procyanidins in the cinnamon bark also were polymerized by reaction with cinnamaldehyde.

Three new phenolic compounds named whiskey tannins A and B and carboxyl ellagic acid were isolated from commercial Japanese whiskey, along with gallic acid, ellagic acid, brevifolin carboxylic acid, three galloyl glucoses, a galloyl ester of phenolic glucoside, 2,3-(S)-hexahydroxydiphenoylglucose, and castacrenin B. Whiskey tannins A and B were oxidation products of a major oak wood ellagitannin, castalagin, in which the pyrogallol ring at the glucose C-1 position of castalagin was oxidized to a cyclopentenone moiety. These tannins originated from ellagitannins contained in the oak wood used for barrel production; however, the original oak wood ellagitannins were not detected in the whiskey. To examine whether the whiskey tannins were produced during the charring process of barrel production, pyrolysis products of castalagin were investigated. Dehydrocastalagin and a new phenolcarboxylic acid trislactone having an isocoumarin structure were isolated, along with castacrenin F and ellagic acid. However, whiskey tannins were not detected in the products.

Tea leaf is rich in pyrogallol-type catechins, and their oxidation is important in the generation of black tea polyphenols. In the present study, the enzymatic oxidation of three pyrogallol-type catechins, (+)- and (−)-gallocatechins and (−)-epigallocatechin, was compared. The reactions yielded unstable quinone products, which were trapped as condensation products with o-phenylenediamine. The oxidation of (+)-gallocatechin proceeded very slowly compared to the reaction of (−)-epigallocatechin, and yielded a proepitheaflagallin-type dimer as the major product, though oxidation of (−)-epigallocatechin gave predominantly dehydrotheasinensin C. The cis-configuration of the C-3 hydroxyl group and the B-ring of (−)-epigallocatechin was apparently crucial for rapid and selective production of dehydrotheasinensin C. Oxidation of (−)-gallocatechin proceeded in a manner similar to that of (+)-gallocatechin, and produced an enantiomer of the (+)-gallocatechin product. The results suggest that enzymes catalyze oxidation of the pyrogallol B-ring to the o-quinone, with subsequent non-enzymatic coupling reactions proceed under highly steric control.Enzymatic oxidation of (+)-gallocatechin yielded the proepitheaflagallin-type dimer as the major product, though oxidation of (−)-epigallocatechin gave dehydrotheasinensin-type products predominantly.

Two new maltol glycosides, maltol 6′-O-β-d-apiofuranosyl-β-d-glucopyranoside and maltol 6′-O-(5-O-p-coumaroyl)-β-d-apiofuranosyl-β-d-glucopyranoside, were isolated from Elsholtzia rugulosa Hemsl. along with 11 known compounds including prunasin and amygdalin. The structures were determined on the basis of spectroscopic and chemical evidence. This is the second example of isolation of cyanogenic glycosides from Lamiaceous plants.

Dunalianosides A-I (1–9), esters of arbutin and related phenolic glucosides, were isolated from the buds of Vaccinium dunalianum Wight (Ericaceae) together with 20 known compounds, and their structures were established on the basis of 1- and 2D NMR spectroscopic evidence. Dunalianosides F–H were dimers of p-hydroxyphenyl 6-O-trans-caffeoyl-β-d-glucopyranoside (10). The latter was obtained in extraordinary high yield (22% of dry weight), and dunalianoside I (9) was found to be a conjugate of arbutin with an iridoid glucoside.Dunalianosides A-I, esters of arbutin and related phenolic glucosides, were isolated from the buds of Vaccinium dunalianum Wight (Ericaceae) together with 20 known compounds.