Seasonal changes in the tannins of Liquidambar formosana reflecting their biogenesis

Fractionation of the tannins in the leaf of Liquidambar formosana collected at different seasons showed that tellimagrandin II is the main component in early spring, while casuarinin and pedunculagin are the main tannins in autumn. Hydrolysable tannins structurally related to them, tellimagrandin I, casuariin, 1,2,4,6-tetra-O-galloyl-β-D-glucose and casuarictin were isolated from the leaf collected in November, and 1,2,6-tri-O-galloyl-β-D-glucose from the leaf in May. From HPLC analyses of leaf extracts collected from April to November, it was clear that the composition changes most rapidly in the spring. The seasonal changes in the structures and amounts of these hydrolysable tannins indicate a particular biogenetic pathway for these substances.     

Gallotannins of the freshwater green alga Spirogyra sp.

The green alga Spirogyra sp. accumulates tetra- through undecagalloylglucosyl gallotannins. The hexa- through undecagalloylglucoses are predominantly based on 1,2,3,4,6-penta-O-galloylglucose, whereas the major pentagalloylglucose is 3-O-digalloyl-1,2,6-tri-O-galloyl-β-D-glucose.     

Gemins D,E and F,ellagitannins from Geum japonicum

Three new ellagitannins, gemin D, E and F were isolated from the leaves of Geum japonicum. The structures of gemin D and F were established as 3-O-galloyl-4,6-O-[(S-hexahydroxydiphenoyl]-D-glucose and 6-O-caffeoyl-2,3-O-[(S-hexahydroxydiphenoyl]-D-glucose, respectively. Gemin E is a novel C-glucosidic ellagitanin having a dehydrohexahydroxydiphenoyl group in the molecule. Gemin D was also isolated from the flower buds of Camellia japonica.     

Oxazoline synthesis of 1,2-trans-2-acetamido-2-deoxyglycosides. Glycosylation with 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-D-galactopyrano)-[2′,1′:4,5]-2-oxazoline

The glycosylating activity of 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-D-galactopyrano)-[2′,1′:4,5]-2-oxazoline has been tested in reaction with partially protected saccharides having free primary or secondary hydroxyl groups or with hydroxy amino acids. 3-O-(2-Acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-D-galactopyranosyl)-N-benzyloxycarbonyl-L-serine benzyl ester (3), 6-O-(2-acetamido-2-deoxy-β-D-galactopyranosyl)-D-galactopyranose (5), p-nitrophenyl 2-acetamido-6-O-(2-acetamido-2-deoxy-β-D-galactopyranosyl)-2-deoxy-β-D-glucopyranoside (7), 6-O-(2-acetamido-2-deoxy-β-D-galactopyranosyl)-D-glucose (9), and 3-O-(2-acetamido-2-deoxy-β-D-galactopyranosyl)-D-glucose (11) were synthesized in high yield.     

Liquidambin,an ellagitannin from Liquidambar formosana

A new ellagitannin, named liquidambin, which could be biogenetically closely correlated with casuarinin and pedunculagin, has been isolated from the leaves of Liquidambar formosana. Its structure was determined as 5-O-galloyl-2,3,4,6-di-O-(S)-hexahydroxydiphenoyl-d-glucose. The structural equilibration due to hydration of the aldehyde group of the glucose core in this tannin was shown from its ¹H and ¹³C NMR spectra.     

Pendulaosides A and B. Two acylated triterpenoid saponins from Harpullia pendula seed extract

Two new acylated triterpenoid saponins named pendulaosides A and B as well as the known phenolic compounds methyl gallate, gallic acid, 1,2,3,6-tera-O-galloyl-β-d-glucose and 1,2,3,4,6-penta-O-galloyl-β-d-glucose, were isolated from the seeds of Harpullia pendula. The structures of pendulaosides A and B were determined using extensive 1D and 2D NMR analysis and mass spectrometry as well as acid hydrolysis, as 3-O-β-d-glucopyranosyl-(1→2)-[α-L-arabinofuranosyl-(1→3)]-β-d-glucuronopyranosyl-22-O-angeloyl-3β,16α,22α,24β,28-pentahydroxylolean-12-ene and 3-O-β-d-glucopyranosyl-(1→2)-[α-L-arabinofuranosyl-(1→3)]-β-d-glucuronopyranosyl-16-O-(2-methylbutyroyl)-3β,16α,22α,24β,28-pentahydroxylolean-12-ene, respectively. To the best of our knowledge the two triterpene parts 22-O-angeloyl-3β,16α,22α,24β,28-pentahydroxylolean-12-ene and16-O-(2-methylbutyroyl)-3β,16α,22α,24β,28-pentahydroxylolean-12-ene have never been characterized before. The two isolated saponins were assayed for their in-vitro cytotoxic activity against the three human tumor cell lines HepG2, MCF7 and PC3. The results showed that pendulaoside A exhibited moderate activity on PC3 cell line with IC50value equal to 13.0 μM and weak activity on HepG2 cell line with IC50 value equal to 41.0 μM. Pendulaoside B proved to be inactive against the three used cell lines.     

Hydrolysable tannins and proanthocyanidins from green tea

Two hydrolysable tannins were isolated from green tea, and their structures were characterized by chemical and spectral means as 1,4,6-tri-O -galloyl-β-d-glucose and 1-O-galloyl-4,6-(?)-hexahydroxydiphenoyl-β-d-glucose. In addition, a new proanthocyanidin gallate was isolated, together with the known procyanidins B-2, B-4 and C-1. The structure of the proanthocyanidin was established as epigallocatechin-(4β → 8)-3-O-galloylepicatechin.     

Synthèse du 4-O-[(s)-1-carboxyéthyl]-d-glucose et de son isomère (R)

Alkylation of benzyl 2,3,6-tri-O-benzyl-β-D-glucopyranoside in N,Ndimethyl formamide with (R)-2-chloropropionic acid gave crystalline benzyl 2,3,6-tri-O-benzyl-4-O-[(S)-carboxyethyl]-β-D-glucopyranoside. After hydrogenolysis of the benzyl group 4-O-[(S)-D-carboxyethyl]-D-glucose was obtained which lactonized very easily. Treatment of benzyl 2,3,6-tri-O-benzyl-4-O-[(S)-1-carboxyethyl]-β-D-glucopyranoside with diazomethane gave cristalline benzyl 2,3,6-tri-O-benzyl-4-O-[(S)-1-(methoxycarbonyl)ethyl]-β-D-glucopyranoside, which was reduced with lithium aluminium hydride to crystalline benzyl 2,3,6-tri-O-benzyl-4-O-[(S)-1-(hydroxymethyl)ethyl]-β-D-glucopyranoside After hydrogenolysis of the benzyl groups 4-O-[(S)-1-(hydroxymethyl)ethyl]-D-glucose was obtained. A similar sequence of reactions was performed with (S)-2-chloropropionic acid.     

Syntheses of 2-acetamido-2-deoxy-4-O-βD-galacto-pyranosyl-D-mannose and -D-glucose and of 2-acetamido-2-deoxy-4-O-βD-mannopyranosyl-D-mannose and -D-glucose

2-acetamido-2-deoxy-4-O-β-D-galactopyranosyl-D-mannose (6) and -D-glucose (7) were prepared by addition of nitromethane to 3-O-β-D-galactopyranosyl-D-arabinose, followed by acetylation, ammonolysis, and application of the Nef reaction. Similarly, 2-acetamido-2-deoxy-4-O-β-D-mannopyranosyl-D-mannose (14) and -D-glucose (15) were prepared by the same scheme from 3-O-β-D-mannopyranosyl-D-arabinose. In the two series of experiments, 6 and 14 were the respective major products. Epimerization of the 2-acetamido-2-deoxy-D-mannose residue in 6 and 14 yielded 7 and 15, respectively.     

Scyllo-quercitol gallates and hexahydroxydiphenoates from quercus stenophylla

A series of gallotannins and ellagitannins based on a scyllo-quercitol core have been isolated from the bark of Quercus stenophylla. On the basis of chemical and spectroscopic evidence, the structures of the gallotannins have been established as 2-O-, 1,2-di-O-, 1,2,3-tri-O-, 1,2,3,4-tetra-O- and 1,2,3,4,5-penta-O-galloyl-scyllo-quercitols, and the ellagitannins as 1,5-di-O-galloyl-2,3-(S)-hexahydroxydiphenoyl-scyllo-quercitol and 1,4-(or 4,5)-di-O-galloyl-2,3-(S)-hexahydroxydiphenoyl-     

Torvonin-A,a spirostane saponin from Solanum torvum leaves

A new steroidal saponin, torvonin-A, has been isolated from S. torvum leaves and its structure has been established as neochlorogenin-3-O-β-L-rhamnopyranosyl (1→2)β-L-rhamnopyranoside.     

Two new phenolic glucosides and an ellagitannin from the leaves of Castanopsis sclerophylla

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.     

Purification and properties of 1-(hydroxycinnamoyl)-glucose:1-(hydroxycinnamoyl)-glucose hydroxycinnamoyltransferase from radish seedlings

A hydroxycinnamoyltransferase (EC 2.3.1.—) which catalyses in vivo the formation of 1,2-di-O-sinapoyl-β-D-glucose has been purified 240-fold from cotyledons of 5-day-old dark-grown seedlings of radish Raphanus sativus L. var. sativus cv. Saxa). The enzyme catalysing a reaction between two identical substrate molecules used 1-O-(hydroxycinnamoyl)-β-D-glucose both as acyl donor and acceptor molecule and exhibited a strict specificity of transfer to the C-2 hydroxyl group of the acceptor. It had an apparent M_r, of 55 000 and showed greatest activity at pH 8.0 (50% at pH 7.0 and 9.0) and 42°. Apparent energy of activation was found to be 62 kJ/mol. There was no requirement for divalent cations or thiols. The Michaelis curve did not show a rectangular hyperbola but was slightly sigmoid. A linear curve was obtained on replotting the Michaelis curve according to Hanes, using squared values of substrate concentrations. The S_0.5 for 1-sinapoyl-, 1-feruloyl- and 1-(p-coumaroyl)-glucose were 0.42, 0.40 and 0.58 mM, respectively, and the ratios of the V_max/S_0.5 values were 100:92:45.     

Anti-hyperglycaemic effects of the Japanese red maple Acer pycnanthum and its constituents the ginnalins B and C

The anti-hyperglycaemic effects of the leaves of Acer pycnanthum K. Koch, and the purification and identification of the active compounds were investigated. Extracts of the leaves showed a potent inhibitory effect on the α-glucosidase in both in vivo and in vitro experiments. The fractionation of the crude extract gave two active compounds, ginnalin B (6-O-galloyl-1,5-anhydro-D-glucitol) and ginnalin C (2-O-galloyl-1,5-anhydro-D-glucitol), by spectroscopic analysis. This is the first report that A. pycnanthum and its constituents may be useful for the prevention or treatment of diabetes mellitus.     

Havanine—a steroidal alkaloid glycoside from Solanum havanense

A new steroidal alkaloid glycoside named havanine has been isolated from the leaves of Solanum havanense and its structure elucidated by spectral data as (25S)-O(3)-β-D-glucopyranosyl-16α-acetoxy-22,26-epiminocholesta-5,22(N)-dien-3β-ol.     

Glycosylation of 2-phenylpropionic acid and its ethyl ester in suspension cultures of Nicotiana tabacum,Dioscoreophyllum cumminsii and Aconitum japonicum

Suspension cultures of Nicotiana tabacum and Dioscoreophyllum cumminsii converted 2-(RS)-phenylpropionic acid and its ethyl ester into 2-(RS)-phenylpropionyl β-D-glucopyranoside, 2-(RS)-phenylpropionyl 6-O-β-D-glucopyranosyl-β-D-glucopyranoside and 6-O-β-D- glucopyranosyl-2-O-[2-(RS)-phenylpropionyl]-D-glucose which accumulated in the cells. A suspension culture of Aconitum japonicum converted these substrates into ethyl 6-O-[2-(RS)-phenylpropionyl]- β-D-glucopyranoside which was mostly excreted into the medium. The diastereomeric mixture of the glucosyl esters of 2-(RS)-phenylpropionic acid was resolved by HPLC to show the ratio of R:S was 1:1.     

Triterpene hexahydroxydiphenoyl esters and a quinic acid purpurogallin carbonyl ester from the leaves of Castanopsis fissa

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.     

Two luteolin o-glucuronides from primary leaves of Secale cereale

Two luteolin O-glucuronides have been located exclusively in the photosynthetically active mesophyll of primary leaves of rye (Secale cereale). Their structures have been elucidated as luteolin 7-O-[β-d-glucuronosyl (1 → 2)β-d-glucuronide]-4′-O-β-d-glucuronide and luteolin 7-O-[β-d-glucuronosyl (1 → 2)β-d-glucuronide]. The former glycoside is a new natural compound.     

Action of tannin on cellular membranes: Novel insights from concerted studies on lipid bilayers and native cells

Hydrolyzable tannin (3,6-bis-O-digalloyl-1,2,4-tri-O-galloyl-β-d-glucose) has a dual effect on the cell membrane: (1) it binds to a plasmalemmal protein of the Chara corallina cell (C₅₀ = 2.7 ± 0.3 μM) and (2) it forms ionic channels in the lipid membrane. Based on these facts, a molecular model for the interaction of tannins with the cell membrane is proposed. The model suggests that the molecules of hydrolyzable tannin bind electrostatically to the outer groups of the membrane protein responsible for the Ca²⁺-dependent chloride current and blocks it. Some tannin molecules penetrate into the hydrophobic region of the membrane, and when a particular concentration is reached, they form ion-conducting structures selective toward Cl^?.     

Metabolic responses of Thellungiella halophila/salsuginea to biotic and abiotic stresses: Metabolite profiles and quantitative analyses

The metabolite profiles of the model crucifer Thellungiella salsuginea (salt cress) ecotype Shandong subjected to various biotic and abiotic stresses were analyzed using HPLC-DAD-ESI-MS. Two different cruciferous microbial pathogens, Albugo candida, a biotrophic oomycete, and Leptosphaeria maculans, a necrotrophic fungus, elicited formation of the phytoalexins wasalexins A and B without causing visual damage on inoculated leaves. Analyses of non-polar and polar metabolites led to elucidation of the chemical structures of five metabolites: 4′-O-(E)-sinapoyl-7-methoxyisovitexin-2″-O-β-d-glucopyranoside, 4′-O-(E)-sinapoylisovitexin-2″-O-β-d-glucopyranoside, 4-O-β-d-glucopyranosyl-7-hydroxymatairesinol, 5′-O-β-d-glucopyranosyldihydroneoascorbigen and 3-O-β-d-glucopyranosylthiane. 3-O-β-d-glucopyranosylthiane, an unique metabolite for which we suggest the name glucosalsuginin, is proposed to derive from the glucosinolate glucoberteroin. In addition, the identification of a broad range of polar metabolites identical to those of other crucifers was carried out. Quantification of several metabolites over a period of eight days showed that concentrations of the polar phytoanticipin 4-methoxyglucobrassicin increased substantially in leaves irradiated with UV light (λ_max 254 nm) relative to control leaves, but not in leaves subjected to other stresses.