Purification of a glutathione S-transferase and a glutathione conjugate-specific dehydrogenase involved in isoprene metabolism in Rhodococcus sp. strain AD45

A glutathione S-transferase (GST) with activity toward 1, 2-epoxy-2-methyl-3-butene (isoprene monoxide) and cis-1, 2-dichloroepoxyethane was purified from the isoprene-utilizing bacterium Rhodococcus sp. strain AD45. The homodimeric enzyme (two subunits of 27 kDa each) catalyzed the glutathione (GSH)-dependent ring opening of various epoxides. At 5 mM GSH, the enzyme followed Michaelis-Menten kinetics for isoprene monoxide and cis-1, 2-dichloroepoxyethane, with Vmax values of 66 and 2.4 micromol min-1 mg of protein-1 and Km values of 0.3 and 0.1 mM for isoprene monoxide and cis-1,2-dichloroepoxyethane, respectively. Activities increased linearly with the GSH concentration up to 25 mM. 1H nuclear magnetic resonance spectroscopy showed that the product of GSH conjugation to isoprene monoxide was 1-hydroxy-2-glutathionyl-2-methyl-3-butene (HGMB). Thus, nucleophilic attack of GSH occurred on the tertiary carbon atom of the epoxide ring. HGMB was further converted by an NAD+-dependent dehydrogenase, and this enzyme was also purified from isoprene-grown cells. The homodimeric enzyme (two subunits of 25 kDa each) showed a high activity for HGMB, whereas simple primary and secondary alcohols were not oxidized. The enzyme catalyzed the sequential oxidation of the alcohol function to the corresponding aldehyde and carboxylic acid and followed Michaelis-Menten kinetics with respect to NAD+ and HGMB. The results suggest that the initial steps in isoprene metabolism are a monooxygenase-catalyzed conversion to isoprene monoxide, a GST-catalyzed conjugation to HGMB, and a dehydrogenase-catalyzed two-step oxidation to 2-glutathionyl-2-methyl-3-butenoic acid.     

Characterization of the gene cluster involved in isoprene metabolism in Rhodococcus sp. strain AD45

The genes involved in isoprene (2-methyl-1,3-butadiene) utilization in Rhodococcus sp. strain AD45 were cloned and characterized. Sequence analysis of an 8.5-kb DNA fragment showed the presence of 10 genes of which 2 encoded enzymes which were previously found to be involved in isoprene degradation: a glutathione S-transferase with activity towards 1,2-epoxy-2-methyl-3-butene (isoI) and a 1-hydroxy-2-glutathionyl-2-methyl-3-butene dehydrogenase (isoH). Furthermore, a gene encoding a second glutathione S-transferase was identified (isoJ). The isoJ gene was overexpressed in Escherichia coli and was found to have activity with 1-chloro-2,4-dinitrobenzene and 3,4-dichloro-1-nitrobenzene but not with 1, 2-epoxy-2-methyl-3-butene. Downstream of isoJ, six genes (isoABCDEF) were found; these genes encoded a putative alkene monooxygenase that showed high similarity to components of the alkene monooxygenase from Xanthobacter sp. strain Py2 and other multicomponent monooxygenases. The deduced amino acid sequence encoded by an additional gene (isoG) showed significant similarity with that of alpha-methylacyl-coenzyme A racemase. The results are in agreement with a catabolic route for isoprene involving epoxidation by a monooxygenase, conjugation to glutathione, and oxidation of the hydroxyl group to a carboxylate. Metabolism may proceed by fatty acid oxidation after removal of glutathione by a still-unknown mechanism.     

Metabolism of 2-Methylpropene (Isobutylene) by the Aerobic Bacterium Mycobacterium sp. Strain ELW1

An aerobic bacterium (Mycobacterium sp. strain ELW1) that utilizes 2-methylpropene (isobutylene) as a sole source of carbon and energy was isolated and characterized. Strain ELW1 grew on 2-methylpropene (growth rate = 0.05 h⁻¹) with a yield of 0.38 mg (dry weight) mg 2-methylpropene⁻¹. Strain ELW1 also grew more slowly on both cis- and trans-2-butene but did not grow on any other C₂ to C₅ straight-chain, branched, or chlorinated alkenes tested. Resting 2-methylpropene-grown cells consumed ethene, propene, and 1-butene without a lag phase. Epoxyethane accumulated as the only detected product of ethene oxidation. Both alkene consumption and epoxyethane production were fully inhibited in cells exposed to 1-octyne, suggesting that alkene oxidation is initiated by an alkyne-sensitive, epoxide-generating monooxygenase. Kinetic analyses indicated that 1,2-epoxy-2-methylpropane is rapidly consumed during 2-methylpropene degradation, while 2-methyl-2-propen-1-ol is not a significant metabolite of 2-methylpropene catabolism. Degradation of 1,2-epoxy-2-methylpropane by 2-methylpropene-grown cells led to the accumulation and further degradation of 2-methyl-1,2-propanediol and 2-hydroxyisobutyrate, two sequential metabolites previously identified in the aerobic microbial metabolism of methyl tert-butyl ether (MTBE) and tert-butyl alcohol (TBA). Growth of strain ELW1 on 2-methylpropene, 1,2-epoxy-2-methylpropane, 2-methyl-1,2-propanediol, and 2-hydroxyisobutyrate was fully inhibited when cobalt ions were omitted from the growth medium, while growth on 3-hydroxybutyrate and other substrates was unaffected by the absence of added cobalt ions. Our results suggest that, like aerobic MTBE- and TBA-metabolizing bacteria, strain ELW1 utilizes a cobalt/cobalamin-dependent mutase to transform 2-hydroxyisobutyrate. Our results have been interpreted in terms of their impact on our understanding of the microbial metabolism of alkenes and ether oxygenates.     

Degradation 1,2-dimethylbenzene by Corynebacterium strain C125

In an attempt to obtain bacteria growing on 1,2-dimethylbenzene as sole carbon and energy source two different strains were isolated. One was identified as an Arthrobacter strain, the other as a Corynebacterium strain. Corynebacterium strain C125 was further investigated. The organism was not capable to grow on 1,3- and 1,4-dimethylbenzene. cis-1,2-Dihydroxycyclohexa-3,5-diene oxidoreductase and 3,4-dimethylcatechol-2,3-dioxygenase activity was found in cell extracts. When 3,4-dimethylcatechol was added to cell extract of 1,2-dimethylbenzene-grown cells, first a compound with the spectral properties of 2-hydroxy-5-methyl-6-oxo-2,4-heptadienoate was formed and subsequently acetate was produced. It is proposed that dioxygenases are involved in the initial steps of 1,2-dimethylbenzene degradation, and ring opening proceeds via meta-cleavage.     

Aliphatic 3,4-epoxyalcohols: Metabolism by epoxide hydrase and mutagenic activity

Rabbit hepatic microsomal epoxide hydrase catalyzes the rapid hydrolysis of 1,2-epoxy-4-heptanol to 1,2,4-heptanetriol. Both diastereomers of the substrate are hydrolyzed, and both product diastereomers are formed. Similarly, both cis- and trans-3,4-epoxy-1-hexanol are hydrolyzed, albeit more slowly, to give 1,3,4-hexanetriol. The trans isomer gives exclusively one diastereomer (erythro) of the triol, while the cis isomer gives the other diastereomer (threo). The product expected if a primary cationic intermediate were to be formed and trapped intramolecularly during the hydrolysis of 1,2-epoxy-4-heptanol, 2-propyl-4-tetrahydrofuranol, was not observed. A comparison of the mutagenic activity in the Ames test of 1-heptane, 1-hepten-4-ol, 1,2-epoxyheptane, and 1,2-epoxy-4-heptanol revealed that only the latter is a detectable mutagen. A vicinal hydroxyl therefore does not interfere significantly with enzymatic epoxide hydrolysis, but it does enhance the bioalkylating potential of even an aliphatic epoxide.     

Hemoglobin adducts and micronuclei in rodents after treatment with isoprene monoxide or butadiene monoxide

1,3-Butadiene and isoprene (2-methyl-1,3-butadiene) are chemically related substances that are carcinogenic to rodents. The overall aim of this work is to elucidate the role of the genotoxic action of diepoxide metabolites in the carcinogenesis of the dialkenes. In vivo doses of the diepoxide metabolites were measured through reaction products with hemoglobin (Hb adducts) in studies of induced micronuclei (MN) in rodents. In the reaction with N-terminal valine in Hb, diepoxybutane and isoprenediepoxide form ring-closed adducts, pyrrolidines [N,N-(2,3-dihydroxy-1,4-butadiyl)valine and N,N-(2,3-dihydroxy-2-methyl-1,4-butadiyl)valine, respectively]. The method applied for Hb-adduct measurement is based on tryptic degradation of the protein and liquid chromatography electrospray ionisation tandem mass spectrometry (LC-ESI-MS/MS) analysis. Mice were given single i.p. injections of the monoepoxides of butadiene and isoprene, 1,2-epoxy-3-butene or 1,2-epoxy-2-methyl-3-butene, respectively. Rats were treated in the same way with 1,2-epoxy-3-butene. In mice pyrrolidine adduct levels increased with increasing administered doses of the monoepoxides. The in vivo dose of diepoxybutane was on average twice as high (0.29+/-0.059 mMh) as the in vivo dose of isoprenediepoxide (0.15+/-0.053 mMh) per administered dose (mmol/kg body weight) of the monoepoxides. In mice the genotoxic effects of the two monoepoxides, measured as the increase in the frequencies of micronuclei (MN), were approximately linearly correlated to the in vivo doses of the diepoxides (except at the highest dose of diepoxybutane). In rats the pyrrolidine-adduct levels from diepoxybutane were below the limit of quantification at all administered doses of 1,2-epoxy-3-butene and no significant increase was observed in the frequency of MN. Measurement of the ring-closed adducts to N-termini in Hb by the applied method permits analysis of in vivo doses of diepoxybutane and isoprenediepoxide, which may be further used for the elucidation of the mechanisms of carcinogenesis of butadiene and isoprene.     

Degradation of Phenanthrene and Anthracene by Cell Suspensions of Mycobacterium sp. Strain PYR-1

Cultures of Mycobacterium sp. strain PYR-1 were dosed with anthracene or phenanthrene and after 14 days of incubation had degraded 92 and 90% of the added anthracene and phenanthrene, respectively. The metabolites were extracted and identified by UV-visible light absorption, high-pressure liquid chromatography retention times, mass spectrometry, ¹H and ¹³C nuclear magnetic resonance spectrometry, and comparison to authentic compounds and literature data. Neutral-pH ethyl acetate extracts from anthracene-incubated cells showed four metabolites, identified as cis-1,2-dihydroxy-1,2-dihydroanthracene, 6,7-benzocoumarin, 1-methoxy-2-hydroxyanthracene, and 9,10-anthraquinone. A novel anthracene ring fission product was isolated from acidified culture media and was identified as 3-(2-carboxyvinyl)naphthalene-2-carboxylic acid. 6,7-Benzocoumarin was also found in that extract. When Mycobacterium sp. strain PYR-1 was grown in the presence of phenanthrene, three neutral metabolites were identified as cis- and trans-9,10-dihydroxy-9,10-dihydrophenanthrene and cis-3,4-dihydroxy-3,4-dihydrophenanthrene. Phenanthrene ring fission products, isolated from acid extracts, were identified as 2,2′-diphenic acid, 1-hydroxynaphthoic acid, and phthalic acid. The data point to the existence, next to already known routes for both gram-negative and gram-positive bacteria, of alternative pathways that might be due to the presence of different dioxygenases or to a relaxed specificity of the same dioxygenase for initial attack on polycyclic aromatic hydrocarbons.     

Flavonoids and tannins of Acacia species

The heartwoods of Acacia giraffae and A. galpinii were selected from South African Acacias as representative of those with abnormally high and minimal tannin contents respectively. A. galpinii contains amongst other analogues, the first natural (+)-2,3-trans-3,4-trans-teracacidin (7,8,4′-trihydroxy-flavan-3,4-diol and novel 3-O-methyl-, 7,8-di-O-methyl- and 7,8,4′-tri-O-methylflavonol analogues. (−)-2,3-cis-3,4-cis-Melacacidin (7,8,3′,4′-tetrahydroxyflavan-3,4-diol) is also present, but tannins are absent. By contrast, from the large excess of leueofisetinidin tannins which characterizes the wood of A. giraffae, only (+)-catechin, (+)-2,3-trans-3,4-trans-leucofisetinidin (7,3′,4′,trihydroxyflavan-3,4-diol and all-trans-(+)-leueofisetinidin-(+)-catechin could be isolated.     

Conjugation of isoprene monoepoxides with glutathione, catalyzed by alpha, mu, pi and theta-class glutathione S-transferases of rat and man

In the present study, the enzymatic conjugation of the isoprene monoepoxides 3,4 epoxy-3-methyl-1-butene (EPOX-I) and 3,4-epoxy-2-methyl-1-butene (EPOX-II) with glutathione was investigated, using purified glutathione S-transferases (GSTs) of the alpha, mu, pi and theta-class of rat and man. HPLC analysis of incubations of EPOX-I and EPOX-II with [35S]glutathione (GSH) showed the formation of two radioactive fractions for each isoprene monoepoxide. The structures of the EPOX-I and EPOX-II GSH conjugates were elucidated with 1H-NMR analysis. As expected, two sites of conjugation were found for both isoprene epoxides. EPOX-II was conjugated more efficiently than EPOX-I. In addition, the mu and theta class glutathione S-transferases were much more efficient than the alpha and pi class glutathione S-transferases, both for rat and man. Because the mu- and theta-class glutathione S-transferases are expressed in about 50 and 40-90% of the human population, respectively, this may have significant consequences for the detoxification of isoprene monoepoxides in individuals who lack these enzymes. Rat glutathione S-transferases were more efficient than human glu tathione S-transferases: rat GST T1-1 showed about 2.1-6.5-fold higher activities than human GST T1-1 for the conjugation of both EPOX-I and EPOX-II, while rat GST M1-1 and GST M2-2 showed about 5.2-14-fold higher activities than human GST M1a-1a. Most of the glutathione S-transferases showed first order kinetics at the concentration range used (50-2000 microM). In addition to differences in activities between GST-classes, differences between sites of conjugation were found. EPOX-I was almost exclusively conjugated with glutathione at the C4-position by all glutathione S-transferases, with exception of rat GST M1-1, which also showed significant conjugation at the C3-position. This selectivity was not observed for the conjugation of EPOX-II. Incubations with EPOX-I and EPOX-II and hepatic S9 fractions of mouse, rat and man, showed similar rates of GSH conjugation for mouse and rat. Compared to mouse and rat, human liver S9 showed a 25-50-fold lower rate of GSH conjugation.     

Synthesis of trans-4-Amino-1-hydroxy-2-methyl-2-butene from Isoprene

A novel synthetic pathway to trans-4-amino-1-hydroxy-2-methyl-2-butene (7), a useful synthetic intermediate of zeatin, is presented here. On selective monophthalimide formation, the trans-1, 4-dibromo-2-methyl-2-butene (10) prepared from isoprene (1) predominantly gives trans-1-bromo-2-methyl-4-phthalimido-2-butene (11). The compound (11) is converted to 7 via trans-1-acetoxy-2-methyl-4-phthalimido-2-butene (6). The overall yield of 7 from 1 is 33.6%. Base-catalyzed hydrolysis of 11 also gives 7 directly. Zeatin can be prepared by the condensation of 7 with 6-chloropurine.     

Cytogenetic and antineoplastic effects by newly synthesised steroidal alkylators in lymphocytic leukaemia P388 cells in vivo

Volatile organic compounds (VOCs) exert their carcinogenic activity through the production of epoxide metabolites. Because of their high reactivity some epoxides are also produced in the chemical industry for the synthesis of other compounds. Therefore, human exposure to VOCs epoxides does occur and may be an important human health concern. In this study, the in vitro genotoxic potential of epoxides originating from 1,3-butadiene (3,4-epoxy-1-butene: EB; 1,2:3,4-diepoxybutane: DEB), isoprene (3,4-epoxy-2-methyl-1-butene: IO), styrene (styrene-7,8-oxide: SO), propylene (propylene oxide: PO) and 1-butene (1,2-epoxy-butane: BO) in human peripheral blood mononuclear cells (PBMCs) and promyelocytic leukaemia cells (HL60) was measured with the comet assay (single-cell gel electrophoresis, SCGE). The effect of inclusion of foetal calf serum (FCS, 5%) in the cell-culture medium and different durations of exposure (2h, 24h) were also investigated. All epoxides tested produced DNA damage in a concentration range that did not reduce cell viability. HL60 cells were more resistant than PBMCs to the DNA damage induced by the different epoxides. With the exception of IO, the treatment for 24h resulted in an increase of DNA damage. FCS slightly protected PBMCs from the genotoxic effects induced by IO and BO, whilst no such effect was noted for the other compounds. Overall, the dose-dependent effects that were seen allowed us to define a genotoxicity scale for the different epoxides as follows: SO>EB>DEB>IO>PO>BO, which is in partial agreement with the International Agency for Research on Cancer (IARC) classification of the carcinogenic hazards.     

Conversion of 5-(1,2-epoxy-2,6,6-trimethylcyclohexyl) -3-methylpenta-cis-2-trans-4-dienoic acid into abscisic acid in plants

(±)-5-(1,2-Epoxy-2,6,6-trimethylcyclohexyl) -3-methyl[2-¹⁴C]penta-cis-2-trans-4-dienoic acid is converted into abscisic acid by tomato fruit in 1.8% yield (or 3.6% of one enantiomer if only one is utilized) and 15% of the abscisic acid is derived from the precursor. The 2-trans-isomer is not converted. The amounts of [2-³H]mevalonate incorporated into abscisic acid have shown that the 40-times higher concentration of (+)-abscisic acid in wilted wheat leaves in comparison with unwilted ones reported by Wright & Hiron (1969) arises by synthesis. The conversion of (±)-5-(1,2-epoxy-2,6,6-trimethylcyclohexyl) -3-methyl-[2-¹⁴C]penta-cis-2-trans-4-dienoic acid into abscisic acid by wheat leaves is also affected in the same way by wilting and it is concluded from this that the epoxide or a closely related compound derived from it is on the biosynthetic pathway leading to abscisic acid. The oxygen of the epoxy group was shown, by ¹⁸O-labelling, to become the oxygen of the tertiary hydroxyl group of abscisic acid.     

Degradation of trans-1,2-dichloroethene by mixed and pure cultures of methanotrophic bacteria

Summary Out of seven chlorinated aliphatic hydrocarbons tested, only trans-1,2-dichloroethene was relatively non-toxic for a mixed methanotrophic culture. The compound was degraded at a rate of 0.4 mol/mg protein·h^-1 and liberation of inorganic chloride was observed. Trans-2,3-dichlorooxirane was formed as an intermediate which was converted further only by chemical transformation with a half life of 31 h. From the consortium, a pure culture was isolated and found to be capable of degradation of trans-1,2-dichloroethene when grown in the presence of methane or methanol. The ability of cometabolic degradation of this compound was not specific for this isolate, since Methylomonas methanica NCIB11130 and Methylosinus trichosporium OB3b also showed degradation of trans-1,2-dichloroethene when grown with methane as sole carbon source.Abbreviations t12DCE trans-1,2-dichloroethene - t23DCO trans-2,3-dichlorooxirane - c23DCO cis-2,3-dichlorooxirane - ¹H-NMR proton nuclear magnetic resonance     

Photo-oxygenation of α-Ionone

Photo-oxygenation of α-ionone was studied to clarify the relationship between the maturity of aroma and photo-oxygenative change of α-ionone. α-Ionone was converted to oxygenated derivatives which were identified as 2,3-epoxy-β-ionone, 3,4-epoxy-α-ionone, 4-keto-β-ionone (trans- and cis-form), 5-keto-α-ionone and 3,4-dihydroxy-α-ionone.     

Gaseous alkene biotransformation and enantioselective epoxyalkane formation by Nocardioides sp. strain JS614

Enantiopure epoxides are valuable intermediates in the synthesis of optically pure biologically active fine chemicals (e.g., pharmaceuticals) that are often difficult to produce by chemical approaches. An attractive alternative is biological synthesis by microorganisms expressing stereoselective enzymes. In this study, we investigated the ability of ethene-grown Nocardioides sp. strain JS614 to produce highly enantio-enriched epoxyalkanes via stereoselective monooxygenase-mediated alkene epoxidation. Ethene-grown JS614 cells transformed propene, 1-butene, and trans-2-butene to their corresponding epoxyalkanes at rates ranging from 27.1 to 44.0 nmol/min mg protein. Chiral gas chromatography analysis revealed that R-1,2-epoxypropane, R-1,2-epoxybutane, and trans-2R,3R-epoxybutane were produced in enantiomeric excess (e.e.) of 98%, 74%, and 82%, respectively. Ethene-grown JS614 cells also preferentially transformed trans-2S,3S-epoxybutane from a racemic mixture, but could not resolve racemic 1,2-epoxypropane. Glucose facilitated increased epoxyalkane production by ethene-grown JS614 cells. However, after 22 h of propene biotransformation with 20 mM glucose, 84% of ethene-grown JS614 cells lost membrane integrity and the remaining live cells were not viable. Propene biotransformation by JS614 was extended beyond 22 h and 54% more epoxypropane was produced when cells were resuspended in fresh buffer + glucose at 8-h intervals. We conclude that JS614 is a promising new biocatalyst for applications that involve enantiopure epoxide production.     

Reductive Dechlorination of Tetrachloroethene to Ethene by a Two-Component Enzyme Pathway

Two membrane-bound, reductive dehalogenases that constitute a novel pathway for complete dechlorination of tetrachloroethene (perchloroethylene [PCE]) to ethene were partially purified from an anaerobic microbial enrichment culture containing Dehalococcoides ethenogenes 195. When titanium(III) citrate and methyl viologen were used as reductants, PCE-reductive dehalogenase (PCE-RDase) (51 kDa) dechlorinated PCE to trichloroethene (TCE) at a rate of 20 μmol/min/mg of protein. TCE-reductive dehalogenase (TCE-RDase) (61 kDa) dechlorinated TCE to ethene. TCE, cis-1,2-dichloroethene, and 1,1-dichloroethene were dechlorinated at similar rates, 8 to 12 μmol/min/mg of protein. Vinyl chloride and trans-1,2-dichloroethene were degraded at rates which were approximately 2 orders of magnitude lower. The light-reversible inhibition of TCE-RDase by iodopropane and the light-reversible inhibition of PCE-RDase by iodoethane suggest that both of these dehalogenases contain Co(I) corrinoid cofactors. Isolation and characterization of these novel bacterial enzymes provided further insight into the catalytic mechanisms of biological reductive dehalogenation.     

Metabolism of Fatty Acid Hydroperoxides by Chlorella pyrenoidosa

The green alga Chlorella pyrenoidosa was examined for its ability to metabolize 13-hydroperoxylinoleic and 13-hydroperoxylinolenic acids. The study showed that Chlorella extracts possessed hydroperoxide dehydrase and other enzymes of the jasmonic acid pathway. However, under normal laboratory conditions for culture growth, neither jasmonic acid nor metabolites of the jasmonic acid pathway were present in Chlorella. In vitro enzyme studies also revealed the presence of hydroperoxide lyase activity that cleaved 13-hydroperoxylinoleic or 13-hydroperoxylinolenic acid into two products, 13-oxo-cis-9,trans-11-tridecadienoic acid and pentane (from linoleic acid) or pentene (from linolenic acid). The lyase was heat-labile, insensitive to 50 millimolar KCN, and had an approximate molecular weight of 48,000 as estimated by gel filtration. Two other products, 13-hydroxy-cis-9,trans-11,cis-15-octadecatrienoic acid and 12, 13-trans-epoxy-9-oxo-trans-10,cis-15-octadecadienoic acid, were also observed. Because these compounds are also products of nonenzymic, Fe(II)-catalyzed hydroperoxide decomposition reactions, their presence suggested that the observed lyase activity may occur via a homolytic decomposition mechanism.     

Chemical and enzymatic synthesis of monomeric procyanidins (leucocyanidins or 3′,4′,5,7-tetrahydroxyflavan-3,4-diols) from (2R,3R)-dihydroquercetin

The major product from the reduction of (2R,3R)-dihydroquercetin with sodium borohydride is the 2,3-trans-3,4-trans isomer of leucocyanidin [(2R,3S,4R-3,3′,4,4′,5,7-hexahydroxyflavan] whereas the enzymatic reduction product is the 2,3-trans-3,4-cis isomer [(2R,3S,4S)-3,3′,4,4′,5,7-hexahydroxyflavan]. The 3,4-trans isomer may be partly converted to the 3,4-cis isomer under mild acid conditions. The 3,4-cis isomer is more acid-labile, and more reactive both chemically with thiols and enzymatically with a diol reductase, than the 3,4-trans isomer.     

Natural and synthetic diastereoisomeric (?)-3′,4′,7-trihydroxyflavan-3,4-diols

1. Rhodesian copalwood (Guibourtia coleosperma) contains three diastereo-isomeric leuco-fisetinidins. These consist of the (−)-2,3-cis–3,4-cis (2R,3R,4R) and (−)-2,3-cis–3,4-trans (2R,3R,4S) 3′,4′,7-trihydroxyflavan-3,4-diols, and the third was shown to be a 2,3-trans–3,4-cis isomer by means of paper ionophoresis. 2. There occurrence in similar proportions as tannin precursors also in the tropical hardwoods G. tessmannii and G. demeusii implies a close taxonomic relationship between these, and with G. coleosperma. 3. Epimerization of the natural (−)-3′,4′,7- trihydroxy-2,3-trans-flavan-3,4-trans-diol affords a mixture from which the (−)-2,3-cis–3,4-cis isomer was separated readily, but the (−)-2,3-trans–3,4-cis isomer was obtained with difficulty. These were formed by epimerization of the (−)-2,3-trans–3,4-trans isomer at C-2 and C-4, and at C-4, respectively.     

Chloroethene Biodegradation in Sediments at 4°C

Microbial reductive dechlorination of [1,2-¹⁴C]trichloroethene to [¹⁴C]cis-dichloroethene and [¹⁴C]vinyl chloride was observed at 4°C in anoxic microcosms prepared with cold temperature-adapted aquifer and river sediments from Alaska. Microbial anaerobic oxidation of [1,2-¹⁴C]cis-dichloroethene and [1,2-¹⁴C]vinyl chloride to ¹⁴CO₂ also was observed under these conditions.