Phytochemistry (v.67, #16)

Rodney B. Croteau by Norman G. Lewis (1704-1705).

Rod Croteau: 35 years of terrific terpene biochemistry by Jonathan Gershenzon (1706-1707).

Structures, biogenetic relationships, and cytotoxicity of pimarane-derived diterpenes from Petalostigma pubescens by Mary H. Grace; Yinghua Jin; George R. Wilson; Robert M. Coates (1708-1715).
Four diterpenes, 5,9-syn-rosanes petalostigmones A and B (1 and 2), the erythorxylane petalostigmone C (3), and the norditerpene lactone pubescenone (4), together with the known ent-cleistanthane diterpene (−)-sonderianol, were isolated from Petalostigma pubescens. Biogenetic schemes are presented to rationalize the structures of these natural products.Extraction of Petalostigma pubescens heartwood followed by chromatographic purifications and crystallizations afforded five tricyclic diterpenes: 5,9-syn-rosanes petalostigmones A and B (1 and 2), the erythroxylane petalostigmone C (3), the norditerpene lactone pubescenone (4), and the known ent-cleistanthane diterpene (−)-sonderianol (5). The structures and relative stereochemistry were elucidated by means of spectroscopic methods, chemical correlations, and, in the cases of 1 and 4, by X-ray crystallographic analyses. The new isolates 14 are assumed to belong to the same absolute configurational family (9αCH3) of ent-pimarane-derived diterpenes as the known co-occurring (−)-5 (10αCH3). Biogenetic schemes originating from a common ent-copalyl diphosphate intermediate are presented to rationalize the structures of these natural products. A novel ring contraction–ring expansion mechanism is suggested to account for the 7-membered B ring of pubescenone. Compounds 15 were evaluated for their cytotoxicity; sonderianol (5) showed the highest activity against mouse leukemia cell lines L1210, P388 and mouse liver cancer cells HEPA1c1c7.
Keywords: Petalostigma pubescens; Euphorbiaceae; Heartwood; Diterpene; Rosane; Erythroxylane; Nor diterpene; Cleistanthane; Biogenetic pathways;

Phytosterol biosynthesis pathway in Mortierella alpina by W. David Nes; Shawn D. Nichols (1716-1721).
The construction of three 24-methyl sterol side chains by the action of a common sterol methyltransferase was suggested by chemical identification studies and incubation of Mortierella alpina mycelium with methionine-methyl-2H3.The Zygomycetes fungus Mortierella alpina was cultured to growth arrest to assess the phytosterol biosynthesis pathway in a less-advanced fungus. The mycelium was found to produce 13 sterols, but no ergosterol. The sterol fractions were purified to homogeneity by HPLC and their identifies determined by a combination of GC–MS and 1H NMR spectroscopy. The principal sterol of the mycelium was cholesta-5, 24-dienol (desmosterol) (83%), with lesser amounts of 24β-methyl-cholesta-5,25(27)-dienol (codisterol) (2%), 24-methyldesmosterol (6%), 24(28)-methylene cholesterol (3%) and lanosterol (3%) and several other minor compounds (3%). The total sterol accounted for approximately 0.07% of the mycelial dry wt. Mycelium fed methionine-methyl-2H3 for 6 days, generated 3 2H-24-methyl(ene) sterols, [C28-2H2]24(28)-methylenecholesterol, [C28-2H3]24-methylcholesta-5,24-dienol and [C28-2H3]24β-methyl-cholesta-5,25(27)-dienol. The formation of the 24-methyl sterols seems to be catalyzed by the direct methylation of a common Δ24-acceptor sterol thereby bypassing the intermediacy of an isomerization step for rearrangement of the Δ24(28)-bond to Δ25(25)-position as operates in Ascomycetes fungi and all plants.
Keywords: Sterol methyltransferase; Cholesterol; Ergosterol biosynthesis; Isotope labeling; Mortierella alpina; Fungal evolution;

Selective disruption of wheat secondary metabolism by herbicide safeners by Ian Cummins; Melissa Brazier-Hicks; Maciej Stobiecki; Rafa Fraǹski; Robert Edwards (1722-1730).
Treatment of wheat seedlings with the herbicide safener cloquintocet mexyl causes a selective loss of flavone C-glycosides of luteolin ≫ apigenin = 3′-O-methylluteolin and an accumulation of the methylated flavone tricin and ferulic acid.In wheat (Triticum aestivum L.), treatment with herbicide safeners enhances the expression of enzymes involved in pesticide detoxification and reduces crop sensitivity to herbicides. Since these same enzymes are involved in plant secondary metabolism, it was of interest to determine whether or not the safener cloquintocet mexyl perturbed phenolic metabolism in wheat seedlings. LC/ESI/MS analysis identified 14 phenolic substrates in the shoots of young wheat plants. Fragmentation imposed by collision induced dissociation identified specific C-glycosidic conjugates of 4′,5,7-trihydroxflavone (apigenin), 3′,4′,5,7-tetrahydroxyflavone (luteolin) and 3′-O-methylluteolin. Treatment of 7-day-old wheat shoots with cloquintocet mexyl resulted in an accelerated depletion of the conjugates of all three flavones, most notably with the glycosides of luteolin. In contrast, safener treatment caused the selective accumulation of 4′,5,7-trihydroxy-3′,5′-dimethoxyflavone (tricin) and the phenylpropanoid ferulic acid. Changes in phenolic content were associated with an increase in O-methyltransferase and C-glucosyltransferase activity toward flavonoid substrates as well as the classic enhancement of detoxifying glutathione transferases. Our results suggest that in addition to altering the capacity of wheat to metabolise herbicides and other xenobiotics, safeners can also cause a selective shift in the metabolism of endogenous phenolics.
Keywords: Gramineae; Triticum aestivum; Flavonoids; C-Glucosyltransferase; C-Glycosides; Glutathione transferases; Herbicide metabolism; O-Methyltransferases; Phenylpropanoids;

Algal photobionts (Coccomyxa, Trebouxia spp.) from lichens were challenged with environmentally relevant concentrations of copper or lead and effects on their lipid metabolism assessed.We evaluated the ability of heavy metals (copper, lead) to alter lipid metabolism in four algal lichen photobionts following short term exposure. Metal concentrations (10 μM) were equivalent to environmentally relevant levels that have been reported to have effects on intact algae. The algae were grown under normal or deficient phosphate conditions to assess any interactions with the heavy metal stress. Given the frequent sensitivity of lichens to copper and lead, there were surprisingly small changes on lipid metabolism, as assessed by radiolabelling from [1-14C]acetate. The main effects, which were seen in a number of cases, were an overall inhibition of total lipid labelling and a relative increase in the labelling of triacylglycerols in the non-polar fraction. Both of these changes can be viewed as reflecting general toxicity of heavy metals. The Coccomyxa photobiont species were more sensitive than Trebouxia species, which fits with the general distribution of the latter in lichens inhabiting harsh environments.
Keywords: Lichen photobionts; Coccomyxa mucigena; Coccomyxa peltigera variolosae; Trebouxia erici; Trebouxia aggregata; Lipid metabolism;

Cultures of the ginseng root pathogen Pythium irregulare selectively metabolize 20(S)-protopanaxadiol ginsenosides (e.g., Rb1, Rb2, Rc and Rd) into a single compound, ginsenoside F2, via an extracellular glycosidase(s).The role of ginseng saponins (ginsenosides) as modulators or inhibitors of disease is vague, but our earlier work supports the existence of an allelopathic relationship between ginsenosides and soilborne microbes. Interestingly, this allelopathy appears to significantly promote the growth of the important ginseng pathogen, Pythium irregulare while inhibiting that of an antagonistic non-pathogenic fungus, Trichoderma hamatum. Herein we report on the apparent selective metabolism of 20(S)-protopanaxadiol ginsenosides by an extracellular glycosidase from P. irregulare. Thus, when P. irregulare was cultured in the presence of a purified (>90%) ginsenoside mixture, nearly all of the 20(S)-protopanaxadiol ginsenosides (Rb1, Rb2, Rc, Rd, and to a limited extent G-XVII) were metabolized into the minor ginsenoside F2, at least half of which appears to be internalized by the organism. No metabolism of the 20(S)-protopanaxatriol ginsenosides (Rg1 and Re) was evident. By contrast, none of the ginsenosides added to the culture medium of the non-pathogenic fungus T. hamatum were metabolized. The metabolism of 20(S)-protopanaxadiol ginsenosides by P. irregulare appears to occur through the hydrolysis of terminal monosaccharide units from disaccharides present at C-3 and/or C-20 of ginsenosides Rb1, Rc, Rb2, Rd and G-XVII to yield one major product, ginsenoside F2 and one minor product (possibly G-III). A similar transformation of ginsenosides was observed using a crude protein preparation isolated from the spent medium of P. irregulare cultures.
Keywords: Panax quinqufolius; Araliaceae; Pythium irregulare; Trichoderma hamatum; Ginseng; Ginsenosides; Extracellular glycosidase;

Metabolite profiling of carotenoid and phenolic pathways in mutant and transgenic lines of tomato: Identification of a high antioxidant fruit line by Marianne Long; David J. Millar; Yukiko Kimura; Georgina Donovan; Jon Rees; Paul D. Fraser; Peter M. Bramley; G. Paul Bolwell (1750-1757).
Mutant and transgenic tomato fruit have been profiled for carotenoids and phenolics to identify high antioxidant lines.Plant secondary metabolism is highly regulated within the major pathways to terpenoids, phenolics and alkaloids. Such regulation can occur at multiple levels from transcription through to the compartmentation of the product. However, the possibility exists for cross-talk between these pathways, the regulation of which is largely unknown at present. Such phenomena are important to understand in the application of plant breeding, where unintended effects of transgenesis or mutation can have an impact on the environment or human health. In an effort to improve dietary antioxidant content of crop plants, the tomato has been a major focus of effort for engineering both lipophilic antioxidants such as carotenoids and hydrophilic antioxidants such as flavonoid glycosides. In this study, a panel of transgenic and mutant tomato lines has been subjected to metabolite profiling in comparison with wild type Ailsa Craig for both carotenoids and phenolics. A range of mutants and transgenic lines were selected showing a range of phenotypes varying from down-regulation through to increased levels of lycopene and β-carotene. All mutants altered in structural genes for carotenoid biosynthesis showed that perturbations in carotenoid biosynthesis do not generally alter phenolic or flavonoids content significantly even when devoid of carotenoids. Reciprocally, the down-regulation of ferulate 5-hydroxylase had no effect on carotenoid content. In contrast mutants defective in light perception such as the high pigment (hp-1) and LA3771 possess elevated chlorogenic acid and rutin as well as increased carotenoid content. These lines can act as the hosts for further genetic manipulation for increased antioxidant content.
Keywords: Lycopersicon esculentum; Solanaceae; Tomato; Carotenoids; Flavonoids; Phenylpropanoids; Metabolite profiling;

A single Catharanthus roseus flower cultivar altered in vindoline accumulation was successfully identified by metabolic profiling. This cultivar had a 10-fold lower tabersonine-16-hydroxylase activity than lines accumulating normal levels of vindoline.The Madagascar periwinkle [Catharanthus roseus (L.) G. Don] is a commercially important horticultural flower species and is the only source of the monoterpenoid indole alkaloids (MIAs), vinblastine and vincristine, key pharmaceutical compounds used to combat a number of different cancers. The present study uses high performance liquid chromatography for metabolic profiling of the MIAs extracted from seedlings and young leaves of 50 different flowering cultivars of C. roseus to show that, except for a single low vindoline cultivar (Vinca Mediterranean DP Orchid), they accumulate similar levels of MIAs. Further enzymatic studies with extracts from young leaves and from developing seedlings show that the low vindoline cultivar has a 10-fold lower tabersonine-16-hydroxylase activity than those of C. roseus cv. Little Delicata. It is concluded that rapid metabolic and more selective enzymatic profiling of Catharanthus mutants could be useful for the identification of a range of altered MIA biosynthesis lines.
Keywords: Catharanthus roseus; Apocynaceae; Metabolic and enzymatic profiling; Monoterpenoid indole alkaloids; Low vindoline cultivar;

Pinus taeda phenylpropenal double-bond reductase: Purification, cDNA cloning, heterologous expression in Escherichia coli, and subcellular localization in P. taeda by Hiroyuki Kasahara; Ying Jiao; Diana L. Bedgar; Sung-Jin Kim; Ann M. Patten; Zhi-Qiang Xia; Laurence B. Davin; Norman G. Lewis (1765-1780).
A phenylpropenal double-bond reductase (PPDBR) was obtained from cell suspension cultures of loblolly pine (Pinus taeda L.). Its cDNA was subsequently cloned, with the functional recombinant protein expressed in Escherichia coli and characterized. PPDBR readily converted both dehydrodiconiferyl and coniferyl aldehydes into dihydrodehydrodiconiferyl and dihydroconiferyl aldehydes, when NADPH was added as cofactor.A phenylpropenal double-bond reductase (PPDBR) was obtained from cell suspension cultures of loblolly pine (Pinus taeda L.). Following trypsin digestion and amino acid sequencing, the cDNA encoding this protein was subsequently cloned, with the functional recombinant protein expressed in Escherichia coli and characterized. PPDBR readily converted both dehydrodiconiferyl and coniferyl aldehydes into dihydrodehydrodiconiferyl and dihydroconiferyl aldehydes, when NADPH was added as cofactor. However, it was unable to reduce directly either the double bond of dehydrodiconiferyl or coniferyl alcohols in the presence of NADPH. During this reductive step, the corresponding 4-proR hydrogen was abstracted from [4R-3H]-NADPH during hydride transfer. This is thus the first report of a double-bond reductase involved in phenylpropanoid metabolism, and which is presumed to be involved in plant defense. In situ mRNA hybridization indicated that the PPDBR transcripts in P. taeda stem sections were localized to the vascular cambium, as well as to radial and axial parenchyma cell types.Additionally, using P. taeda cell suspension culture crude protein extracts, dehydrodiconiferyl and coniferyl alcohols could be dehydrogenated to afford dehydrodiconiferyl and coniferyl aldehydes. Furthermore, these same extracts were able to convert dihydrodehydrodiconiferyl and dihydroconiferyl aldehydes into the corresponding alcohols. Taken together, these results indicate that in the crude extracts dehydrodiconiferyl and coniferyl alcohols can be converted to dihydrodehydrodiconiferyl and dihydroconiferyl alcohols through a three-step process, i.e. by initial phenylpropenol oxidation, then sequential PPDBR and phenylpropanal reductions, respectively.
Keywords: Pinus taeda; Pinaceae; Loblolly pine; Phenylpropenal double bond reductase; Lignans; Lignins; Dihydroconiferyl aldehyde; Dihydrodehydrodiconiferyl aldehyde;

This work reports the use of a calibrated computational approach to provide reasonable estimates of semiquinone stability in quinone natural products and related compounds as a first approximation of redox cycling ability.Quinone metabolites perform a variety of key functions in plants, including pathogen protection, oxidative phosphorylation, and redox signaling. Many of these structurally diverse compounds have been shown to exhibit potent antimicrobial, anticancer, and anti-inflammatory properties, although the exact mechanisms of action are far from understood. Redox cycling has been proposed as a possible mechanism of action for many quinone species. Experimental determination of the essential thermodynamic data (i.e. electrochemical and pK a values) required to predict the propensity towards redox cycling is often difficult or impossible to obtain due to experimental limitations. We demonstrate a practical computational approach to obtain reasonable estimates of these parameters.
Keywords: Hartree–Fock; Density functional theory; Quinone; Semiquinone; Quinol; Redox cycling; Superoxide; Reactive oxygen; Ubiquinone; Semiquinone stability constant; Electrochemistry;

An unusual glucoside from Cleistanthus gracilis by Paulo M. Pinho; Waree Naengchomnong; Anake Kijjoa; Nair Nazareth; Artur M.S. Silva; Graham Eaton; Werner Herz (1789-1792).
Roots and stems of Cleistanthus gracilis furnished a glucoside gracicleistanthoside, the glucoside of 2-hydroxy-8-azabicyclo-(5,2,0)-4,9-epoxynona-5,7-diene.Extraction of roots and stems of Cleistanthus gracilis furnished common triterpenes, plant sterols and the unusual glucoside (+) gracicleistanthoside, the glucoside of 2-β-hydroxy-8-azabicyclo-(5,2,0)-4β,9β-epoxynona-5,7-diene.
Keywords: Cleistanthus gracilis; Phyllanthaceae; Gracicleistanthoside; Glucoside of 2-hydroxy-8-azabicyclo-(5,2,0)-4,9-epoxynona-5,7-diene;

Saponins from the seeds of Mimusops laurifolia by Jacqueline Eskander; Catherine Lavaud; Isabelle Pouny; Hesham S.M. Soliman; S.M. Abdel-Khalik; I.I. Mahmoud (1793-1799).
Three bidesmosidic 16α-hydroxyprotobassic acid saponins were isolated from the seeds of Mimusops laurifolia along with six known saponins, butyroside C, arganine D, Mi-saponin A, tieghemelin A, arganine A and arganine C. The structures were established by spectroscopic methods..Nine saponins were isolated from the seeds of Mimusops laurifolia. Their structures were established using one- and two-dimensional NMR spectroscopy and mass spectrometry. Three of them are identified as: 3-O-(β-d-apiofuranosyl-(1 → 3)-β-d-glucuronopyranosyl)-28-O-(α-l-rhamnopyranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid, 3-O-(β-d-glucopyranosyl-(1 → 3)-β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid and 3-O-(β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosyl)-28-O-(α-l-rhamnopyranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-α-l-arabinopyranosyl)-16α-hydroxyprotobassic acid.
Keywords: Mimusops laurifolia; Sapotaceae; Triterpenoid saponins; 16α-hydroxyprotobassic acid;

A review of the literature and current state of knowledge of the Nep1-like proteins from plant pathogens and saprophytes. The proteins are distinguished by their ability to rapidly activate defense response and cause cell death in dicotyledonous plants.An emerging group of proteins found in many plant pathogens are related to their ability to cause plant cell death. These proteins may be identified by the presence of a common NPP1 (necrosis-inducing Phytophthora protein) domain, and have collectively been named NLPs (Nep1-like proteins). The NLPs are distinguished by their wide distribution across taxa and their broad spectrum of activity against dicotyledonous plants. The function of NLPs is not known but there is strong evidence that they may act as positive virulence factors, accelerating disease and pathogen growth in plant hosts. Interest in NLPs is gaining momentum as more members of this protein family are discovered in more species of plant pathogens.
Keywords: Bacteria; Cell death; Defence; Disease; Elicitor; Fungus; Oomycete; Pathogen; Toxin; Virulence;

Various sampling protocols were employed to study the chemical composition of yew needle waxes with high spatial resolution. GC–MS analyses of the resulting preparations provided direct evidence that the tubular wax crystals on the needle surfaces contained high percentages of alkanediols and nonacosan-10-ol on the abaxial and adaxial surfaces of the needles, respectively.Needles of Taxus baccata L. were covered with tubular epicuticular wax crystals varying in diameters (100 and 250 nm) and lengths (300–500 and 500–1000 nm) on the abaxial and adaxial surfaces, respectively. Various sampling protocols were employed to study the chemical composition of the needle waxes on three different levels of spatial resolution. First, a dipping extraction of whole needles yielded the total cuticular wax mixture consisting of very long chain fatty acids (21%), alkanediols (19%), phenyl esters (15%), and secondary alcohols (9%) together with small amounts of aldehydes, primary alcohols, alkanes, alkyl esters, and tocopherols. Second, waxes from both sides of the needle were sampled separately by brushing with CHCl3-soaked fabric glass. Both sides showed very similar qualitative composition, but differed drastically in quantitative aspects, with nonacosan-10-ol (18%) and alkanediols (33%) dominating the abaxial and adaxial waxes, respectively. Third, the epi- and intracuticular wax layers were selectively sampled by a combination of mechanical wax removal and brushing extraction. This provided direct evidence that the tubular wax crystals contained high percentages of nonacosane-4,10-diol and nonacosane-5,10-diol on the abaxial surface, and nonacosan-10-ol on the adaxial surface of the needles. Together with these compounds, relatively large amounts of fatty acids and smaller percentages of aldehydes, primary alcohols, alkyl esters, and alkanes co-crystallized in the epicuticular layer. In comparison, the intracuticular wax consisted of higher portions of cyclic constituents and aliphatics with relatively high polarity. The formation of the tubular crystals is discussed as a spontaneous physico-chemical process, involving the establishment of gradients between the epi- and intracuticular wax layers and local phase separation.
Keywords: Taxus baccata; Taxaceae; Cuticular wax; Yew needles; Surface composition; Secondary alcohols;

Insect-antifeedant and antibacterial activity of diterpenoids from species of Plectranthus by Julia Wellsow; Renée J. Grayer; Nigel C. Veitch; Tetsuo Kokubun; Roberto Lelli; Geoffrey C. Kite; Monique S.J. Simmonds (1818-1825).
Acetone extracts of leaves of species of Plectranthus (Lamiaceae) were tested for insect-antifeedant and antibacterial activity. An insect-antifeedant beyerane diterpenoid (1) was isolated from P. saccatus, together with several known abietane diterpenoids having both antibacterial and antifeedant activity from P. puberulentus and P. forsteri ‘Marginatus’.Bio-assay guided fractionation of an acetone extract of leaf material from Plectranthus saccatus Benth. resulted in the isolation of a beyerane diterpenoid. This compound, characterised by spectroscopic methods as ent-3β-(3-methyl-2-butenoyl)oxy-15-beyeren-19-oic acid, showed insect antifeedant activity against Spodoptera littoralis. Known quinonoid abietane diterpenoids obtained from new sources included a mixture of the (4R,19R) and (4R,19S) diastereoisomers of coleon A from P. aff. puberulentus J.K. Morton, coleon A lactone from P. puberulentus J.K. Morton, and coleon U and coleon U quinone from P. forsteri ‘Marginatus’ Benth. These compounds, and the crude acetone extracts from the leaf surfaces of 11 species of Plectranthus, were tested for antifeedant activity against S. littoralis, antibacterial activity against Bacillus subtilis and Pseudomonas syringae and antifungal activity against Cladosporium herbarum. The coleon A mixture showed potent antifeedant activity against S. littoralis, whereas coleon U showed the greatest antimicrobial activity.
Keywords: Plectranthus; Lamiaceae; Diterpenoids; Insect antifeedant; Antimicrobial activity;

Tropolactones A–D, four meroterpenoids from a marine-derived fungus of the genus Aspergillus by Mercedes Cueto; John B. MacMillan; Paul R. Jensen; William Fenical (1826-1831).
Cytotoxic meroterpenoids, tropolactones A–D were isolated from the whole broth extract of a marine-derived fungus of the genus Aspergillus. Their structures were established through a variety of two-dimensional NMR techniques. The absolute configuration of tropolactone A was determined using the modified Mosher’s method.Four cytotoxic meroterpenoids, tropolactones A–D, were isolated from the whole broth extract of a marine-derived fungus of the genus Aspergillus. The structures of the meroterpenoids were established through a variety of two-dimensional NMR techniques. The absolute configuration of tropolactone A was determined using the modified Mosher method. Tropolactones A–C contain an interesting substituted 2,4,6-cycloheptatriene (tropone) ring, which presumably arises through an oxidative ring expansion from tropolactone D. Tropolactones A, B and C showed in vitro cytotoxicity against human colon carcinoma (HCT-116) with IC50 values of 13.2, 10.9 and 13.9 μg/mL.

Beccaridiol, an unusual 28-nortriterpenoid from the leaves of Diplectria beccariana by Dae Sik Jang; Bao-Ning Su; Alison D. Pawlus; Young-Hwa Kang; Leonardus B.S. Kardono; Soedarsono Riswan; Johar J. Afriastini; Harry H.S. Fong; John M. Pezzuto; A. Douglas Kinghorn (1832-1837).
A C29-triterpene, beccaridiol (1), a dihydrochalcone natural product, 2′,4′-dihydroxy-3-(4-methoxyphenyl)-propiophenone, as well as three known compounds, have been isolated from an EtOAc-soluble extract of the leaves of Diplectria beccariana.A C29-triterpene, beccaridiol (1), a dihydrochalcone natural product, 2′,4′-dihydroxy-3-(4-methoxyphenyl)-propiophenone (2), as well as three known compounds, 4′-hydroxy-1′,2′-dihydro-β-ionone, 4′-O-methyldavidigenin (3), and ursolic acid, have been isolated from an EtOAc-soluble extract of the leaves of Diplectria beccariana. Beccaridiol (1) was characterized as an ursane-type 28-nortriterpene possessing an unusual aromatic E-ring by spectroscopic data interpretation. The relative configuration of this unusual isolate was established by analyzing the observed NOESY NMR correlations, and the absolute stereochemistry of 1 was then determined based on the circular dichroism (CD) spectrum of its 2,3-di-p-bromobenzoate (1b) derivative. All isolates were evaluated for their potential cancer chemopreventive properties utilizing a cell culture assay to determine quinone reductase induction.
Keywords: Diplectria beccariana; Melastomataceae; Nortriterpenoid; Beccaridiol; Dihydrochalcone; Circular dichroism; Quinone reductase;

Antioxidant activity of prenylated hydroquinone and benzoic acid derivatives from Piper crassinervium Kunth by Lydia F. Yamaguchi; João Henrique G. Lago; Tatiane M. Tanizaki; Paolo Di Mascio; Massuo J. Kato (1838-1843).
A prenylated hydroquinone derivative was isolated from leaves of Piper crassinervium. Its in vitro antioxidant capacity and other prenylated hydroquinones, 4-hydroxybenzoic acids, had their antioxidant activities evaluated using inhibition assays of luminol luminescence, DPPH, and lipoperoxidation.Growing evidence suggests that RNOS (reactive nitrogen and oxygen species) are involved in the damage of biomolecules, contributing to the aetiology of several human diseases. Thus, the demand for antioxidants has stimulated the search for new compounds with potential use in this field. The in vitro antioxidant potential of prenylated hydroquinones and prenylated 4-hydroxy-benzoic acids from fruits of P. crassinervium was evaluated in terms of their capacity to suppress both DPPH (2,2-diphenyl-1-picrylhydrazyl) radical and chemiluminescence produced from luminol, using 2,2′-azo-bis(2-amidinopropane) (ABAP) as a peroxyl radical source. The inhibition of lipid peroxidation was assessed using liposomes from phosphatidylcholine as a membrane model. The prenylated hydroquinones had higher antioxidant activity than the benzoic acids and, among the hydroquinones, the E isomer was more efficient than the Z isomer.
Keywords: Piper crassinervium; Piperaceae; Prenylated hydroquinones; Prenylated benzoic acids; Antioxidants; Lipoperoxidation; DPPH; Chemiluminscence;