Phytochemistry (v.128, #C)

Rare phenolic structures found in the aerial parts of Eriosema laurentii De Wild. by Sylvin Benjamin Ateba; Dieudonné Njamen; Claus Gatterer; Tamara Scherzer; Martin Zehl; Hanspeter Kählig; Liselotte Krenn (5-11).
Recent pharmacological and toxicological investigations of Eriosema laurentii (Leguminosae) have underlined the plausibility of the use of this plant in traditional African medicine. A very complex pattern of phenolic compounds was detected in the tested extracts. Based on these preceding results a detailed phytochemical study was performed and resulted in the isolation and identification of eleven compounds. All are reported in this plant for the first time and four of those are previously undescribed secondary metabolites: 3,4′,6,8-tetrahydroxyflavanone-7-C-glucoside and 3,4′,6,8-tetrahydroxyflavone-7-C-glucoside with an extremely rare substitution pattern as well as 1-[2,4-dihydroxy-3-(2-hydroxy-3-methylbut-3-en-1-yl)phenyl]-3-phenylpropan-1-one and 1-[2,4-dihydroxy-3-(2-hydroxy-3-methylbut-3-en-1-yl)phenyl]-3-(4-methoxyphenyl)-propan-1-one. Their structures were elucidated unambiguously by extensive MS- and NMR-experiments.Display Omitted
Keywords: Eriosema laurentii De Wild; Leguminosae; 3,4′,6,8-tetrahydroxyflavanone-7-C-glucoside; 3,4′,6,8-tetrahydroxyflavone-7-C-glucoside; 1-[2,4-dihydroxy-3-(2-hydroxy-3-methylbut-3-en-1-yl) phenyl]-3-phenylpropan-1-one; 1-[2,4-dihydroxy-3-(2-hydroxy-3-methylbut-3-en-1-yl)phenyl]-3-(4-methoxyphenyl)-propan-1-one; Flavonoids; Hydroxybenzoic acids;

Truncations of xyloglucan xylosyltransferase 2 provide insights into the roles of the N- and C-terminus by Alan T. Culbertson; Adrienne L. Smith; Matthew D. Cook; Olga A. Zabotina (12-19).
Xyloglucan is the most abundant hemicellulose in the primary cell wall of dicotyledonous plants. In Arabidopsis, three xyloglucan xylosyltransferases, XXT1, XXT2, and XXT5, participate in xylosylation of the xyloglucan backbone. Despite the importance of these enzymes, there is a lack of information on their structure and the critical residues required for substrate binding and transferase activity. In this study, the roles of different domains of XX2 in protein expression and catalytic activity were investigated by constructing a series of N- and C-terminal truncations. XXT2 with an N-terminal truncation of 31 amino acids after the predicted transmembrane domain showed the highest protein expression, but truncations of more than 31 residues decreased protein expression and catalytic activity. XXT2 constructs with C-terminal truncations showed increased protein expression but decreased activity, particularly for truncations of 44 or more amino acids. Site-directed mutagenesis was also used to investigate six positively charged residues near the C-terminus and found that four of the mutants showed decreased enzymatic activity. We conclude that the N- and C-termini of XXT2 have important roles in protein folding and enzymatic activity: the stem region (particularly the N-terminus of the catalytic domain) is critical for protein folding and the C-terminus is essential for enzymatic activity but not for protein folding.Xyloglucan xylosyltransferase 2 N-terminus is involved in protein folding and the C-terminus is most likely involved in substrate binding or catalysis.Display Omitted
Keywords: Arabidopsis thalania; Truncated proteins; Xyloglucan xylosyltransferase activity; Xyloglucan;

The effects of meteorological conditions (temperature, rainfall, photosynthetically active solar radiation (PAR) and sunshine duration) and plant growth stages on the quantitative composition of a secondary metabolite – essential oil and its main compounds, in the carvacrol chemotype of Thymus pulegioides L. (Lamiaceae) cultivated in open ground were studied under the same micro-edaphoclimatic environmental conditions for six years. The essential oil was isolated by hydrodistillation, the analysis of monoterpenic phenol carvacrol and the biogenetic precursors (monoterpene hydrocarbons p-cymene and γ-terpinene) were carried out annually using GC-FID and GC-MS. In the carvacrol chemotype investigated in this study, the yield of essential oil varied from 0.72% to 0.98% (CV = 12%) at full flowering stage. Regression analysis showed a significant negative relationship between the amount of essential oil and both temperature and rainfall during T. pulegioides flowering (July) and the period from April (beginning of vegetation) to July, but a strong positive relationship with photosynthetically active solar radiation during April–July (beta = 0.658, p < 0.05). The percentage of carvacrol, p-cymene and γ-terpinene ranged between 16.88 and 29.29% (CV = 18%), 5.54–11.33% (CV = 23%) and 20.60–24.43% (CV = 6%) respectively. Regression analysis showed the significant positive relationship between the percentage of carvacrol and sunshine duration at the flowering stage (in July) (beta = 0.699, p < 0.05); while the negative relationship was established between the percentages of precursors of carvacrol and photosynthetically active solar radiation and sunshine duration. The accumulation of p-cymene, the percentage of which varied most strongly from all investigated chemical compounds, showed significant positive relationships with temperature and rainfall during the period April–July and temperature in July (beta = 0.617, beta = 0.439 and beta = 0.429 respectively, p < 0.05). The analysis of plant growth stages showed that the highest amount of essential oil in carvacrol chemotype of T. pulegioides accumulated at ripening/seed maturity stage. The percentage of carvacrol increased gradually from the stem elongation to the post-flowering/seed maturity stage, overtaking the full flowering stage by 22%. The highest carvacrol content in the T. pulegioides carvacrol chemotype coincided with the highest oil yield during the fruiting stage. The amount of essential oil was also measured at the second full flowering stage, because after cutting the aerial part of the plant at the full flowering stage T. pulegioides often bloom for a second time: the carvacrol chemotype accumulated by 21% lower yield of essential oil at this stage compared to the first flowering, however, only traces of carvacrol and its precursors were found at the second full flowering stage.Display Omitted
Keywords: Thymus pulegioides (Lamiaceae); Large thyme; Hydrodistillation; GC-FID; GC-MS; Essential oil; Carvacrol; p-Cymene; γ-Terpinene; Meteorological conditions; Plant growth stage;

High concentrations of aromatic acylated anthocyanins found in cauline hairs in Plectranthus ciliatus by Monica Jordheim; Kate Calcott; Kevin S. Gould; Kevin M. Davies; Kathy E. Schwinn; Øyvind M. Andersen (27-34).
Vegetative shoots of a naturalized population of purple-leaved plectranthus (Plectranthus ciliatus, Lamiaceae) were found to contain four main anthocyanins: peonidin 3-(6″-caffeoyl-β-glucopyranoside)-5-β-glucopyranoside, peonidin 3-(6″-caffeoyl-β-glucopyranoside)-5-(6‴-malonyl-β-glucopyranoside), peonidin 3-(6″-E-p-coumaroyl-β-glucopyranoside)-5-(6‴-malonyl-β-glucopyranoside), and peonidin 3-(6″-E-p-coumaroyl-β-glucopyranoside)-5-β-glucopyranoside. The first three of these pigments have not been reported previously from any plant. They all follow the typical anthocyanin pattern of Lamiaceae, with universal occurrence of anthocyanidin 3,5-diglucosides and aromatic acylation with p-coumaric and sometimes caffeic acids; however, they differ by being based on peonidin. The four anthocyanins were present in the leaves (22.2 mg g−1 DW), and in the xylem and interfascicular parenchyma of the stem. They were exceptionally abundant, among the highest reported for any plant organ, in epidermal hairs on some of the stem internodes (101 mg g−1 DW). Anthocyanin content in these hairs increased more than three-fold from the youngest to the fourth-youngest internodes. In situ absorbances (λmax ≈ 545 nm) were bathochromic in comparison to absorbances of the isolated anthocyanins in their flavylium form in acidified aqueous solutions (λmax = 525 nm), suggesting that the anthocyanins occur both in quinoidal and flavylium forms in constant proportions in the anthocyanic hair cells. The most distinctive observation with respect to relative proportions of individual anthocyanins was found in de-haired internodes, for which anthocyanin caffeoyl-derivatives decreased, and anthocyanin coumaroyl-derivatives increased, from the youngest to the fourth-youngest internode.Four main aromatic acylated anthocyanins, three of which without previous documentation in any plant, were identified in extremely high amounts (101 mg g−1 DW) in cauline hairs of purple-leaved plectranthus (Plectranthus ciliatus, Lamiaceae).Display Omitted
Keywords: Plectranthus ciliatus; Lamiaceae; Anthocyanins; Trichomes; Hairs; Identification; Quantification; NMR;

Anthocyanins of the anthers as chemotaxonomic markers in the genus Populus L.. Differentiation between Populus nigra, Populus alba and Populus tremula by Cristina Alcalde-Eon; Ignacio García-Estévez; Julián C. Rivas-Gonzalo; David Rodríguez de la Cruz; María Teresa Escribano-Bailón (35-49).
Three main species of Popululs L. (Salicaceae) have been reported to occur in the Iberian Peninsula: Populus nigra L., Populus alba L. and Populus tremula L. The degree of pilosity of the bracts of the male catkins is a key character for their differentiation. The anthers of these poplar species possess anthocyanins that provide them a red colouration. Since these poplars are wind-pollinated and, consequently, do not need to attract pollinators, anthocyanins in the anthers might be acting as photoprotectors, shielding pollen grains from excessive sunlight. In order to verify this hypothesis, the first objective of this study was to establish if there is any relationship between the degree of pilosity of the bracts (related to the physical shading of the pollen grains) and the levels and types of anthocyanins in the anthers of these three species. This study also aimed to check the usefulness of the anthocyanins of the anthers as chemotaxonomic markers, through the study of the differences in the anthocyanin composition between these poplar species. Anthocyanins were identified from the data supplied by HPLC-DAD-MSn analyses. Seventeen different compounds, including mono-, di- and triglycosides and anthocyanin-derived pigments (F-A+ dimers) have been identified. Cyanidin 3-O-glucoside was the major compound in all the samples (>60% of the total content), which may be in accordance with the photoprotective role proposed for them. However, qualitative and quantitative differences were detected among samples. Cyanidin and delphinidin 3-O-sambubiosides have been detected only in the anthers of P. tremula as well as cyanidin 3-O-(2″-O-xyloxyl)rutinoside, making them valuable chemotaxonomic markers for this species. Hierarchical Cluster and Principal Components Analyses (HCA and PCA) carried out with the anthocyanin percent composition data have allowed a separation of the samples that is in accordance with the initial classification of the samples made from the morphological characters of the specimens. Furthermore, these analyses have revealed intraspecific differences among samples that point out to different clones or varieties of a same species.The three main species of Populus L. in the Iberian Peninsula can be differentiated through the anthocyanin composition of the anthers proving the usefulness of anthocyanins as chemotaxonomic markers.Display Omitted
Keywords: Populus nigra L.; Populus alba L.; Populus tremula L.; Salicaceae; Poplar; HPLC-DAD-MSn; Anthocyanins and anthocyanin-derived pigments; Anthers;

A new view on the codonocarpine type alkaloids of Capparis decidua by Yvonne Forster; Abdul Ghaffar; Stefan Bienz (50-59).
Several spermidine alkaloids are described in literature as constituents of the root bark of Capparis decidua. Since some of the proposed structures, however, are in conflict with the expected biosynthetic paths, an extract of the root bark of the plant was re-investigated. Four major spermidine alkaloids of the codonocarpine type were identified and their structures elucidated: of the four compounds, isocodonocarpine was described previously for C. decidua and cadabicine was proposed as a possible constituent as well. Codonocarpine was found for the first time in an extract of C. decidua but was previously isolated from a closely related plant. Capparidisinine, finally, is an alkaloid with a structure that has never been described before. The structures of the four alkaloids are substantiated by NMR and MS data, and the four compounds are in logical agreement with biosynthetic considerations: they would arise from α,ω-bis-adducts of spermidine with coumaric and/or ferulic acids, followed by phenol oxidation.The four spermidine alkaloids cadabicine (1), isocodonocarpine (3), codonocarpine (9), and capparidisinine (10) were identified as constituents of the root bark of Capparis decidua. Compounds 1 and 9 were found for the first time in this plant, and compound 10 is a new alkaloid that has not been described before.Display Omitted
Keywords: Capparis decidua; Capparaceae; Spermidine alkaloid; Codonocarpine; Structure elucidation;

Terpenoids from Flueggea virosa and their anti-hepatitis C virus activity by Chih-Hua Chao; Ju-Chien Cheng; De-Yang Shen; Hui-Chi Huang; Yang-Chang Wu; Tian-Shung Wu (60-70).
Phytochemical study of the methanolic root extract of Flueggea virosa allowed for the characterization of 18 non-alkaloid terpenoids. Their structures have skeletons composed of six rearranged ent-podocarpanes, 11 ent-podocarpanes, and a 3,4-seco-30-nor-friedelane. These were characterized based on 2D NMR, IR, UV, and MS spectroscopic analysis and their absolute configurations were determined by single-crystal X-ray studies, as well as by 1H NMR spectroscopic analysis for the corresponding chiral derivatives. The isolates were evaluated for therapeutic potential against hepatitis C virus (HCV) infection to human hepatoma Huh7.5 cells.Terpenoids with anti-HCV activity were identified from Flueggea virosa. The 9(10 → 20)-abeo-ent-podocarpanes were reported from this genus for the first time. The amide coupling reaction on 3,4-seco-30-nor-friedelane yielded unexpected compounds.Display Omitted
Keywords: Flueggea virosa; Euphorbiaceae; Anti-hepatitis C virus; ent-Podocarpane; 3,4-seco-30-nor-Friedelane;

HIV-inhibitory michellamine-type dimeric naphthylisoquinoline alkaloids from the Central African liana Ancistrocladus congolensis by Gerhard Bringmann; Claudia Steinert; Doris Feineis; Virima Mudogo; Julia Betzin; Carsten Scheller (71-81).
Five michellamine-type dimeric naphthylisoquinoline alkaloids (NIQs), named michellamines A2, A3, A4, B2, and B3, have been isolated from the root bark of the Central African liana Ancistrocladus congolensis J. Léonard (Ancistrocladaceae), along with their two known parent compounds, the michellamines A and B, which had so far only been detected in the Cameroonian species Ancistrocladus korupensis. Five monomeric representatives, viz., korupensamine D, ancistrobrevine B, hamatine, 5′-O-demethylhamatine, and 6-O-methylhamatine, already known from related Ancistrocladus species, have likewise been identified. The structure elucidation was achieved by spectroscopic analysis including HRESIMS, 1D and 2D NMR, and by chemical and chiroptical methods. The michellamines A2, A3, B3, and A4 were evaluated for their cytotoxic and anti-HIV activities at a concentration range of 0–100 μM against the HIV reference strain IIIB/LAI in A3.01 T lymphoblast cell cultures, and their effects were compared to the ones displayed by the known michellamines A and B. Inhibitory activities for HIV replication were monitored for the michellamines A2 (IC50 = 29.6 μM), A3 (IC50 = 15.2 μM), A4 (IC50 = 35.9 μM), and B (IC50 = 20.4 μM). The michellamines A and B3, by contrast, did not inhibit HIV replication. No cytotoxicity was observed. Furthermore, the chemotaxonomic significance of the previously undescribed michellamines is discussed.Display Omitted
Keywords: Ancistrocladus congolensis; Ancistrocladaceae; Naphthylisoquinoline alkaloids; Michellamines; Anti-HIV activities;

Isolation and characterisation of 13 pterosins and pterosides from bracken (Pteridium aquilinum (L.) Kuhn) rhizome by Rizgar Hassan Mohammad; Mohammad Nur-e-Alam; Martina Lahmann; Ifat Parveen; Graham J. Tizzard; Simon J. Coles; Mark Fowler; Alex F. Drake; Derren Heyes; Vera Thoss (82-94).
Systematic phytochemical investigations of the underground rhizome of Pteridium aquilinum (L.) Kuhn (Dennstaedtiaceae) afforded thirty-five pterosins and pterosides. By detailed analysis of one- and two-dimensional nuclear magnetic resonance spectroscopy, circular dichroism (CD) and high-resolution mass spectrometric data, thirteen previously undescribed pterosins and pterosides have been identified. Interestingly, for the first time 12-O-β-D-glucopyranoside substituted pterosins, rhedynosides C and D, and the sulfate-containing pterosin, rhedynosin H, alongside the two known compounds, histiopterosin A and (2S)-pteroside A2, were isolated from the rhizomes of subsp. aquilinum of bracken. In addition, six-membered cyclic ether pterosins and pterosides, rhedynosin A and rhedynoside A, are the first examples of this type of pterosin-sesquiterpenoid. Additionally, the three previously reported compounds (rhedynosin I, (2S)-2-hydroxymethylpterosin E and (2S)-12-hydroxypterosin A) were obtained for the first time from plants as opposed to mammalian metabolic products. Single crystal X-ray diffraction analysis was applied to the previously undescribed compounds (2R)-rhedynoside B, (2R)-pteroside B and (2S)-pteroside K, yielding the first crystal structures for pterosides, and three known pterosins, (2S)-pterosin A, trans-pterosin C and cis-pterosin C. Rhedynosin C is the only example of the cyclic lactone pterosins with a keto group at position C-14. Six selected pterosins ((2S)-pterosin A, (2R)-pterosin B and trans-pterosin C) and associated glycosides ((2S)-pteroside A, (2R)-pteroside B and pteroside Z) were assessed for their anti-diabetic activity using an intestinal glucose uptake assay; all were found to be inactive at 300 μM.Thirteen previously undescribed pterosins and pterosides were isolated from bracken rhizomes in north of Wales. Their structures were elucidated using NMR spectroscopic and high resolution FT-ICR-MS data.Display Omitted
Keywords: Pteridium aquilinum; Dennstaedtiaceae; Bracken pterosins; Pterosides; Norsesquiterpenes; Sesquiterpenoids; Pterosins A and B; Circular dichroism; SGLT1 and GLUT2 transporters;

Phenylbenzoisoquinolindione alkaloids accumulate in stamens of Xiphidium caeruleum Aubl. flowers by Yu Chen; Christian Paetz; Riya C. Menezes; Bernd Schneider (95-101).
Xiphidium caeruleum (Haemodoraceae) flower organs such as carpels, pedicels, petals, and stamens were separately investigated for their phytochemical profile. The stamens appeared to be a rich source of previously undescribed phenylbenzoisoquinolindiones, a group of phenylphenalenone-derived alkaloids, also named aza-phenylphenalenones. Nine previously undescribed compounds with an identical aza-phenylphenalenone core structure but different amino acid-derived side chains at position 2 were isolated and their structures elucidated by nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). In addition, some previously reported phenylbenzoisoquinolindiones, phenylbenzoisochromenones and flavonoids were found in stamens and other parts of the flowers. The specific occurrence of heterocyclic phenylphenalenone-type compounds in X. caeruleum suggests these are involved in physiological or ecological processes.Nine previously undescribed phenylbenzoisoquinolindione alkaloids with identical aza-phenylphenalenone core structure and with different amino acid-derived side chains at position 2 were identified. Phenylbenzoisoquinolindiones specifically occur in flower organs of the Haemodoraceae, subfamily Haemodoroideae.Display Omitted
Keywords: Xiphidium caeruleum; Haemodoraceae; Phenylbenzoisochromenones; Phenylbenzoisoquinolinones; Phenylphenalenones;