Benzophenone glycosides from Gnidia involucrata

A new gnidiflavanone-flavonol dimer and other constituents from Gnidia apiculata

A new 3,8''-flavanone-flavonol dimer gnidiflavanone-flavonol (1) and 10 known compounds (2-11), including four rare primula-type flavones 2-5, were isolated from the roots of Gnidia apiculata. Compounds 2-5 and 7 were reported for the first time from the plant family Thymelaeceae. Structures of the isolated compounds were established by spectroscopic data, including 1D and 2D NMR (COSY, HMBC, HSQC and ROESY) and mass spectrometry, as well as by the comparison with literature data. The crude roots extract and isolated compounds were evaluated for antimicrobial and antiplasmodial activities. Among isolated compounds, 6-hydroxyflavone (4) and 6-O-acetylflavone (4a) showed antiplasmodial activity against chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains of Plasmodium falciparum.

Xanthones: Biosynthesis and Trafficking in Plants, Fungi and Lichens

Xanthones are a class of secondary metabolites produced by plant organisms. They are characterized by a wide structural variety and numerous biological activities that make them valuable metabolites for use in the pharmaceutical field. This review shows the current knowledge of the xanthone biosynthetic pathway with a focus on the precursors and the enzymes involved, as well as on the cellular and organ localization of xanthones in plants. Xanthone biosynthesis in plants involves the shikimate and the acetate pathways which originate in plastids and endoplasmic reticulum, respectively. The pathway continues following three alternative routes, two phenylalanine-dependent and one phenylalanine-independent. All three routes lead to the biosynthesis of 2,3',4,6-tetrahydroxybenzophenone, which is the central intermediate. Unlike plants, the xanthone core in fungi and lichens is wholly derived from polyketide. Although organs and tissues synthesizing and accumulating xanthones are known in plants, no information is yet available on their subcellular and cellular localization in fungi and lichens. This review highlights the studies published to date on xanthone biosynthesis and trafficking in plant organisms, from which it emerges that the mechanisms underlying their synthesis need to be further investigated in order to exploit them for application purposes.

Luteolin: A promising natural agent in management of pain in chronic conditions

Pain due to chronic conditions is a frequent and insufficiently addressed problem. Current drug options for pain management (either in cases of chronic inflammatory conditions or neuropathy) do not adequately treat pain. Moreover, they are associated with important adverse events in long term use. Luteolin is a flavonoid widely present in the plant kingdom and its sources have been assembled in a comprehensive list of this paper. Luteolin has shown in several research studies a range of pharmacological properties; anti-inflammatory, antioxidant, neuroprotective, and analgesic. In this article, we summarize the effects and potential benefits from introducing luteolin as an adjuvant agent in established protocols for pain management. We review the most indicative in vivo and in vitro evidence of how luteolin can target the molecular pathways involved in pathogenesis of chronic inflammatory and neuropathic pain. The data reviewed strongly support luteolin's promising benefits in pain management and raise the need for further clinical trials that can establish its role in clinical practice.

Advances in plant-derived C-glycosides: Phytochemistry, bioactivities, and biotechnological production

C-glycosides represent a large group of natural products with a C-C bond between the aglycone and the sugar moiety. They exhibit great structural diversity, wide natural distribution, and significant biological activities. By the end of 2021, at least 754 C-glycosides and their derivatives have been isolated and characterized from plants. Thus far, 66 functional C-glycosyltransferases (CGTs) have been discovered from plants, and provide green and efficient approaches to synthesize C-glycosides. Herein, advances in plant-derived C-glycosides are comprehensively summarized from aspects of structural diversity and identification, bioactivities, and biotechnological production. New strategies to discover novel C-glycosides and CGTs, as well as the applications of biotechnological methods to produce C-glycosides in the future are also discussed.

New Alpha-Amylase Inhibitory Metabolites from Pericarps of Garcinia mangostana

Two new benzophenones: garcimangophenones A (6) and B (7) and five formerly reported metabolites were purified from the pericarps EtOAc fraction of Garcinia mangostana ((GM) Clusiaceae). Their structures were characterized by various spectral techniques and by comparing with the literature. The α-amylase inhibitory (AAI) potential of the isolated metabolites was assessed. Compounds 7 and 6 had significant AAI activity (IC50 9.3 and 12.2 µM, respectively) compared with acarbose (IC50 6.4 µM, reference α-amylase inhibitor). On the other hand, 5 had a moderate activity. Additionally, their activity towards the α-amylase was assessed utilizing docking studies and molecular dynamics (MD) simulations. The docking and predictive binding energy estimations were accomplished using reported crystal structure of the α-amylase (PDB ID: 5TD4). Compounds 7 and 6 possessed highly negative docking scores of −11.3 and −8.2 kcal/mol, when complexed with 5TD4, respectively while acarbose had a docking score of −16.1 kcal/mol, when complexed with 5TD4. By using molecular dynamics simulations, the compounds stability in the complexes with the α-amylase was analyzed, and it was found to be stable over the course of 50 ns. The results suggested that the benzophenone derivative 7 may be potential α-amylase inhibitors. However, further investigations to support these findings are required.

Ethnobotanical Study of Medicinal Plants Used by Traditional Healers to Treat Cancer-Like Symptoms in Eleven Districts, Ethiopia

There is no ethnobotanical study conducted specifically on medicinal plants traditionally used to treat cancer in Ethiopia. Yet, traditional herbalists in different parts of the country claim that they have been treating cancer-like symptoms using herbal remedies. The objective of this study was to document medicinal plants traditionally used to treat cancer-like symptoms in eleven districts, Ethiopia. Traditional herbalists were interviewed using semistructured questionnaires, and field visits were also carried out to collect claimed plants for identification purpose. Seventy-four traditional herbalists, who claimed that they knew about and/or had used medicinal plants to treat cancer-like symptoms, were selected using the snowball method and interviewed. Herbalists used their intuition and relied on the chronicity, growth of external mass, and spreading of the disease to other parts of the body, as a means to characterize cancer symptoms. Furthermore, in some of the study districts, herbalists reported that they treat patients who had already been diagnosed in modern healthcare institutions prior to seeking help from them. The inventory of medicinal plants is summarized in a synoptic table, which contains the scientific and vernacular names of the plants, their geographical location, the parts of the plants, and the methods used to prepare the remedies. A total of 53 traditionally used anticancer plants, belonging to 30 families, were identified during the survey. The most frequently reported anticancer plants were Acmella caulirhiza Del (Asteraceae), Clematis simensis Fresen. (Ranunculaceae), Croton macrostachyus Del. (Euphorbiaceae), and Dorstenia barnimiana Schweinf. (Moraceae). Organizing traditional healers, documenting their indigenous knowledge, and scientifically validating it for the development of better cancer therapeutic agents constitute an urgent and important task for policymakers and scientists.

Chemical Constituents of Root Barks of Gnidia involucrata and Evaluation for Antibacterial and Antioxidant Activities

The genus Gnidia, with species close to 152, is traditionally used to treat wide ranges of ailments in humans and animals. Gnidia involucrata is one of the species found in Ethiopia and traditionally used as a laxative, antirheumatic agent, insecticide, antibacterial agent, and antimalarial agent. In view of its traditional use, the root bark was sequentially extracted with n-hexane, EtOAc, and MeOH to afford 0.78%, 4%, and 6% crude extracts, respectively. The chromatographic separation of the EtOAc extract using silica gel column chromatography yielded three pure compounds: tetratriacontanyl caffeate (1), 12-O-dodeca-2,4-dienoylphorbol-13-acetate (2), and naringenin (3). This is the first report of the isolation of 1 and its kind from the genus and most probably from the Thymelaeaceae family. The structures of these compounds were characterized and identified by NMR and mass spectrometric analyses and comparison with literature data. The EtOAc extract and isolated compounds were assessed for their in vitro antibacterial and antioxidant activities. The EtOAc extract (1.5 mg/mL) showed significant inhibitory activity against S. aureus, E. coli, P. mirabilis, and K. pneumonia bacterial strains with the highest inhibition zone observed against S. aureus (23 mm), which is even greater than that of the reference drug ciprofloxacin (22 mm). However, the inhibition displayed on these bacterial strains for the three pure compounds was marginal with variable degrees of potency between the compounds. The better activity of the crude extract could be due to the synergistic interactions of several phytochemicals present in the extract, which cannot be the case when pure compounds are evaluated alone. The antioxidant activities of the extracts and isolated compounds were evaluated using DPPH and ferric thiocyanate methods. The EtOAc and MeOH extracts and compounds 1 and 2 were found to inhibit the DPPH radical by 70.7, 66.9, 85.8, and 52.8%, respectively. The EtOAc extract and compound 1 inhibited peroxidation of lipids by 84 and 86%, respectively. The radical scavenging displayed by compound 1 was significant compared with that displayed by ascorbic acid, indicating the strong antilipid peroxidation potential of the extract of root barks of G. involucrata. Therefore, the extracts of the root bark of G. involucrata can be used as a remedy in combating diseases caused by bacteria and free radicals provided that further comprehensive evaluation could be recommended for the conclusive decision on potential candidacy of this plant.

Glycosides of ursane-type triterpenoid, benzophenone, and iridoid from Vangueria agrestis (Fadogia agrestis) and their anti-infective activities

Four ursane-type triterpenoid glycosides (1-4), two benzophenone glycosides (5 and 6), and one iridoid glucoside (7) were isolated and characterized from the dried roots of Vangueria agrestis. Compounds 1 (3-O-[α-L-rhamnopyranosyl-(1→2)-β-D-xylopyranosyl]pomolic acid 28-O-β-D-glucopyranosyl ester) and 5 (2-O-[β-D-apiofuranosyl-(1→6)-β-D-glucopyranosyl]-6,4'-dihydroxy-4-methoxy benzophenone) were found to be new metabolites. The identity of all compounds has been accomplished, primarily, based on 1 D and 2 D NMR and HRESMS analysis. Compounds 6 and 2, showed inhibitory effect against Trypanosoma brucei with IC₅₀ 22.3 µM for 6 and IC₅₀ 11.1 µM, IC₉₀ 12.3 µM for 2.

Toxicological investigation of acute and chronic treatment with Gnidia stenophylla Gilg root extract on some blood parameters and histopathology of spleen, liver and kidney in mice

Background

In southeast Ethiopia, people locally use the roots of Gnidia stenophylla Gilg (Thymelaeaceae) to cure malaria and other diseases with no literature evidence substantiating its safety. The aim of this study was, therefore, to investigate the safety of the aqueous root extract of G. stenophylla after acute (single dose) and repeated sub chronic oral administration in mice.

Results

A single oral administration of the extract at 500, 1000, 2000 and 4000 mg/kg body weight did not induce any behavioral change and mortality in both sexes. The oral LD₅₀ of the extract was found to be above 6000 mg/kg body weight in mice. Chronic treatment with the extract for 13 weeks did not induce any sign of illness and/or death and had no adverse effect on the body weight. Dose-related elevations of erythrocytes, hematocrit, hemoglobin, platelets and neutrophils differential and significant decrease in the number of lymphocyte were observed. Liver sections of mice treated with 800 mg/kg body weight, revealed mild inflammations around the portal triads and central veins; whereas the spleen and kidneys appeared normal with no detectable gross morphological and histopathological alteration at both doses.

Conclusions

The results of this study revealed that aqueous root extract of G. stenophylla Gilg at antimalarial dose is safe even when taken for a longer period. At a higher dose, the extract may have a potential to increase some hematological indices but may induce mild hepatotoxicity as a side effect.

Electronic supplementary material

The online version of this article (10.1186/s13104-017-2964-3) contains supplementary material, which is available to authorized users.

Preparative separation of the polar part from the rhizomes of Anemarrhena asphodeloides using a hydrophilic C18 stationary phase

The goal of this study was to develop a method that utilized a hydrophilic C18 stationary phase in the preparative high performance liquid chromatography to isolate the polar part from the rhizomes of Anemarrhena asphodeloides. The results showed that an initial mobile phase of pure water for the separation could greatly increase the retention and solubility of the polar compounds at the preparative scale. Introducing polar groups on the surface of the hydrophilic C18 column together with the use of optimized mobile phase compositions improved the column separation selectivity for polar compounds. Eleven previously undescribed compounds in Anemarrhena asphodeloides were obtained, indicating that the method developed in this study would facilitate the purification and separation of the polar part of traditional Chinese medicines.

Effect of Oral Administration of Gnidia Stenophylla Gilg Aqueous Root Extract on Food Intake and Histology of Gastrointestinal Tract in Mice

Background

Aqueous preparations of a medicinal plant, Gnidia stenophylla Gilg (Thymelaeaceae) are commonly used to cure malaria and other ailments in Ethiopia. This study evaluated the safety of the plant extract by determining its effects on food intake and histology of gastrointestinal tract (GIT) after oral administration for 13 weeks in albino mice.

Methods

Thirty mice were equally assigned to three groups. Group I served as control and received a vehicle while groups II and III were given 400 and 800 mg/kg body weight/day plant extract respectively, orally, for 13 weeks. At the end of the study, the mice were scarified and postmortem gross and histopathological evaluations were performed on their stomachs and intestines.

Results

Chronic oral treatment with the extract for 13 weeks did not induce any sign of illness and death and had no effect on food intake of the mice. Furthermore, extract treatment at both doses did not produce any detectable gross morphological change in GIT. Microscopic evaluation of sections of the stomach, duodenum and jejunum of the mice treated with 400 mg/kg body weight did not show any histopathological change. In the mice treated with 800 mg/kg body weight, however, the GIT sections revealed cytoplasmic vacuolation, hydropic degeneration and excessive erosion of the surface mucosal cells.

Conclusion

The results of this study revealed that aqueous root extract of G. stenophylla at effective antimalarial dose is safe even when taken for a longer period in mice. At a higher dose, however, the extract may induce gastrointestinal irritation. Further studies on other vital organs and non-rodent species including humans are recommended.

Two new phenolic glycosides isolated from the fruits of Citrus aurantium

The present study was designed to investigate the chemical constituents of the fruit of Citrus aurantium L.. The compounds were isolated and purified by various chromatographic techniques, and their structures were elucidated on the basis of physicochemical properties and spectral data. Two new phenolic glycosides (compounds 1 and 2) were obtained and identified as 1-O-3, 5-dihydroxyphenyl-(6-O-4-hydroxybenzoyl)-β-D-glucopyranoside (1) and 1-O-3, 5-dihydroxyphenyl-(6-O-3-methoxy-4-hydroxy benzoyl)-β-D-glucopyranoside (2), respectively.

Benzophenone C-glucosides and gallotannins from mango tree stem bark with broad-spectrum anti-viral activity

The high mutation rate of RNA viruses has resulted in limitation of vaccine effectiveness and increased emergence of drug-resistant viruses. New effective antivirals are therefore needed to control of the highly mutative RNA viruses. The n-butanol fraction of the stem bark of Mangifera indica exhibited inhibitory activity against influenza neuraminidase (NA) and coxsackie virus 3C protease. Bioassay guided phytochemical study of M. indica stem bark afforded two new compounds including one benzophenone C-glycoside (4) and one xanthone dimer (7), together with eleven known compounds. The structures of these isolated compounds were elucidated on the basis of spectroscopic evidences and correlated with known compounds. Anti-influenza and anti-coxsackie virus activities were evaluated by determining the inhibition of anti-influenza neuraminidase (NA) from pandemic A/RI/5+/1957 H2N2 influenza A virus and inhibition of coxsackie B3 virus 3C protease, respectively. The highest anti-influenza activity was observed for compounds 8 and 9 with IC50 values of 11.9 and 9.2μM, respectively. Compounds 8 and 9 were even more potent against coxsackie B3 virus 3C protease, with IC50 values of 1.1 and 2.0μM, respectively. Compounds 8 and 9 showed weak cytotoxic effect against human hepatocellular carcinoma and human epithelial carcinoma cell lines through MTT assay.

Mangiferin prevents guinea pig tracheal contraction via activation of the nitric oxide-cyclic GMP pathway

Previous studies have described the antispasmodic effect of mangiferin, a natural glucoside xanthone (2-C-β-Dgluco-pyranosyl-1,3,6,7-tetrahydroxyxanthone) that is present in mango trees and other plants, but its mechanism of action remains unknown. The aim of this study was to examine the potential contribution of the nitric oxide-cyclic GMP pathway to the antispasmodic effect of mangiferin on isolated tracheal rings preparations. The functional effect of mangiferin on allergic and non-allergic contraction of guinea pig tracheal rings was assessed in conventional organ baths. Cultured tracheal rings were exposed to mangiferin or vehicle, and nitric oxide synthase (NOS) 3 and cyclic GMP (cGMP) levels were quantified using western blotting and enzyme immunoassays, respectively. Mangiferin (0.1–10 µM) inhibited tracheal contractions induced by distinct stimuli, such as allergen, histamine, 5-hydroxytryptamine or carbachol, in a concentration-dependent manner. Mangiferin also caused marked relaxation of tracheal rings that were precontracted by carbachol, suggesting that it has both anti-contraction and relaxant properties that are prevented by removing the epithelium. The effect of mangiferin was inhibited by the nitric oxide synthase inhibitor, Nω-nitro-L-arginine methyl ester (L-NAME) (100 µM), and the soluble guanylate cyclase inhibitor, 1H-[1], [2], [4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 µM), but not the adenylate cyclase inhibitor, 9-(tetrahydro-2-furyl)adenine (SQ22536) (100 µM). The antispasmodic effect of mangiferin was also sensitive to K⁺ channel blockers, such as tetraethylammonium (TEA), glibenclamide and apamin. Furthermore, mangiferin inhibited Ca²⁺-induced contractions in K⁺ (60 mM)-depolarised tracheal rings preparations. In addition, mangiferin increased NOS3 protein levels and cGMP intracellular levels in cultured tracheal rings. Finally, mangiferin-induced increase in cGMP levels was abrogated by co-incubation with either ODQ or L-NAME. These data suggest that the antispasmodic effect of mangiferin is mediated by epithelium-nitric oxide- and cGMP-dependent mechanisms.

Secondary metabolites from a marine-derived fungus Aspergillus carneus Blochwitz

Prenylated indole alkaloids, carneamides A-C (1-3), quinazolinone derivatives, carnequinazolines A-C (5-7), aryl C-glycosides, carnemycin A, B (8, 9) and a drimane sesquiterpenoid (10), together with known compounds (11-21) were isolated from the marine-derived fungus Aspergillus carneus (Trichocomaceae) KMM 4638. The antimicrobial and cytotoxic activities of the several alkaloids were examined.

Benzophenone glycosides and epicatechin derivatives from Malania oleifera

A new benzophenone C-glycoside, malaferin A (1), and two new epicatechin derivatives, malaferin B (2) and malaferin C (3), together with five known compounds were isolated from Malania oleifera. In addition, (-)-epicatechin-3-O-benzoate (6) was isolated for the first time from a natural resource. Structures of 1-3 were determined on the basis of their spectroscopic methods, including 1D and 2D NMR techniques. All of the compounds were evaluated for anti-HIV activities.

Xanthone and benzophenone glycosides from the stems of Cratoxylum formosum ssp. pruniflorum

Two new xanthone glycosides, namely pruniflorosides A and B (1, 2), a new benzophenone glycoside, prunifloroside C (3), and a new xanthone, pruniflorone S (4) were isolated from the stems of Cratoxylum formosum ssp. pruniflorum, along with six known xanthones (5-10). Their structures were determined on the basis of extensive spectroscopic analysis. In addition, their retinoid X receptor α (RXRα) transcriptional activities were evaluated in vitro.

Cellular reactive oxygen species inhibitory constituents of Hypericum thasium Griseb

The phytochemical investigation of the ethyl acetate extract of Hypericum thasium has led to the characterization of four benzophenone derivatives 1-4, a known benzophenone 5 and four known flavonoids, quercetin (6), quercitrin (7), isoquercetin (8), and 3, 8''-biapigenin (9). Lucigenin- and luminal-based chemiluminescence assays were employed to monitor the inhibitory activity of these compounds towards the production of reactive oxygen species (ROS) by human polymorphoneutrophils (PMNs). The assay results showed that benzophenones 1 and 3 are extracellular inhibitors of ROS production, while flavonoids 6, 8, and 9 can modulate intracellular ROS production.

Benzophenone C-glucosides from Polygala glomerata Lour

Four new benzophenone C-glucosides, glomeratides A (1), B (2), C (3), and D (4), along with a known compound arrilanin G (5), have been isolated from the whole plant of Polygala glomerata Lour. Their structures were determined by extensive analyses of their spectral data. Compounds 1-5 showed hepatoprotective activities against d-galactosamine-induced toxicity in WB-F344 rat hepatic epithelial stem-like cells.

Phytochemistry in the microgram domain - a LC-NMR perspective

Plants represent an extraordinary reservoir of novel molecules and there is currently a resurgence of interest in the vegetable kingdom as a possible source of new lead compounds for introduction into therapeutical screening programs. In order to discover potential new bioactive natural products, the dereplication of crude plant extracts performed prior to isolation work is of crucial importance for avoiding the isolation of a known constituent. In this respect, chemical screening strategies have been developed using hyphenated techniques (LC/UV-DAD, LC-MS and LC-NMR). In our laboratory, these techniques have been fully integrated into the isolation process and are used for the chemical screening of crude plant extracts in complement with on-line or at-line bioassays. LC-UV-MS is used as a first dereplication step in combination with UV and MS databases, while LC-NMR is performed in a second step for de novo on-line structure determination. This approach enables the partial or the complete on-line identification of natural products in complex matrices such as crude plant extracts. These methods also give a unique possibility to study unstable compounds, which rapidly degrade or which are not separable at a preparative level. In the multi-hyphenated approach used (hypernation), LC-NMR plays a key role since it provides the most detailed structural information. The relatively low sensitivity of this technique, however, requires that strategies for high loading of plant extracts are developed and compromises for solvent selection have to be made. For more demanding experiments, at-line strategies based on the microfractionation of the LC-peak of interest and recording of spectra in fully deuterated solvents in microflow probes represent a promising alternative.

Preparative separation of isovitexin and isoorientin from Patrinia villosa Juss by high-speed counter-current chromatography

High-speed counter-current chromatography (HSCCC) with a solvent system composed of ethyl acetate-n-butanol-water (2:1:3, v/v/v) was used to isolate and separate two C-glycosylflavones from Patrinia villosa Juss, a traditional Chinese medicine. The separation produced 42.9 mg isovitexin and 20.1 mg isoorientin with purities of 99.3% and 98.5%, respectively as determined by high-performance liquid chromatography (HPLC) in one step elution from 250 mg crude extract, and identification was performed by MS, 1H NMR and 13C NMR. It is the first report of discovering isovitexin and isoorientin from the plant of Patrinia genus.

Antioxidative constituents from the leaves of Hypericum styphelioides

Two new compounds have been isolated from the leaves of Hypericum styphelioides. Their structures have been established on the basis of mass spectrometry and 2D NMR techniques as 1,3,5-trihydroxy-2-(2',2'-dimethyl-4'-isopropenyl)cyclopentanylxanthone (1) and 3,5-dihydroxybenzophenon-4-beta-d-glucoside (2). Known compounds 5-O-demethylpaxanthonin (3) and 3-geranyl-1-(3-methylbutanoyl)phloroglucinol (4) were also isolated and characterized. Compounds 1-4 were evaluated for their antioxidative properties in Trolox equivalent antioxidant activity (TEAC) and chemiluminescence (CL) assays.

Evariquinone, isoemericellin, and stromemycin from a sponge derived strain of the fungus Emericella variecolor

From a strain of the fungus Emericella variecolor derived from the marine sponge Haliclona valliculata, two new natural products, evariquinone and isoemericellin, were isolated after HPLC-UV, -MS, and -NMR studies of the extract and their structures were elucidated by mass spectrometry and NMR experiments. Evariquinone showed antiproliferative activity towards KB and NCI-H460 cells at a concentration of 3.16 microg/ml. Furthermore, the fungus was found to produce the known metabolites stromemycin, shamixanthone, and 7-hydroxyemodin. Chemical degradation, NMR decoupling experiments, and spin-system simulation provided evidence for the double bonds in stromemycin to be all E-configured. ROESY experiments established the monosaccharide moiety to be glucose.

Benzophenone synthase and chalcone synthase from Hypericum androsaemum cell cultures: cDNA cloning, functional expression, and site-directed mutagenesis of two polyketide synthases

Benzophenone derivatives, such as polyprenylated benzoylphloroglucinols and xanthones, are biologically active secondary metabolites. The formation of their C13 skeleton is catalyzed by benzophenone synthase (BPS; EC 2.3.1.151) that has been cloned from cell cultures of Hypericum androsaemum. BPS is a novel member of the superfamily of plant polyketide synthases (PKSs), also termed type III PKSs, with 53-63% amino acid sequence identity. Heterologously expressed BPS was a homodimer with a subunit molecular mass of 42.8 kDa. Its preferred starter substrate was benzoyl-CoA that was stepwise condensed with three malonyl-CoAs to give 2,4,6-trihydroxybenzophenone. BPS did not accept activated cinnamic acids as starter molecules. In contrast, recombinant chalcone synthase (CHS; EC 2.3.1.74) from the same cell cultures preferentially used 4-coumaroyl-CoA and also converted CoA esters of benzoic acids. The enzyme shared 60.1% amino acid sequence identity with BPS. In a phylogenetic tree, the two PKSs occurred in different clusters. One cluster was formed by CHSs including the one from H. androsaemum. BPS grouped together with the PKSs that functionally differ from CHS. Site-directed mutagenesis of amino acids shaping the initiation/elongation cavity of CHS yielded a triple mutant (L263M/F265Y/S338G) that preferred benzoyl-CoA over 4-coumaroyl-CoA.

Flavone-coumarin hybrids from Gnidia socotrana

Phytochemical investigation of leaves and twigs of Gnidia socotrana (Balf. f.) Gilg (Thymelaeaceae), a plant occurring endemically on Socotra Island (Yemen), afforded six novel natural products: two compounds consisting of a flavone and a coumarin moiety connected by a C-C linkage, 7,7'-dihydroxy-3,8'-biscoumarin and three substances with the rare spiro-bis-gamma-lactone structure. The structures were elucidated on the basis of their spectroscopic data.

Two benzophenone O-arabinosides and a chromone from Hypericum annulatum

Two benzophenone O-arabinosides, annulatophenonoside (1) and acetylannulatophenonoside (2) were isolated from the methanol extract of the herb of Hypericum annulatum. The structures of the benzophenones were established as 2-O-alpha-L-arabinofuranosyl-3',5',6-trihydroxy-4-methoxybenzophenone (1) and 2-O-alpha-L-3"-acetylarabinofuranosyl-3',5',6-trihydroxy-4-methoxybenzophenone (2) based on spectral and chemical evidence. A chromone, 5,7-dihydroxy-3-methylchromone (3) was isolated from the chloroform extract. Although it has been previously synthesized it is encountered in a plant source for the first time. Co-occurrence of the two new benzophenone O-arabinosides along with the biogenetically related 1,5,7-trihydroxy-3-methoxyxanthone was not found.

Benzophenone O-glucoside, a biogenic precursor of 1,3,7-trioxygenated xanthones in Hypericum annulatum

Two benzophenones, hypericophenonoside (1) and annulatophenone (2) were isolated from the methanol extract of the herb of Hypericum annulatum. The structures of the benzophenones were established as 2'-O-beta-D-glucopyranosyl-2,4,5',6-tetrahydroxy benzophenone (1) and 2,3',5',6-tetrahydroxy-4-methoxybenzophenone (2) based on spectral and chemical evidence. Hypericophenonside is the second benzophenone O-glycoside found in nature. Acid and enzymatic hydrolysis of (1) led directly to the formation of 1,3,7-trihydroxyxanthone (gentisein). This fact confirmed the hypothesis that some xanthones could be formed in plants by dehydration of 2,2'-dihydroxybenzophenones, and the intermediate precursors appear to be benzophenone O-glycosides ortho to the carbonyl function.