Antifungal stilbenoids from Stemona collinsae

Fifteen new stilbenoids including 11 phenylbenzofurans, the stemofurans A-K (1-11), and four dihydrostilbenes, the stilbostemins A (15), C (17), E (19), and F (20), were isolated and identified from a methanolic extract of Stemona collinsae roots together with five known derivatives, the stilbenes pinosylvin (13) and 4'-methylpinosylvin (14), the dihydrostilbenes, stilbostemins B (16) and D (18), and the dihydrophenanthrene racemosol (12) as well as (+)-sesamin, coniferyl alcohol, and stigmasterol. Bioautographic tests with Cladosporium herbarum displayed antifungal activity for stilbenoids of all four structural types. Ten derivatives were tested against five microfungi using the microdilution technique linked with digital image analysis of germ tubes.

Feeding deterrence and contact toxicity of Stemona alkaloids-a source of potent natural insecticides

On the basis of chronic feeding bioassays with neonate larvae of Spodoptera littoralis reared on an artificial diet, the methanolic leaf and root extracts from Stemona collinsae displayed very high insect toxicity compared to those of two Aglaia species, a commercial Pyrethrum extract, and azadirachtin, whereas S. tuberosa extracts demonstrated low activity in roots and no activity in leaves. Beyond that, in leaf disk choice tests against fifth instar larvae, S. collinsae showed strong antifeedant activity, whereas S. tuberosa was characterized by remarkable repellency. The anti-insect properties of both species were based on pyrrolo[1,2-a]azepine alkaloids, from which didehydrostemofoline (asparagamine A) was the major compound of the roots of S. collinsae, exhibiting the highest toxicity in feeding assays. Saturation and hydroxylation of the side chain in the co-occurring stemofoline and 2'-hydroxystemofoline, respectively, led to an increasing loss of activity. Contact toxicity tests with stemofoline and didehydrostemofoline exhibited even higher activities than those of Pyrethrum extract. Tuberostemonine was the dominating alkaloid in the roots of S. tuberosa, showing outstanding repellency but no toxic effects.

Bisamides, lignans, triterpenes, and insecticidal Cyclopenta[b]benzofurans from Aglaia species

Twelve new derivatives of bisamides [piriferinol (5), edulimide (7)], lignans [lariciresinol acetat (10)], triterpenes [4-bis-norcycloartane-type triterpenes (11a, 12a+b, 13a+b)], cyclopenta[b]benzofurans [pannellin (15), pannellin 1-O-acetate (16), 3'-methoxypannellin (17)], and an aromatic butyrolactone [aglalactone (18)] were isolated and identified from lipophilic leaf, stem, and root extracts of Aglaia spp. elaeagnoidea, edulis, grandis, silvestris, and tomentosa. Two cyclopenta[b]benzofurans (flavaglines), pannellin (15) and pannellin 1-O-acetate (16), displayed very strong insecticidal activity against Spodoptera littoralis and Lymantria dispar, comparable with the activity of azadirachtin.

Antioxidant dehydrotocopherols as a new chemical character of Stemona species

From the roots of various Stemona species four new dehydrotocopherols (chromenols) were isolated and their structures and stereochemistry elucidated by spectroscopic methods. The double bond between C-3 and C-4 proved to be a typical chemical character of the genus found in most of the species. Various C-methylations of the aromatic ring reflect differences in methyltransferase activities and agreed with the current species delimitations showing an exclusive accumulation of dehydro-delta-tocopherol for the Stemona tuberosa group, whereas different provenances of Stemona curtisii were characterized by dehydro-gamma-tocopherol accompanied by small amounts of dehydro-alpha-tocopherol. From Stemona collinsae all four tocopherols were isolated with a clear preponderance of dehydro-delta-tocopherol accompanied by smaller amounts of the rare dehydro-beta-tocopherol. Stemona burkillii and a group of unidentified species showed a weak accumulation trend towards dehydro-alpha-tocopherol, whereas Stemona cochinchinensis and especially Stemona kerrii clearly differed by a preponderance of chromanol derivatives. In Stemona cf. pierrei no tocopherols could be detected at all. Based on TLC tests and microplate assays with the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH*) the antioxidant capacities of all chromenol derivatives were comparable with that of alpha-tocopherol showing no significant differences among each other, except for a more rapid kinetic behaviour of the 5,7,8-methylated dehydro-alpha-tocopherol.

Dihydrophenanthrenes and other antifungal stilbenoids from Stemona cf. pierrei

Three new dihydrophenanthrenes, stemanthrenes A-C, along with the new dihydrostilbene stilbostemin G were isolated and identified from the underground parts of Stemona cf. pierrei together with the known pinosylvin, 4'-methylpinosylvin, dihydropinosylvin, stilbostemins B, D, and E as well as the pyrrolo[1,2-a]azepine alkaloids protostemonine and stemonine. The structures of all new stilbenoids, elucidated by NMR analyses, showed a common substitution pattern for aromatic ring A and characteristic C-methylations for ring B. The trivial name racemosol, previously reported for S. collinsae, was renamed to stemanthrene D due to its priority for another compound. Bioautographic tests on TLC plates with Cladosporium herbarum displayed high antifungal activity for compounds with an unsubstituted aromatic ring A, e.g. pinosylvin, but only weak effects for the higher substituted stilbostemin G and stemanthrenes A-C. Similar results were obtained by germ tube inhibition of five microfungi using 2-fold serial broth dilutions determined by a microplate reader. Because of weak inhibition and chemical instability of stemanthrenes, no EC(50) and EC(90) values could be calculated.

Cyclopenta[b]benzofurans from Aglaia species with pronounced antifungal activity against rice blast fungus (Pyricularia grisea)

Eight flavaglines, six cyclopenta[b]benzofurans, a cyclopenta[bc]benzopyran, and a benzo[b]oxepine, together with an aromatic butyrolactone were isolated from Aglaia odorata, A. elaeagnoidea, and A. edulis (Meliaceae) and tested against the three plant pathogens Pyricularia grisea, Fusarium avenaceum, and Alternaria citri for antifungal properties. Using the microdilution technique linked with digital image analysis of germ tubes, the benzofurans displayed strong activity, whereas the benzopyran, benzoxepine, and butyrolactone were inactive at the highest concentration tested. P. grisea, responsible for rice blast disease, was the most susceptible fungus against all benzofurans, with rocaglaol as the most active derivative. Based on EC(50), EC(90), and MIC values, the antifungal activity of rocaglaol was clearly higher than of the reference compounds, blasticidin S and Benlate.

Infraspecific variation of sulfur-containing bisamides from Aglaia leptantha

Six new amides, leptaglin (1), hemileptaglin (2), aglanthin (3), agleptin (4), isoagleptin (5), and leptanthin (6), together with known lignans yangambin, eudesmin, grandisin (7), epigrandisin (8), and dehydrodiconiferyl alcohol, were isolated and identified from the lipophilic leaf and stem bark extracts of Aglaia leptantha. The dominating sulfur-containing bisamides contained either putrescine or the corresponding pyrrolidine ring as the diamine part, linked to phenylacetic and/or methylthiopropenoic acid moieties showing a remarkable infraspecific variation in eight individuals from two different habitats. Structures were determined by MS and NMR, including lanthanide-induced shifts.

Structural relationships of stemona alkaloids: assessment of species-specific accumulation trends for exploiting their biological activities

On the basis of a comparison of 42 Stemona samples, representing eight different species collected and cultivated in Thailand, species-specific accumulation trends of Stemona alkaloids were analyzed. An overview was achieved by comparative HPLC analyses of methanolic crude extracts of underground parts coupled with diode array or evaporative light scattering detectors. All major compounds were isolated and their structures elucidated by NMR and MS analyses. Protostemonine- and stichoneurine-type derivatives dominated, from which the latter characterize S. tuberosa and S. phyllantha accumulating species-specific isomers of tuberostemonine (3). The widespread S. curtisii and S. collinsiae clearly deviate by protostemonine-type derivatives dominated by stemofoline (10) and/or didehydrostemofoline (11). Further diversification within this structural type results from a mutual accumulation of derivatives with a pyrrolo- or pyridoazepine nucleus, leading to chemical variability in S. curtisii and S. aphylla.

Silvaglins and related 2,3-secodammarane derivatives - unusual types of triterpenes from Aglaia silvestris

Lipophilic crude extracts of leaves, stem and root bark of six different provenances of Aglaia silvestris were compared to determine species-specific chemical trends as well as infraspecific variability. 3,4-Secodammarane triterpenes formed the basic chemical equipment accompanied by the 2,3-seco derivative aglasilvinic acid, probably representing the precursor of the silvaglin A and isosilvaglin A characterised by a five membered ring A. In addition, the pregnane steroid pregnacetal was isolated and identified together with the known sesquiterpenes alpha-muurolene and viridiflorol, and the bisamide pyramidatin. Depending on the collection site all major triterpenes showed two different stereochemical trends either towards 20R or 20S configuration, giving rise to isolation and identification of the two isomers methylisofoveolate B (20S,24R) and methylfoveolate B (20R,24S) as well as the known derivatives shoreic acid (20S,24R), isoeichlerianic acid (20R,24S), and methylisoeichleriate (20R,24S). The structures were elucidated by 2D-NMR experiments and silvaglin A additionally by X-ray diffraction. The structural diversity and distribution of triterpenoids within the genus Aglaia is highlighted with respect to chemotaxonomic implications.

Bioactive amides from Glycosmis species

Besides the known imide ritigalin (9), six new phenethyl/styrylamine-derived amides isolated from lipophilic leaf extracts of Glycosmis cf. mauritiana, Glycosmis cf. cyanocarpa, and Glycosmis crassifolia displayed pronounced antifungal and/or insecticidal activity against Cladosporium herbarum and Spodoptera littoralis, respectively, the methylthiocarbonic acid derivatives niranin (1), dehydroniranin A (2), and dehydroniranin B (3) as well as the isovaleric and senecioic acid derivatives thalebanin B (4), dehydrothalebanin B (5), and dehydrothalebanin A (6).

Amide-esters from Aglaia tenuicaulis--first representatives of a class of compounds structurally related to bisamides and flavaglines

Six amide-esters and two sulphur-containing bisamides were isolated from the leaves, stem and root bark of Aglaia tenuicaulis together with two bisamides from the leaves of A. spectabilis. Their structures were elucidated by spectroscopic methods. The co-occurrence of amide-esters and bisamides suggests close biosynthetic connections replacing only one nitrogen atom of putrescine with oxygen. Putrescine appears to be the common building block linked to various acids from which the cinnamoyl moiety represents the prerequisite for an incorporation of bisamides into flavaglines. Corresponding amide-esters are apparently not incorporated, but closely related amide-alcohol derivatives were found as part of benzopyran and benzofuran flavaglines. The structure of a amide-alcohol is described, representing an artifact due to hydrolysis of an amide-ester during TLC purification. A hypothetical amide-amine building block is suggested to form the characteristic pyrimidinone structures only found in benzofuran flavaglines. Structural and biosynthetic connections between amide-esters, bisamides and flavaglines are discussed and the chemotaxonomic significance of accumulating specific derivatives within the genus Aglaia is highlighted.

Prenylated flavanones and flavanonols as chemical markers in Glycosmis species (Rutaceae)

Fifteen prenylated or geranylated flavanones and flavanonols were isolated from the leaf extracts of different Glycosmis species collected in Thailand and Malaysia. All structures were elucidated by spectroscopic methods, especially 1D and 2D NMR. Six compounds were described for the first time and two were only known so far as synthetic products. The chemotaxonomic significance of flavanoid accumulation within the genus Glycosmis is highlighted.

Pandanus alkaloids in Stemonaceae: finding of a plausible biogenetic origin of Stemona alkaloids

The isolation of (Z,Z)-pandanamine (1) and its corresponding isomers (Z,E)-pandanamine (2) and (E,E)-pandanamine (3) from Stichoneuron calcicola of the family Stemonaceae is of outstanding chemosystematic importance. This alkaloid was previously only known from the family Pandanaceae, where it was accompanied by a series of pyrrolidines, collectively called Pandanus alkaloids. The pyrrolidines pandamarilactonines A (4), B (5), C (6), and D (7) were also detected in the present study, most likely representing artificial cyclization products of pandanamine (1-3) formed by acidic conditions during chromatographic separation on silica gel. Similar structures were found in various Stemona alkaloids, suggesting a close relationship between the two plant families. Structurally, pandanamine (1-3) can be regarded as a direct precursor of croomine (8), originally isolated from Croomia, a genus closely related to Stichoneuron, but later also found in various Stemona species. The co-occurrence of pandanamine (1-3), croomine (8), and stichoneurin (9) in the family Stemonaceae represents a sound argument for a new interpretation of the biogenetic origin of Stemona alkaloids and at the same time substantiates the removal of the family from the order Dioscoreales and its inclusion into Pandanales, as already suggested by DNA sequencing.

Pyrrolo- and pyridoazepine alkaloids as chemical markers in Stemona species

Broad-based phytochemical investigations on 31 Stemona species and geographical provenances led to an overview concerning characteristic accumulation trends and the distribution of different Stemona alkaloids. Two major metabolic differences suggested a taxonomic segregation of the complex Stemona tuberosa group from the other species, and was supported by morphological characters. Whereas most of the Stemona species were characterised by protostemonine type alkaloids, the S. tuberosa group clearly deviated by accumulation trends towards tuberostemonine or croomine derived alkaloids belonging to two different skeletal types. Also of chemotaxonomic relevance was the structural divergence of protostemonine type alkaloids into pyrrolo- or pyridoazepine derivatives represented by stemofoline or oxystemokerrine, respectively, as major constituents. Their common occurrence in different provenances of S. curtisii, also deviating from the other species by various chromosome numbers, deserves special taxonomic attention. Species specific chemical markers were given by the unique accumulation of didehydrostemofoline (=asparagamine A) in S. collinsae and stemokerrine in S. kerrii. In contrast to previous reports, no bisdehydro derivatives with an aromatic pyrrole ring were detected supporting the hypothesis that these alkaloids are artifacts. A new stereoisomer of tuberostemonine was isolated and identified by spectroscopic methods.

Prenylated sulfonyl amides from Glycosmis species

Nine new sulfur containing amides were isolated from the lipophilic leaf extracts of different varieties of Glycosmis chlorosperma and G. ex aff. pseudoracemosa mainly collected in Thailand. Their structures were elucidated by spectroscopic methods. All amides were shown to be characterized by a methylsulfonylpropenoic acid moiety linked to a p-geranyloxy- or p-prenyloxy-phenethylamide rest. The compounds differ by different states of oxidation (i) at the 2-position of the ethylamine unit, (ii) at the aromatic m-position of phenethylamine, or (iii) at the terminal methyl group of the geranyloxy side chain.

Sesquiterpene lactones and other constituents from a cytotoxic extract of Michelia floribunda

The pentane and CHCl3 fractions of a crude extract of Michelia floribunda exhibited cytotoxic activity when tested in KB and P388 tumor cell cultures. Repeated chromatography led to the isolation of three cytotoxic sesquiterpene lactones (costunolide, parthenolide, and santamarine) and a cytotoxic isoquinoline alkaloid (liriodenine). Inactive sesquiterpene lactones obtained during the course of this study included dihydroparthenolide and two new glucosides of dihydrotamaulipin A and dihydroreynosin (1 and 2). The structures of these new compounds were determined through interpretation of their spectroscopic data including 2D-NMR spectroscopy. Syringin was also isolated from the extract.

Chemovariation and antibacterial activity of extracts and isolated compounds from species of Ixora and Greenea (Ixoroideae, Rubiaceae)

Background

A large number of secondary metabolites can be obtained from plants used for traditional medicine in two related genera (Ixora and Greenea) in the subfamily Ixoroideae (Rubiaceae), but there are only a few detailed studies on their bioactivities. Therefore, the main goals of this study were to determine the antibacterial activities of lipophilic extracts from plants of some Ixora and Greenea species native to Thailand, and to isolate some pure compounds from those extracts. Moreover, we compared the occurrence of compounds in different plant parts of samples from different habitats to better understand their variation.

Methods

A total of 56 lipophilic extracts were obtained from the leaves, stem bark, and root bark of eight Ixora and two Greenea species collected at various locations in Thailand. Isolated compounds were identified using nuclear magnetic resonance. Antimicrobial activities were evaluated against four Gram-positive and nine Gram-negative human pathogenic bacterial strains.

Results

Extracts from I. javanica, I. nigricans, I. brunonis, and G. montana, along with isolated scopoletin, exhibited antibacterial activities against Gram-positive methicillin-resistant Staphylococcus aureus ATCC 43300, with minimum inhibitory concentration values ranging from 64 to 256 µg/mL. The occurrence of scopoletin, isofraxidin, and geniposidic acid in lipophilic extracts showed some variation among different plant parts and species.

Conclusions

Lipophilic extracts of Ixora and Greenea species have the potential to be developed as anti-Gram-positive agents, in particular to counter infections of methicillin-resistant S. aureus strains. The chemical profiles showed differences between floristic regions but similarity within the same plant parts.

Part 1: Antiplasmodial, cytotoxic, radical scavenging and antioxidant activities of Thai plants in the family Acanthaceae

Crude extracts (CH(2)Cl(2) and MeOH) of 20 plants in the family Acanthaceae were screened for their antiplasmodial, cytotoxic, antioxidant, and radical scavenging activities. These plants included Asystasia nemorum, Barleria cristata, B. strigosa, Dicliptera burmanni, Eranthemum tetragonum, Hygrophila ringens, Justicia balansae, J. procumbens, Lepidagathis incurva, Peristrophe lanceolaria, Phaulopsis dorsiflora, Ruellia kerrii, Strobilanthes auriculata, S. corrugata, S. cusia, S. dimorphotricha, S. karensium, S. maxwellii, S. pateriformis, and S. brandisii. CH(2)Cl(2) extracts of A. nemorum, S. corrugata, S. cusia, S. maxwellii, S. pateriformis, and S. brandisii, as well as MeOH extracts of J. balansae and J. procumbens, showed antiplasmodial activity with IC(50) values of 10-100 µg/mL. CH(2)Cl(2) extracts of nine plants including D. burmanni, H. ringens, J. balansae, J. procumbens, L. incurva, P. lanceolaria, P. dorsiflora, S. corrugata, and S. maxwellii showed cytotoxic activity with IC(50) values of 3.5-46.0 µg/mL. MeOH extracts (at 100 µg/mL) of R. kerrii and S. auriculata could effectively scavenge DPPH free radicals (82-83% inhibition) and superoxide anion radicals (79% and 88% inhibition). In the ORAC antioxidant assay, MeOH extracts of B. cristata, J. procumbens, R. kerrii, and S. auriculata exhibited activity with ORAC units of 3.1-3.9.

Sequencing analysis of the medicinal plant Stemona tuberosa and five related species existing in Thailand based on trnH-psbA chloroplast DNA

In Thailand, Stemona tuberosa Lour. , S. phyllantha Gagnep. , S. collinsae Craib , S. burkillii Prain , S. aphylla Craib and S. sp. are found. The identification based on morphological characters alone is difficult and can lead to confusion regarding chemical constituents and biological activities. The tuberous roots of S. tuberosa have long been used for treatment of respiratory diseases and as anthelmintics. However, accurate identification of S. tuberosa is needed to ensure efficacy. Sequence comparison indicated that these Stemona spp. could be identified from the sequence of the trnH- psbA locus. As a result of different sequence lengths, the PCR products generated from newly designed primers could be used to preliminarily group the two species, S. tuberosa and S. phyllantha, apart from others. However, these products could be further sequenced to discriminate among Stemona spp.

Green Microalgae Strain Improvement for the Production of Sterols and Squalene

Sterols and squalene are essential biomolecules required for the homeostasis of eukaryotic membrane permeability and fluidity. Both compounds have beneficial effects on human health. As the current sources of sterols and squalene are plant and shark oils, microalgae are suggested as more sustainable sources. Nonetheless, the high costs of production and processing still hinder the commercialization of algal cultivation. Strain improvement for higher product yield and tolerance to harsh environments is an attractive way to reduce costs. Being an intermediate in sterol synthesis, squalene is converted to squalene epoxide by squalene epoxidase. This step is inhibited by terbinafine, a commonly used antifungal drug. In yeasts, some terbinafine-resistant strains overproduced sterols, but similar microalgae strains have not been reported. Mutants that exhibit greater tolerance to terbinafine might accumulate increased sterols and squalene content, along with the ability to tolerate the drug and other stresses, which are beneficial for outdoor cultivation. To explore this possibility, terbinafine-resistant mutants were isolated in the model green microalga Chlamydomonas reinhardtii using UV mutagenesis. Three mutants were identified and all of them exhibited approximately 50 percent overproduction of sterols. Under terbinafine treatment, one of the mutants also accumulated around 50 percent higher levels of squalene. The higher accumulation of pigments and triacylglycerol were also observed. Along with resistance to terbinafine, this mutant also exhibited higher resistance to oxidative stress. Altogether, resistance to terbinafine can be used to screen for strains with increased levels of sterols or squalene in green microalgae without growth compromise.

Chemical constituents of Clausena lenis

Phytochemical examination of Clausena lenis Drake (Rutaceae), collected in Thailand, led to the isolation of seven coumarins, four furoquinolines, two amides, and one flavonoid glycoside. Four of these compounds, one coumarine derivative named as gravelliferone A (3), two furoquinoline derivatives (kokusagenin A (8) and B (9)) and one amide, clausenalansamide H (13), are reported for the first time. Compound 3 was isolated from the root bark, compound 8 from the stem bark and compounds 9 and 13 from the leaves. The molecular structures of all isolated compounds were established by means of NMR experiments combined with mass spectrometry. Preliminary tests of the lipophilic stem bark extract against various human pathogenic bacteria strains revealed promising effects against Staphylococcus aureus ATCC 43300.