Complete 1H and 13C NMR data assignment of new constituents from Severinia buxifolia.

Phytochemical analysis of different organs of the rutaceaeous plant Severinia buxifolia led to the isolation of a new limonoid, a new acridone alkaloid, and a new flavone. Structure elucidation and signal assignment were achieved by the extensive use of 1D and 2D NMR experiments (selective 1D NOE, COSY, NOESY, HSQC, HMBC).

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.

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.

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.

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.

Flavaglines and triterpenoids from the leaves of Aglaia forbesii.

Three structurally complex flavaglines of the cyclopenta[bc]benzopyran type, named desacetylpyramidaglains A, C, D (1-3), and the triterpene 23, 24, 25-trihydroxycycloartan-3-one (4) were isolated from the leaves of Aglaia forbesii together with the two rare pregnane steroids 2beta,3beta-dihydroxy-5alpha-pregn-17(Z)-en-16-one and 2beta,3beta-dihydroxy-5alpha-pregn-17(E)-en-16-one, as well as the bisamide pyramidatine, the sesquiterpene spathulenol, and the widespread triterpenoids lupeol, lupenone, and a mixture of beta-sitosterol and stigmasterol. Their structures were elucidated by 1D and 2D NMR spectroscopy and mass spectrometry. Compounds 3, 4, 5, and 6 were tested for antituberculosis and antiviral activity.

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.

Anti-inflammatory activity of two diterpenes of Hyptis suaveolens from El Salvador.

Separation and isolation of the two main compounds suaveolol and methyl suaveolate from leaves of chichinguaste (Hyptis suaveolens Poit., Lamiaceae) could be achieved by means of repeated column chromatography and repeated preparative thin layer chromatography. Their chemical structures were approved by MS, 1H NMR, 13C NMR and 2D-NMR experiments. The anti-inflammatory activity of the two compounds was tested for the first time as inhibition of croton oil-induced dermatitis of the mouse ear. Suaveolol and methyl suaveolate showed nearly the same dose-dependent topical anti-inflammatory activity, only two to three times lower than that of the reference drug indomethacin. The anti-inflammatory properties of these compounds could contribute to the antiphlogistic activity of extracts of Hyptis species and confirm the rational use of Hyptis suaveolens extracts in dermatological diseases.

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.

Two pyrrolo[1,2-a]azepine type alkaloids from Stemona collinsae Craib: structure elucidations, relationship to asparagamine A, and a new biogenetic concept of their formation.

The alkaloids 1',2'-didehydrostemofoline (2) and 2'-hydroxystemofoline (3) from Stemona collinsae Craib (Stemonaceae) were studied by X-ray crystallography and NMR spectroscopy, and they are compared with the parent compound stemofoline (1). The X-ray analysis of the CH2Cl2 solvate of 2'-hydroxystemofoline (3) allowed the determination of the absolute configuration of this compound unequivocally, whereas optical rotation was used to infer the absolute configuration of 1',2'-didehydrostemofoline (2). Based on these results, it is shown that asparagamine A isolated from Asparagus racemosus Willd. (Asparagaceae) is identical to 1',2'-didehydrostemofoline obtained from S. collinsae Craib, and that the reported plant source of asparagamine A was most likely a Stemona species. In the context of the current investigations, a novel concept on the biosynthesis of Stemona alkaloids has been worked out and is presented here.

Insecticidal pyrido[1,2-a]azepine alkaloids and related derivatives from Stemona species.

Eight new alkaloids, the pyrido[1,2-a]azepines stemokerrin, methoxystemokerrin-N-oxide, oxystemokerrin, oxystemokerrin-N-oxide, and pyridostemin, along with the pyrrolo[1,2-a]azepines dehydroprotostemonine, oxyprotostemonine, and stemocochinin were isolated from four Stemona species together with the known compounds protostemonine, stemofoline, 2'-hydroxystemofoline, and parvistemonine. Their structures were elucidated by 1H and 13C NMR including 2D methods and two key compounds additionally by X-ray diffraction. Besides the formation of a six membered piperidine ring, additional oxygen bridges and N-oxides contributed to structural diversity. The co-occurrence of pyrrolo- and pyridoazepines suggested biosynthetic connections starting from more widespread protostemonine type precursors. Bioassays with lipophilic crude extracts against Spodoptera littoralis displayed very strong insecticidal activity for the roots of S. curtisii and S. cochinchinensis, moderate activity for S. kerrii, but only weak effects for the unidentified species HG 915. The insect toxicity was mainly caused by the accumulation of stemofoline, oxystemokerrin, and dehydroprotostemonine displaying two different modes of action. Based on the various insecticidal activities of 13 derivatives structure-activity relationships became apparent.

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.