Markus Bacher

Thapsakins: possible biogenetic intermediates towards insecticidal cyclopenta[b]benzofurans from Aglaia edulis

Abstract Nine new flavaglines, cyclopenta[bc]benzopyrans (thapsakins) and benzo[b]oxepines (thapoxepines), were isolated from the lipophilic root extract of Aglaia edulis together with two known cyclopenta[b]benzofurans, aglaroxin A and pannellin. The structures were established on the basis of extensive use of NMR spectroscopic methods (C,H-COSY, NOESY, HMBC, lanthanide induced shifts). Aglaroxin A and pannellin exhibited the strongest insect toxicity toward neonate larvae of Spodoptera littoralis. Possible biogenetic connections between the three skeletal types are outlined and chemosystematic implications of flavagline formation are discussed.

Pyranoquinolones and acridones from Vepris bilocularis

Besides already known furoquinolones and acridones, three new pyrano-2-quinolones and one new acridone were isolated from the leaves of south Indian Vepris bilocularis. The novel alkaloids were identified by spectroscopic means and named 7-methoxyflindersine, 7-prenyloxyflindersine, N-methyl-7-prenyloxy-flindersine and vebilocine.

Stress induced carbazole phytoalexins in Glycosmis species

Induced formation of a series of carbazole alkaloids was observed in leaves of Glycosmis parviflora and G. pentaphylla after wounding, UV-irradiation, and particularly after inoculation with the fungus Botrytis cinerea. Chemical variation between different provenances and even individuals of G. parviflora led to an accumulation of different derivatives from which three proved to be undescribed natural products. Their structures were identified by spectroscopic methods and named carbalexins A, B, and C. Bioautographic tests on TLC plates with Cladosporium herbarum exhibited strong antifungal activity for the new carbalexins as well as for the already known 2-hydroxy-3-methylcarbazole, but only weak effects for the pyranocarbazole glycoborinine. Detailed experiments with marked infection areas confirmed the restricted accumulation of carbazole derivatives which could not be detected in non-infected areas of the same leaf. Apart from carbazoles, in some individuals of G. parviflora an additional accumulation of the pyranoquinolones flindersine and methylflindersine was induced, which supports the already previously discussed biogenetic connections between carbazoles and prenylated quinolones.

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.

Prenylated phenylpropenes from Coleonema pulchellum with antimicrobial activity

The lipophilic root extract of Coleonema pulchellum was analysed and tested for antifungal and antibacterial activity. Eight previously undescribed prenyloxy and geranyloxy phenylpropenes, were isolated as major compounds together with the known evofolin-C as well as the lignans (+/-)-sesamin and (+/-)-prenylpiperitol, the diterpene (-)-pimara-9(11),15-dien-19-oic acid and the 2,4-decadienoic acid isobutylamide. All structures were established by spectroscopic evidence. From the new phenylpropenes, named evofolin-C-acetate, colenemol, colenemal, prenycol acetate, dehydroprenycol acetate, precolpuchol, colpuchol and colpuchol acetate, the dihydroxylated precolpuchol displayed the strongest antifungal and antibacterial activity against Cladosporium herbarum and Staphylococcus aureus, respectively.

Organ-specific chemical differences in Glycosmis trichanthera

The lipophilic leaf, stem and root extracts of Glycosmis trichanthera are characterized by distinct chemical profiles, containing sulphur-containing amides in the leaves, prenylated acridone alkaloids in the stem bark, and quinoline alkaloids together with a 3,7-diprenylated indole in the root bark. Two isomeric sulphones derived from methylthio-propenoic acid phenethylamides, named trichanthin-A and -B, and the 3,7-diprenylated indole proved to be new natural products. Structure elucidation of the new compounds is described by spectroscopic evidence. Bioautographic tests with Cladosporium herbarum showed only moderate antifungal activity for trichanthin-B and methylgerambullin.

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). Copyright

Oximes from seeds of Atalantia ceylanica

Abstract The lipophilic seed extract of Atalantia ceylanica is characterized by two new oximes, ataloxime A and B, and the known furanocoumarins bergapten, xanthotoxin, heraclenin, oxypeucedanin and imperatorin. The structures of the oximes were elucidated by spectroscopic methods, whereas the furanocoumarins were identified by HPLC-UV and TLC comparisons with authentic samples. The oximes displayed contact toxicity against freshly hatched larvae of the pest insect Spodoptera littoralis but did not show antifungal activities against Cladosporium herbarum.

Quality assessment and antiplasmodial activity of West African Cochlospermum species

The present study focuses on development of phytochemical methods for quality assessment of two West-African Cochlospermum species (Cochlospermum planchonii and Cochlospermum tinctorium) traditionally used for malaria treatment in Burkina Faso. Antimalarial activity of preparations from dried rhizomes (decoction) was tested against the chloroquine-sensitive Plasmodium strain 3D7 using the histidine-rich protein II (HRP2) drug susceptibility assay and compared with extract preparations using organic solvents of different polarity. Two main apocarotenoids were isolated from rhizomes of C. planchonii and unambiguously identified as dihydrocochloxanthine and cochloxanthine by spectroscopic methods. Comparative HPLC analyses of thirty-nine (39) samples from markets and from collections in natural habitats of both species showed a high variability in the accumulation of cochloxanthines and related carotenoids which were proven to be characteristic for rhizomes of both species and generally absent in leaves. Furthermore, content of total phenolics and antioxidant activities (DPPH and FRAP) as well as haemolytic activity of various extracts was tested. The HPLC method presented here was validated and provides a good separation of both compounds including 10 minor carotenoids. Extracts from both species and pure cochloxanthine offered pronounced antioxidant activities and weak haemolytic activity while, in contrast, dihydrocochloxanthine had a strong haemolytic effect at the highest concentration analysed. However, cochloxanthine as well as dihydrocochloxanthine showed erythroprotective effects against the haemolytic activity of the reference saponin. Moderate antiplasmodial activity between 16 and 63 μg/ml were observed with all tested extracts, and lower IC50 values were obtained with pure dihydrocochloxanthine (IC50=6.9 μg/ml), cochloxanthine (IC50=6.8 μg/ml), the DCM fraction (IC50=2.4 μg/ml) and the ethyl acetate fraction (IC50=11.5μg/ml) derived from a methanolic extract of C. planchonii. This study shows a major variability of carotenoid content and antiplasmodial activity of both C. planchonii and C. tinctorium. The high haemolytic activity of dihydrocochloxanthine (at 100 μg/ml) should be considered as a selection criterion for choosing species phenotypes for treatment.