Larvicidal and IGR activity of extract of Tanzanian plants against malaria vector mosquitoes.

BACKGROUND & OBJECTIVES: This paper reports the larvicidal activity of seventeen Tanzanian plant species against the malaria vector, Anopheles gambiae s.s. Giles larvae. Some of the plants are used traditionally as sources of insecticidal materials. METHODS: The crude extracts from the leaves, stem and root barks of the investigated plants were obtained by solvent extraction and then bio-assayed following WHO protocols showed LC50 values 10 to 400 ppm after 24 h exposure. The structures were determined on interpretation of spectroscopic data. RESULTS: The most active extracts were those from the stem and root barks of Annona squamosa, Uvaria faulknerae, U. kirkii and Uvariodendron pycnophyllum, all of which had LC50 values between 10 and 100 ppm. Long-term exposure beyond 24 h also showed more susceptibility of the larvae to the extracts. Larvae deformities by forming tail-like structures were observed for the methanol extracts of Tessmannia martiniana var pauloi. INTERPRETATION & CONCLUSION: The results suggest that the investigated plant extracts are promising as larvicides against An. gambiae s.s. Giles mosquitoes and could be useful leads in the search for new and biodegradable plant derived larvicide products.

(+/-)-Schefflone: a trimeric monoterpenoid from the root bark of Uvaria scheffleri.

The trimeric monoterpene and mildly mosquito larvicidal agent, (+/-)-schefflone, that is an apparent derivative of the antiparasitic aromatic monoterpene espintanol, was isolated from the antimalarial extracts of the root bark of Uvaria scheffleri, together with espintanol. Structural determination of (+/-)-schefflone was achieved from spectroscopic data and confirmed by single-crystal X-ray diffraction analysis. (+/-)-Schefflone can be considered a product of a non-enzymatic Diels-Alder-type cycloaddition reaction of the quinonemethide derivative of espintanol as the diene and dienophile.

Antifungal Enantiomeric Styrylpyrones from Sanrafaelia ruffonammari and Ophrypetalum odoratum.

Phytochemical investigation of Sanrafaelia ruffonammari Verd and Ophrypetalum odoratum Diels that belongs to the rare genera confined to East African coastal forests led to the isolation of enantiomeric styrylpyrone dimer, (±)-5-methoxy-7-phenyl-[4-methoxy-2-pyronyl]-1-(E)-styryl-2-oxabicyclo-[4.2.0]-octa-4-en-3-one (1) alongside (+)-6-styryl-7,8-epoxy-4-methoxypyran-2-one (2) and the enantiomeric (+)- (3) and (-)-6-styryl-7,8-dihydroxy-4-methoxypyran-2-ones (4). Their structures were established by means of spectroscopic methods. In this paper we reveal for the first time the occurrence of styrylpyrones in East African biodiversity. (+)-6-Styryl-7,8-epoxy-4-methoxypyran-2-one (2) and the dihydroxystyrylpyrone enantiomer (3) showed in vitro antifungal activity against Candida albicans at a concentration of 24.4 and 26.2 µM with zones of inhibition of 17 and 9 mm, respectively. Compound 2 exhibited strong activity in the brine shrimp test with LC50 = 1.7 µg/mL. Their high cytotoxic and antifungal activities render them candidates for further scientific attention for drug development programs against cancer and microbial infections.

Bioactive isoflavones from Dalbergia vacciniifolia (Fabaceae).

Three new 5-dehydroxy isoflavone compounds, 6,2'-dimethoxy-7,4'-dihydroxyisoflavone (1), 6,2',4'-trimethoxy-7-hydroxyisoflavone (2), and 6,2',4',5'-tetramethoxy-7-O-[beta-D-apiofuranosyl-(1 --> 6)-beta-D-glucopyranoside] isoflavone (3), along with a known isoflavone, 6,2',4',5'-tetramethoxy-7-hydroxyisoflavone (4), were isolated from the ethanolic extract of Dalbergia vacciniifolia Vatke. Their structures were established by spectroscopic techniques including one- and two-dimension NMR. Compound 1 showed mild cytotoxic activity against brine shrimp larvae with a LC50 value of 266 microg/mL.

Antimosquito and antimicrobial clerodanoids and a chlorobenzenoid from Tessmannia species.

The clerodane diterpenoids trans-kolavenolic acid, 18-oxocleroda-3,13(E)-dien-15-oic acid, ent-(18-hydroxycarbonyl)-cleroda-3,13(E)-dien-15-oate, 2-oxo-ent-cleroda-3,13(Z)-dien-15-oic acid and trans-2-oxo-ent-cleroda-13(Z)-en-15-oic acid, and the chlorobenzenoid O-(3-hydroxy-4-hydroxycarbonyl-5-pentylphenyl)-3-chloro-4-methoxy-6-pentyl-2-oxybenzoic acid were isolated from Tessmannia martiniana var pauloi and T. martiniana var matiniana. Structures were established based on interpretation of spectroscopic data. Some of the compounds exhibited significant antimosquito, antifungal and antibacterial activities.

Anti-mosquito and antimicrobial nor-halimanoids, isocoumarins and an anilinoid from Tessmannia densiflora.

The nor-halimane diterpenoid tessmannic acid and its methyl, 2-methylisopropyl and 1-methylbutyl esters, the unusual isocoumarins 8-hydroxy-6-methoxy-3-pentylisocoumarin and 7-chloro-8-hydroxy-6-methoxy-3-pentylisocoumarin, and 5-pentyl-3-methoxy-N-butylaniline were isolated from the stem and root bark extracts of Tessmannia densiflora Harms (Caesalpiniaceae) that showed mosquito larvicidal activity. The structures were determined on interpretation of spectroscopic data. Tessmannic acid and its methyl ester exhibited antibacterial and antifungal activity. The compounds also caused high larvae and adult Anopheles gambiae mosquitoe mortality effects, and stronger mosquito repellency than that shown by the standard repellent DEET, hence indicating Tessmannia species to be potential sources of bioactive natural products.