Bioactive single-ring acetogenins from seed extracts of Annona muricata.
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Biomedical subjects
Publications and source records attributed to J K Rupprecht.
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Several acetogenins, characteristic of the Annonaceae, have been found to exhibit pesticidal and feeding-deterrent activities against a variety of pests and are undergoing commercial development as pesticides. The sensitizing potential of one of these plants, pawpaw, Asimina triloba Dunal, was examined in the current study. The potential of Fraction F020 (a pesticidal crude extract of pawpaw stem bark) to sensitize and elicit an allergic contact dermatitis response was determined by using a modified guinea pig maximization test (GPMT). Fraction F020 is a weak sensitizer and the active compound, asimicin, a trihydroxy-bistetrahydrofuran fatty acid gamma-lactone, is a weak irritant.
Fractionation of the EtOH extract of the bark of Asimina triloba, monitoring by brine shrimp lethality, has led to the isolation and structural elucidation of a novel highly cytotoxic Annonaceous acetogenin, trilobacin [1], in addition to six known compounds: asimicin 2], bullatacin [3], bullatacinone [4], N-p-coumaroyltyramine [5], N-trans-feruloyltyramine [6], and (+)-syringaresinol [7]. Acetogenin 1 was identified as a diastereomer of asimicin [2] by spectral and chemical methods, and both 1 and 2 showed potent and selective cytotoxicities in the NCI human tumor cell line screen.
Various plant parts of the paw paw tree (Asimina triloba Dunal, Annonaceae) were extracted and partitioned to concentrate the mixture of acetogenins into a standardized pesticidal extract (F005). A bioassay with brine shrimp larvae (Artemia salina Leach) was used to determine the relative potencies of the various extracts. The small twigs (0-0.5 cm diameter) yielded the most potent extract (LC50 = 0.04 ppm); the stem wood (LC50 = 4.9 ppm) and leaves (LC50 = 53.7 ppm) yielded the poorest activities. The unripe fruits, seeds, root wood, root bark, and stem bark were notably potent and, generally, yielded > 2% of their dry weight as F005. The smaller diameter stems were more potent than the larger stems. We conclude that, by pollarding the trees, the entire twigs and small branches of paw paw could be processed to produce a potent acetogenin mixture; this biomass could be made available in quantities needed for commercialization of the pesticidal product and could be renewable through regrowth from the parent trunk and larger branches.
Gigantecin (I), a novel tetrahydroxy-di-tetrahydrofuran fatty acid gamma-lactone (acetogenin), was isolated from an ethanolic extract of the stem bark of Goniothalamus giganteus Hook. f., Thomas (Annonaceae), by means of activity-directed fractionation (brine shrimp lethality test). This new compound is extremely cytotoxic to human tumor cells, inhibits crown gall tumors on potato discs, and is active in an assay designed to detect antimitotic agents (9 ASK).
Sylvaticin (I), a new tetrahydroxy annonaceous acetogenin with nonadjacent tetrahydrofuran rings, has been isolated from the dried fruits of Rollinia sylvatica St. Hil. (Annonaceae). This compound is extremely cytotoxic to human tumor cells and shows promising insect control properties.
Using brine shrimp lethality for activity-directed fractionation, goniothalamicin (I), a new tetrahydroxy-mono-tetrahydrofuran fatty acid gamma-lactone (acetogenin), has been isolated from ethanolic extracts of the stem bark of Goniothalamus giganteus Hook. f., Thomas (Annonaceae). This novel compound was found to be cytotoxic and insecticidal and inhibited the formation of crown gall tumors on potato discs. Annonacin (II), the only other reported mono-tetrahydrofuran acetogenin, was also isolated; the previously reported 9ASK (astrocytoma reversal) activity of II was confirmed, and II is now also found to be weakly active against 3PS murine leukemia.
Screening of crude extracts of the bark of Annona bullata showed cytotoxic and pesticidal activities. By monitoring with brine-shrimp lethality, two novel, extremely potent acetogenins, bullatacin [1] and bullatacinone [2], were isolated. Spectral and chemical methods identified bullatacin as a diastereomer of asimicin. Bullatacinone represents bullatacin with the lactone cleaved and reformed at the 4-OH. Compounds 1 and 2 show selective cytotoxicities in human tumor cell lines, and certain susceptible cells give ED50 values as low as 10(-12)-10(-15) micrograms/ml. Bullatacin was pesticidal at concentrations as low as 1 ppm, but bullatacinone lacked pesticidal activities. The known compounds liriodenine and (-)-kaur-16-en-19-oic acid were also isolated and were lethal to brine shrimp but were not significantly cytotoxic.
Activity-directed fractionation of the stem bark of Annona squamosa, monitoring with brine shrimp lethality, led to the isolation of the highly bioactive acetogenins bullatacin [1] and bullatacinone [2], thus demonstrating a new abundant plant source for these potent compounds. A new keto-monotetrahydrofuran acetogenin with a ketolactone terminus, as first seen in bullatacinone [2], was also isolated, characterized by spectral analyses, and named squamone [3]. The cytotoxicities of 3 were increased significantly by reduction of the two keto groups to hydroxyls, and the tetrahydrosquamone [7] and bullatacinone [2] both showed selective cytotoxicities to MCF-7 human breast carcinoma. Liriodenine and (-)-kaur-16-en-19-oic acid were also isolated.
The Annonaceous acetogenins are a series of apparently polyketide-derived fatty acid derivatives that possess tetrahydrofuran rings and a methylated gamma-lactone (sometimes rearranged to a methyl ketolactone) with various hydroxyl, acetoxyl, and/or ketoxyl groups along the hydrocarbon chain. They exhibit a broad range of potent biological activities (cytotoxicity, antitumor, antimalarial, antimicrobial, immunosuppressant, antifeedant, and pesticidal). The sources, isolation, chemistry, biogenesis, and biological actions of these compounds, published to date, are tabulated and discussed. Strategies for structural elucidation are reviewed, and structural revisions and refinements are suggested for some of the previously published compounds.