Bioassay-directed fractionation of an antiproliferative ethanol extract of the leaves and twigs of Piptocoma antillana (Asteraceae) afforded two new goyazensolide-type sesquiterpene lactones named 5-O-methyl-5-epiisogoyazensolide (1) and 15-O-methylgoyazensolide (2), together with the known compounds 1-oxo-3,10-epoxy-8-(2-methylacryloxy)-15-acetoxygermacra-2,4,11(13)-trien-6(12)-olide (3) and 5-epiisogoyazensolide (4). The structure elucidation of all compounds was carried out based on NMR and mass spectroscopic data analyses. The relative and absolute configurations of all the isolated compounds were determined from their CD and NOESY NMR spectra. Compounds 1–4 showed moderately potent antiproliferative activities against A2780 ovarian cancer cells, with IC50 values of 1.5±0.5, 0.6±0.3, 1.62±0.05, and 1.56±0.04 µM, respectively. They also displayed antimalarial activity against Plasmodium falciparum, with IC50 values of 6.2 ± 0.5, 2.2 ± 0.5, 8.0 ±0.4, and 9.0±0.6 µM, respectively.
Antiproliferative bioassay-guided fractionation of the ethanolic extract
of the endemic Madagascan plant Metaporana sericosepala led to
the first natural product isolation of a butenolide diterpene which was
synthesized during an anti-inflammatory study in 1988. The structure of the
compound was elucidated as 3-homofarnesyl-4-hydroxybutenolide (1)
by analysis of its spectroscopic data, including 1D- and 2D-NMR data and
chemical evidence. The once synthetic compound can now also be considered as a
natural product. Compound 1 had modest antiproliferative activity
towards the A2780 ovarian cancer cell line with an IC50 value of 8
μM.
An ethanol extract of leaves of the plant species
Malleastrum sp. collected in northern
Madagascar afforded the new clerodane diterpene
18-oxo-cleroda-3,13-dien-16,15-olide (1), together
with the three known clerodane diterpenes 16,18-dihydroxykolavenic acid lactone
(2), solidagolactone (3) and (−)-kolavenol
(4), and the known labdane diterpene
3-oxo-ent-Iabda-8(17),13-dien-15,16-olide (5). Compounds
1, 3, and 4 showed moderate
antiproliferative activities against the A2780 ovarian cancer cell line, with
the IC50 values of 3.01 ± 0.8, 7.84 ± 0.2, and 17.9
± 3 μM, respectively. The structure elucidations of all compounds
were carried out based on analysis of NMR and mass spectroscopic data. The
relative stereochemistry of compound 1 was determined by NOESY NMR
spectrum.
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