A bioassay-guided fractionation of the EtOH extract of the Madagascan plant Terminalia calcicola H. Perrier (Combretaceae) led to the isolation of two new cytotoxic xanthones, termicalcicolanone A (1) and termicalcicolanone B (2). The structures of the new compounds were established on the basis of one and two dimensional NMR spectroscopic data. Both compounds showed modest antiproliferative activity toward the A2780 human ovarian cancer cell line.In our continuing search for bioactive molecules from the Madagascar rainforests as part of an International Cooperative Biodiversity Group (ICBG) program, 1 we obtained extracts of various parts of the tree Terminalia calcicola H. Perrier (Combretaceae) collected in Madagascar. The EtOH extract of the immature fruit proved to have moderate antiproliferative activity, with an IC 50 value of 14 µg/mL against the A2780 human ovarian cancer cell line. This extract was thus selected for bioassay-guided fractionation based on its cytotoxicity and also on the absence of any previous detailed phytochemical studies on this species.Previous phytochemical studies have revealed the genus of Terminalia to be a rich source of secondary metabolites, such as lignans, 2 flavonoids, 3 terpenoids, 4 and tannins. 5 Some of these metabolites have shown a wide range of biological activities, including anti-HIV-1, 2 antimalarial, 2 antifungal, 2,4 antibacterial, 4,6 and cytotoxic 5 activities. The anthelminthic and haemolytic properties of the terpene esters from T. macroptera have been studied. 4 The antioxidant effects of aqueous extract of T. chebula have also been investigated. 7Activity-guided fractionation of the dichloromethane extract (IC 50 , 10 µg/mL) by passage over a C18 open column, followed by purification of active fractions using C18 HPLC, led to the isolation of the two new compounds, 1 and 2. Table 1, including one carbonyl group, two aromatic rings with six oxygenated carbons, and two prenyl groups. The H-1″ resonance appeared at δ H 4.68, which was a more deshielded value than that usually found for this functionality, due to the effect of the C-9 carbonyl group. 9 Clearly, both the C-1 hydroxy and the C-8 3-methyl-but-2-enyl groups were peri to the carbonyl group. The ortho coupled aromatic H-5 and H-6 showed 3 J HMBC correlations (Figure 1) to C-7 and C-8a, and C-8 and C-10a, respectively, while H-1″ correlated to C-7, C-8, C-8a, C-2″, and C-3″, which provided further evidence for the position of the 3-methyl-but-2-enyl group at C-8. The HMBC correlations between the hydrogen-bonded proton (1-OH) and C-1, C-2, and C-9a, H-1′ and C-1, and H-2′ and C-2 were also observed, indicating that the 3′,3′-dimethylpyrano ring was fused at C-2 and C-3, which was confirmed by a ROESY correlation between the hydrogenbonded proton and H-1′. Based on the molecular formula of 1, the remaining two hydroxy groups must be located at C-4 and C-7, respectively. Thus, the structure of 1 was determined to be 5,8,12Termicalcicolanone B (2) was also obtained as a yellow powder. It was ...

Bioassay-guided fractionation of an ethanol extract of the leaves and inflorescence of Mallotus oppositifolius collected in Madagascar led to the isolation of the two new bioactive dimeric phloroglucinols, mallotojaponins B (1) and C (2), together with the known mallotophenone (3). The structures of the new compounds were determined on the basis of spectroscopic evidence, including their 1- and 2D-NMR spectra, mass spectrometry, and an X-ray crystal structure. Compounds 1 and 2 showed potent antimalarial activity against chloroquine-resistant Plasmodium falciparum, with IC50 values of 0.75 ± 0.30 and 0.14 ± 0.04 μM, while 3 was inactive in this assay. Compounds 1–3 also displayed strong antiproliferative activity against the A2780 human ovarian cancer cell line (IC50 1.10 ± 0.05, 1.3 ± 0.1 and 6.3 ± 0.4 μM, respectively).

Aim To determine the role of regional forcing on plot‐level species diversity and composition, and to quantify the relative importance of biogeographical and climatic factors in explaining woody plant diversity and composition at the local‐, island‐ and archipelago‐scale. Location Forty‐one tropical islands of the Indo‐Pacific region from Madagascar to Hawai‘i Island. Methods We analysed the diversity and composition of tropical woody plant communities located across 113 plots, 41 islands and 19 archipelagos. We used generalized linear mixed‐effects models and generalized dissimilarity models to determine the role of regional forcing at the island and archipelago scale and to assess the relative importance of biogeographical (area and isolation of islands or archipelagos, geographical distance between plots) and climatic factors in explaining differences in local diversity and composition (species turnover). Analyses were conducted at different geographical scales (local, island and archipelago) and taxonomic levels (species, genus and family). Results Variation in local (plot‐level) diversity (as species density, the number of species per 100 woody plants) was primarily explained by island and archipelago identity. Maximum species density was positively correlated with the area of an island (or archipelago) and negatively correlated with the isolation of an archipelago. Local climatic variability was also a significant predictor of species density, but less important than regional forcing. Climate variables explained < 20% of the variation in species turnover across all plots. The importance of geographical distance between plots relative to climate in driving species turnover decreased from the species to family level, and from the regional to island level. Main conclusions Regional forcing was the key driver of local diversity and composition on islands. Island area and archipelago isolation are likely driving local diversity through their effects on the pool of island species. Geographical distance between plots is the main factor explaining species turnover, while at higher taxonomic levels, climatic factors and niche conservatism are the main drivers.

We conducted a survey along three belt transects located at increasing distances from the coast to determine whether a non-random arboreal ant assemblage, such as an ant mosaic, exists in the rainforest on the Masoala Peninsula, Madagascar. In most tropical rainforests, very populous colonies of territorially dominant arboreal ant species defend absolute territories distributed in a mosaic pattern. Among the 29 ant species recorded, only nine had colonies large enough to be considered potentially territorially dominant; the remaining species had smaller colonies and were considered non-dominant. Nevertheless, the null-model analyses used to examine the spatial structure of their assemblages did not reveal the existence of an ant mosaic. Inland, up to 44% of the trees were devoid of dominant arboreal ants, something not reported in other studies. While two Crematogaster species were not associated with one another, Brachymyrmex cordemoyi was positively associated with Technomyrmex albipes, which is considered an invasive species—a non-indigenous species that has an adverse ecological effect on the habitats it invades. The latter two species and Crematogaster ranavalonae were mutually exclusive. On the other hand, all of the trees in the coastal transect and at least 4 km of coast were occupied by T. albipes, and were interconnected by columns of workers. Technomyrmex albipes workers collected from different trees did not attack each other during confrontation tests, indicating that this species has formed a supercolony along the coast. Yet interspecific aggressiveness did occur between T. albipes and Crematogaster ranavalonae, a native species which is likely territorially dominant based on our intraspecific confrontation tests. These results suggest that the Masoala rainforest is threatened by a potential invasion by T. albipes, and that the penetration of this species further inland might be facilitated by the low density of native, territorially dominant arboreal ants normally able to limit its progression.