Abstract
In addition to the trichilianones A–D recently reported from Trichilia adolfi, a continuing investigation of the chemical constituents of the ethanol extract of the bark of this medicinal plant yielded the five new limonoids 1–5. They are characterized by having four fused rings and are new examples of prieurianin-type limonoids, having a ε-lactone which in 4 and 5 is α, β- unsaturated. The structures of the isolated metabolites were determined by high field NMR spectroscopy and HR mass spectrometry. The new metabolites were shown to have the ε-lactone fused with a tetrahydrofuran ring which is connected to an oxidized hexane ring joined with a cyclo-pentanone having a 3-furanyl substituent. As the crude extract possesses antileishmanial activity, the compounds were assayed for cytotoxic and antiparasitic activities in vitro in murine macrophage cells (raw 264.7 cells) and in Leishmania amazoniensis as well as L. braziliensis promastigotes. Metabolites 1–3 and 5 showed moderate cytotoxicity (between 30–94 µg/mL) but are not responsible for the antileishmanial effect of the extract.
Highlights
The Meliaceae family of plants includes species dispersed in tropical areas of America, Africa and Asia [1,2]
The Trichilia genus, part of this family, comprises several species that have been studied as they are used in traditional medicine, and phytochemical investigations have revealed that limonoids are typical constituents
Limonoids are characterized for having various carbon skeleta, being highly oxygenated and often substituted with a 3-furanyl moiety [3]
Summary
The Meliaceae family of plants includes species dispersed in tropical areas of America, Africa and Asia [1,2]. The methyl 18-H3, which is a singlet, gives HMBC correlations to C-12, C-13, C-14 and C-17, suggesting that is attached to the non-protonated C-13 This reveals the following partial carbon skeleton: C-24/25–C-4–C-5– C-10–C-9–C-8–C-14–C-13–C-18. The missing substituent on C-17 is a 3-furanyl group, and this partial structure was determined in the same way as with the trichilianones [21] by COSY, HMBC and 1J(C,H) couplings constants This forms the third ring accounting by itself for three unsaturations, and the NMR data are quite similar to those reported for other limonoids containing a 3-furanyl substituent [23]. The saturation index for 4 was 13, one more than the previously discussed trichilones, and the examination of the NMR 1D 1H and 13C NMR spectra reveals the presence of five carbonyl groups and three C-C double bonds This suggests that 4 consists of five rings. NOESY experiments show that the relative configuration of 5 is the same as in 4
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