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Trichilianones A-D, Novel Cyclopropane-Type Limonoids from Trichilia Adolfi

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Trichilianones A-D, Novel Cyclopropane-Type Limonoids from Trichilia Adolfi molecules Article Trichilianones A-D, Novel Cyclopropane-Type Limonoids from Trichilia adolfi Ivan Limachi 1,2 , Mariela Gonzalez-Ramirez 1, Sophie Manner 1 , Juan C. Ticona 2, Efrain Salamanca 2, Alberto Gimenez 2 and Olov Sterner 1,* 1 Department of Chemistry, Centre for Analysis and Synthesis, Lund University, 22100 Lund, Sweden; [email protected] (I.L.); [email protected] (M.G.-R.); [email protected] (S.M.) 2 Instituto de Investigaciones Farmaco Bioquimicas, Universidad Mayor de San Andres, La Paz, Bolivia; [email protected] (J.C.T.); [email protected] (E.S.); [email protected] (A.G.) * Correspondence: [email protected]; Tel.: +46-70-5306649 Abstract: The fractionation of an ethanol extract of the bark of Trichilia adolfi yielded four novel limonoids (trichilinones A-D, 1–4), with five fused rings and related to the hortiolide-type limonoids. Starting with an "-lactone, which is α,β-unsaturated in trichilinones A and D (1 and 4), attached to a tetrahydrofuran ring that is connected to an unusual bicyclo [5.1.0] hexane system, joined with a cyclopentanone with a 3-furanyl substituent [(2-oxo)-furan-(5H)-3-yl in trichilinone D (4)], the four compounds isolated display a new 7/5/3/5/5 limonoid ring system. Their structures were established based on extensive analysis of NMR spectroscopic data. As the crude extract possessed anti-leishmanial properties, the compounds were assayed for cytotoxic and anti-parasitic activities in vitro in murine macrophages cells (Raw 264.7) and leishmania promastigotes (L. amazoniensis Citation: Limachi, I.; and L. braziliensis), respectively. The compounds showed moderate cytotoxicity (approximately Gonzalez-Ramirez, M.; Manner, S.; 70 µg/mL), but are not responsible for the leishmanicidal effect of the extract. Ticona, J.C.; Salamanca, E.; Gimenez, A.; Sterner, O. Trichilianones A-D, Keywords: Trichilia adolfi; cyclopropane-limonoids; cytotoxicity; leishmanicidal activity Novel Cyclopropane-Type Limonoids from Trichilia adolfi. Molecules 2021, 26, 1019. https://doi.org/10.3390/ molecules26041019 1. Introduction The genus Trichilia is vast, comprising flowering plants belonging to the Meliaceae Academic Editor: Jane Ward family. Additionally included in Trichilia are trees widely distributed across the tropical forests in America, Europe, Africa and Asia [1]. In South America, Trichilia species are Received: 19 January 2021 used in traditional medicine by several cultures throughout the continent, for example, Accepted: 11 February 2021 in Bolivia, where this has been conserved in the traditional medicine of the Tacana [2]. Published: 15 February 2021 An ethnobotanical report reviewing the medicine of the Tacana identified three Trichilia species, T. inaeqilatera, T. pleeanea and T. adolfi, as plants that have been used to treat lung, Publisher’s Note: MDPI stays neutral kidney and liver pains [3]. The treatment consists of preparing an infusion of the bark with regard to jurisdictional claims in published maps and institutional affil- boiled in water, which was drunk daily and the procedure was widespread among the iations. Tacanas. During an ongoing screening of Bolivian plants for metabolites with antiparasitic activities [4], an ethanol extract of the bark of T. adolfi was found to possess antileishmanial properties. As this species is poorly investigated for contents of secondary metabolites, a phytochemical study including the testing of isolated metabolites for antileishmanial activities, motivated the examination presented here. Copyright: © 2021 by the authors. The secondary metabolites of other Trichilia species have been studied, and a large Licensee MDPI, Basel, Switzerland. number of limonoids and other terpenoids have been isolated. To some extent, these This article is an open access article distributed under the terms and were investigated in various biological assays. Limonoids are compounds based on the conditions of the Creative Commons triterpenoid class, and as a family of phytochemicals, they display a huge diversity. Struc- Attribution (CC BY) license (https:// turally, they are highly oxygenated tetranortriterpenoids with various carbon skeleta, creativecommons.org/licenses/by/ normally possessing furan and lactone rings, and structurally classified by their basic four 4.0/). rings [5] as well as modifications in these. The most representative examples found in the Molecules 2021, 26, 1019. https://doi.org/10.3390/molecules26041019 https://www.mdpi.com/journal/molecules Molecules 2021, 26, 1019 2 of 13 Molecules 2021, 26, 1019 triterpenoid class, and as a family of phytochemicals, they display a huge diversity.2 of 13 Structurally, they are highly oxygenated tetranortriterpenoids with various carbon skel- eta, normally possessing furan and lactone rings, and structurally classified by their basic four rings [5] as well as modifications in these. The most representative examples found genusin the genusTrichilia Trichiliaare the are trichilin-type the trichilin-type limonoids limonoids [6] that[6] that conserve conserve the the four-ring four-ring system sys- of thetem triterpeneof the triterpene precursor precursor intact, theintact, mexicanolide-type the mexicanolide-type limonoids limonoids [7], the [7], phragmalin-type the phrag- limonoidsmalin-type [limonoids8], and the [8], prieurianin-type and the prieurianin-type limonoids limonoids [9]. Examples [9]. Examples of these of arethese shown are in Figureshown1 in. Figure 1. Figure 1. RelatedRelated compounds compounds isolated isolated from from other other sources. sources. An initial focus was toto useuse limonoidslimonoids asas bio-pesticides,bio-pesticides, andand aa well-knownwell-known exampleexample that receivedthat received much much attention attention is the is potent the potent antifeedant antifeedant azadirachtin, azadirachtin, isolated isolated from from the seedsthe of theseeds neem of the tree neem (Azadirachta tree (Azadirachta indica)[ indica10]. However,) [10]. However, recent recent studies studies are more are more oriented oriented towards theirtowards antibiotic their antibiotic [11], cytotoxic [11], cytotoxic [12] and [12] anticancer and anticancer [13] properties. [13] properties. The present present study study is is focused focused on on the the charac characterizationterization of ofmetabolites metabolites present present in an in an extract of the bark of Trichilia adolfi adolfi (see(see Experimental Experimental section section fo forr details). details). The The structures structures of theof the isolated isolated metabolites metabolites were were elucidated elucidated after after an extensivean extensive spectroscopic spectroscopic analysis analysis based essentially on the elemental composition determined by high-resolution mass spectrometry and 1D NMR as well as 2D NMR experiments. The cytotoxicity of pure compounds was evaluated in vitro in cell cultures of murine macrophages (Raw 264.7), while the leishmani- cidal properties were evaluated in the two leishmania-promastigote strains Leishmania amazoniensis and L. braziliensis (see Experimental section for details). Molecules 2021, 26, 1019 3 of 13 2. Results and Discussion The structures of the novel compounds isolated are shown in Figure2, while the 1H and 13C NMR data are given in Tables1 and2. The COSY correlations observed for compounds 1–4 are summarized in Figure3, the HMBC correlations in Figure4, and the NOESY correlations in Figure5. 2.1. Structure Determination of Trichilianone A (1) Trichilianone A (1, name proposed by us and derived from the plant genus name Trichilia) was isolated as a white amorphous powder, although repeated re-crystallization in methanol/water (1:2) eventually gave crystals with the melting point 181 ◦C. Sadly, any attempt to obtain an X-ray structure of these failed, however, the elemental composition of 1 could be determined by LC-HRMS experiments. The [M + H]+ ion was observed at Molecules 2021, 26, 1019 3 of 13 m/z 543.2252 which corresponds to C29H35O10 (calculated 543.2230). This is in accordance with the 1D 1H and 13C NMR data (13C spectra as both protons decoupled as well as DEPT spectra). See Tables1 and2 for NMR data, SI for spectra, and Figures3–5 for 2D NMR basedcorrelations. essentially The 1Don 1theH andelemental13C NMR composition display signals determined for 34 by protons, high-resolution of which onemass is spectrometryexchangeable, and and 1D 29 NMR carbons. as well The unsaturationas 2D NMR experiments. index of 1 is The consequently cytotoxicity 13, of and pure as compoundsthe NMR data was suggest, evaluated the in presence vitro in ofcell four cultures carbonyl of murine groups macrophages and three carbon–carbon (Raw 264.7), whiledouble the bonds leishmanicidal hints that 1propertiescontains sixwere rings. evaluated In addition, in the the two 1D leishmania-promastigote NMR data indicate the presencestrains Leishmania of twelve amazoniensis non-protonated and carbons,L. braziliensis of which (see oneExperimental is a ketone section and three for aredetails). ester or lactone carbonyls, eight methine groups of which four appear to be olefinic while two are 2.saturated Results butand oxygenated, Discussion two methylene groups, and seven methyl groups of which one is a methoxyThe structures group. The of elucidationthe novel compounds of the structure isolated of 1 required are shown extensive in Figure 2D 2, NMR while analyses, the 1H andduring 13C which NMR thedata COSY, are HMQC,given in HMBCTables and1
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