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Cytotoxic kurubasch aldehyde from Trichilia emetica
To cite this Article: , 'Cytotoxic kurubasch aldehyde from Trichilia emetica', Natural Product Research, 21:1, 13 - 17 xxxx:journal To link to this article: DOI: 10.1080/14786410600921698 URL: http://dx.doi.org/10.1080/14786410600921698
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Natural Product Research, Vol. 21, No. 1, January 2007, 13–17
Cytotoxic kurubasch aldehyde from Trichilia emetica MAMINATA TRAOREyzx, LIN ZHAI{, MING CHEN{, CARL ERIK OLSENk, NACOULMA ODILE?, GUISSOU I. PIERRE$, OUE´DRAGO J. BOSCOyx, GUIGEMDE´ T. ROBERTyk and S. BRØGGER CHRISTENSEN*z yDirection Regionale de Institut de Recherche en Sciences de la Sante´ (IRSS-DRO), Bobo-Dioulasso, BP 545, Burkina Faso zThe Danish University of Pharmaceutical Sciences, Universitetsparken 2, DK-2100 Copenhagen Ø, Denmark xLaboratoire de Parasitologie-Etnologie, Centre Muraz, Bobo-Dioulasso, BP 390, Burkina Faso {Department of Clinical Microbiology, National University Hospital 7806, Tagensvej 20, DK-2200 Copenhagen N, Denmark kDepartment of Natural Sciences, Royal Veterinary and Agricultural University, Bu¨lowsvej 17, DK-1870 Frederiksberg C, Denmark ?University of Ouagadougou, Ouagadogo, BP 7021, Burkina Faso $Institut de Recherche en Science de la Sante´ (IRSS), Ouagadougou, BP 7192, Burkina Faso (Received 28 April 2006; in final form 20 July 2006) Kurubasch aldehyde, a sesquiterpenoid with an hydroxylated humulene skeleton, was isolated as free alcohol from Trichilia emetica Vahl. (Meliaceae), belonging to the order Sapindales. Related substances have been previously found in plants as esters of aromatic acids, and these plants were species belonging to the distant order Apiales. This is the first report of humulenes found in the genus Trichilia and only the second of humulenes in the order Sapindales. The aldehyde is a modest inhibitor of the growth of Plasmodium falciparum (IC50 76 mM) and slow-proliferating breast cancer cells MCF7 (78 mM), but a potent inhibitor of proliferation of S180 cancer cells (IC50 7.4 mM). Keywords: Trichilia emetica; Kurubasch aldehyde; Antiplasmodial activity; Cytotoxicity
1. Introduction Trichilia emetica Vahl. (Meliaceae) [synonyms T. somalensis Chiov., T. jubensis Chiov., T. roka (Forssk. Nom. Nud.) Chiov, Rhochetia choensis Del.] is a shrub or a small tree native to Africa [1,2]. The plant is extensively used in tribal medicine [3,4], and extracts from leaves, stem, and bark, have been found to possess antitrypanosomal [5],
*Corresponding author. Email:
[email protected] Natural Product Research ISSN 1478-6419 print/ISSN 1029-2349 online ß 2007 Taylor & Francis http://www.tandf.co.uk/journals DOI: 10.1080/14786410600921698
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antiplasmodial [5,6], antischistosomidal [7] antitrypanosomal, and antileishmanial [8] activities. In general, the extracts appear to be toxic against mammalian cell lines [1,8], limiting the use of the plant extracts for therapeutic uses. The first phytochemical studies of T. emetica related the antifeedant activities of the extracts to the presence of secolimonoids [9–12]. Later studies have shown modest cytotoxicity of two of the limonoids, nymania A and Tr-B, but limited toxicity of the remaining limonoids [1].
2. Results and discussion This study revealed that kurubasch aldehyde is a cytotoxic principal in the roots of T. emetica. The alcohol was characterized as the known benzoate (2), the NMR spectra of which were in agreement with those published for 2, except for some minor disagreements in the 13C NMR spectrum. The signal for C-15 was reported to be found at 218.1 [13], whereas we found it at 196.1. Kurubasch aldehyde has previously only been found to be naturally occurring as an ester of either benzoic (2) or vanillic acid [14]. Trichilia emetica has previously been reported to be a valuable source for the very apolar secolimonoids [9–12]. This study was focused on a more polar fraction, which could explain the absence of limonoids in the investigated fraction. Only limonoids has been found in Meliaceae and is consequently a good chemotaxonomic marker [15]. In contrast, searches in the reviews of Fraga [16] have revealed that humulenes have been found in many parts of the Plant Kingdom, most frequently in Asterales and Apiales. Previously only two humulenes, 1(10)-epoxy-4,7-humuladiene and 1(10),4-diepoxy-7-humulene have been found in one species, Guarea guidonia belonging to Meliaceae [17], but both of these humulenes possess an oxygenation pattern very different from that found in kurubasch aldehyde. The kurubasch aldehyde esters were found in G. guidonia (Apiaceae) [13], a plant family very distant from Meliaceae [15]. Thus, the present finding demonstrates a surprising diversity of humulenes found in Meliaceae. Unfortunately no optical rotation was reported for the esters of kurubasch aldehyde [13], preventing a comparison of the absolute configuration of the humulenes found in the different orders of the Plant Kingdom. Addition of 1 to cell cultures revealed a strong growth inhibiting effect towards cell line S180 (IC50 7 3 mM, thapsigargin IC50 26 nM), breast cancer cell line (MCF7 78 15 mM, thapsigargin IC50 2.9 mM) and towards Plasmodium falciparum 3D7 merozoits (IC50 76 10 mM, chloroquin IC50 3 nM).
3. Experimental 3.1. General experimental procedures NMR spectra were recorded on a Varian Mercury 300 MHz spectrometer at 20 C in CDCl3 using TMS as an internal reference. Optical rotation was measured on a Perkin Elmer 241 polarimeter.
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3.2. Plant material Roots of the tree T. emetica Vahl. (Meliaceae) were collected (21 March 2003) at Dieri, a village located 5 km from Orodara, one of the most humid regions of Burkina Faso. The plant material was authenticated by Dr Mamounata Belem, Centre National de la Recherche Scientifique et Technologigue (CNRST), Ouagadougou. A voucher specimen is kept in the herbarium of CNRST under the number 8002.
3.3. Extraction and isolation Grounded roots of T. emetica (400 g) were extracted for 24 h with ethanol (2 L). The residue (38 g) after concentration was suspend in EtOAc and extracted with water. The organic layer was concentrated to give 11 g, and the aqueous layer concentrated to give 25 g. The residue from the organic layer was dissolved in MeOH (100 mL), concentrated on 50 g of celite, and placed on a column of 1100 g of silica gel 60 (40–63 mm, Merck, 5 50 cm2). The column was eluted with toluene–MeOH: (95 : 5, 1500 mL). Homogenous fractions (1000–1400 mL) were concentrated to give 1.0 g of an oil. Kurubasch aldehyde (18 mg, tR 12.5 min) was finally obtained by HPLC on a Luna RP-18 column (5 20 cm2; eluent MeOH–H2O, 70 : 30) added AcOH (1%). 1
2
9 8
RO
3
10
4 OHC 15
CH3
6 5 H3C 12
7 11 CH3 13
1 = −H 2=
O
Kurubasch aldehyde (1). [(E,E)-3-Formyl-7,11,11-trimethylundeca-2,6-dienol] was 1 isolated in a yield of 0.045%. ½25 D 5.0 (c 0.065, CHCl3); H NMR: 9.40 (1H, d, J ¼ 1.2 Hz, H-15), 6.50 (1H, d, J ¼ 10.2 Hz, H-5), 5.09 (1H, t, J ¼ 8.1 Hz, H-1), 4.25 (1H, d, J ¼ 10.2 Hz, H-6), 2.64 (1H, dt, J ¼ 12.3, 3.6 Hz, H-2), 2.2 (3H, m, H-20 , H-3, H-30 ), 2.18 (1H, m, H-9), 1.6–1.5 (2H, m, H-8, H-80 ), 1.48 (3H, br s, H-14), 1.42 (1H, m, H-90 ), 1.23 (1H, m, H-7), 1.04 (1H, m, H-70 ), 1.02 (3H, s, H-12), 1.01 (3H, s, H-13); 13C NMR: 195.7 (CH, C-15), 151.3 (CH, C-5), 143.9 (C, C-4), 136.8 (C, C-10), 123.6 (CH, C-1), 74.5 (CH, C-6), 37.4 (C, C-11), 36.2 (CH2, C-7), 35.5 (CH2, C-9), 25.6 (CH2, C-3), 24.8 (CH2, C-2), 23.7 (CH2, C-8), 22.7 (CH3, C-12), 22.6 (CH3, C-13), 19.5 (CH3, C-14). HREIMS: Found; 236.1718 (Calcd for C15H24O2; 236.1776); 208.1732 (Calcd for C14H24O; 208.1827). Kurubasch aldehyde benzoate (2). To a solution of kurubasch aldehyde (1, 1.5 mg) in dichoromethane (10 mL) was added 4-dimethylaminopyridine (4 mg) and benzoic
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anhydride (4 mg). After 2 h N,N0 -dicyclohexylcarbodiimide (2 mg) was added. After stirring overnight 1 M HCl (10 mL) was added, the organic layer isolated and the aqueous phase was extracted with CH2Cl2 (10 mL). The combined organic phases was dried and concentrated. Compound 2 (1.2 mg, 24%) was isolated by column chromatography over 1 g of LiChroprep RP-18 (40–63 mm, Merck, 0.5 2 cm2, 1.5 g), eluted with methanol–water (9 : 1, 20 mL) added AcOH (1%). CD (CH3CN): max (") ¼ 209 (50), 290 (35); 13C NMR: ¼ 196.1 (CH, C-15), 165.9 (C¼O), 147.1 (CH, C-5), 147.1 (C, C-4), 137.1 (C, C-10), 133.4 (CH, Cp), 129.9 (CH, Co), 128.7 (CH, Cm), 124.5 (CH, C-1), 73.1 (C, C-6), 38.2 (C, C-11), 36.1 (CH2, C-7), 36.1 (CH2, C-9), 26.0 (CH2, C-2), 25.7 (CH2, C-3), 24.8 (CH2, C-8), 24.2 (CH3, C-12), 23.2 (CH3, C-13), 19.8 (CH3, C-14). The 1H NMR spectrum was in agreement with that published earlier [13].
3.4. Antiplasmodial assay Assays for antiplasmodial activity using a chloroquin-sensitive P. falciparum strain were performed as described in detail elsewhere [18] by using chloroquin as a positive control.
3.5. Cytotoxic assay Two different cancer cell lines, S180 (murine sarcoma) and MCF7 (breast cancer), both purchased from National Cancer Institute, were tested by a high-flux anticancer-drugscreening method [19]. Briefly, cancer cells were incubated with the test compound in different concentrations at 37 C for 48 h. Cultures were fixed with trichloroacetic acid, then stained with sulforhodamine B and read at 490 nm by ELISA reader.
Acknowledgement This work was supported by Danida, Carlsbergfondet and Apotekerfonden af 1991.
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