Biochemical Systematics and Ecology 38 (2010) 342–345 Contents lists available at ScienceDirect Biochemical Systematics and Ecology journal homepage: www.elsevier.com/locate/biochemsyseco Anthraquinones, sterols, triterpenoids and xanthones from Cassia obtusifolia Sylvain Vale`re T. Sob a,d,*, Hippolyte K. Wabo a, Alembert T. Tchinda c, Pierre Tane a, Bonaventure T. Ngadjui b, Yang Ye d,** a Department of Chemistry, University of Dschang, Box 67 Dschang, Cameroon b Department of Organic Chemistry, University of Yaounde I, Box 812, Yaounde, Cameroon c Institute of Medical Research and Medicinal Plants Studies (IMPM), P.O. Box 6163, Yaounde, Cameroon d State Key Laboratory of Drug Research & Natural Products Chemistry Department, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zu-Chong-Zhi Road, Zhangjiang Hi-Tech Park, Shanghai 201203, People’s Republic of China article info Article history: Received 28 September 2009 Accepted 13 February 2010 Keywords: Cassia obtusifolia Leguminosae Anthraquinones Sterols Terpenoids Xanthones Chemotaxonomy 1. Subject and source The genus Cassia belongs to the medically and economically important family Leguminosae (Syn. Fabaceae), sub-family Caesalpinioideae. (Joshi and Kapoor, 2003). It consists of about 500–600 species, most from America. In Africa, this genus is exceptionally found in humid dense forest. (Aubre´ville, 1968). Cassia obtusifolia Lam (Syn. Senna obtusifolia, Chamaecrista obtusifolia), pantropical specie, near of but different from Cassia tora L., asiatic and oceanic species, known in India and Fidji island (Aubre´ville, 1968). It is a branched, annual or perennial herb, or under-shrub which grows to a height of 2 m. The seeds of Cassia obtusifolia L. and C. tora L. are called ketsumeishi in Japan and are used as laxative, tonic and diuretic (Kitanaka and Takido, 1981). Also called juemingzi in Chinese, these seeds have been widely used in traditional Chinese medicine for the treatment of red and tearing eyes, headache and dizziness, constipation, asthenic, hepatitis and diuretic agents and also to improve visual acuity, etc. (Guo et al., 1998; Kitanaka et al., 1998). The twigs of Cassia obtusifolia were collected in November 2007 in Bokito (Bafia), Centre Region of Cameroon, and identified by Mr. Nana Victor, botanist at the National Herbarium of Cameroon where a voucher specimen (No. 39848/HNC) has been deposited. * Corresponding author at: Department of Chemistry, University of Dschang, Box 67 Dschang, Cameroon. Tel.: þ237 79 33 35 07; fax: þ237 33 45 12 02. ** Corresponding author. Tel.: þ86 21 50806726; fax: þ86 21 50807088. E-mail addresses: [email protected] (S.V.T. Sob), [email protected] (Y. Ye). 0305-1978/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.bse.2010.02.002 S.V.T. Sob et al. / Biochemical Systematics and Ecology 38 (2010) 342–345 343 2. Previous work In a previous work, we described the presence of a xanthone, 1,8-dihydroxy-3-methoxy-6-methylxanthone, a polyketide derivative, (4R*,5S*,6E,8Z)-ethyl-4-((E)-but-1-enyl)-5-hydroxypentdeca-6,8-dienoate, together with 20 other secondary metabolites, including 2 steroids, 4 xanthones, 10 anthraquinones, 2 triterpenoids, 1 fatty ester, and (E)-eicos-14-enoic acid (Sob et al., 2008) from the ethyl acetate and methanol extracts of the leaves of this species collected in October 2004 at Mount Eloumden (Yaounde) in the Centre Region of Cameroon. In addition, three anthraquinones (Takido, 1958), three anthraqui- none glycosides (Yun-Choi and Kim, 1990), two naphthopyrones (Kitanaka et al., 1998), torosachrysone and two naphthalenic lactones (Kitanaka and Takido, 1981) were also previously isolated from this plant. 3. Present study Air-dried and powdered twigs (500 g) of Cassia obtusifolia were extracted by percolation at room temperature with ethyl acetate (3 Â 8 L). After evaporation in vacuo, a crude extract was obtained (56.15 g). The residue was further extracted with methanol (3 Â 8 L) to afford a methanol extract (34.24 g). The ethyl acetate extract was subjected to open dry flash column chromatography over silica gel and eluted with step gradients of PE–EtOAc and EtOAc–MeOH to yield seven major fractions (A1–A7): A1 (24.6 g, PE–EtOAc 9:1), A2 (11.7 g, PE–EtOAc 9:1, 8:2), A3 (1.2 g, PE–EtOAc 8:2), A4 (6.1 g, PE–EtOAc 7:3), A5 (1.22 g, PE–EtOAc 1:1 and 0:100), A6 (2.7 g, EtOAc–MeOH 95:5), and A7 (4.2 g, EtOAc–MeOH 9:1 and 0:100). Further purification of fraction A1 by repeated silica gel column chromatography with gradient of PE–EtOAc and Sephadex LH-20 using CHCl3–MeOH (1:1) as eluent yielded compounds 1 (76 mg) and 2 (71 mg). A2 underwent the same purification procedure to give 3 (11 mg), and 4 (32 mg). Fractions A3 and A4 were purified in the same manner to afford 5 (15 mg) and 6 (2.4 mg) respectively. The methanol extract was subjected to dry flash column chromatography with a step gradient of CH2Cl2–MeOH to give nine major fractions (B1–B9): B1 (1.75 g, CH2Cl2–MeOH 100:0), B2 (2.12 g, CH2Cl2–MeOH 95:5), B3 (1.27 g, CH2Cl2–MeOH 9:1), B4 (4.5 g, CH2Cl2–MeOH 9:1), B5 (1.26 g) and B6 (1.60 g) were eluted with CH2Cl2–MeOH (85:15), B7 (2.6 g, CH2Cl2–MeOH 8:2), B8 (4.4 g, CH2Cl2–MeOH 7:3), and B9 (3.0 g, CH2Cl2–MeOH 0:100). Repeated column chromatography of fraction B1 eluting with a gradient of CH2Cl2–acetone followed by purification through Sephadex LH-20 eluting with CH2Cl2–MeOH (1:1) and HPLC (with a CH3CN–H2O gradient) or MPLC on a Baeckstro¨m Separo AB column (15 mm i.d) gave 7 (2 mg), 8 (1.8 mg) and 9 (1.6 mg). Fraction B2 was re-chromatographed on a silica gel column with a step gradient of PE–EtOAc and further purified by HPLC (with a CH3CN–H2O gradient) to give 10 (6 mg), 11 (3.2 mg) and 12 (4.1 mg). Fraction B4 was purified by preparative TLC plates using CH2Cl2–acetone (95:5) as eluent, followed by MPLC on a Baeckstro¨m Separo AB column (15 mm i.d), gel permeation over Sephadex LH-20 (CH2Cl2–MeOH, 1:1) and HPLC (with a CH3CN–H2O gradient) to yield 13 (3.4 mg), 14 (2.6 mg), 15 (5.2 mg), 16 (3.2 mg) and 17 (2 mg). Fractions B5 and B6 treated in the same manner, gave 18 (3.7 mg) and 19 (5 mg), 20 (8.4 mg) and 21 (2.3 mg), respectively, while fraction B7 underwent the same purification procedure to give 22 (2 mg), 23 (1.3 mg), 24 (5.7 mg) and 25 (8.1 mg). Compounds 1–25 (Fig. 1) were respectively identified as stigmasterol (Forgo and Ko¨ve´r, 2004), lupeol (Kuiate et al., 2007), friedelin (Klass and Tinto, 1992), betulinic acid (Sholichin et al., 1980), (24S)-24- ethylcholesta-5,22(E),25-trien-3b-ol (Gaspar et al., 1996), a-amyrin (Do Vale et al., 2005), chrysophanol (Choi et al., 2004), questin (Takido, 1960), 1,8-dihydroxy-3-methoxy-6-methylxanthone (Sob et al., 2008), 1-hydroxy-7-methoxy-3-methylan- thraquinone (Guo et al., 1998), 7-methylphyscion (Monache et al., 1992), 1,8-dihydroxy-3-methoxy-6-methylanthraquinone (physcion) (Choi et al., 2004), obtusifolin (Sob et al., 2008; Takido, 1958), aloe-emodin (Zhou et al., 2006), emodin (Zhou et al., 2006), rhein (Wu and Yen, 2004), 1,5-dihydroxy-3-methoxy-7-methylanthraquinone (Kazmi et al.,1994), chrysophanein (Anu and Rao, 2001; Wong et al., 1989), euxanthone (Sob et al., 2008), isogentisin (Ellis and Whalley, 1976 ), 8-O-methyl- chrysophanol (Barba et al., 1992), 1,7-dihydroxy-3-methylxanthone (Wader and Kudav, 1987), gluco-obtusifolin (Yun-Choi and Kim, 1990), gluco-aurantioobtusin (Yun-Choi and Kim, 1990), gluco-chrysoobtusin (Yun-Choi and Kim, 1990), by inter- pretation of their spectral data, including EIMS, UV, IR,1D and 2D NMR, and comparison with literature data or by Co-TLC with authentic samples found in our laboratory. 4. Chemotaxonomic significance The anthraquinones chrysophanol, emodin, aloe-emodin, parietin, gluco-obtusifolin, gluco-aurantioobtusin, gluco- chrysoobtusin, chrysophanein, questin, rhein and obtusifolin were previously isolated from C. tora (Hyun et al., 2009; Jang et al., 2007; Kim et al., 2004; Tapan et al., 2001; Wong et al., 1989; Wu and Yen, 2004), chrysophanol and emodin from Cassia siamea (Ajaiyeoba et al., 2008; Lu¨ et al., 2001), chrysophanol and parietin from Cassia racemosa (Rosa et al., 2007), chrysophanol, emodin, aloe-emodin, parietin and rhein from Cassia alata (Hazrina et al., 2008; Vivian et al., 2008), chrysophanol and chrys- ophanein from Cassia fistula (Kuo et al., 2002), chrysophanol and parietin from Cassia sophera (Joshi et al.,1985), chrysophanol and parietin from Cassia javanica (Tiwari and Sharma, 1981), chrysophanol and 1,5-dihydroxy-3-methoxy-7-methyl anthraquinone from Cassia italica,(Kazmi et al., 1994, 2006; Magano et al., 2008). Emodin, parietin and 1-hydroxy-7-methoxy-3-methyl anthraquinone were also isolated from Cassia laevigata (Singh et al., 1980), emodin from Cassia occidentalis, Cassia nigricans and Cassia grandis (Chukwujekwu et al., 2006; Gonza´lez et al.,1996; Kambou et al., 2008), questin and 8-O-methylchrysophanol from Cassia lindheimeriana and Cassia corymbosa (Barba et al., 1992), 7-methylphyscion from Cassia trachypus and Cassia singueana (Monache et al.,1992; Mutasa et al.,1990), aloe-emodin from Cassia angustifolia (Wu et al., 2007) and Chrysophanein from Cassia kleinii (Anu and Rao, 2001). 344 S.V.T. Sob et al. / Biochemical Systematics and Ecology 38 (2010) 342–345 Fig.