Rearranged abietane diterpenoids from the roots of Clerodendrum trichotomum and their cytotoxicities against human tumor cells Wen-Xuan Wang a,b , Juan Xiong a , Yu Tang a , Jing-Jing Zhu b , Ming Li a , Yun Zhao b , Guo-Xun Yang a , Gang Xia b , Jin-Feng Hu a,b,⇑ a Department of Natural Products Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai 201203, People’s Republic of China b Department of Natural Products for Chemical Genetic Research, Key Laboratory of Brain Functional Genomics, Ministry of Education & Shanghai Key Laboratory of Brain Functional Genomics, East China Normal University, No. 3663 Zhongshan Road N, Shanghai 200062, People’s Republic of China article info Article history: Received 20 October 2012 Received in revised form 5 December 2012 Accepted 28 January 2013 Available online 22 February 2013 Keywords: Clerodendrum trichotomum Lamiaceae Rearranged abietane diterpenoids Cytotoxicities abstract The roots of the medicinal ornamental plant Clerodendrum trichotomum yielded a series of rearranged abietane diterpenoids, including three 17(15 ? 16)-abeo-abietane (1–3) and three 17(15 ? 16), 18(4 ? 3)-diabeo-abietane (4–6) derivatives. Their structures were elucidated by means of spectroscopic methods. The absolute configuration of (10R,16R)-12,16-epoxy-11,14,17-trihydroxy-6-methoxy- 17(15 ? 16)-abieta-5,8,11,13-tetraene-7-one (1) was deduced by a combination of single crystal X-ray diffraction analysis and the observed Cotton effects in its circular dichroism (CD) spectrum. All isolates were tested for their cytotoxicities against five human cancer cell lines (BGC-823, Huh-7, KB, KE-97, and Jurkat). Among them, compounds 4, 6, 9, 10, 12, and 14, each possessing a common 17(15 ? 16),18(4 ? 3)-diabeo-abietane framework, were found to have remarkable cytotoxic effects with IC 50 values ranging from 0.83 to 50.99 lM. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Clerodendrum trichotomum Thunberg (Lamiaceae, formerly Ver- benaceae) (Breteler, 2005; Kadereit, 2004; Yuan et al., 2010) is an ornamental plant widely distributed in southern and southwestern China. Its dried leaves and stems have been used as a folk medicine for treatment of arthritis and hypertension (Jiangsu New Medical College, 1986). Previous chemical and pharmacological studies on the leaves and stems of this plant mainly resulted in the separation of phenylethanoid glycosides (Chae et al., 2004, 2005, 2006, 2007; Kang et al., 2003; Kim et al., 2001, 2009; Lee et al., 2006, 2011; Na- gao et al., 2001) and flavonoid glycosides (Min et al., 2005; Okigawa et al., 1970) with broad bioactivities, such as anti-inflammatory (Choi et al., 2004; Kim et al., 2009; Lee et al., 2006; Park and Kim, 2007), antihypertensive (Kang et al., 2003; Lu et al., 1994), antipro- liferative (Nagao et al., 2001), anti-asthmatic (Lee et al., 2011), anti- oxidative (Chae et al., 2004, 2005, 2006, 2007), anti-HIV (Kim et al., 2001), and immunotoxic (Lee and Moon, 2010) properties. The leaves of C. trichotomum also yielded a few neo-clerodane diterpe- noids, some of which exhibited antifeeding (Kato et al., 1972, 1973) or feeding stimulant effects (Kawai et al., 1998, 1999; Nishida et al., 1989). Several indolizinoindole blue pigments were isolated from the fruits of this plant (Iwadare et al., 1974; Toyoda et al., 1982). However, the chemistry of the roots of C. trichotomum has been little investigated, and only a few lupane triterpenes and one clerosterol derivative have been so far identified by a Japanese group in the 1960s (Kawano et al., 1967). In a continuation of our project towards the discovery of new antitumor agents from natu- ral products (Wu et al., 2011), the roots of C. trichotomum was re- investigated. In this study, a number of new and known rearranged abietane diterpenoids (1–14) were isolated and characterized. Re- ported herein are the isolation and structure elucidation of these abietane derivatives and their cytotoxicities. 2. Results and discussion 2.1. Structure elucidation The ultrasonication-assisted petroleum ether (PE)/EtOAc and the 90% EtOH extracts of the roots of C. trichotomum were individ- ually subjected to repeated column chromatography (CC) over sil- ica gel, MCI gel, Sephadex LH-20, and semi-preparative HPLC to afford 14 compounds (1–14)(Fig. 1). By comparison of their spec- troscopic data and physicochemical properties with those reported in the literature, the known compounds were determined to be villosin C (7)(Ulubelen et al., 1994), 12,16-epoxy-11,14-dihy- droxy-6-methoxy-17(15 ? 16)-abeo-abieta-5,8,11,13, 15-pentae- ne-3,7-dione (8)(Barros et al., 2003), uncinatone (9)(Dorsaz 0031-9422/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.phytochem.2013.01.008 ⇑ Corresponding author at: Department of Natural Products Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai 201203, People’s Republic of China. Tel./fax: +86 21 51980172. E-mail addresses: jfhu@fudan.edu.cn, jfhu@brain.ecnu.edu.cn (J.-F. Hu). Phytochemistry 89 (2013) 89–95 Contents lists available at SciVerse ScienceDirect Phytochemistry journal homepage: www.elsevier.com/locate/phytochem