641-643 N2-24.fm

The Euphorbiaceae family is one of the largest families in the plant kingdom. It comprises 263 genera and about 7300 species of almost cosmopolitan distribution. Euphorbia, the largest genus of Euphorbiaceae, with about 1600 species is characterized by the presence of milky latex. This genus has been the subject of numerous chemical studies. E. altotibetica is a perennial herb mainly growing in northwestern China and is often used for the treatment of curing skin tinea and tumefaction in folk. To our best knowledge, only a few phytochemical studies have been published on E. altotibetica to date. As a part of systematic research on Euphorbia species, a new lathyrane-type diterpenoid, named altotibetol (1), was isolated from the whole plant of E. altotibetica. This paper describes the isolation, structure elucidation, and cytotoxic activities of this new compound. Compound 1 was isolated as a colorless oil with an value of +6.25 (c 0.40, CHCl3). A molecular formula of C22H32O5 and seven degrees of unsaturation were established for 1 on the basis of the observed sodiated molecular ion peak at m/z 399.2140 [M + Na] in its HR-ESI-MS (calcd. for C22H32O5Na, 399.2142). The IR absorption bands at 3414, 1740, 1646, and 1615 cm1, respectively, indicated the presence of hydroxyl, carbonyl, and double bond groups in the molecule. The H and C-NMR spectra (Table 1) exhibited typical resonances for one acetoxy group [H 2.04 (3H, s); C 169.7, 21.6]. In addition, with the aid of the CNMR and DEPT spectra, five quaternary carbons, eight methines, two methylenes, and five methyl groups were detected, accounting for a 20-carbon-containing diterpene skeleton. The carbon resonance at C 194.7 (C-14) demonstrated the presence of one ,-unsaturated carbonyl group in the molecule. Furthermore, two trisubstituted olefins were evident from the carbon resonances at C 120.3 (C-5), 145.9 (C-6), 145.6 (C-12), and 132.9 (C-13) and the protons resonances at H 6.11 (1H, brd, J = 10.8, H-5) and 6.57 (1H, brd, J = 11.2, H-12). The above functionalities accounted for four degrees of unsaturation, and the remaining three degrees of unsaturation required the presence of three additional rings in the molecule. The characteristic H-NMR signals at H 1.15 (1H, m, H-9), 1.42 (1H, dd, J = 8.0, 11.2, H-11), 1.19 (3H, s, H-18), 1.09 (3H, s, H-19) and C-NMR signals at C 30.7 (C-11), 29.5 (C-9), 29.1 (C-18), 24.4 (C-10), and 16.2 (C-19) indicated a gem-dimethyl-substituted cyclopropane ring, which was further confirmed by HMBC spectrum (Fig. 2). The above information suggested that the basic structure of 1 was a lathyrane diterpenoid skeleton. Analysis of the H-H COSY spectrum (Fig. 2) provided a little information on the partial structures. The following structural fragments were elucidated on the basis of the correlated proton sequences: –CH2–CH(CH3)–CH(OH)–CH–CH= [unit A, H 2.25 (1H, m, H-1), 2.67 (1H, m, H-1), 2.18 (1H, m, H-2), 3.84 (1H, dd, J = 4.0, 6.8, H-3), 2.62 (1H, dd, J = 6.8, 10.8, H-4), 6.11 (1H, brd, J = 10.8, H-5)], and –CH(OH)– CH2–CH–CH–CH= [unit B, H 4.04 (1H, dd, J = 2.8, 10.8, H-7), 2.37 (1H, m, H-8), 1.70 (1H, m, H-8), 1.15 (1H, m, H-9), 1.42 (1H, dd, J = 8.0, 11.2, H-11), 6.57 (1H, brd, J   D 24 Table 1. NMR spectral data of compound 1