A Novel Triterpenoid from Petasites tricholobus

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【刊名】Chinese Chemical Letters


Some genus of Petasites was used as folk medicine in China for detoxification, detumescence and treatment of viper bite1. In order to find the medical value, we studied the chemical constituents of Petasites tricholobus. A novel triterpenoid compound 1, possessing a migrated ursane skeleton with ?5, 10 double bond and 7, 8 - epoxy in the molecule, was isolated from this plant. Its structure elucidation was reported here. Compound 1, m.p. 186 – 187 °C, [α]17D + 43 (c 0.2, CHCl3), was isolated as white powder. Its EIMS spectrum showed the molecular ion peak at m/z 456, combined with the 1H and 13CNMR (DEPT) data, the molecular formula was deduced to be C30H48O3. Figure 1 Compound 1 and the key correlations observed in NOESY spectrum of 1The 1H and 13CNMR (DEPT) spectrum of 1 displayed the signals of six tertiary methyls, two secondary methyls, eight methenes, six methines (three of them were connected with oxygen) and eight quarternary carbons, which indicated that compound 1 was a pentacyclic triterpenoid possessing a tetrasubstituted double bond (δC 126.4,134.9, C), two methines connected with hydroxy (δH 3.50, 3.75 and δC 75.2, 77.2) and an epoxide group (δH 3.16 and δC 67.1 C, 51.3 CH) (Table 1). The IR spectrum also revealed the presence of hydroxy (3380 cm-1) and double bond (1665 cm-1). The skeleton of compoud 1 was constructed by the correlations of eight methyls in HMBC spectrum (Table 1). In the HMBC spectrum, the correlations of H-1 (δH 2.02, 1.96) with C-10 (δC 134.9), H-2 (δH 1.64, 1.60) with C-10 (δC 134.9), C-1 (δC 20.9), C-3 (δC 75.2), C-4 (δC 39.0), CH3-23 (δH 1.05) with C-3 (δC 75.2), C-5 (δC 126.4), CH3-24 (δH 0.94) with C-3 (δC 75.2), C-5 (δC 126.4) and H-6 (δH 2.62, 2.24) with C-5 (δC 126.4) indicated that a double bond was between C-5 and C-10 and a hydroxyl group was located at C-3. The fragment peaks in EIMS at m/z 412 (1), 44 (17) and 43 (100), which were caused by RDA cleavage (Figure 1), further confirmed the presence of the5(10)-ene structure. The correlations of H-7 (δH 3.16) with C-8 (δC 67.1), and H-6 (δH 2.62, 2.24) with C-7 (δC 51.3), C-8 (δC 67.1) confirmed that the epoxide group was between C-7 and C-8, and the correlations of CH3-28 (δH 1.23) with C-16 (δC 77.2), H-15 (δH1.13, 1.59) with C-16 (δC 77.2) indicated that the second hydroxyl group was at C-16. The coupling contants of H-3 (dd, J = 6.4/4.4 Hz), H-16 (dd, J = 12.8/5.2 Hz) and H-7 (brd, J = 3.2 Hz) showed the presence of α-hydroxy at C-3, C-16 and 7α, 8α-epoxy. The correlations of H-7 (δH 3.16) with CH3-26 (δH 1.24) in NOESY spectrum further supported the α configuration of epoxy. The 25, 26, 28, 29 methyls and H-18 were on β side, which can be deduced from the cross peaks in NOESY spectrum (Figure 1). The correlations between H-19 and 27, 30 methyls, at the same time, not having correlation between 26 and 27 methyls indicated that 27 and 30 methyls were on α side. The skeleton of 1 and relative configurations of these methyls were the same as that of rhoiptelenol2,3. Based on the above evidence, compound 1 was determined as D:B- friedoursane-3α, 16α-dihydroxy-7α, 8α-epoxy-5(10)-ene, and named as petatrichol A.Acknowledgments This project was supported by the NNSFC (No. 2997201).A Novel Triterpenoid from Petasites tricholobus1. Jiangsu New Medical Collage, Chinese Medicine Dictionary, Shanghai People's Publishing House. Shanghai, 1977, p. 2483. 2. J. Kitajima, M. Arai, Y. Tanaka, Chem. Pharm. Bull., 1994, 42 (3), 608. 3. Z. H. Jiang, R. H. Zhou, K. Masuda, H. Ageta, Phytochemistry, 1995, 40 (1), 219.