Ent-Abietane and ent-Labdane Diterpenoids from Isodon parvifolius
Chemical and pharmaceutical bulletin
In previous phytochemical investigations of the genus Isodon (family Labiatae), tetracyclic ent-kauranoids were the most extensively studied because of their various activities, including antibacterial, anti-inflammatory and especially antitumor activities. 1) However, some tricyclic diterpenoids were also reported in several Isodon species. 1-6) Isodon parvifolius (BATALIN) H. HARA, a perennial undershrub, is mainly distributed in the Tibet Autonomous Region and Sichuan Province, People's
... ince, People's Republic of China. In early studies, ent-isopimarane type tricyclic diterpenoids were isolated from this plant originating from the Tibet Autonomous Region. 7) In our search for new natural substances, a further study of this species collected from Sichuan Province, led to the isolation of three new ent-abietanoids parvifolines L-N (1-3), along with five known ent-abietanoids, rubescensin P (4), 5) rubescensin I (5), 5) enanderianin P (6), 8) rubescensin J (7), 5) and 14b,16-dihydroxy-3a,18-[(1-methylethane-1,1diyl)dioxy]-ent-abieta-7,15(17)-diene (8), 5) and one known ent-labdane type diterpenoid, 8b,13b-oxidoeperu-14-en-18oic-acid (9). 9) This is the first example of ent-abietane and ent-labdane type diterpenoids from I. parvifolius. The isolation and structural elucidation of the new diterpenoids were described in this paper. Results and Discussion Compound 1 was obtained as white amorphous powder. Its molecular formula was determined to be C 20 H 32 O 4 from the positive high resolution electrospray ionization mass spectroscopy (HR-ESI-MS) quasi-molecular ion peak at m/z 359.2198 [MϩNa] ϩ , indicating five degrees of unsaturation. From the 13 C-NMR spectra, two olefinic quaternary carbons (d C 152.7, 141.2), an olefinic methine (d C 124.1), an olefinic methylene (d C 110.8), two oxygenated methines (d C 80.6, 74.6), two oxygenated methylenes (d C 64.8, 64.5), three methines (d C 51.1, 48.6, 47.4), five methylenes (d C 38.3, 28.7, 25.8, 23.8, 23.4), two nonoxygenated quaternary carbons (d C 42.5, 35.0) and two methyls (d C 23.7, 16.4) were observed. Compared with the classical ent-kaurane diterpenoids, one characteristic nonoxygenated quaternary carbon was absent in the high field of the 13 C-NMR spectrum of 1. The information mentioned above and the tricyclic diterpenoids isolated from the plants of the same genus, suggested that compound 1 was an ent-abietanoid. The NMR data of 1 were very similar to those of rubescensin I (5).