The plant Aconitum piepunense HAND-MAZZ. Symb. Sin. grows in Diqing county, Yunnan province, China at an elevation of 3000 m.1) To our knowledge, no phytochemical investigation of this plant has been undertaken. In the course of our continued studies of diterpenoid alkaloids from Aconitum and Delphinium plants, two new C 19 -diterpenoid alkaloids, piepunensine A (1) and 18-acetylcammaconine (2), along with five known norditerpenoids pengshenine B (3), talatisamine (4), aconosine (5), yunaconitine (6), and talatizidine (7) were isolated from the roots of Aconitum piepunense. This paper reports the isolation and structural elucidation of these alkaloids. Results and DiscussionDuring the course of isolation, five known alkaloids pengshenine B (3), 6) talatisamine (4), 7) aconosine (5), 8) yunaconitine (6), 9) and talatizidine (7) 10) were obtained and their structures were identified by comparison of the NMR data with reported values and co-TLC behavior with authentic samples. It is emphasised that piepunensine A (1) is the first known naturally occuring aconitine-type diterpenoid alkaloid with both the lactam and N-deethyl groups.The molecular formula of piepunensine A (1) (C 22 H 33 NO 6 ) was determined by HR-ESI-MS [MϩNa] ϩ 430.2200. The NMR spectra strongly suggested an aconitinetype alkaloid for 1.2) Its NMR and IR spectra displayed absence of an N-ethyl group and characteristic signals at d ) and 13 C-NMR (d 71.5 s, 75.1 d) spectra also showed to have one each of secondary hydroxyl (14-OH) and tertiary hydroxyl group (8-OH). On the basis of these observations, the structure of piepunensine A was established as 1.18-Acetylcammaconine (2) was isolated as white amorphous powder with mp 123-125°C. The HR-ESI-MS at m/z 450.2862 corresponded to the protonated molecular ion [MϩH] ϩ (C 25 H 40 NO 6 ). The NMR spectrum of 2 exhibited characteristic features of the aconitine-type C 19 -diterpenoid alkaloids, 2) bearing an N-ethyl group (d H 1.06, 3H, t, Jϭ7.2 Hz; d C 13.5 q, 49.3 t), two methoxyl groups (d H 3.28, 3.34, each 3H, s; d C 56.2 q, 56.4 q), and an acetyl group (d H 2.06, s; d C 20.8 q, 171.0 s). Comparison of the MS and NMR spectra of 2 with those of cammaconine (8) 4) showed that it had an additional acetyl group instead of a hydroxyl group. The 13 C-NMR spectra of 2 and 8 are very similar except for C-4 and C-18 due to the substituted effect (OH→OAc) Two new C 19 -diterpenoid alkaloids, piepunensine A (1) and 18-acetylcammaconine (2), have been isolated from the roots of Aconitum piepunense together with five known alkaloids pengshenine B (3), talatisamine (4), aconosine (5), yunaconitine (6), and talatizidine (7). The structures of the new alkaloids were established on the basis of spectral data (1D-and 2D-NMR, HR-MS).
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