Research in the chemistry of diterpenoid alkaloids

This paper summarizes some of our recent research on diterpenoid and norditerpenoid alkaloids. Structures for delatisine, vakhmatine, vakhmadine, ajabicine, tangirine, septatisine, andersobine, and deacetylheterophylloidine are discussed. A novel furanohetisine-type alkaloid isolated from the seeds of Delphinium elafum L. is delatisine (1). The 1% nmr spectrum revealed twenty carbons, none of which could be assigned to a methoxyl or N-methyl group. These groups were also absent in the 1H nmr spectrum, thus suggesting that delatisine is a diterpenoid alkaloid (C20). The molecular formula was established as C20H25N03 by HRMS. DEPT showed: 4 quaternary carbons (s) at 6 145.7, 52.7, 50.5, 45.7; 10 methines (d) at 6 100.2, 79.6, 75.7, 72.2, 66.3, 64.4, 62.0, 55.4, 50.2, 50.0; 5 methylenes (t) at 6 108.2, 41.6, 37.3, 34.3, 33.9; and 1 methyl (4) at 6 21.9. Characteristic carbon and proton resonances indicated a hetisane-type exocyclic methylene group. The signal at 6 100.2 indicated a carbinolamine ether. Using long-range COSY, fixed evolution HETCOR and nOe's, the structure shown below was assigned to delatisine. This structure is unusual in that there is no other diterpenoid alkaloid which contains an oxygen bridge between C-2 and C-19 to form a furan ring. A single crystal X-ray diffraction analysis confirmed the structure assigned by nmr studies (1). H 0, Ha Two new water-soluble alkaloids named vakhmatine and vakhmadine have been recently isolated from Aconitum palmatum Don (2). The molecular formula for vakhmatine (C20H27N04) was established from the HRMS of the tetraacetate. The infra red and 1% nmr spectra showed the absence of carbonyl groups so one can conclude there are four hydroxyl groups in the molecule. The similarity of the 1% nmr spectra of vakhmatine and hetisine suggested a close relationship. The existence of a doublet at 6 95.5, and the absence of a