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Demethylation of some aconitine-type norditerpenoid alkaloids was carried out with trimethylsilyl iodide and with HBr in glacial AcOH. Aconitine (10), cammaconine (23), delphinine (3), falconerine (18), lappaconitine (22), and talatizamine (24) afforded partially demethylated products. When methoxyl groups are present at the C-16 and C-18 positions, these are demethylated, and the methoxyl group at the C-1 position underwent demethylation in none the alkaloids studied except falconerine (18). With HBr-AcOH, in the case of alkaloids possessing a C-3 hydroxyl group, the methoxymethyl at C-18 formed a tetrahydrofuran, cyclizing at the C-6 position. Detailed NMR spectral studies (1H, 13C, 1H homonuclear COSY, HETCOR, and selective INEPT) carried out on the demethylation products have enabled accurate chemical shift assignments to be made for the demethylated alkaloids.

From the aerial parts of Consolida oliveriana (DC) Schröd. a new norditerpenoid alkaloid consolidine (2) has been isolated, in addition to the known alkaloids pubescenine (1), gigactonine, and delsoline and the diterpenoid alkaloid ajaconine (4). The structure of alkaloid 2 was established on the basis of its physical and spectroscopic data including detailed NMR studies. A detailed NMR study on ajaconine (4) resulted in the revision of 11 13C chemical shift assignments.

Three new hetisane-type diterpenoid alkaloids, davisinol (6), 18-benzoyldavisinol (7), and Davisin (9) have been isolated from Delphinium davisii Munz. and their structures established by detailed spectroscopic studies. Accurate 1H- and 13C-NMR assignments have been made for kobusine (8), a related hetisane-type alkaloid, and karakoline (5), a norditerpenoid alkaloid. The known norditerpenoid alkaloids 14-acetylperegrine (4), 6-deacetylperegrine (3), and karakoline (5) and the diterpenoid alkaloids hetisine and hetisinone were also isolated.

Vakhmatine [1] and the new diterpenoid alkaloid 13-O-acetylvakhmatine [3] have been isolated from the polar alkaloidal fractions of the seeds of Consolida ambigua, together with ajacine, delcosine, gigactonine, and takaosomine. Structure 3 has been established on the basis of spectroscopic data and chemical correlation with 1.

Extracts of the twigs and stems of the mangrove plant Aegiceras corniculatum demonstrated toxicity to fish (Tilapia nilotica). 5-O-Methylembelin was isolated and was shown to be toxic to fish at a concentration of 1 ppm within a period of 75 min. The structure of 5-O-methylembelin was determined by a study of spectroscopic properties and comparison with an authentic synthetic sample.

The isolation and structure determination of the alkaloid ent-norsecurinine (4) from Phyllanthus niruri L. is described. The structure and absolute stereochemistry have been confirmed by an X-ray analysis of ent-norsecurinine hydrochloride.