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Selective Demethylation of Some Aconitine-Type Norditerpenoid Alkaloids

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...

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Bibliographic Details
Published in:Journal of natural products (Washington, D.C.) D.C.), 1997-05, Vol.60 (5), p.439-443
Main Authors: Joshi, Balawant S, Srivastava, Santosh K, Barber, Angela D, Desai, Haridutt K, Pelletier, S. William
Format: Article
Language:English
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Summary: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.
ISSN:0163-3864
1520-6025
DOI:10.1021/np9606862