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 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.
Joshi
B S
BS
Institute for Natural Products Research, University of Georgia, Athens 30602-2556, USA.
Srivastava
S K
SK
Barber
A D
AD
Desai
H K
HK
Pelletier
S W
SW
D000157:Aconitine / Q000737:chemistry*; D000470:Alkaloids / Q000737:chemistry*; D003640:Dealkylation; D004224:Diterpenes / Q000737:chemistry*; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D014297:Trimethylsilyl Compounds
D000470:Alkaloids; D004224:Diterpenes; D007202:Indicators and Reagents; D014297:Trimethylsilyl Compounds; D000157:Aconitine