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Selective Demethylation of Some Aconitine-Type Norditerpenoid Alkaloids

Balawant S. JoshiInstitute for Natural Products Research, and Department of Chemistry, The University of Georgia, Athens, Georgia 30602-2556Santosh K. SrivastavaInstitute for Natural Products Research, and Department of Chemistry, The University of Georgia, Athens, Georgia 30602-2556Angela D. BarberInstitute for Natural Products Research, and Department of Chemistry, The University of Georgia, Athens, Georgia 30602-2556Haridutt K. DesaiInstitute for Natural Products Research, and Department of Chemistry, The University of Georgia, Athens, Georgia 30602-2556S. William PelletierInstitute for Natural Products Research, and Department of Chemistry, The University of Georgia, Athens, Georgia 30602-2556

1997en

ABI

Annotatsiya

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.

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DOI: 10.1021/np9606862

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