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Oligomeric flavanoids. Part 8. The first profisetinidins and proguibourtinidins based on C-8 substituted (–)-fisetinidol units and related C -ring isomerized analogues

1990; Issue: 2 Linguagem: Inglês

10.1039/p19900000209

2050-8255

Johannes C. S. Malan, Jacobus A. Steenkamp, Jan P. Steynberg, Desmond A. Young, E. Vincent Brandt, Daneel Ferreira,

Phytochemistry and Biological Activities

Structural examination of the phenolic metabolites of Colophospermum mopane reveals the presence of the first profisetinidins and proguibourtinidins based on C-8 substituted (–)-fisetinidol units i.e. the (4α,8)-bis-(–)-fisetinidol (1), (+)-epifisetinidol-(4α,8)-(–)-fisetinidol (3), and the (+)-guibourtinidol-(4α,8)-(–)-fisetinidol (5). They are accompanied by the related functionalized tetrahydropyrano[2,3-h]chromenes (9), (11), (13), (15), and (17), and by a 2,4-diaryl-6-(2,-benzopyranyl)chroman (19), the first C-ring isomerized analogue derived from a B-ring coupled profisetinidin. Efforts towards the synthesis of the (4,8)-bis-fisetinidols from 6-bromo-(–)-fisetinidol and the appropriate flavan-3,4-diol, lead to the biaryl type biflavanoids (33) and (35). Their genesis is explained in terms of an oxidative substitution reaction initiated by bromonium ion.