Oligomeric flavanoids. part 14. Proguibourtinidins based on (-)-fisetinidol and (+)-epifisetinidol units
1990; Elsevier BV; Volume: 46; Issue: 8 Linguagem: Inglês
10.1016/s0040-4020(01)88380-0
ISSN1464-5416
AutoresJohannes C. S. Malan, Petrus J. Steynberg, Jan P. Steynberg, Desmond A. Young, Barend B. C. B. Bezuidenhoudt, Daneel Ferreira,
Tópico(s)Biological Activity of Diterpenoids and Biflavonoids
ResumoAbstract The rare series of proguibourtinidins ( 3,4', 7-trihy- droxy functionality) based on the fisetinidol (3,3',4',7-tetrahydroxy functionality) 5-deoxy flavan-3-ol unit is extended by identification of (+)-guibourtinidol-(4β,6)-(-)-fisetinidol and the (+)-guibourtini- dol-(4α,6) and (4β,6)-(+)-epifisetinidols. These metabolites are formed in low yields via acid-catalyzed coupling of (+)-guibourtaca- cidin and (-)-fisetinidol, the high activation energy of generating a 4-C benzylic carbocation being attributable to the poor electron donating properties of the phenol B-ring of the flavan-3,4-diol. Stereo-electronic principles operating in the in vitro process pre- sumably also control their formation in Nature.
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