Synthesis of condensed tannins. Part 4. A direct biomimetic approach to [4,6]- and[4,8]-biflavanoids
作者:Jacobus J. Botha、Daneel Ferreira、David G. Roux
DOI:10.1039/p19810001235
日期:——
their condensation with nucleophilic flavan-3-ols to form [4,6]- and [4,8]-biflavanoids at ambient temperatures and under mildly acidic aqueous conditions apparently simulates the initial step in condensedtannin formation in a number of natural sources. The stereospecificity (or stereoselectivity) of the reaction is conditioned mainly by the 2,3-cis or 2,3-trans stereochemistry of the parent flavan-3
Oligomeric flavanoids. Part 26. Structure and synthesis of the first profisetinidins with epifisetinidol constituent units
作者:Petrus J. Steynberg、Jan P. Steynberg、E. Vincent Brandt、Daneel Ferreira、Richard W. Hemingway
DOI:10.1039/a701334e
日期:——
The natural occurrence of the first oligomeric profisetinidins with
(2R,3R)-2,3-cis-epifisetinidol chain extender
units is demonstrated in the bark of Pithecellobium dulce
(Guamúchil). Semi-synthesis using the appropriate flavan-3-ol and
flavan-3,4-diol precursors permits unequivocal structural and
stereochemical assignment of the novel dimeric
epifisetinidol-(4β,8)-catechin and epicatechins 16 and 18,
the trimeric
bis-epifisetinidol-(4β,6:4β
,8)-catechin and epicatechins 33 and 35, the
fisetinidol-(4α,8)-catechin-(6,4β)-
epifisetinidol 37 and
fisetinidol-(4α,8)-epicatechin-(6,4β)-
epifisetinidol 39.