Epifisetinidol- -catechin

Epifisetinidol-(4p —> 8)-catechin Epifisetinidol-(4p —> 8)-epicatechin Pithecellobium dulce 114... 

The elegance of this simple biomimetic approach to the synthesis of proanthocyanidin oligomers was demonstrated during synthesis of the mixed profisetinidin trimers (22) and (23), i.e. analogues possessing different ABC and GHI chain extender units. Triflavanoid (22) with its fisetinidol ABC and epifisetinidol GHI units was formed by acid-catalyzed reaction of fisetinidol-(4a->8)-catechin (24) (57) and epifise-... 

The protonated species (73/74) presumably also served as precursor to the 4P-deuteriotri-0-methylfisetinidol (82) by delivery of hydride ion from the P-face in a predominant Sn2 mode. Compound (82) persistently formed also when fisetinidol-(4a- 8)- and (4p- 8)-catechin hepta-O-methyl ethers (68) and (70) were treated with Na(CN)BD3 in TEA. This observation prompted an investigation of the structural features of the substrates that direct the stereochemistry of the delivery of hydride ion at C(4) in intermediates of type (73/74). Whereas treatment of the epifisetinidol-(4p- 8)-catechin hepta-O-methyl ether (85) with Na(CN)BD3 afforded the 4P-deuteriotri-0-methylepifisetini-dol (87) (18.5%), tetra-O-methylcatechin (75) (32%) and the (25)-l,3-dideuterio-l,3-diarylpropan-2-ol [6%, enantiomer of compound (80)], the nEfisetinidol-(4p- 8)-catechin hepta-O-methyl ether (86) gave 4a-deuteriotri-O-methyl- nf-fisetinidol [13%, the enantiomer of compound (82)], tetra-O-methylcatechin (75) (24%) and the (25)-l,3-dideuterio-l,3-diarylpropan-2-ol [12%, enantiomer of (80)]. 

Thus, the formation of the 4P-deuteriofisetinidol- and epifisetinidol derivatives (82) and (87) from the reduction of the profisetinidin permethylaryl ethers (68), (70), and (85) with Na(CN)BD3 in TEA, and of the enantiomer of compound (82) during reduction of the fisetinidol-(4p- 8)-catechin derivative (86), indicated that the deuterium ion is consistently delivered to C(4) of a protonated species of type (73 / 74) from the side opposite to the 2-aryl group of the C-ring. This... 

With the knowledge that flavan-3,4-diols are freely associated with flavan-3-ols [e. g. (H-)-catechin, (—)-epicatechin, ( —)-fisetinidol, ( + )-epifisetinidol] in tannin mixtures comprised of these molecular entities, experimental conditions were sought which would permit formation of C-4 —C-6 or 8 interflavanoid links. The conditions selected had to be sufficiently mild to avoid self-condensation of the flavan-3,4-diol, to avoid anthocyanidin formation as a side-reaction, to permit stereochemical conclusions (i. e. the reaction should be under kinetic rather than under thermodynamic control), and to allow assessments regarding the re-gioselectivity of the condensation. 

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