Fisetinidol- -catechin

Steynberg, J.P. et al.. Oligomeric fiavanoids. Part 4. Base-catalyzed conversions of (—)-fisetinidol-(+)-catechin profisetinidins with 2,3-trflwj-3,4-cw-flavan-3-ol constituent units, J. Chem. Soc., Perkin Trans. 1, 1331, 1988. 

Bonnet, S.L., J.P Steynberg, B.C.B. Bezuidenhoudt, C.M. Saunders, and D. Ferreira Oligomeric Flavanoids. Part 20. Structure and Synthesis of Phlobatannins Related to the (4p,6 4a,8)-Bis-fisetinidol-catechin Profisetinidin Triflavanoid. Phytochemistry, 43, 215 (1996). 

Dimers Fisetinidol-(4a —> 8)-6-Me-catechin Commercial wattle bark extract 32... 

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-... 

Treatment of the fisetinidol-(4a—>8)-catechin (24) (57), representing a typical tannin unit of commercial wattle extract, with sodium cyanoborohydride [Na(CN)BH3] 84) in trifluoroacetic acid (TFA) for 6h at 0°C gave products comprising the starting material (24), catechin (5) (15%) and the (2jR)-l-(2,4-dihydroxyphenyl)-3-(3,4-dihydroxyphe-nyl)propan-2-ol (77) (Scheme 6). Similar treatment of the fisetinidol-(4P- 8)- and -(4a- 6)-catechins (69) and (71) (57) with their respective... 

Similar conditions also effected cleavage of the interflavanyl bond in the fisetinidol-(4a-+8)-catechin permethylaryl ether (68) to afford tetra-0-methylcatechin (75) (21%), the l,3-diarylpropan-2-ol (78) (12%), and tri-O-methylfisetinidol (81) (12%). Such a rupture of the interflavanyl bond in the permethylaryl ether (68) introduced an important dimension to these cleavages in relation to the chemistry of the 5-deoxyoligo-flavanoids where the additional chromatographic steps involved with derivatization are often prerequisites for sample purity. The liberation of the chain-terminating flavan-3-ol unit (5) or (75), irrespective of... 

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... 

Scheme 8. Base-catalyzed pyran ring rearrangements of fisetinidol-(4a—>8)- and (4p— 8)-catechin 4-0 (E-ring) methyl ethers (100) and (101) ] 1...

Fig. 3. Fisetinidol-(4a-> 8>-catechin (A profisetini-Fig. 2. Gallocatechin-(4a - 8)-epigallocatechin (a din from Acacia baileyana). IL. Y. Foo Phytochem-...

Fig. 2.3 Flavonoid diversity in the heartwood constituents of Colophospermum mopane (Leguminosae subfamily Caesalpinioideae). Stmctural types present with illustrative example(s) flavonol fisetin (11) dihydroflavonol (+)-taxifolin (12) flavan-3-ols (+)-catechin (13) and (-)-fisetinidol (14) flavan-3,4-diol (+ )-gleditsin (15) peltogynoid epimopanol (16) profisetinidin fisetinidol-(4a 8)-catechin (17) proguibourtinidin guibourtinidol-(4a— 8)-catechin (18) propeltogynidin (-)-epipeltogynane-(4a 6)-(-)-fisetinidol (19) trimeric profisetinidin fiseti-nidol.(4a— 6)-catechin-(8— 4a)-fisetinidol (20) tetrahydropyranochromene 21 and hexahydropyranochiomene 22.

---