Tannins from the heartwoods of Schinopsis spp. (quebracho) and Rhus spp. (karee) represent mutual condensation products of their associated precursors (2S,3RI4S) (-) -leucofisetinidin, (2RI3S) -(+)catechin and, to a minor extent, (2R,3R) -(-)epicatechin. The unique enantiomeric relationship between the electrophile and two nucleophiles at C-2 is reflected both in the biflavanoid metabolites comprising four [4,6] and [4,8] -(+) -fisetinidol-(+) -catechins and [4,8] -(+) -fisetinidol-(-) -epicatechin, and in the extension of the former group to four ' angular ' triflavanoid [4,6 :4,8] -bi-[ (+)-fisetinidol] -( +)catechin diastereoisomers. Stoicheiometric control of in vitro condensation of the precursors provide similar oligomeric mixtures with selective or specific emphasis on either bi-or tri-flavanoids respectively. H N.m.r. coupling constants and chemical shift parameters derived from these compounds and their (-) -fisetinidol analogues are of potential diagnostic value at higher oligomeric levels.Genesis of significant concentrations of (2S,3R,4S)-2,3-trans-3,4-trans-3',4',7-trihydroxyflavan-3,4-diol [( 1), (-)-leucofisetinidin, 5.7-9.5%] and of (2R,3S)-2,3-trans-3',4',5,7-tetra-in the peripheral heartwood of the quebracho [Schinopsis balansae Engl. and S. lorentzii (Gris.) Engl.], coupled with evidence of their decline with aging radially towards the central heartwood,' correlates with a progressive increase in the numberaverage mass of the phenolic mixture (610 -1 203) and with recognition of the predominant heartwood tannins as pr~fisetinidins.~~~ Limited but more direct indication of participation of both precursors in the formation of tannins of quebracho extract, one of the world's major commercial tanning materials, was obtained by our recent isolation (and synthesis) of two [4,8]-( +)-fisetinidol-( -t)-catechins [(3), (2S, 3R,4R : 2'R,3'S) and (9, (2S,3R,4S : 2'R,3'S)] with absolute configurations at C-2 and C-3 which reflect the unique enantiomeric relationship between the parent The range of oligomeric analogues exclusive to the Anacardiaceae by virtue of their stereochemistry is at present extended to bi-and tri-flavanoids from the heatwoods of the quebracho S. balansae) mountain karee (Rhus leptodictya Diels) and karee (R. lancea L.f.). Confirmatory biomimetic-type synthesis furnishes either bi-or tri-flavanoids selectively through simple stoicheiometric control.The pairs of diastereoisomeric [4,8]-and [4,6]-profisetinidins (3), (9, (7), and (9) of 2,3-trans-3,4-trans : 2',3'-trans and 2,3-trans-3,4-cis : 2',3'-trans relative and indicated [(3), (9, (7), and (9); Table l)] absolute configurations were isolated from both quebracho and mountain karee heartwoods and were identified as their heptamethyl ether diacetates (4), ( 6), (8) and (10) in the approximate proportions 11 : 5 : 3 : 1 and 1 I : 1 1 : 2 : 1, respectively, with [4,8]interflavanoid bonding predominating over [4,6] and 3,4-rrans configurations generally over 3,4-cis for each type of linkage. In addition the mountain karee was shown by ...
