Portal de Periódicos da CAPES

Oligomeric flavanoids. Part 4. Base-catalysed conversions of (–)-fisetinidol-(+)-catechin profisetinidins with 2,3-trans-3,4-cis-flavan-3-ol constituent units

1988; Issue: 12 Linguagem: Inglês

10.1039/p19880003331

2050-8255

Jan P. Steynberg, Johann F. W. Burger, Desmond A. Young, E. Vincent Brandt, Jacobus A. Steenkamp, Daneel Ferreira,

Cancer Treatment and Pharmacology

Additional novel members of the class of natural 'phlobaphene' condensed tannins, representing the products of C-ring isomerization of 2,3-trans-3,4-cis-(–)-fisetinidol units present in (4β,6)- and (4β,8)-biflavanoid profisetinidins have been characterized. These comprise the functionalized 8,9-trans-9,1 0-trans-3,4,9,10-tetrahydro-2H,8H-pyrano[2,3-h]chromenes (2) and (11), and 8,9-cis-9, 10-trans analogue (8), and a 6,7-cis-7,8-trans-[2,3-f]-regioisomer (27). Analogues (8) and (11) are prototypes of a unique class of phlobatannins in which the resorcinol A- and pyrocatechol B-rings are interchanged relative to their positions in the more common isomers. Their formation represents a novel rearrangement of profisetinidins with 2,3-trans-3,4-cis-flavan-3-ol units, e.g. (1) with concomitant inversion of absolute configuration at 3-C(C), under base catalysis. The proposed structures of the natural products were confirmed by synthesis via base-catalysed conversion of (–)-fisetinidol-(4β,8)- and (4β,6)-(+)-catechin O-methyl ethers (1) and (14).