Phlobatannins, a novel class of ring-isomerized condensed tannins
Abstract
Four members of a novel class of natural ‘phlobaphene’ condensed tannins, representing the products of stereospecific ring-isomerization of those 2,3-trans-3,4-trans-(–)-fisetinidol units present in ‘conventional’[4,8]-bi-and [4,6:4,8]-tri-flavanoid profisetinidins, are defined as functionalized 8,9-trans-9,10-cis-3,4,9,10-tetrahydro-2H,8H-pyrano[2,3-h]chromene (1) and the homologous hexahydrodipyrano[2,3-f,2′,3′-h]chromene (5) by nuclear Overhauser effect difference spectrometry.