OLIGOMERIC FLAVANOIDS .18. DIMERIC PROROBINETINIDINS FROM ROBINIA-PSEUDACACIA

The range of naturally occurring prorobinetinidins is extended by char acterization of the novel robinetinidol-leucorobinetinidins 3, 5, 7, a nd 9, the robinetinidol-dihydrorobinetins 11, 13, and 15, a robinetini dol-robinetin 17, and a robinetinidol-flavone analogue 19. The diversi ty regarding the oxidation level of the chain terminating moieties sug gests that the biflavanoids in Robinia pseudacacia may be interrelated via oxidation/reduction of these units. The conspicuous absence of th e effects of dynamic rotational isomerism about the interflavanyl bond in the H-1 NMR spectra of some of the derivatives is explained in ter ms of a preferred conformation of this bond rather than to 'free rotat ion'.