Pinocembrin structure

Structurally, the only unusual chalcone of woody tissues is rubranine (30) from Aniba rosaedora, which is a citral-chalcone condensation product. The possibility of rubranine being an artifact of the isolation procedure was considered by Montero and Winternitz (28), who synthesized it by condensing the essential oil citral with pinocembrin in the presence of the alkaloid anibine, which also occurs naturally in Aniba wood. However, De Alleluia and coworkers (7) later confirmed that it was a natural product from the evidence that it was optically active, and that it could be isolated by very brief washing of the wood with hexane. 

Malus leaf. That it was an intermediate was indicated by its rapid conversion during chromatographic purification into chrysin 7-glucoside. More recently, a second dibenzoylmethane, namely the 2,6-dihydroxy-4-methoxy-derivative, was reported in Populus nigra buds. More careful examination of this latter material, however, showed it to have the isomeric cyclic structure of a 2-hydroxyflavanone, i.e. (29). This was proved by Lx., m.s., and n.m.r. studies and also by synthesis. Its co-occurrence in Populus buds with the 7>methyl ethers of galangin, chrysin, and pinocembrin suggests it has a biogenetic role. In retrospect, it seems likely that Williams compound in Malus has a similar cyclic structure [i.e. (30)] rather than the open-chain form. Re-examination of... 

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