Biflavonoids and Proanthocyanidins

A number of important reviews of the biflavonoids have been prepared, and works by Baker and Ollis (13) published in 1961, Locksley (232) in 1973, and Geiger and Quinn in 1975 (125) and 1982 (126) are recommended reading for those undertaking study of these compounds. The review by Baker and Ollis (13) provides a particularly interesting account of the difficulties encountered in the elucidation of the structures of these compounds in the early years prior to modern spectroscopic methods. Excellent summaries of isolation procedures for the flavonoids are provided by Markham (237, 238) and Hostettmann and Hostett-mann (163). Readers are referred to these, the review of biflavonoids by Geiger and Quinn (126), and references cited herein for details. Compilations of chro- 

Various interconversion reactions are used for the synthesis of analogs. Partial methylation and demethylation (3, 16, 130, 249-251, 263, 264), rearrangement of C-8 C-8 to C-6 C-8 biphenyl isomers, and dehydrogenation reactions converting flavones to flavanones have been employed (3, 16, 227, 251, 264, 293). Many biflavonoids have now been synthesized and references are compiled in Locksley s (232) and Geiger and Quinn s (125, 126) reviews. 

Unfortunately, there is no commonly accepted trivial nomenclature for these compounds their full systematic names, not to mention their often complex common names, are extremely cumbersome. Geiger and Quinn have proposed a new system (125) but it, like the trivial procyanidin nomenclature initiated by Weinges (381), requires frequent reference for understanding and has become very difficult to use as the number of new compounds has grown. Locksley (232) has proposed a system in which the position of substitution of the upper (I) and lower (II) units is defined from the usual numbering of the parent flavonoid, and each unit is also described from the parent monomer. Thus, the common biflavone amentoflavone is named apigeninyl-(I-3, II-8)-apigenin, etc. Locksley s nomenclature is used in this chapter (232). 

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Hemingway, R.W., Biflavonoids and proanthocyanidins, in Natural Products of Woody Plants 1 Chemicals Extraneous to the Lignocellulosic Cell Wall, Rowe, J.W., Ed., Springer Verlag, New York, 1989, chap. 7.6. 

Hemingway, R.W. Biflavonoids and Proanthocyanidins. In Natural Products of Woody Plants I (J.W. Rowe, ed.), p. 571. Berlin, Springer-Verlag, 1989. 

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