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Isoflavonoids of the Leguminosae

Ateleia herbert-smithii, a new source of novel isoflavones. Photo: G.P. Lewis.

The isoflavonoids are one of the most distinctive and important classes of the naturally occurring flavonoids. Their distribution in plants is restricted compared to other flavonoids, and they are found predominantly in subfamily Papilionoideae of the Leguminosae. Well-known examples that have attracted interest because of their biological properties include the isoflavones of soy and red clover (oestrogenic), rotenones (insecticidal) and induced compounds with anti-fungal activity produced under stress conditions (phytoalexins). A recent focus of research in this area at Kew has been on the isoflavonoids of Ateleia (Annex 1) and Cicer.

The primary aim of the project is to produce a reference work entitled 'Isoflavonoids of the Leguminosae 1997-2004', commissioned by the Royal Society of Chemistry for publication in Natural Product Reports in 2006-7. Earlier reviews of the scientific literature relating to isoflavonoids to the end of 1991 appeared in four volumes of the Advances in Flavonoids series, edited by the late Jeffrey Harborne and others. Subsequently, the literature from 1992 to 1996 was reviewed in two articles by Boland and Donnelly in Natural Product Reports (1995, 12, 321 and 1998, 15, 241). No comparable review has been published covering the period from 1997 onwards. A survey of the literature on isoflavonoids from 1997-2004 indicates that there are approximately 450 new examples of these compounds, more than 90% of which originate from the Leguminosae. The use of molecular techniques (DNA sequencing) in the same period has led to advances in legume systematics which have been incorporated into the recently published volume, Legumes of the World. This will be used as the reference point for the taxonomy underpinning the review.

All the major isoflavonoid subclasses will be surveyed, including their glycosides, dimers, heterodimers and oligomers. Points of interest relating to the source, biosynthesis, identification and properties of new compounds will be discussed, together with wider issues such as chemosystematic or ecological significance. Chemical syntheses of new isoflavonoids introduced in the review will be cited, but general procedures for isoflavonoid synthesis and the production of well-known compounds will not. The review will be illustrated by structure drawings and other figures, and conclude with an extensive bibliography.

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