Anthraquinones from mevalonic acid

Chrysophanol (XXIII), an anthraquinone isolated from the leaves of Rumex alpinus (Polygonaceae), is also formed from acetate (and presumably therefore derived via the acetate-malonate pathway) (Leistner and Zenk, 1969) and not, as previously considered, from shikimic acid and mevalonate. Only anthraquinones such as alizarin lacking a C-methyl group and not hy-droxylated in ring A are made in this way, despite an apparent similarity in structure thus at least two independent routes also exist for the synthesis of these compounds and reflect the diversity available for the biogenesis of multiringed phenols in plants. 

One of the open questions in anthraquinone biosynthesis is the nature of the branching compound X (Fig. 4). In vitamin K2 biosynthesis 1,4-dihydroxy-2 naphthoic acid (V) is involved (vide supra). It may also be an intermediate in phylloquinone s and anthraquinone biosynthesis. Feeding experiments established that anthraquinones in Rubia, Morinda and Galium >28,2 9 derived from shikimic acid, a-ketoglutaric acid and mevalonic acid with -succinylben-zoic acid being a key intermediate. Incorpo-... 

As is true for the naphthoquinones, anthraquinones are synthesized by a variety of routes in plants and fimgi (Pack-ter, 1980). Most are derived from either acetate-malonate or isochorismate-a-ketoglutaric acid-mevalonate pathways. Anthraquinones also are produced frequently in plant tissue cultures (Ellis, 1988). Tissue cultures of Cinchona species (Rubiaceae) produce at least 30 different anthraquinones. 

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