ABSTRACT
Pueraria lobata Ohwi accumulates isoflavonoids as main secondary metabolites in various organs, e.g. roots, stems, leaves and flowers (Hakamatsuka et al., 1994). Isoflavonoid is a subgroup of flavonoids whose basic carbon skeleton is constructed by a combination of shikimate pathway and acetate-malonate pathway (Figure 7.1). Biosynthetic pathway leading to isoflavonoid frameworks shares the early part of the pathway (often referred to general phenyl propanoid pathway) from phenylalanine to p-coumaroyl CoA with several other plant phenolics such as simple phenylpropanoids, lignins, coumarins and quinones. The construction of flavonoid skeleton from p-coumaroyl CoA and three molecules of malonyl CoA to form chalcone, and the isomerization of chalcone into flavanone are common biosynthetic reactions among all flavonoid subgroups. The first committed step of isoflavonoid-specific pathway is a migration of the side phenyl group (B-ring) of the flavanone molecule from C-2 to the adjacent C-3 position. One structural feature of Pueraria isoflavonoids is the lack of oxygen function at C-5 and this reduction process has been proven to occur in the course of chalcone formation (Stoessl andStothers, 1979).
