Phenylpropanoids, Aromatic Polyketides

　Both phenylpropanoids and aromatic polyketides are natural organic compounds of plant origin biosynthesized via the shikimic acid pathway. Phenylalanine and tyrosine are their precursors.¹⁾ Phenylpropanoids are classi?ed in the group of compounds in which side chains with three carbons are attached to a benzene ring. They are ingredients of essential oils obtained from anis, cinnamon bark, and clove and are used for fragrances and aromatherapy.
　Aromatic polyketides are designated as compounds in which carbon chains are extended with malonyl-CoA onto phenylpropanoids.²⁾ Diarylheptanoids are biosynthesized from two cinnamyl-CoA units and one malonyl-CoA. Their two aromatic rings are connected with an aliphatic seven-carbon chain. Stilbenoids, chalconoids, flavonoids and isoflavonoids are formed from a cinnamyl-CoA with three malonyl-CoA units. Chalconoids, flavonoids and isoflavonoids possess a C₆-C₃-C₆ skeleton whereas stilbenoids have a C₆-C₂-C₆ skeleton which arises by decarboxylation during the biosynthesis. Most of them have phenolic hydroxy groups and show antioxidative activity. Some of them show physiologic activities towards plants, such as phytoalexins, with the budding of seeds and adjusting of growth. Isoflavonoids are a unique compound group: they are biosynthesized via the phenyl group migration from flavonoids.²⁾ To date, they are found only in the Leguminosae/Fabacaeae plant family. This distinct biosynthesis triggered researchers to investigate detailed biosynthetic mechanisms.