Styrylpyrones

Cinnamic acids, as their coenzyme A esters, may also function as starter units for chain extension with malonyl-CoA units, thus combining elements of the shikimate and acetate pathways (see page 80). Most commonly, three C2 units are added via malonate giving rise to flavonoids and stilbenes, as described in the next section (page 149). However, there are several examples of products formed from a cinnamoyl-CoA starter plus one or two C2 units from malonyl-CoA. The short poly-^-keto chain frequently cyclizes to form a lactone derivative (compare triacetic acid lac-tone, page 62). Thus, Figure 4.37 shows the proposed derivation of yangonin via cyclization of the di-enol tautomer of the polyketide formed from 4-hydroxycinnamoyl-CoA and two malonyl-CoA extender units. Two methylation reactions complete the sequence. Yangonin and a series of related structures form the active principles of kava root (Piper methysticum; Piperaceae), a herbal remedy popular for its anxiolytic activity.

chain extension; acetate pathway with a cinnamoyl-CoA starter group

4-hydroxycinnamoyl-CoA

2 x malonyl-CoA SCoA V

2 x malonyl-CoA SCoA V

yangonin

Figure 4.37

yangonin

Figure 4.37

di-enol tautomer

di-enol tautomer

Enol Tautomer Lactone
OO
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