steps leading to the C 6 -C 3 building block (phenylpyruvic acid, L-phenylalanine)
include decarboxylation, aromatization, and dehydroxylation. Generally two of the
C 6 -C 3 building blocks combine to form terphenylquinones and reaction pathway
continues to pulvinic acid derivatives. Classes of lichen substances which are
derived by shikimate pathway are therphenylquinones and pulvinic acid derivates
(Fig. 33)
Terphenylquinones
Phenylquinones are well-documented examples of lichen secondary products
derived by the shikimic acid pathway and are widespread especially among fungi.
Terphenylquinones are formed by condensation of two (probably activated)
phenylpyruvic acid derivatives. Only two terphenylquinones, polyporic acid and
thelephoric acid, are known.
Fig. 33 Classes of lichen substances which are derived by shikimate pathway
9 Lichen Metabolites: An Overview of Some Secondary Metabolites and Their. . .
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