Pulvinic biosynthesis

Simple alkylated polyhydroxyterphenyls like penioflavin (114), isolated from Peniophora sanguinea, can be derived formally from a C-18 terphenylquinone as precursor and subsequent formation of a new carbon-carbon bond [94]. The biosynthesis of xylerithrin (118) and related pigments from P. sanguinea, according to the studies of Von Massow [113, 114], requires the insertion of a third unbranched phenylpropanoid unity on a pulvinic acid intermediate derived from a terphenylquinone, as indicated in Scheme 2. 

Alternatively, the pulvinone nucleus of pigment (115) could derive via oxidative decarboxylation of the hypothetical intermediate (9) already implicated in the biosynthesis of grevillins, terphenylquinones (and hence pulvinic acids), and the pigment (10). 

As a final alternative, the biosynthesis of fungal cyclopentenones may by-pass the terphenylquinone and pulvinic acid pathway altogether. Condensation of two 4-(hydroxyphenyl)pyruvate moieties, either directly or via the now familiar intermediate (9), could lead to the a-... 

Mosbach, K. On the Biosynthesis of Lichen Substances 2. The Pulvinic Acid Derivative Vulpinic Acid. Biochem. Biophys. Res. Commun. 17, 363 (1964). 

The biosynthesis of pulvinic acids in lichens has recently been shown to proceed via enzymatic oxidative rearrangement of hydroxyterphenyl-quinones (see biosynthesis section). As early as 1928, Kogl had provided... 

Maass, W. S. G., and A. C. Neish Lichen Substances II. Biosynthesis of Calycin and Pulvinic Dilactone by the Lichen, Pseudocyphellaria crocata. Canad. J. Botany 45, 59 (1967). 

Phenolic compounds are widespread products of secondary metabolism of lichen, and antioxidant activity is most frequently associated with their presence. Lichen phenolics are mainly depsides, depsidones and dibenzofurans, whereas vascular plant phenolics include tannins, lignins and flavonoids. Orsellinic acid is the basic unit in the biosynthesis of hchen phenolics. Lichen phenols are generally secreted by the fungal partner and deposited as crystals on the surface of the ceU wall of the fungal hyphae. Lichen phenols are primarily acetate-polymalonate derived with the exception of pulvinic acid derivates which are synthesised via... 

Synthetic and biosynthetic work on the lichen pulvinic acids, e.g. pulvinic acid (23), calycin (24), and pinastric acid (25), has been reviewed recently by Pattenden (265). Maass (231) has studied the biosynthesis of... 

The biosynthesis of phenylalanine derivatives goes through shikimic acid and phenylalanine in contrast to the aromatic units of the anthraquinones, depsides, depsidones, depsones, dibenzofuranes, and xanthones, which are formed on a polyacetate pathway. This justifies a separate classification for the phenylalanine derivatives, which include polyporic acid, thelephoric acid, and pulvinic acid derivatives, all deeply pigmented (yellow, orange, red, or violet). 

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