Variegatic acid

Boletes bruising yellow - deep blue Variegatic acid, Xerocomic acid... 

CIgH12O5, Mr 308.29, orange prisms, mp. 216- 217 °C. A pigment of numerous lichens. The biosynthesis proceeds from polyporic acid. The methyl ester of R, vulp(in)ic acid, is a typical lichen acid. Hydroxylated P. derivatives are important mushroom pigments, e. g., gomphidic acid, variegatic acid, and xerocomic acid the latter two compounds are responsible for the typical blue color reaction of many Boletus and Xero-comus species on bruising the fruit bodies. 

Hydroxylated pulvinic acids are responsible for the yellow and red colours of most boletes. They also cause the characteristic blueing of the flesh which occurs when the fruit bodies of many species are cut or bruised. Because the distribution of the hydroxylated pulvinic acids such as variegatic acid (73) and xerocomic acid (72) is restricted to the order Boletales, their isolation from Gomphidius 608), Omphalotus 128, 397, 584), Hygrophoropsis 91, 126, 127, 198), Coniophora 86,... 

Variegato- Present in almost all species which contain variegatic acid (73), in many... 

The hydroxylated pulvinic acids such as variegatic acid (73) may be characterised in the form of their dilactone peracetates, e.g. (75) (Scheme 10), which exhibit sharp melting points, in contrast to the parent pigments, and give rise to diagnostic infrared absorption above 1800 cm 73). Dilactone formation also occurs on electron impact and the mass spectral fragmentation of pulvinic dilactones has proved valuable in structural elucidation 452, 453, 607, 608). On treatment with diazomethane the hydroxypulvinic acids are converted into the... 

The blue colour formed on oxidation of variegatic acid (73) by oxidases or by alkaline potassium ferricyanide is due to the formation of delocalised hydroxyquinone methide anions of type (77) (Scheme 10) (607). The electronic spectrum of anions such as (77) is in close accord with that of the blue anion (78) generated by oxidation of catechol in the presence of Meldrum s acid (700). Due to its nature as a vinylo-gous carboxylic acid a substantial proportion of the hydroxyquinone methide (77) is present in the form of its anion even at neutral pH. 

Besides atromentic acid, xerocomic acid, and variegatic acid a number of less common pulvinic acid derivatives have been isolated from Basidiomycetes (Table 11). 

Isoxerocomic acid (84) and some of its derivatives are produced by cultures of Serpula lacrimans 89, 90). Variegatic acid (73) is also produced by this most destructive and insidious wood-rotting fungus and may be used for on-site detection by thin layer chromatography 125). 

A series of variegatic acid derivatives (93) to (95) specifically methylated at the 3-hydroxy group is formed in cultures of Hygrophoropsis... 

During preliminary studies on the North American bolete Boletus morrisii a polar pigment has been isolated from dried fungal material for which a glycosidically bound variegatic acid structure is probable 364). 

Boletus spp., Xerocomus spp., Suillus variegatus and other boletes (Table 8) Yellow - blue Variegatic acid (73) and/or Xerocomic acid (72) - Anions of the type (77) (Scheme 10)... 

Beaumont, P.C., R.L. Edwards, and G.C. Elsworthy Constituents of the Higher Fungi VIII. The Blueing of Boletus Species. Variegatic Acid, a Hydroxytetronic Acid from Boletus Species and a Reassessment of the Structure of Boletol. J. Chem. Soc. (London) C 1968, 2968. 

Variegatic Acid, a New Tetronic Acid Responsible for the Blueing Reaction in the Fungus Suillus Boletus) variegatus (Swartz ex Fr.). Chem. Commun. 1967, 373. 

Chalciporus piperatus, Boletaceae), accompanied by the second main pigment chalcitrin (9-145), norbadione A, variegatic acid and variegatorubin. 

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