Quinones from lichens

The UV data of 11 quinones from lichens are summarized in Table 8. 

C 4H s04, Mr 272.30, black-violet prisms, mp. 264-266°C, [a]g -p365 (CH3OH). An o- naphtho-quinone from the mycosymbiont of the lichen Trype-thelium eluteriae. 

The simplest quinones are o- and p-benzoquinone [(3) and (4) respectively]. This quinonoid structural feature is widespread in naturally occurring compounds isolated from moulds, fungi, lichens, plants and insects,52 which include not only substituted benzoquinones but also substituted polycyclic quinones [i.e. the substituted analogues of, for example, 1,2-naphthoquinone (5), 9,10-anthraquinone (6), and 9,10-phenanthraquinone (7)]. 

Mushrooms and various fungi and lichens are rich in enol metabolites and many exhibit significant bioactivities , such as usnic acid (14) which serves as a regulator for plant growth and shows antitumor and antibiotic activities " . The widely distributed quinone polyporic acid (15a, PPA) from the Purple-Dye Polypore mushroom (Hapalopilus nidu-lans) and other sources is a weak inhibitor (IC50 = 0.1 to >1.5 mM " ) of dihydroorotate... 

Two naphthofurandiones, namely the 2-ethyl derivative of 84 and 89, were isolated from heartwood of P. peroba, in addition to lapachol, lapachone, and benzochromendiones (68N38). Related quinones 90 (mixtures of enantiomers) were isolated from wood of Rademachera sinica (81JCS(P1)2764). Helicquinone (91) was isolated from Helicteres angustifolia (87P578) and haemoventosin (92), a colored compound, was isolated from a lichen, Haematomma ventosum (71ACS483). 

The quinones are widely distributed in nature, and about 1200 different quinones have been observed in bacteria, in all plant phyla except mosses, and in animal phyla like echinoderms (sea urchin) and arthropods (insects) (53,54). They may occur in all parts of a plant however, a large propcntion are present in roots, heartwood and bark. The quinones range in color from yellow, through red, purple to almost black. They make relatively little contribution to color in higher plants their color is perhaps most conspicuous in some fungi, lichen, and insects (Coccidae). 

Benzo-l,4-quinoid structures occur in nature as the final oxidation products ofvarious mono- and polycyclic compounds. Most simple benzo-1,4-quin ones occur in microorganisms (moulds), higher fungi and lichens, and less frequently in higher plants and some insects. Common substances are glycosides occurring in colourless reduced forms (such as derivatives of hydroquinone known by the systematic name of benzene-l,4-diol). Coloured quinones are formed from these precursors by hydrolysis catalysed by saccharases and by enzymatic oxidation or autoxidation of aglycones. 

Mathey (528) isolated from the lichen Laurera sanguinaria the quinone isohypocrellin and proposed structure 539. 

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