2 -Hydroxyflavone

Oleanonic acid, 6-hydroxyflavone, xanthotoxol, gjycyrrhetic acid acetate... 

As already mentioned, subtribe Oncidiinae has been considered as a probable sister group of the Ornithocephalinae Oncidium species so far surveyed lack flavone C-glycosides, and possess new and unusual 6-hydroxyflavone glycosides. Thus, different flavonoid patterns did not support a close association of these two subtribes. 

In other instances, flavones and flavonols with particular patterns of oxidation are of sufficiently restricted distribution among plant groups to be useful for systematic purposes. For example, in addition to the usual flavones [apigenin (5), luteolin (4), and chryseriol (38) (Fig. 11.3), usually as the 7-(7-glucuronides], plants of the Lamiaceae, Scrophulariaceae, and related families frequently contain 8-hydroxyflavones, 6-hydroxyflavones, or 6-methoxyflavones in glycosidic combination. 8-Hydroxyflavones based on apigenin and luteolin are restricted to the Lamiaceae (Tomas-Barberan et al., 1988). 

Flavones are an important class of flavonoids, having the basic structure of 2-phenylchromen-4-one (2-phenyl-l-benzopyran-4-one). Naturally occurring flavones include apigenin (4, 5,7-trihydroxyflavone), luteolin (3, 4, 5,7-tetrahydroxyflavone), tangeritin (4, 5,6,7,8-penta-methoxyflavone), 6-hydroxyflavone, baicalein (5,6,7-trihydroxyfla-vone), chrysin (5,7-OH), wogonin (5,7-OH, 8-OCH3), and scutellarein (5,6,7,4 -tetrahydroxyflavone). Flavoxate and diosmin are synthetic flavones that are yellow in color. 

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