Dibenzo-a-pyrones

Altemaria, one of the most common moulds contaminating foods and feeds, produces many metabolites with different chemical structures. Two metabolites of m or concern because of their toxicity and/or natural occurrence in a number of fungal contaminated commodities are the dibenzo-a-pyrone derivatives altomariol (AOH) and altenuisol (ATS). 

Reactions of substituted bis(3-aIkoxybenzoyl) peroxides in neat phenols afford mainly 8-alkoxy-677-dibenzo[fc, d]pyran-6-ones and orf/zo-benzoyloxylation products of the phenol. For example, bis(3,4-dimethoxybenzoyl) peroxide (561) in neat p-methylphenol was completely decomposed in 1 h at 60 °C with the formation of a dibenzo-a-pyrone derivative 562 (60%) together with an ortho-ortho coupled product 563 (21%) and benzoate 564 (5%). In contrast, dibenzoyl peroxides having no mefa-electron-releasing substituents gave mainly ort/zo-benzoyloxyphenols. For example, decomposition of bis(4-methoxybenzoyl)... 

Methoxy-6-bromobenzoic acid and phloroglucine boiled 1 min. in 1 N NaOH, containing a little CuS04 —d-methoxyA -dihydroxy-dibenzo-a-pyrone. Y 70%. (F. e. with lower yields s. E. Lederer and J. Polonsky, Bl. 1948, 831.)... 

Bradbum N, Coker RD, Blunden G, Turner CH, Crabb TA (1994) 5 -Epialtenuene and Neoaltenuene, Dibenzo-a-pyrones from Alternaria alternata Cultured on Rice. Phytochemistry 35 665... 

Other metabolites like 5,7-dihydroxy-8-methoxychroman-4-one (37) and possibly a coumarin derivative (35) have also been found in the bulb wax of E. comosa. From the bulb tissue of different Eucomis spp. a series of sterol derivatives, dibenzo-a-pyrones and a dicarboxylic acid have been isolated (69, 82). 

Ghosal, S. Mitochondria-targeted antioxidants comprising coenzyme QIO, reduced CoQlO, oxygenated dibenzo-a-pyrone, or amino acyl ester, for treatment of mitochondrial diseases. PCX Int. Appl. WO 2008016554, 2008 Chem. Abstr. 2008, 148, 222003. 

Chemically xanthones (9H-xanthen-9-ones) are heterocychc compounds with the dibenzo-y-pyrone framework (1, Fig. 1). The xanthone nucleus is mun-bered according to a biosynthetic convention with carbons 1-4 being assigned to acetate-derived ring A and carbons 5-8 to the shikimate-derived ring B. The other carbons are indicated as 4a, 4b, 8a, 8b, 9, and 9a for structure elucidation pmposes [4]. 

Fused benzene rings aid nucleophilic attack on pyridines, pyridinium and pyrylium ions, and pyrones the loss of aromaticity involved in the formation of the initial adduct is less in monobenzo derivatives and still less in linear dibenzo derivatives than in monocyclic compounds. For the same reason, the tendency for this initial adduct to re-aromatize is less for benzopyridines. Fused benzene rings also influence the point of attack by nucleophilic reagents attack rarely occurs on a carbon atom shared with a benzene ring. Thus, in linear dibenzo derivatives, nucleophilic attack is at the y-position (157). 

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