Xanthone-2-carboxylic acid

Xanthone, 2-hydroxy-1,3,4,7-tetramethoxy-molecular dimensions, 3, 624 Xanthone, 1,3,7-trihydroxy-synthesis, 3, 837 Xanthone-1-carboxylic acid reactions... 

Moran et al. recently reported receptor 20 that contains two pyridazine-2,4-dione units as polar anchor groups anellated to an aromatic framework [28] as well as the xanthone compound 21 where one of the binding sites is a ben-zoylamido group [29]. Compound 20 fits the binding pattern required for malonic acids, whereas 21 forms complexes with aromatic carboxylic acids like p-ethoxybenzoic add in CDCI3. 

Xanthone is unreactive towards hydrazine and phenylhydrazine. The oxime is obtained by reaction of xanthione (xanthene-9-thione) with hydroxylamine, or from xanthone and hydroxylamine in pyridine. When the oxime is heated in water with phenylhydrazine, the phenylhydrazone is formed. In acid solution, xanthone reacts normally with 2,4-dinitro-phenylhydrazine but xanthone-1 -carboxylic acid (435) gives the pyridazinone (436), possibly via the hydrazone (57JCS1922). When the oxime is heated with phosphorus pentachloride it undergoes a Beckmann rearrangement to give the amide (437) (70MI22300). 

The pyran-4-one ring (whether annulated to benzene or not) exerts an effect on some attached groups, for example, on the ease with which protons are detached from methyl groups and on the pKa of some carboxylic acids. Annulation of a benzene ring to the pyran-4-one increases the latter s stability to electrophiles and the effect is even more marked when two benzene rings are fused to the pyran, as in xanthone. 

Dimethylamino)vinyl)chromones 813 undergo a [2+2] cycloaddition reaction with DMAD to form the intermediate 814, which rearrange to afford xanthones in modest yield (Scheme 229) <1997J(P1)2167, 1999J(P1)3005>. ( )-2-(2-(Dimethylamino)vinyl)chromones 813 can also react with iV-phenylmaleimide 815 and chromone-3-carboxylic acid 816 to afford xanthones in modest yield (Scheme 230) <1997J(P1)2167, 1999J(P1)3005>. 

The free-radical-scavenging activity of compounds was evaluated in the TEAC and CL assays. The first measures the relative abiUty of antioxidant substances to scavenge the radical cation 2,2 -azinobis(3-ethylbenzothiozoline-6-sulfonate) (ABTS" ) as compared to a standard amount of the synthetic antioxidant Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid). The CL assay measures the inhibition of iodophenol-enhanced chemiluminescence by a horseradish peroxidase/perborate/luminol system. Trolox was used as the reference antioxidant. The results showed that xanthones exhibited free-radical-scavenging activity at potency levels comparable to those of reference antioxidant compounds quercetin and rutin, while the benzophenone and phloroglucinol type compoimds had more moderate activities [87]. 

The mass spectrum of 5-hexyl-7-(5-methylsulphonimidoyl)xanthone-2-carboxylic acid exhibits a peak which has m/z that is 14 units higher than the molecular peak. It has been shown that this arises from an intermolecular transfer of a methyl group (which occurs also when the compound is heated) but a carboxylic acid group is essential. 

The oxidation of the unsaturated compound II gives, in addition to the acid HI already mentioned, a small amount of a monobasic acid, C17H14O7 (m.p. 304° methyl ester, m.p. 252°), which is regarded as 2,3,8-trimethoxy-xanthone-5-carboxylic acid (VI). Its formation was considered to be analogous to the formation of fluorenone in the oxidation of phenanthrene... 

Cyanochromone exhibits high stereoselectivity in [4+2]-cycloaddition reactions with electron-rich dienes which lead to partially reduced xanthones <97JOC7904>. The dienamine (44) affords xanthones on reaction with N-phenylmaleimide and with chromone-3-carboxylic acid through loss of dimethylamine from the [4+2]-cycloadduct. However, more reactive dienophiles such as DMAD undergo a [2+2] cycloaddition followed by an intramolecular [4+2] reaction to give the xanthone (Scheme 13) <97JCS(P1)2167>. 

Early in our work we found that xanthone-2-carboxylic acid (1) had significant activity as an inhibitor of the PCA reaction in rats - of the order of 100 mg/kg after i.v. administration. 

Further work showed that other tricyclic systems provided compounds which were equally active. Thus, we found that thio-xanthone-(2, X = S) acridone-(2, X = NH) anthraquinone-(2, X = CO) and flurenone-(2, X = bond)-2-carboxylic acids all had activity comparable with that of the xanthone acid and similar findings were reported by other groups. Only those compounds with the carboxylic acid function in the 2-position were significantly active the other isomers were weakly active or inactive. 

Sulfonation occurred, as expected para to the electron-donating hetero oxygen atom. 5-Substituted xanthone-2-carboxylic acid derivatives 120 reacted with excess chlorosulfonic acid under forcing conditions to give the corresponding 7-sulfonyl chlorides 121. ... 

An alternative synthesis of xanthone-2-carboxylic acids (173) has been pro-posed which involves the photo-Fries rearrangement of o-methoxy-benzoates... 

Benzenetriols on cyclocondensation with hydroxybenzoic acids gave 1,3-dihydroxyxanthones which were converted into various 0-derivatives containing carboxyl or amino groups.Several xanthones [e.g., (165)] have been synthesized by ring closure of the ketones (164) with ethanolic potash.Benzoxanthones are represented in nature by several compounds such as the quinone bikaverin. Several members of this class [e.g., (166)] were prepared by base-induced condensation of 2-hydroxyacetophenones with dimethyl homophthalates, and reduced benzoxanthanone (167) which is potentially of interest as an antitumour compound, was obtained by condensation of 2-methylchromone-3-carboxylic acid with methyl 4-oxocyclohexanecarboxylate. 

Friedel-Crafts cyclization of phenoxy ether 70 leads to the corresponding xanthone TJ Exhaustive oxidation of the methyl group leads to the carboxyl lie acid, xanoxate (72). ... 

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