Chromones and Xanthones

Protolichesterinic acid MuroUc acid Lichesterinic acid Neuropogonic acid 

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

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Recanatini, M., Bisi, A., Cavalli, A., et al. (2001) A new class of nonsteroidal aro-matase inhibitors design and synthesis of chromone and xanthone derivatives and inhibition of the P450 enzymes aromatase and 17 alpha-hydroxylase/C 17,20-lyase. ./. Med. Chem. 44, 672-680. 

S. Gobbi, A. Rampa et al. (2001). A new class of nonsteroidal aromatase inhibitors Design and 1293. synthesis of chromone and xanthone derivatives... 

Metal hydrides usually reduce the carbonyl to alcohol but LAH converts xanthone into a dixanthyl ether (454) or xanthene (453) according to the conditions. The latter product is also obtained by the Wolff-Kishner-Huang-Minlon reduction. Metal-liquid ammonia opens the pyran-4-one ring of chromones and flavones to form dihydrochalcones and other compounds (79JOC1494). 

The phenolics include anthocyanins, anthraquinones, benzofurans, chromones, chromenes, coumarins, flavonoids, isoflavonoids, lignans, phenolic acids, phenylpropanoids, quinones, stilbenes and xanthones. Some phenolics can be very complex in structure through additional substitution or polymerization of simpler entities. Thus xanthones can be prenylated and flavonoids, lignans and other phenolics can be glycosylated. Condensed tannins involve the polymerization of procyaninidin or prodelphinidin monomers and hydrolysable tannins involve gallic acid residues esterified with monosaccharides. As detailed in this review, representatives of some major classes of plant-derived phenolics are potent protein kinase inhibitors. 

Ketones derived from pyrans are called pyranones (also commonly pyrones), and the parent compounds are pyran-2-one 17 and pyran-4-one 18. Trivial names are used for the related benzo analogs coumarin 19, isocoumarin 20, dihydrocoumarin 21, chromone 22, xanthone 23, and chromanone 24. 

Both the hetero and carbonyl oxygen atoms of maltol, 3-hydroxy-2-methylpyran-4-one, are replaced by sulfur on treatment with Lawesson s reagent. While the ketone —> thione conversion can be achieved with various sulfur reagents, the heteroatom exchange is unusual and appears specific for Lawesson s reagent (Equation 179). This reaction does not occur with either related chromones or xanthones <2006CC206>. 

Examples of thermochemical considerations of cupric enolates include the study of the binding of Cu + with kojic acid (16), a cyclic a-ketoenol. Comparison was made between the divalent cations of U02 +, Cu +, Zn +, Ni +, Co +, Cd +, Ca + where these metals are listed in decreasing order of binding constants over 6 powers of 10. In this case carbon-bonded metal seems most unreasonable because it would ruin the chelation as well as any aromaticity in the pyrone ring. It is admittedly an assumption that pyrones are aromatic. There are no one-ring pyrones for which there are enthalpy of formation data for gas phase species, as opposed to the benzoannelated compounds coumarin (I7)i07a, I07b chromone (is) " " "and xanthone (19) . Plausible, but unstable, Cu(II) enolates eliminate copper and form the 1,4-dicarbonyl compounds as shown in equation 8. 

Determination of the structure of natural and synthetic xanthones using spectroscopy is considerably more difficult than for chromones and flavones but publication of the analysis of spectra of known compounds assists with this problem. Multiple linear regression analysis has been applied to predict 13C n.m.r. shift increments for 272 polymethoxyxanthones and their... 

The iron-catalyzed synthesis of dihydro-2H-pyrans, 2H- and 4H-chromenes, chromones, isocoumarins and xanthenes were described in a broad review on the synthesis of heterocycles (14T4827), while the synthesis of 2H-pyran and chroman derivatives, coumarins and xanthone-type compounds was described in a review of recent progress on the chemistry of dimethyl acetylenedicarboxylate (14S537). The synthesis of several polysubstituted spirooxidole-2-amino-4H-pyrans, mainly through three-component reactions, was also described in a review on the synthesis of biologically active spirooxindoles (14T9735). 

There are several ways in which phenols have been categorized. Harbome and Simmonds categorized polyphenols based on the number of carbon atoms, which includes simple phenols (Ce) phenolic acids and related compounds (Ce—Ci) acetophenones and phenyl acetic acids (Cg—C2) cinnamic acids, cinamyl aldehydes, and alcohols (Cg—C3) coumarins, isocoumarins, and chromones (Cg—C3) flavonoids (C15) biflavonyls (C30) stilbenes (Cg—C2—Cg) benzophenones and xanthones (Cg—C2—Cg) quinones (Cg, Cio, Cm) betacyanins (Cjg) and lignans, lignins, tannins, and phlobaphenes (which are dimmers, oligomers, or polymers) [19]. Polyphenols have also been categorized by some researchers based on their... 

Moreover, according to chemical structure, polyphenols can be divided in classes as simple phenols, benzoquinones, phenolic acids, acetophenones, phenylacetic acids, hrodroxycinnamic acids, phenylpropenes, coumarins, isocoumarins, chromones, naphthoquinones, xanthones, stilbenes, anthraquinones, lignans, neolignans, lignins, and flavonoids. The latter allow to consider 13 subclasses with more than 5,000 compounds (Fig. 74.2). 

Pyran-4-ones and their monobenzo derivatives undergo ring opening when treated with aqueous alkali. This reaction has been widely used in the investigation of structure of chromones, flavones and isoflavones but xanthones are little affected. The nucleophile attacks the 1,2-bond in a rate-determining step whose rate constant varies with the electron density in the ground state at C-2. A kinetic study of the reaction with several chromones supports the mechanism shown in Scheme 25 (79ACH(101)73). 

Interest in the antibiotic bikaverin (531), a fungal metabolite with a benzo[Z>]xanthone skeleton, has culminated in its total synthesis (76JCS(Pl)499). The chromone moiety (530) was constructed as shown and the xanthone was obtained by cyclization of the acid chloride (Scheme 196). 

Chromone carbaldehyde 407 reacts with o-benzoquinodimethane 408 in a Diels-Alder reaction and concomitant deformylation to give a diastereomeric mixture of tetrahydrobenzo[ ]xanthones 409. Subsequent oxidation provides benzo[ ]xanthones 410 in good yields (Scheme 67) <2002T997>. 

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>. 

Chromone-3-carbaldehydes undergo Diels-Alder reactions with ort o-benzoquinodimethane 819 and deformyla-tion to yield initially benzo[b]-1,6,6a, 12a-tetrahydroxanthones 820, which are easily transformed into their corresponding benzo[ ]xanthones upon treatment with I2-DMSO (Scheme 232) <2002T105>. 

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