Flavones esters

Modification of the substitution pattern on the same chromone gives a compound with smooth muscle relaxant activity, flavoxate (184). The synthesis of this flavone ester is initiated with methylation of the hydroxypropiophenone 177 to 178 followed by reduction of the nitro group to yield aniline 179. 

BAKER VENKATARAMAN Flavone synthesis Rearrangement of aromatic keto esters ot phenols to tiavones... 

Diphenylboric acid-2-aminoethyl ester reacts to form complexes with 3-hydroxy-flavones with bathochromic shift of their absorption maximum. 

Flavone formation is believed to proceed through a similar mechanism as the synthesis of chromones, albeit aromatic acid anhydrides and their corresponding salts are used. The first step is benzoylation of 12 to give the ester 14. Enolization and o-alkylation then affords the enolbenzoate 15. Enolbenzoate 15 then undergoes an acyl transfer to yield... 

A solvent-free synthesis of flavones was recently reported by microwave-assisted reaction of phloroglucinol 231 and differently substituted /1-ketoesters 232 [148]. The reaction was simply carried out by mixing the phenol and the ester in an open test tube followed by irradiation for 2-3 min. The internal temperature reached 240 °C and yields were in the range from 68 to 96%. Scheme 85 describes the application of this procedure to the synthesis of the natural product chrysin 233. 

Method B The acid chloride (3.6 mmol), the 2-hydroxyacetophenone (3 mmol), and TBA-HS04 (0.5 g, 1.5 mmol) in PhH (20 ml) are refluxed with aqueous K2C03 or KOH (10%, 20 ml) for 2-3 h until the ester is completely formed. The organic phase is separated, washed well with H20, dried (MgS04), and evaporated. The residue is taken up in PhH (50 ml) containing TosOH (1.5 g) and cyclized by azeotropic distillation to yield the flavone (>90%). Alternatively, the residue is stirred for 4 h in concentrated H2S04 (4 ml) at 0°C and then poured onto ice to yield the flavone. 

Classical organic chemistry provides a wide variety of potential analytes for electron ionization, the only limitation being that the analyte should be accessible to evaporation or sublimation without significant thermal decomposition. These requirements are usually met by saturated and unsaturated aliphatic and aromatic hydrocarbons and their derivatives such as halides, ethers, acids, esters, amines, amides etc. Heterocycles generally yield useful El spectra, and flavones, steroids, terpenes and comparable compounds can successfully be analyzed by El, too. Therefore, El represents the standard method for such kind of samples. 

The importance of NF-kB to inflammation, apoptosis resistance and tumour progression has resulted in the development of unique NF-kB inhibitors as part of cancer therapeutic regimens for GI and other cancers. Efforts are also being made to understand the efficacy of using natural substances obtained from plants, such as feverfew (e.g. parthenolide), bee glue (e.g. caffeic acid phenylethyl ester), tea (e.g. EGCG), spices (e.g. curcumin from turmeric) and mulberry figs (e.g. morin, a flavone) for the prevention both of persistent NF-kB activation and of the development of inflammatory pre-neoplastic lesions. 

DMSO resulted in an intramolecular ester condensation (Baker Venkataraman-type rearrangement) to give a Cl 5 phenol the cyclization of which furnished the 0-benzyl-protected flavone-C-glycoside. After deprotection, isoembigenin was obtained. 

Fesen MR, Pommier Y, Leteurtre F, Hiroguchi S, Yung J, Kohn KW. Inhibition of HIV-1 integrase by flavones, caffeic acid phenethl ester (CAPE) and related compounds. Biochem Pharmacol 1994 48 595-608. 

Structure-activity relationship. The endothelium-independent vasodilator effects showed by flavonoids are related to the structure of the compound tested. Structure- activity relationships have been studied to flavonoids selected from five groups flavonols, flavones, flavanones, isoflavones, and flavanols in rat isolated aorta on the contractions induced by noradrenaline, KC1 and the phorbol ester derivative PMA, as well as the interactions of these flavonoids with isoprenaline and sodium nitroprusside, Table (2). 

Photochemically induced ring cleavage reactions have also been reported in a,/i-epoxydiazomethyl ketones" and in a,/f-epoxy esters (glycidic esters).100 Two separate photoreactions are involved, however, in the rearrangement of phenyl epoxycinnamate (118) to the flavone (119), as shown in Scheme 7.101... 

In practice, the Konstanecki-Robinson synthesis of chromones commences with O-benzoylation not C-benzoylation, to afford ester 9.24. Base-catalysed rearrangement produces the required 1,3-diketone 9.21, via intramolecular benzoylation of the intermediate enolate. Acid-catalysed dehydration then affords flavone 9.19. 

Methyl ethers and esters are also found as volatile constituents in a wide range of flowers and fragrant herbs. For example, methyleugenol is found in the essential oil of herbs such as sweet basil and in the floral headspace of a wide range of flowers.7"10 Defense compounds and phytoalexins are commonly O-methylated as well. These compounds include the 3 -O-methylated form of the flavonoid quercetin as well as the 7-O-methyl ester of the flavone apigenin (Fig. ll.l).11,12 While not within the scope of this paper, it should be noted that protein O-methylation is common.13,14 One interesting protein modification known to occur in Arabidopsis thaliana is the a-carboxyl methylation of prenylated proteins.15 This modification has been shown in mammals and yeast to be important in protein targeting and membrane association.16,17... 

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