Regioselective hydroxylation of 2-hydroxychalcones by dimethyldioxirane towards polymethoxylated flavonoids

The flavone nucleus is part of a large number of natural products and medicinal compounds. In this presentation the novel regioselective hydroxylation of hydroxyarenes with DMD is described. The results showed further that flavonoids with 5-hydroxy group were selectively oxyfunctionalized at the para-position C8 carbon atom by DMD. Finally, according to this methodology, the naturally occurring isosinensetin, tangeretin, sinensetin, nobiletin, natsudaidain, gardenin B, 3,3′,4′,5,6,7,8-heptamethoxyflavone, quercetin and its derivatives were synthesized.     

The fluorescence properties of luteolines

The fluorescence properties of luteoline and its possible methyl ethers (a representative class of naturally occurring flavonoids) were investigated, together with the effect of diagnostic shift reagents such as sulfuric acid, aluminium trichloride, and borax. The results demonstrate that fluorimetry is a suitable tool for the identification and structure elucidation of minute samples of flavones, in particular if combined with absorption spectrometry. ThepK _a values of all trimethylethers were determined for the ground and first excited singlet states and related to the effects of basic reagents.

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Die Fluoreszenzeigenschaften der Luteoline

Zusammenfassung Es wurden die Fluoreszenzeigenschaften der Luteoline (einer repräsentativen Klasse von natürlich vorkommenden Flavonoiden) sowie der Effekt diagnostischer Verschiebungsreagentien wie z. B. Schwefelsäure, Aluminiumtrichlorid und Borax untersucht. Die Ergebnisse zeigen, daß die Fluorimetrie eine geeignete Methode zur Identifikation und Strukturaufklärung auch geringster Probenmengen sein kann, besonders in Kombination mit Absorptionsmessungen. DiepK _s -Werte aller möglichen Trimethylether wurden für Grund- und ersten angeregten Zustand bestimmt und zu den Effekten der basischen Reagentien in Bezug gebracht.

     

A new synthesis of flavones and pyranoflavone by intramolecular photochemical Wittig reaction in water

A new synthetic approach toward the synthesis of flavones and pyranoflavone has been developed by light induced intramolecularphotochemicalWittigreaction in water onto aryloxycarbonyl groups and suitably substituted phosphonium bromides sans any phase transfer catalyst or promoter.     

Chemical Constituents from the Root and Aerial Parts of Rosa taiwanensis

The root and aerial parts of Rosa taiwanensis Nakai contain the chemical constituents phenols, unsaturated acids, loliolide, abscisic acid, flavones, sterols, lupeol, betulin, betulinic acid, oleanolic acid and ursolic acid derivatives. Among them, 2α,3α-dihydroxyurs-12,19-dien-28-oic acid and its C-3 epimer are new compounds.     

Molecularly imprinted polymers—potential and challenges in analytical chemistry

Among the variety of biomimetic recognition schemes utilizing supramolecular approaches molecularly imprinted polymers (MIPs) have proven their potential as synthetic receptors in numerous applications ranging from liquid chromatography to assays and sensor technology. Their inherent advantages compared to biochemical/biological recognition systems include robustness, storage endurance and lower costs. However, until recently only few contributions throughout the relevant literature describe quantitative analytical applications of MIPs for practically relevant analyte molecules and real-world samples. Increased motivation to thoroughly evaluate the true potential of MIP technology is clearly attributed to the demands of modern analytical chemistry, which include enhanced sensitivity, selectivity and applicability of molecular recognition building blocks at decreasing costs. In particular, the areas of environmental monitoring, food and beverage analysis and industrial process surveillance require analytical tools capable of discriminating chemicals with high molecular specificity considering increasing numbers of complex environmental contaminants, pollution of raw products and rigorous quality control requested by legislation and consumer protection. Furthermore, efficient product improvement and development of new products requires precise qualitative and quantitative analytical methods. Finally, environmental, food and process safety control issues favor the application of on-line in situ analytical methods with high molecular selectivity. While biorecognition schemes frequently suffer from degrading bioactivity and long-term stability when applied in real-world sample environments, MIPs serving as synthetic antibodies have successfully been applied as stationary phase separation matrix (e.g. HPLC and SPE), recognition component in bioassays (e.g. ELISA) or biomimetic recognition layer in chemical sensor systems. Examples such as MIP-based selective analysis of flavones/flavonoids in wine, the determination of mycotoxins in beverages and analysis of organic contaminants in environment samples will elucidate the perspectives of this technology and will be contrasted with the challenges of rational MIP design providing control on binding site density, receptor capacity and selectivity.     

山楂叶中总黄酮含量的测定

用索氏提取法提取山楂叶中黄酮化合物.以芦丁为标准品,对其进行络合显色,在最大吸收峰500nm处测定提取物中总黄酮的含量.山楂叶中总黄酮的含量以芦丁计算为9.16%,平均加样回收率为98.53%.方法简便、快速、重现性好,可作为检测山楂叶中黄酮含量的一种手段.     

Synthesis of 3-alkenyl-2-arylchromones and 2,3-dialkenylchromones via acid-catalysed retro-Michael ring opening of 3-acylchroman-4-ones

3-Acylchromones and 3-acylflavones, readily available by acylation of 2′-hydroxydibenzoylmethane with acid anhydrides in the presence of base, undergo efficient conjugate reduction with NaBH₄ in pyridine to give the corresponding chroman-4-ones/flavanones in high yields. The reduction is both regio- and chemoselective. Treatment of the chroman-4-ones with MeSO₃H generates the 3-alkenyl-2-arylchromones by a dehydrative rearrangement initiated by retro-Michael cleavage of the pyranone ring. This reduction-rearrangement sequence can be extended to 2-alkyl-3-alkenoylchromones to generate 3-alkenyl-2-styrylchromones, the first examples of 2,3-dialkenylchromones.     

Regioselective synthesis of flavone derivatives via DMAP-catalyzed cyclization of o-alkynoylphenols

A catalytic amount of DMAP promoted cyclization of o-alkynoylphenols via a 6-endo cyclization mode leading to flavone derivatives in high yields without forming 5-exo cyclized aurone derivatives. Utilizing this method, methoxy substituted flavone and alkyl substituted γ-benzopyranone derivatives were synthesized.     

Methoxylation and Glycosylation Effect on the Redox Mechanism of Citroflavones

The methoxylation and glycosylation effect on the redox mechanism of citroflavones, isorhoifolin, linarin, diosmetin and diosmin, was investigated. All citroflavones’ hydroxyl groups can be electrochemically oxidised, and the oxidation at the B‐ring occurs at a lower potential than at the A‐ring. The electrochemical oxidation is irreversible, pH‐dependent, with occurrence of one or two oxidation products, which undergo reversible redox reactions, depending on the number of OH substituents on the molecule. The glycosylation leads to a steric effect and decreasing of the oxidation peak currents whereas the methylation involves the formation of nonelectroactive oxidation products.     

Far infrared-assisted extraction followed by MEKC for the simultaneous determination of flavones and phenolic acids in the leaves of Rhododendron mucronulatum Turcz

A method based on micellar electrokinetic chromatography with amperometric detection and far infrared‐assisted extraction has been developed for the simultaneous determination of two flavones (rutin and farrerol) and three phenolic acids (syringic acid, vanillic acid, and 4‐hydroxybenzoic acid) in the dried leaves of Rhododendron mucronulatum Turcz., a commonly used traditional Chinese medicine. The effects of some important factors such as the voltage applied on the infrared generator, irradiation time, the concentration of borate and sodium dodecylsulfate (SDS), separation voltage, and detection potential were investigated to acquire the optimum conditions. The detection electrode was a 300‐μm diameter carbon disc electrode. The five analytes could be well separated within 8 min in a 40 cm‐long capillary at a separation voltage of 12 kV in a 50 mM borate buffer (pH 9.2) containing 50 mM SDS. The relationship between peak current and analyte concentration was linear over about three orders of magnitude with the detection limits (S/N=3) ranging from 0.20 to 0.46 μM. The results indicated that far infrared irradiations significantly enhanced the extraction efficiency. The extraction time was substantially reduced to 6 min compared with 3 h for conventional hot solvent extraction.