Synthesis of Flavanol-4-ol and its Spectroscopic Properties in Aqueous Solution

Abstract

The polyhydroxybenzene derivatives can act as antioxidants in living organisms and for this reason considerable effort has been devoted to them.1,2 Particularly, the plantderived polyphenols have received great attention due to their various biological activities, i.e., anticarcinogenic, antiatherosclerotic, antimicrobial, and antioxidant properties.1-8 Polyphenolic substances are commonly referring to the subgroup flavanols that belong to the flavonoid family. They can be easily found in green tea, red wine and numerous fruits and vegetables.9-11 In addition many of the phenolic phytochemical compounds can also been related to the presence of flavanol moieties in their structure.One of the such substances is catechin (5,7,3',4'-tetrahydroxyflavan-3-ol) that is the major constituent of green tea and also one of the flavanol compounds. This substance is known to repair vitamin E as well as to be very efficient scavengers for biologically damaging oxy radicals, such as the superoxide radical and singlet oxygen.12,13 However, catechin is oxidized in water easily to form a yellow solution where the color of the solution varies with time.10 This is because the catechol moiety on the B-ring in catechin is oxidized in an aqueous solution.10,14 Recently, we confirmed that the oxidation in a basic solution is much faster than in the neutral catechin solution.14 Besides, the oxidation depended strongly on the pH values of the solution where higher pH values led to faster oxidation rate of catechin. However, flavan-4-ol (2-Phenylchroman-4-ol) is not contained catechol moiety in the molecule.In this paper, we have synthesized flavan-4-ol (2-phenylchroman-4-ol) and the spectroscopic properties of the substance were evaluated to explain its oxidation in the aqueous solution. Experimental Section1-(2-Hydroxyphenyl)ethanon, benzaldehyde were purchased from Sigma Chemical Co. (St. Louis, U.S.A.) and used without further purification. The other chemicals were reagent grade and used as received. Flavan-4-ol (2-phenylchroman-4-ol) was synthesized by starting from 1-(2-hydroxyphenyl)-ethanone with benzaldehyde in ethanol. Flavan-4-ol synthesized was very slightly soluble in water. Therefore, we first prepared the stock solution of flavan-4-ol in methanol. To prepare the aqueous flavan-4-ol, an aliquot of flavan-4-ol stock solution was transferred to a flask and then vaporized by bubbling high purity argon (99.999%) through. The compound was then dissolved in water using double distilled water, which was obtained by passing distilled water through a Barnstead (U.S.A.) Nanopure II deionization system. The pH of the solution was adjusted by adding HClO 4 , NaOH or ammonium chloride buffer solutions which were prepared from air-free distilled water. These buffer solutions did not absorb any UV light with wavelength longer than 240 nm and therefore would not overlap with the characteristic peaks of flavan-4-ol.The UV/vis absorption spectra of the solutions were then taken by a UV/vis spectrophotometer (Uvikon, model 943, Italy) at room t...

Stenotrophomonas maltophilia: A Gram-Negative Bacterium Useful for Transformations of Flavanone and Chalcone

“…The substrates for biotransformation were as follows: 7-methoxyflavanone ( 1 ) was purchased from Sigma Chemical Company (St. Louis, MO, USA); 5,7-dimethoxyflavanone ( 2 ) was obtained following the method by Yeom et al [ 31 ]; and 2′-hydroxy-3-methoxychalcone ( 3 ) was obtained following the method by Yadav et al [ 32 ].…”

Cyclization of flavokawain B reduces its activity against human colon cancer cells

“…5,7-Dimethoxyflavanone (4) used in the experiments on the colorectal cell lines LoVo and LoVo/ Dx was obtained from 2 0 -hydroxy-4 0 ,6 0 -dimetoxychalcone (3) according to the previously described method. 11,12 Then, 5 g of the substrate was dissolved in ethanol (75 ml) with the addition of sodium acetate (8 g), and the reaction mixture was refluxed for 48 h. Crystallization from ethanol afforded pure flavanone (4). 5,7-Dimethoxyflavanone (4) was used as a standard for HPLC analysis.…”

Enantioselective reduction of flavanone and oxidation of cis- and trans-flavan-4-ol by selected yeast cultures

“…Flavanone was obtained from 2 -hydroxychalcone (3) according to the previously described method [26]. 10 g of the substrate was dissolved in ethanol (75 ml) with addition of sodium acetate (8 g) and the reaction mixture was refluxed for 48 h. Crystallization from ethanol afforded pure (±)-flavanone.…”