Synthesis and characterization some flavonoids derivatives

The flavonoids represent an important group of pigment that occurs in the plant kingdom. The flavones, one of the flavonoids, possess interesting biological actions. The antioxidant activity of flavones is reported to be associated with those bearing hydroxyl functions. In the present study, several steps of reaction have been carried out to synthesize the derivatives of luteolin, which are polyhydroxyl flavones. The first step of the reaction was the methylation of 2,4,6-trihydroxyacetophenone with methyl iodide to afford 2-hydroxy-4,6-dimethoxyacetophenone. On aldol condensation of 2-hydroxy-4,6- dimethoxyacetophenone with 3,4-dimethoxybenzaldehyde yielded 3,4,4,6- tetramethoxychalcone. This was followed by the oxidative cyclisation of chalcone with SeO2 to give 3,4,5,7-tetramethoxyflavone. The protection of hydroxyl functions of 2,4,6-trihydroxyacetophenone and 3,4-dihydroxybenzaldehyde with methoxy methyl chloride to form 2-hydroxy-4,6-bis(methoxymethyloxy)-acetophenone and 3,4-bis (methoxymethyloxy)-benzaldehyde was carried out. Both compounds were reacted via the aldol condensation to form 3,4,4,6-tetrakis(methoxymethyloxy)-chalcone. Treatment of 3,4,4,6-tetrakis(methoxymethyloxy)-chalcone with excessive sodium acetate afforded us 3,4,5,7-tetrahydroxyflavanone or eriodictyol (39) as a single product in high yield.The free radical scavenging activity of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical by synthesized flavonoids using the electron spin resonance (ESR) technique and UV spectrophotometry method showed that 3,4,5,7- tetrahydroxyflavanone is a strong antioxidant. Compounds were characterized by spectroscopic techniques, i.e. infrared (IR), ultraviolet (UV) spectrophotometry, mass spectrometry (MS) and nuclear magnetic resonance (1H NMR and 13C NMR)

(E)-1-(2-Hydroxy-4,6-dimethoxyphenyl)-3-[4-methoxy-3-(3-methylbut-2-en-1-yl)phenyl]prop-2-en-1-one

A novel prenylated chalcone, (E)-1-(2-hydroxy-4,6-dimethoxyphenyl)-3-[4-methoxy-3-(3-methylbut-2-en-1-yl)phenyl]prop-2-en-1-one was synthesized and the structure of the title compound was established by 1H and 13C nuclear magnetic resonance (NMR), mass spectrometry (MS) and Fourier transform infrared (FT-IR) spectroscopy

Synthesis of 4’,5,7-trihydroxyflavanone and 3’,4’,5,7-tetrahydroxyflavanone and antioxidant activity

Natural flavonoid, namely 4’,5,7-trihydroxyflavanone and 3’,4’,5,7-tetrahydroxyflavanone were synthesised via its chalcone. The initial step was to synthesize derivatives of 2-hydroxyacetophenone and benzaldehyde by protecting the phenolic hydroxyl groups. The respective chalcone was synthesised by Claisen-Schmidt condensation. 4’,5,7-Trihydroxyflavanone and 3’,4’,5,7-tetrahydroxyflavanone were synthesised by acid hydrolysis and subsequent treatment with sodium acetate of the respective chalcones, 2’-hydroxy-4,4’-6’-tris(methoxymethyloxy)chalcone and 2’-hydroxy-3,4,4’,6’-tetrakis(methoxymethyloxy)chalcone. 3’,4’,5,7-Tetrahydroxyflavanone was found to be more potent as an antioxidant agent than 4’,5,7-trihydroxyflavanone with 83.11% inhibition and IC50 8.57 ?g/mL in the radical scavenging activity by ESR method

Synthesis of polyhydroxylated flavonoids

Flavonoids are a group of polyphenolic compounds ubiquitously found in the plant kingdom. Flavonoids have gained recent interest because of their broad pharmacological activities. In the present study, several polyhydroxylated flavonoids namely, 3,4-bis(benzyloxy)-3-hydroxyflavone, 3,4,5,7-tetrahydroxyflavanone, 4,5,7-trihydroxyflavanone and 4,5,7-trihydroxy-3-prenylflavanone have been synthesised. These target compounds were synthesised via its chalcones as the key precursor. The initial step in the synthesis was to prepare various derivatives of 2- hydroxyacetophenone and benzaldehyde by protection of the phenolic hydroxyl groups. The approach for the synthesis of chalcones is by the Claisen-Schmidt condensation of the respective 2-hydroxyacetophenones and benzaldehydes under basic condition to give the corresponding 2-hydroxychalcones. 3,4-Bisbenzyloxy- 3-hydroxyflavone was synthesised from 3,4-bis(benzyloxy)-2-hydroxychalcone by the Algar-Flynn-Olyamada (AFO) oxidative method. The natural occurring flavanones, 3,4,5,7-tetrahydroxyflavanone and 4,5,7-trihydroxyflavanone were prepared from 2-hydroxy-3,4,4,6-tetrakis (methoxymethyloxy)chalcone and 2- hydroxy-4,4,6-tris(methoxymethyloxy) chalcone respectively, by acid hydrolysis and subsequent treatment with sodium acetate. The last feature in the synthesis was the preparation of 4,5,7-trihydroxy-3-prenylflavanone starting from the prenylation of 4-hydroxybenzaldehyde, protection of the phenolic group, formation of 2- hydroxy-4,4,6-tris(methoxymethyloxy)-3-prenylchalcone and followed by acid hydrolysis and cyclisation of the chalcone led to the production 4,5,7-trihydroxy-3- prenylflavanone in 89.3% yield. The antibacterial activity of the targeted compounds and its chalcone precursor were demonstrated by the filter paper disc diffusion method. The antioxidant activity were evaluated based on the free radical scavenging activity of the flavonoids against 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical by using UV and Electron Spin Resonance techniques. Structures were confirmed spectroscopically by UV, IR, NMR (1H and 13C), COSY and MS

Synthesis and antimicrobial activity of 4′,5,7-trihydroxy-3′- prenylflavanone

4′,5,7-Trihydroxy-3′-prenylflavanone was synthesized and tested for antibacterial effects against Bacillus subtilis, Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The synthesized compounds were characterized using UV, IR, MS and 1H and 13C NMR data. The antibacterial screening of the synthesized compounds were performed in vitro by the filter paper disc diffusion method