Synthesis, Characterization and Antimicrobial activity of Some Flavones

 

K. Prasada Rao¹٭, K. Santha Kumari² and S. Mohan¹

¹Dept. of Chemistry, Bapatla Engineering College, Bapatla (Autonomous)-522101, Andhra Pradesh, India.

²Dept. of Chemistry, St’Anna’s Engineering College, Chirala -523156, Andhra Pradesh, India.

*Corresponding Author E-mail: prasad17467@gmail.com

 

Flavonoids are ubiquitous in photo synthesizing cells and are commonly found in fruit, vegetables, nuts, seeds, stems, flowers, tea, wine, propolis and honey. For centuries, preparations containing these compounds as the principle physiologically active constituents have been used to treat human diseases. These are abundant in polygonaceae, rutaceae, leguminosae, umbelliferae and compositae. 2(subtituted phenyl) – 4H- Chromen – 4 – one’s were synthesized from substituted chalcones. The compounds obtained were identified by spectral data and screened for antimicrobial activity.

 

 

INTRODUCTION:

Flavonoids are phenolic compounds widely distributed in plants. Most of the flavonoids studied are poly hydrated derivatives which appear to selectively react with free radicals or systems related to the induction of inflammatory processess^1-3. The word flavonoid comes from the Latin flavus which means yellow; however some flavonoids are red, blue, purple, or white⁴. Flavonoids occupy a special place in the realm of natural and synthetic organic chemistry owing to their useful biological activities such as anti-oxidant^5-9, anti-cancer¹⁰, anti-microbial¹¹, cytotoxicity¹² as well as anti-tumor activities¹³.

 

The chemicals were purchased from either E-Merk or Qualigens (AR quality) reagents, pure distilled solvents were used throughout the work. Reactions were monitored by TLC using Merck precoated aluminium plate silica gel 60 F254 thin layer plates. Column chromotography was performed on silica gel (Merck, 60-120 mesh). Flavones were synthesized from hydroxyl chalcones using ethanol as reaction solvent. The chemicals and solvents were of laboratory grade and were purified. The synthetic pathway is presented in Scheme1, physicochemical data, spectral data and anti-microbial data for synthesized compounds are given in Table 1, Table 2 and Table 3.

 

During the past few years various methods have been reported for the synthesis of flavonoids^14-18. The present work deals with the synthesis of substituted flavones (IIa-c) from substituted chalcones (Ia-c) in presence of alkali. The test compounds were characterized by elemental analysis, IR and ¹H-NMR spectral data. These compounds were screened for their antimicrobial activity by the Agar well diffusion method.

 

MATERIALS AND METHODS:

Melting points were determined with open capillary. IR spectra were recorded in KBr on a JASCO FT/IR-5300. ¹H-NMR spectra were recorded on Brucker spectrometer at 300MHz in CdCl₃, (900w). Elemental analysis was carried out on a Flash Ea 1112 series Chn report thermo finnigan.

 

Table 1: Physicochemical data of flavones

S.no	Compound code	Mol. formula	Yield (%)	M.P (0C)	M. wt. (gm)	Elemental analysis:   %found (%calculated)
						C	H	O
1	IIa	C15H12O 2	69	94	224	78.2 (77.9)	8.5 (8.2)	13.82 (13.85)
2	IIb	C16H12O3	67	99	252	73.64 (75.84)	7.59 (7.69)	18.44 (18.46)
3	IIc	C17H15O4	72	150	283	70.56 (71.65)	7.26 (7.3)	22.12 (22.13)

 

 

Table 2: Spectral data of synthesized flavones

S. no	Compd. code	IR (cm-1 , KBr)			1 H-NMR (CDCl3/δ (ppm)
		υ (C=O)	υ (C=C) (aroma)	υ(C-O)
1	IIa	1615.7	1454.9	1145.5	6.95 (s, 1H, pyrone ring), 7.14 (2H, dd, J=2.6 and 7.6 Hz, Ar-H), 7.47-7.51 (4H, m , Ar-H), 7.75 (2H, dd, J=7.8 and 2.6 Hz, Ar-H).
2	IIb	1686.01	1457.21	1167.91	3.85 (3H, s, Ar-OCH3), 6.76 (s, 1H, pyrone ring), 7.12 (2H, dd, J=2.6 and 7.6 Hz, Ar- H), 7.17-7.42 (4H, m, Ar-H), 7.48 (2H, dd, J=7.8 and 2.6 Hz, Ar-H).
3	IIc	1694.7	1465	1250.5	4.1 (s, 3H, OCH3), 4.16 (s,3H,  OCH3) , 6.99 (s,1H, 3-H) ,7.13 (d,1H, J=8.1 Hz, 5’-H),7.34 (d, 1H, J= 1.2 Hz, 2’-H),  7.53 ( d,1H,J=7.8Hz 6-H), 7.51 (dd, 2H,  J=8.3 and 1.4Hz8-H), 7.39( dt, 1H, J=8.2  and 1.8 Hz,7-H),     8.3 dd,1h. J=7.6, 1.8Hz, 5-H).

 

 

1.      Synthesis of 2- phenyl benzopyrone:

2.5 gms of 2-hydroxy chalcone and 30 ml of DMSO and a crystal of I₂ as a catalyst was kept in reflux. The completion of reaction (monitored by TLC), the mixture was cooled, diluted with ethyl acetate and filtered. The filtrate was washed with dilute 20% sodiumthiosulphate to remove I₂ and subsequently washed with water. After evaporation of ethyl acetate the crude mixture was purified by column chromatography using hexane: ethyl acetate (9:1) eluent to affored corresponding flavone. The compound was collected on a buckner funnel under suction pump. The solid is washed with water thoroughly and dried and recrystallized from absolute ethanol to give 2-phenyl benzopyrone.

Synthesis of 2(4-methoxy phenyl)-4H- chromen-4-one:

A mixture of 2.2 gms of 2-hydroxy-4-methoxy chalcone and 30 ml of DMSO and a crystal of I₂ as a catalyst, 2(4-methoxy phenyl)-4H- chromen-4-one was obtained by the above described procedure.

 

2.      Synthesis of 2(3, 4-di methoxy phenyl)-4H- chromen-4-one: Reaction of 2-hydroxy-3, 4-di methoxy chalcone (2.3 gms) with 30 ml of DMSO and I₂ as a catalyst give 2(3, 4-di methoxy phenyl)-4H- chromen-4-one by the above procedure.

 

RESULTS AND DISCUSSION:

In the present study, series of flavones (IIa-c) were prepared by substituted chalcones (Ia-c) using DMSO, NaOH and ethanol as solvent (Scheme 1). This procedure afforded various flavones in good yields possessing potent antimicrobial activity. The purity of the compounds was determined by TLC and elemental analysis. Elemental analysis showed that the percentage of carbon, hydrogen and oxygen and the obtained results are given in Table 1. The structure of the synthesized compounds was confirmed by IR and ¹H-NMR spectral studies. All the compounds give the characteristic IR peak that proved that the presence of particular functional group and ¹H-NMR helps to find the different types of protons present in the structure and the obtained results are given in Table 2.

 

2-phenyl benzopyrone have the molecular formula C₁₅H₁₂O _2. The IR band at 1615.7 cm^-1 suggests the presence of (C=O) group. A band at 1454.9 cm^-1 indicate that the presence of (C=C) (aromatic) group. A band at 1145.5 cm^-1 suggests the presence of (C-O) group. Melting point of the compound is 94⁰C which is uncorrected.

 

The molecular formula of 2-(4-methoxy phenyl)-4H-chromen-4-one is C₁₆H₁₂O_3. The IR band at 1686 cm^-1 suggests the presence of (C=O) group. A band at 1457.21 cm^-1 indicate that the presence of (C=C) (aromatic) group. A band at 1167.91 cm^-1 suggests the presence of (C-O) group. Melting point of the compound is 99⁰C which is uncorrected.

 

2-(3, 4-dimethoxy phenyl)-4H-chromen-4-one have the molecular formula C₁₇H₁₅O_4. The IR band at 1694.7 cm^-1 suggests the presence of (C=O) group. A band at 1465 cm^-1 indicate that the presence of (C=C) (aromatic) group. A band at 1250.5 cm^-1 suggests the presence of (C-O) group. Melting point of the compound is 150⁰C which is uncorrected.

 

 

Table 3: Antimicrobial data of synthesized flavones

S. No	Compound code	Mean zone of inhibition (in cm)
		Xanthomonas campestris	Agrobacterium tumifaciens
1	IIa	1.1	1.3
2	IIb	0.8	1.4
3	IIc	0.4	0.8

 

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Received on 29.01.2013         Modified on 10.02.2013

Accepted on 20.02.2013         © AJRC All right reserved