Synthesis and Evaluation of Substituted Imidazolones for Antibacterial and Antioxidant Activities

 

Uddandam Aruneswari¹, Sreerama Usha rani¹, M Aruna Devi² and Galla Rajitha¹*

¹Institute of Pharmaceutical Tech., Sri Padmavathi Mahila Visvavidyalayam (Women’s University), Tirupati-517 502

²Trinity College of Pharmaceutical Sciences, Karimnager, A.P., India.

*Corresponding Author E-mail: rajitha_galla@yahoo.com

ABSTRACT:

A series of 4-(substituted benzylidene)-1-(5-phenyl-1,3,4-thiadiazol-2-yl)-2-phenyl -1H-imidazol-5(4H)-ones were synthesized by condensation of 4-benzylidene-2-phenyl-oxazol-5-one with 2-amino-5-phenyl-1,3,4-thiadiazoles in presence of sodium acetate in glacial acetic acid. The intermediate 4-benzylidene-2-phenyl-oxazol-5-ones  were prepared by condensing benzaldehydes with benzoyl glycine in presence of acetic anhydride and sodium acetate. The chemical structures of synthesized compounds were confirmed by means of IR, ¹H NMR. All the compounds (10-18) were screened for antibacterial and antioxidant activities. Among all, the compounds 12, 16 exhibited highest antibacterial activity against all the four strains. Compound 12 exhibited highest nitric oxide scavenging activity and most of these compounds showed significant DPPH scavenging activity.

 

 

 

INTRODUCTION:

Imidazolones and their derivatives are known for their potential pharmacological properties. Since imidazolones have been found to be associated with their various biological activities such as anticonvulsant activity¹, antitumor activity², antibacterial activity³, antiparkinsonism activity⁴, antihelmintic activity⁵, antimicrobial activity⁶ etc., this class of compounds has become a synthetic target for organic and medicinal chemists. Furthermore, imidazolones having thiadiazole nucleus have also been shown antiinflammatory activity⁷. These observations promoted us to synthesize the title compounds with presumption that incorporation of thiadiazole nucleus would produce new compounds with significant antibacterial and antioxidant properties.

 

 

MATERIALS AND METHODS:

Anti bacterial activity:

The antibacterial activity of the test compounds were studied systematically against four different strains of bacteria (two gram-positive and two gram-negative) by agar diffusion method.

 

Filter paper disc method⁸:

The newly synthesized compounds were screened for their antibacterial activity against Escherichia coli, Bacillus subtilis, Staphylococcus aureus and Proteus vulgaris bacterial strains by disc diffusion method. The discs measuring 6.25 mm in diameter were punched from whatman no. 1 filter paper. Batches of 100 discs are dispensed to each screw capped bottles and sterilized by dry heat at 140 ^o C for an hr. The test compounds were prepared by different concentrations using dimethylsulfoxide.1 ml containing 100 times the amount of chemical in each disc was added to each bottle which contains 100 discs. The discs of each concentration were placed in triplicate in nutrient agar medium seeded with fresh bacteria separately. The incubation was carried out at 37^oC for 24 hrs. Solvent and controls were kept and zones of inhibition and minimum inhibitory concentrations (MIC) were noted. The results of such studies are given in the Table 2.

 

Antioxidant Activities:

Assay of Nitric Oxide (NO) Scavenging activity⁹:

Sodium nitroprusside (10mM) in phosphate buffer pH 7.4, was incubated with 100 mM concentrations of drug dissolved in a suitable solvent (dioxin /methanol) and tubes were incubated at 25^oC for 120 mins. Control experiment without test compound were conducted in an identical manner. 2 mL of incubation solution was removed and diluted with 2 mL of   Griess reagent. The absorbance of the chromophore formed during diazotization of nitrite with sulphanilamide and subsequent coupling with N-napthylethylene diamine was read at 546 nm.

Table No :1 Physical data and yields of 4-(substituted benzylidene)-1-(5-substituted-1,3,4-thiadiazol-2-yl)-2-phenyl-1H-imidazol-5(4H)-one

Compound	R	M.P.(°C)	Yield %	Formula
10	H	102-106	72	C24H16N4OS
11	4 – CH3	105-108	75	C25H18N4OS
12	4 – OCH3	118-120	69	C25H18N402S
13	4 –N(CH3)2	215-217	85	C26H21N5OS
14	3,4-(OCH3)2	115-118	78	C26H20N4O3S
15	3,4,5-(OCH3)3	120-122	75	C27H22N4O4S
16	4-Cl	152-154	60	C24H14N4OSCl
17	4–OH, 3 – OCH3	114-116	69	C25H18N4O3S
18	4-CH(CH3)2	118-120	68	C27H22N4OS

 

TABLE No: 2 Anti bacterial activity of 4-(substituted benzylidene)-1-(5-substituted-1,3,4-thiadiazol-2-yl)-2-phenyl-1H-imidazol-5(4H)-one

Compd	R	Zone of inhibition in mm
		B.s	S.a	E.c	P.v
10	H	7	NA	12	NA
11	4 – CH3	14	11	11	9
12	4 – OCH3	15	16	13	14
13	4 –N(CH3)2	6	8	13	7
14	3,4-(OCH3)2	NA	NA	NA	NA
15	3,4,5-(OCH3)3	11	12	NA	13
16	4-Cl	15	14	14	15
17	4–OH,3–OCH3	14	15	12	13
18	4-CH(CH3)2	NA	NA	11	NA

Zone of inhibition of test compounds at a concentration of 100µg/Ml was measured

B.s   : Bacillus subtilis,       S.a   : Staphylococcus aureus

E.c   : Escherichia coli,       P.v   : Proteus vulgaris,    NA : Not active

 

Interaction with stable free radical DPPH¹⁰:

DPPH assay was performed as described. Solutions of various drugs at 100 mM concentration were added to 100 mM DPPH in 95 % ethanol and tubes were kept at an ambient temperature for 20 min and absorbance was measured at 517 nm. Ethanol was used as blank and DPPH solution in ethanol served as the control.

 

TABLE No: 3 Antioxidant activity of 4-(substituted benzylidene)-1-(5-substituted-1,3,4-thiadiazol-2-yl)-2-phenyl-1H-imidazol-5(4H)-one

Compd	R	Nitric oxide scavenging activity at 100 mM	Reduction of DPPH at 100 mM
10	H	13	NA
11	4 – CH3	15	NA
12	4 – OCH3	51	38
13	4 –N(CH3)2	45	36
14	3,4-(OCH3)2	30	24
15	3,4,5-(OCH3)3	14	NA
16	4-Cl	41	37
17	4–OH, 3 – OCH3	37	31
18	4-CH(CH3)2	19	16

NA :            Not Active (Activity < 10%)

 

EXPERIMENTAL:

Melting points were determined in open capillaries and were uncorrected. The IR spectra were recorded using KBr pellets on a Perkin Elmer 1760 spectrophotometer or Bruker Avance (300 MHz) spectrometer using TMS as an internal standard(chemical shift in δ ppm).

 

General Method of Synthesis of 2-Phenyl-4-(substituted benzylidene) oxazol-5-ones: (1-9)

The various 2-Phenyl-4-(substituted benzylidene)-oxazol-5-ones 1-9 were prepared by reported procedure¹¹.

 

 

 

Table No: 4 Infra Red/ ¹H-NMR spectral study of the synthesized compounds

Compd.	IR (cm-1)	1H-NMR (δ, ppm)
10	1638.8 (C=O), 1558.4 (C=C),1022.2 (C-N), 640.9 (C-S)	7.6-7.8 (m, 15H, Ar-H & olefinic)
11	1639.82 (C=O), 1559.41 (C=C),1020.32 (C-N), 642.38  (C-S)	2.4 (s, 3H, CH3) 7.4-7.8 (m, 15H, Ar-H & olefinic)
12	1628.4(C=O), 1542.4 (C=C),1015.4 (C-N), 638.3 (C-S)	------
13	1632.4(C=O), 1521.3 (C=C),1018.7 (C-N), 621.3 (C-S)	------
14	1561.0(C=C),1244.8(O-CH3),1019.2 (C-N),643.6 (C-S)	3.8 (s,6H, 2 Ar-OCH3)  7.1-8 (m, 14H, Ar-H & olefinic)
15	1622.4(C=O), 1525.6(C=C),1020.4 (C-N), 622.6  (C-S)	3.6 (s,6H, 3 Ar(OCH3)3)  7.2-8 (m, 14H, Ar-H & olefinic)
16	1624(C=O), 1554.8 (C=C),1034.5 (C-N),631  (C-S)	-------
17	3436.6(Ar-H),1641.8(C=O)1561.4(C=C),1021.2 (C-N),642.7  (C-S)	-------
18	1632.4(C=O), 1521.3 (C=C),1018.7 (C-N), 621.3 (C-S)	-------

Scheme

 

General Method of synthesis of Compounds: (10-18)

Synthesis of 4-benzylidene-3-(5-phenyl-1,3,4-thiadiazol-2-yl)2-phenylimidazolidin-4-one:(10)

A mixture of oxazolone (10 m mol), 2-amino-5- phenyl-1, 3, 4-thiadiazole (10 m mol) and sodium acetate (5 grams freshly fused) in glacial acetic acid (15 ml) was refluxed for 9 hrs and cooled. The separated solid was filtered and recrystallized from methanol. The various 4-(substituted benzylidene)-1-(5-substituted-1,3,4-thiadiazol-2-yl)-2-phenyl-1H-imidazol-5(4H)-ones 11-18 were prepared in a similar manner. The physicochemical data of compounds (10-18) is given in Table 1.

 

RESULTS AND DISCUSSION:

A series of imidazolone derivatives were synthesized. The structures of these compounds were established by means of IR, ¹H-NMR. The spectral study of the synthesized compounds is shown in Table 4.

 

Antibacterial activity:

The title compounds were screened for antibacterial activity against Bacillus subtilis and Staphylococcus aureus (gram-positive), Escherichia coli and Proteus vulgaris (gram-negative) strains.  Antibacterial activities of these compounds were tested by using disc diffusion method. The data was given in table-3. Among all, the compounds 12, 16 exhibited highest activity against all the four strains. Compound 17 was found to moderately active against Staphylococcus aureus (gram-positive) and Proteus vulgaris (gram-negative) bacteria. The compound 11 was found to be moderately active against Bacillus subtilis.

 

Nitric Oxide Scavenging activity

The compound 12 exhibited highest activities, compounds 13, 16 showed good activity and compound 17 showed moderate activities.

 

Reduction of Stable free radical DPPH

The Compounds 12, 13, 16, 14, 17 and 18 showed significant activity.

 

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Received on 05.10.2010        Modified on 25.10.2010

Accepted on 04.11.2010        © AJRC All right reserved