Synthesis and pharmacological studies of some new imidazole derivatives

 

Sonwane RR^*, Asnani AJ, Kawade DP

J. L. Chaturvedi College of Pharmacy, Electronic Zone Building, M.I.D.C., Hingna road, Nagpur-440 016.

*Corresponding Author E-mail: rsonwane2@gmail.com

 

ABSTRACT:

The present research work was aimed to synthesis some new imidazole derivatives. The twenty derivatives of 2-substituted 5-[(2-subtituted-4,5 diphenyl-1H-imidazol-1-yl)methyl]-2,3 dihydro-1,3,4 oxadiazole has been synthesized using appropriate synthetic route. The structure and purity of all synthesized derivatives were confirmed by IR, H¹NMR, Mass spectral studies and physicochemical properties.  These synthesized compounds were screened for analgesic and anti-inflammatory activity by using Hot Plate Method and Carrageenan Induced Rat Paw Edema Method and they showed significant activity when given orally. Toxicity study of all synthesized compounds has been determined and LD ₅₀ was found to be ≥ 100 mg/Kg. Compounds IV-a, d, f, i, k, m, n, p, s and compound t shows significant analgesic and anti-inflammatory activity. It was observed that the compounds have unsubstituted phenyl ring or 3-nitro phenyl ring at 2 position of oxadiazole ring shows significant activity.

 

 

INTRODUCTION:

Imidazole is an aromatic heterocyclic diazole with the general molecular formula C₃H₄N₂. Imidazole or iminazoline is an azopyrole in which nitrogen atom separated by one carbon atom. The imino nitrogen is assigned position-1 while the tertiary nitrogen atom position-3¹.

 

Various imidazole derivatives have been discovered earlier in the 1840s. But imidazole was first synthesized in 1858 from glyoxal and formaldehyde in ammonia, and is called glyoxaline².

 

Imidazole is amphoteric in nature. That is, it can function as both an acid and as a base. As an acid, the pK_a of imidazole is 14.5, making it less acidic than carboxylic acids, phenols, and imides, but slightly more acidic than alcohols. The acidic proton is located on N-1. As a base, the pK_a of the conjugate acid (cited above as pK_BH⁺ to avoid confusion between the two) is approximately 7, making imidazole approximately sixty times more basic than pyridine. The basic site is N-3³.

 

Various substituted imidazole derivatives possess a lot of promising pharmacological activities like anti-microbial⁴, anti-fungal⁵, analgesics⁶, anti-inflammatory⁶, anti-fungal⁶, anxiolytic⁷, cardiovascular⁷, anti-hypertensive⁷, and anti- viral⁸, anti- tubercular⁸, anti-parasitic⁹, platelet aggregation inhibitors⁹, and anti-epileptic agents⁹. Imidazole can be also be used as anti-neoplastic¹⁰, anti-ulcerative¹⁰, anti-hyperthyroid¹¹, muscarinic receptor antagonist¹² and hypnotic agents¹², respectively.

 

Literature findings, especially on its analgesic and anti-inflammatory and the continued interest in the imidazole molecule after its discovery more than century ago have prompted the synthesis of new imidazole derivatives and screen them for their pharmacological activity¹³.

 

Thus, in the present research investigation, twenty different derivatives of 2-substituted 5-[(2-subtituted-4,5 diphenyl-1H-imidazol-1-yl)methyl]-2,3 dihydro-1,3,4 oxadiazole were synthesized and evaluated them for analgesic and anti-inflammatory activity.

 

MATERIAL AND METHODS:

All the chemicals used in the present work were AR grade and LR grade, purchased from Loba, Merck and Fisher scientific fine chemicals. The melting points were recorded by open capillary using LABHOSP melting point apparatus and were uncorrected. The purity and homogeneity of the synthesized compounds was routinely ascertained by the thin layer chromatography, performed on plates coated with silica gel- G using the solvent system Ethyl acetate: Methanol (9:1). The absorption maxima of the synthesized compounds were recorded in methanol (analytical grade, 1mg/100mL). The methanolic solutions of the synthesized compounds were scanned on Shimadzu UV 1601 spectrophotometer, Japan; in the region 200-400 nm. The IR spectra were recorded in KBr disc on FTIR Shimadzu 8400 S Japan. The 1H-NMR spectra were recorded on Bruker Avance II 400 NMR spectrometer using DMSO as solvent and TMS as an internal solvent. The Mass spectra were recorded on Waters Q –Toff-micro spectrometer.  The above mention physicochemical data of all synthesized compounds were given in the Table No. 2.  The Analgesic and Anti-inflammatory activity evaluation were carried out using hot plate method on mice and carrageenan- induced paw edema in albino rats and compared with the group receiving a standard drug Tramadol and indomethacine respectively.

 

Experimental:

A.      Preparation of 2 substituted-4,5 diphenyl-1H-imidazole (comp. Ia-d)

A mixture of benzil (10.52 g, 0.025 mol), ammonium acetate (19.88 g 0.129 mol) and formaldehyde (1.50 mL, 0.025 mol) in glacial acetic acid (100 mL) was heated under reflux for 6 h. After refluxing, the reaction mixture was allowed to stand to attain room temperature. The solid residue of comp. Ia was obtained after the addition of water (350 mL), filtered and recrystallized from absolute ethanol. Melting point and R_f value of the product was determined. Using the above procedure, three different derivatives comp. Ib-d were synthesized by using different substituted aromatic aldehyde (Table 1)

 

B.       Preparation of ethyl (2-substituted-4,5 diphenyl-1H-imidazol-1-yl) acetate (comp. IIa-d)

To the solution of comp. Ia (6.00 g, 0.1 mol) in 100 ml dry acetone was heated with ethyl chloro acetate (2.80 mL, 0.11 mol) on a water bath for 3hrs in presence of anhydrous potassium carbonate (1.4 g, 0.10 mol). The reaction mixture was cooled and filtered to separate potassium chloride and unreacted potassium carbonate. Acetone was evaporated and the comp. IIa isolated, recrystallized from ethanol. Melting point and R_f value of the product was determined. Using the above procedure, three different derivatives comp. IIb-d were synthesized.

 

C.       Preparation of (2-substituted-4,5 diphenyl-1H-imidazol-1-yl) acetohydrazide (comp. IIIa-d)

A mixture of comp. IIa (5.20 g, 0.01 mol) and 99% hydrazine hydrate (0.90 mL, 0.015 mol) in ethanol (20 mL) was refluxed for about 3hrs. The reaction mixture was then allowed to cool to room temp. The separated yellow coloured crystalline solid were filtered, and recrystallised from ethanol the comp. IIIa was obtained. Melting point and R_f value of the product was determined. Using the above procedure, three different derivatives comp. IIIb-d were synthesized.

 

D.      Preparation of 2-substituted 5-[(2-subtituted-4,5 diphenyl-1H-imidazol-1-yl)methyl]-2,3 dihydro -1,3,4 oxadiazole (IVa-t)

A mixture of comp. IIIa (1.00 g,3 mmol) and benzaldehyde (0.60 g, 3 mmol), in absolute ethanol (20 mL), was treated with piperidine (0.1 mL). The clear solution was then heated under reflux for 2 h. Ethanol was evaporated and the product isolated were crystallized from ethanol to gets 2-substituted 5-[(2-subtituted-4,5 diphenyl-1H-imidazol-1-yl)methyl]-2,3 dihydro -1,3,4 oxadiazole. Using the above procedure, nineteen different derivatives comp. IVa-t was synthesized by using different substituted aromatic aldehyde and comp. IIIa-b. (Table 1)

The physicochemical data of all synthesized compounds like molecular weights, molecular formula, melting point, % yield and R_f  values were given in the Table No. 2.

 

Synthetic scheme:

 

General structure:

 

Table 1: Synthesized derivative of 2-Substituted 5-[(2-subtituted-4,5 diphenyl-1H-imidazol-1-yl)methyl]-2,3 dihydro -1,3,4 oxadiazole

 

Sr. No.	Compound code	R1	R2
1	IV- a	-H
2	IV- b
3	IV- c
4	IV- d
5	IV- e
6	IV- f
7	IV- g
8	IV- h
9	IV- i
10	IV- j
11	IV- k
12	IV- l
13	IV- m
14	IV- n
15	IV- o
16	IV- p
17	IV- q
18	IV- r
19	IV- s
20	IV- t

 

 

Table 2: Physicochemical data of synthesized derivatives (IV-a to IV-t)

Compound Code	Compound Name	Mol. Formula	Mol. Wt	m.p. (oC)	% yield	Rf value	λ max
IV- a	2-Phenyl-5-[4,5 diphenyl -1H-imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C24H26N4O	386.5	212-214	55.3	0.52	301.0
IV- b	2 (4-Hydroxy phenyl)-5-[4,5 diphenyl -1H-imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C24H26N4O2	402.5	198-200	52.5	0.61	305.0
IV- c	2 (2-Nitro phenyl)-5-[4,5 diphenyl -1H-imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C24H25N5O3	431.5	192-194	60.4	0.57	302.0
IV- d	2 (3-Nitro phenyl)-5-[4,5 diphenyl -1H-imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C24H25N5O3	431.5	226-228	58.0	0.63	303.0
IV- e	2 (4-Chloro phenyl)-5-[4,5 diphenyl -1H- imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C24H25N4OCl	420.9	188-190	62.5	0.67	319.0
IV- f	2-Phenyl-5-[2-methyl-4,5 diphenyl -1H-imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C25H28N4O	400.5	218-220	72.5	0.42	314.0
IV- g	2 (4-Hydroxy phenyl)-5-[2-methyl-4,5 diphenyl -1H- imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C25H28N4O2	416.5	195-197	70.4	0.58	324.5
IV- h	2 (2-Nitro phenyl)-5-[2-methyl-4,5 diphenyl-1H -imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C25H27N5O3	445.5	201-203	65.5	0.69	302.5
IV- i	2 (3-Nitro phenyl)-5-[2-methyl-4,5 diphenyl -1H- imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C25H27N5O3	445.5	232-234	58.0	0.75	290.0
IV- j	2 (4-Chloro phenyl)-5-[2-methyl-4,5 diphenyl -1H -imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C25H27N4OCl	434.5	205-207	69.5	0.81	300.0
IV- k	2-Phenyl-5-[2,4,5 triphenyl -1H- imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C30H30N4O	462.6	201-203	40.5	0.85	309.0
IV- l	2 (4-Hydroxy phenyl)-5-[2,4,5 triphenyl -1H- imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C30H30N4O2	478.6	225-227	55.4	0.71	312.0
IV- m	2 (2-Nitro phenyl)-5-[2,4,5 triphenyl -1H-imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C30H29N5O3	507.6	175-177	58.5	0.45	300.0
IV- n	2 (3-Nitro phenyl)-5-[2,4,5 triphenyl -1H-imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C30H29N5O3	507.6	189-191	52.5	0.55	310.5
IV- o	2 (4-Chloro phenyl)-5-[2,4,5 triphenyl -1H- imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C30H29N4OCl	497.0	179-181	60.5	0.49	304.5
IV- p	2-Phenyl-5-[2-(4-methoxy phenyl)-4,5 diphenyl -1H- imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C31H32N4O2	492.6	166-168	77.5	0.35	318.5
IV- q	2 (4-Hydroxy phenyl)-5-[2-(4-methoxy phenyl)-4,5 diphenyl -1H-imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C31H32N4O3	508.6	216-218	69.0	0.54	324.0
IV- r	2 (2-Nitro phenyl)-5-[2-(4-methoxy phenyl)-4,5 diphenyl -1H-imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C31H31N5O4	537.6	233-235	72.0	0.84	307.0
IV- s	2 (3-Nitro phenyl)-5-[2-(4-methoxy phenyl)-4,5 diphenyl -1H-imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C31H31N5O4	537.6	214-216	67.5	0.71	309.5
IV- t	2 (4-Chloro phenyl)-5-[2-(4-methoxy phenyl)-4,5 diphenyl -1H-imidazol-1-yl]methyl-2,3 dihydro-1,3,4 oxadiazole	C31H31N4O2Cl	527.0	175-177	62.0	0.77	314.5

IV-a: λ max 301.0 (methanol); IR (KBr, V max, cm^-1): 2930.23 (-CH₂ stretching), 2998.03 (-CH stretching), 1600.04 (-NH deformation), 1680.07 (Ar C=C stretching), 1339.05 (C-N stretching), 1298.93 (C-C stretching), 1099 (C-O stretching), ¹ H-NMR (DMSO-d6, δ ppm): 5.65 [s, 1H, CH], 7.1-7.6 [m, 5H, Ar-ring], ,10.1 [s, 1H, NH], MS: m/z 515 (M⁺)

IV-b: λ max 305.0 (methanol); IR (KBr, V max, cm^-1): 3470.36 (-OH stretching), 2935.33 (-CH₂ stretching), 2995.12 (-CH stretching), 1613.44 (-NH deformation), 1672.17 (Ar C=C stretching), 1340.15 (C-N stretching), 1291.83 (C-C stretching), 1095.20 (C-O stretching), ¹ H-NMR (DMSO-d6, δ ppm): 5.41 [s, 1H, CH], 7.2-7.5 [m, 5H, Ar-ring], ,10.3 [s, 1H, NH], 8.7 [s, -OH], MS: m/z 389 (M⁺)

IV-c: λ max 302.0 (methanol); IR (KBr, V max, cm^-1): 1542.30 (-NO₂ stretching), 2930.23 (-CH₂ stretching), 2989.16 (-CH stretching), 1601.94 (-NH deformation), 1675.27 (Ar C=C stretching), 1347.25 (C-N stretching), 1295.23 (C-C stretching), 1080.10 (C-O stretching), ¹ H-NMR (DMSO-d6, δ ppm): 5.53 [s, 1H, CH], 7.2-7.5 [m, 5H, Ar-ring], ,10.3 [s, 1H, NH],8.02 [s, ON₂], MS: m/z 403 (M⁺)

IV-d: λ max 303.0 (methanol); IR (KBr, V max, cm^-1): 1545.60 (-NO₂ stretching), 2932.43 (-CH₂ stretching), 2997.66 (-CH stretching), 1608.74 (-NH deformation), 1679.77 (Ar C=C stretching), 1350.15 (C-N stretching), 1289.23 (C-C stretching), 1087.11 (C-O stretching), ¹ H-NMR (DMSO-d6, δ ppm): 5.63 [s, 1H, CH], 7.2-7.4 [m, 5H, Ar-ring], ,10.5 [s, 1H, NH], 8.1 [s, ON₂], MS: m/z 435 (M⁺)

IV-e: λ max 319.0 (methanol); IR (KBr, V max, cm^-1): 710.60 (-Cl stretching), 2932.43 (-CH₂ stretching), 2987.46 (-CH stretching), 1614.24 (-NH deformation), 1676.87 (Ar C=C stretching), 1348.55 (C-N stretching), 1290.53 (C-C stretching), 1089.01 (C-O stretching),¹H-NMR (DMSO-d6, δ ppm): 5.60 [s, 1H, CH], 7.1-7.3 [m, 5H, Ar-ring], ,10.1 [s, 1H, NH], 3.2 [s, Cl], MS: m/z 438 (M⁺)

IV-f: λ max 314.0 (methanol); IR (KBr, V max, cm^-1): 2937 (-CH₂ stretching), 2850 (-CH stretching), 1600.04 (-NH deformation), 1681.07 (Ar C=C stretching), 1342.05 (C-N stretching), 1288.93 (C-C stretching), 1096.30 (C-O stretching), ¹H-NMR (DMSO-d6, δ ppm): 2.05 [s, 3H, CH3], 7.4-7.6 [m, 5H, Ar-ring], 10.3 [s, 1H, NH], MS: m/z 422 (M⁺)

IV-g: λ max 324.5 (methanol); IR (KBr, V max, cm^-1): 3469.27 (-OH stretching), 2935 (-CH₂ stretching), 2850 (-CH stretching), 1600.04 (-NH deformation), 1678.07 (Ar C=C stretching), 1338.05 (C-N stretching), 1282.93 (C-C stretching), 1090.00 (C-O stretching), ¹H-NMR (DMSO-d6, δ ppm): 2.25 [s, 3H, CH3], 7.4-7.8 [m, 5H, Ar-ring], 10.1 [s, 1H, NH], 8.6 [s, -OH], MS: m/z 401 (M⁺)

IV-h: λ max 302.5 (methanol); IR (KBr, V max, cm^-1): 1538.33 (-NO₂ stretching), 2947 (-CH₂ stretching), 2860 (-CH stretching), 1604.10 (-NH deformation), 1680.18 (Ar C=C stretching), 1346.22 (C-N stretching), 1272.79 (C-C stretching), 1096 (C-O stretching), ¹H-NMR (DMSO-d6, δ ppm): 2.15 [s, 3H, CH3], 7.4-7.5 [m, 5H, Ar-ring], 10.8 [s, 1H, NH], 8.1 [s, NO₂], MS: m/z 417 (M⁺)

IV-i: λ max 290.0 (methanol); IR (KBr, V max, cm^-1): 1540.03 (-NO₂ stretching), 2955 (-CH₂ stretching), 2871 (-CH stretching), 1600.25 (-NH deformation), 1672.48 (Ar C=C stretching), 1337.45 (C-N stretching), 1270.63 (C-C stretching), 1100 (C-O stretching), ¹H-NMR (DMSO-d6, δ ppm): 2.18 [s, 3H, CH3], 7.1-7.3 [m, 5H, Ar-ring], 10.5 [s, 1H, NH], 8.09 [s, NO₂], MS: m/z 450 (M⁺)

IV-j: λ max 300.0 (methanol); IR (KBr, V max, cm^-1): 2960 (-CH₂ stretching), 2860 (-CH stretching), 1604.66 (-NH deformation), 1660.87 (Ar C=C stretching), 1353.94 (C-N stretching), 1268.93 (C-C stretching), 1082.78 (C-O stretching), 692.40 (C-Cl stretching), ¹H-NMR (DMSO-d6, δ ppm): 2.1 [s, 3H, CH3], 7.1-7.4 [m, 5H, Ar-ring], 10.1 [s, 1H, NH], 3.3 [s, Cl], MS: m/z 452 (M⁺)

IV-k: λ max 309.0 (methanol); IR (KBr, V max, cm^-1): 2966.33 (-CH₂ stretching), 2829.38 (-CH stretching), 1600.88 (-NH deformation), 1668.23 (Ar C=C stretching), 1348.94 (C-N stretching), 1250.07 (C-C stretching), 1088.00 (C-O stretching), ¹H-NMR (DMSO-d6, δ ppm): 7.0-7.2 [m, 5H, Ar-ring], 10.7 [s, 1H, NH], MS: m/z 472 (M⁺)

IV-l: λ max 312.0 (methanol); IR (KBr, V max, cm^-1): 3450.27 (-OH stretching), 2956.13 (-CH₂ stretching), 2809.18 (-CH stretching), 1604.08 (-NH deformation), 1651.13 (Ar C=C stretching), 1340.34 (C-N stretching), 1245.77 (C-C stretching), 1095.78 (C-O stretching), ¹H-NMR (DMSO-d6, δ ppm): 7.1-7.3 [m, 5H, Ar-ring], 10.9 [s, 1H, NH], 8.7 [s, -OH], MS: m/z 482 (M⁺)

IV-m: λ max 300.0 (methanol); IR (KBr, V max, cm^-1): 1530.00 (-NO₂ stretching), 2956.13 (-CH₂ stretching), 2809.18 (-CH stretching), 1604.08 (-NH deformation), 1662.13 (Ar C=C stretching), 1345.34 (C-N stretching), 1248.77 (C-C stretching), 1085.78 (C-O stretching), ¹H-NMR (DMSO-d6, δ ppm): 6.9-7.1 [m, 5H, Ar-ring], 10.1 [s, 1H, NH], 8.1 [s, -ON₂], MS: m/z 509 (M⁺)

IV-n: λ max 310.5 (methanol); IR (KBr, V max, cm^-1): 1535.00 (-NO₂ stretching), 2946.45 (-CH₂ stretching), 2819.00 (-CH stretching), 1600.01 (-NH deformation), 1674.03 (Ar C=C stretching), 1335.12 (C-N stretching), 1240.52 (C-C stretching), 1090.58 (C-O stretching), ¹H-NMR (DMSO-d6, δ ppm): 7.2-7.3 [m, 5H, Ar-ring], 10.1 [s, 1H, NH], 8.5 [s, -ON₂], MS: m/z 511 (M⁺)

IV-o: λ max 304.0 (methanol); IR (KBr, V max, cm^-1): 2970.13 (-CH₂ stretching), 2830.18 (-CH stretching), 1615.08 (-NH deformation), 1660.53 (Ar C=C stretching), 1340.64 (C-N stretching), 1235.57 (C-C stretching), 1085.01 (C-O stretching), 700.40 (C-Cl stretching),¹H-NMR (DMSO-d6, δ ppm): 7.0-7.2 [m, 5H, Ar-ring], 9.9 [s, 1H, NH], 3.3 [s, Cl], MS: m/z 500 (M⁺)

IV-p: λ max 318.5 (methanol); IR (KBr, V max, cm^-1): 2940.12 (-CH₂ stretching), 2830.05 (-CH stretching), 1610.12 (-NH deformation), 1500.53 (Ar C=C stretching), 1300.68 (C-N stretching), 1250.02 (C-C stretching), 1090.51 (C-O stretching),¹H-NMR (DMSO-d6, δ ppm): 2.5 [t, 3H,-OCH3], 7.3-7.5 [m, 5H, Ar-ring], 10.1 [s, 1H, NH], MS: m/z 496 (M⁺)

IV-q: λ max 324.0 (methanol); IR (KBr, V max, cm^-1): 3450.27 (-OH stretching),  2971.03 (-CH₂ stretching), 2855.33 (-CH stretching), 1612.42 (-NH deformation), 1662.06 (Ar C=C stretching), 1385.00 (C-N stretching), 1248.99 (C-C stretching), 1100.10 (C-O stretching), ¹H-NMR (DMSO-d6, δ ppm): 2.5 [t, 3H,-OCH3], 7.2-7.9 [m, 5H, Ar-ring], ,10.2 [s, 1H, NH], 8.6 [s, -OH], MS: m/z 516 (M⁺)

IV-r: λ max 307.0 (methanol); IR (KBr, V max, cm^-1): 1535.00 (-NO₂ stretching), 2980.13 (-CH₂ stretching), 2860.03 (-CH stretching), 1600.02 (-NH deformation), 1671.06 (Ar C=C stretching), 1381.02 (C-N stretching), 1258.89 (C-C stretching), 1080.10 (C-O stretching), ¹H-NMR (DMSO-d6, δ ppm): 2.5 [t, 3H,-OCH3], 7.2-7.3 [m, 5H, Ar-ring], 10.2 [s, 1H, NH], 8.5 [s, -ON₂], MS: m/z 540 (M⁺)

IV-s: λ max 309.5 (methanol); IR (KBr, V max, cm^-1): 1525.00 (-NO₂ stretching), 2982.13 (-CH₂ stretching), 2872.10 (-CH stretching), 1605.06 (-NH deformation), 1680.76 (Ar C=C stretching), 1371.82 (C-N stretching), 1268.89 (C-C stretching), 1100.10 (C-O stretching),¹H-NMR (DMSO-d6, δ ppm): 2.4 [t, 3H,-OCH3], 7.7-7.9 [m, 5H, Ar-ring], 10.4 [s, 1H, NH], 8.3 [s, -ON₂], MS: m/z 542 (M⁺)

IV-t: λ max 314.0 (methanol); IR (KBr, V max, cm^-1): 2970.33 (-CH₂ stretching), 2850.03 (-CH stretching), 1602.42 (-NH deformation), 1661.96 (Ar C=C stretching), 1390.62 (C-N stretching), 1250.89 (C-C stretching), 1085.10 (C-O stretching), 700.00 (C-Cl stretching), ¹H-NMR (DMSO-d6, δ ppm): 2.5 [t, 3H,-OCH3], 7.2-7.9 [m, 5H, Ar-ring],10.5[s, 1H, NH], 3.3 [s, Cl], MS: m/z 530 (M⁺)

 

Pharmacological evaluation:

All the experimental procedures and protocols used in this study were reviewed and approved by the Institutional Animal Ethical Committee (IAEC) of College, constituted in accordance with the guidelines of the Committee for the Purpose of Control and Supervision of Experiment on Animals (CPCSEA), Government of India.

 

Registration number and date of registration

648/02/c/CPCSEA            date: 30/09/2003

 

 

Toxicity Study ¹⁴:

The SD or Wister rats of either sex of weight 190-210 g were selected. Animals were housed standard condition of temperature 22^o (± 3^o C) and relative humidity (30-70%) with 12:12 light: dark cycle. The animals were fed with standard diet (pellets) and water ad libitum.

 

Acute toxicity was determined in rats by employing various logarithmic doses administered by oral route. Each group contained six wistar rats were orally administered with 10 mg/kg, 20 mg/kg, 40 mg/kg, 80 mg/kg and 100 mg/kg of synthesized compounds and kept in polystyrene cages. Behavioral changes were recorded at the interval of 30 min. for 4 h and also mortality after 24 h was recorded. One group was used as a control receiving only 1% w/v solution of tween 80 and calculated LD₅₀.

 

All the compounds synthesized were tested for acute toxicity test. No toxicity was observed at the doses of 10, 20, 40, 80, 100 mg/kg of body weight.  It was observed no animal was died at the dose of 100 mg/kg of body weight.

 

Analgesic activity¹⁵:

The analgesic activity of all the test compounds was evaluated by using Hot Plate Method and the instrument used for this purpose was Eddy’s hot plate.

 

The albino mice having body weight 20-25 g were divided into twenty two groups with six animals per cage. The first group was for control, second group for standard drug (Tramadol) and rest of twenty groups were for the synthesized compounds. The solutions of the test compounds were prepared in Tween 80 (1 % w/v).

 

The test and standard compound were administered orally at dose of 20 mg/kg. The basal reaction time, for jump response and paw liking , when animals placed on hot plate (maintained at constant temperature of 55⁰C) was observed and reaction time of animals on hot plate at 0, 0.5, 1.0 and 1.5 hour after administration of the test and standard compounds, was also noted. The percent increase in reaction time (as an index of analgesia) after 1.5 hour was calculated and reported in Table 3. Comparison of the analgesic activities exhibited by the test and standard drug is shown in fig. 1.

 

% inhibition = [1-(before treatment /after treatment)] x 100

 

Fig. 1: Analgesic activity of synthesized compounds (IVa-t)

 

Table 3: Percent analgesia of the test and standard drug with MEAN and SEM Values (IVa-t)

 

 

Note: Analgesic activities of the test compounds were compared w.r.t control. Data are expressed as % analgecic activity ± S.E.M. (n = 6) and analyzed by one-way ANOVA followed by Bonferroin t test to determine the significance of the difference between the control group and rats treated with the test compounds. The difference in results were considered significant when P < 0.05. All statistical calculations were carried out using Graph Pad® Prism 5.0 (USA) statistical software

 

Anti-inflammatory activity¹⁵:

The anti-inflammatory activity of all the test compounds was evaluated by Carrageenan-Induced Rat Paw Edema Method.

 

Male or female Sprague-Dawley rats with a body weight between 100-120 g were divided into twenty two groups with six animals per cage. The animals were starved overnight. To insure uniform hydration, the rats receive 5 ml of water by stomach tube (controls) or the test drug (100 mg/Kg) and standard drug (indomethacine) (100 mg/Kg) dissolved or suspended in the same volume. One hour later, the rats were challenged by a subcutaneous injection of 0.05 ml of 1% solution of carrageenan into the plantar side of the left hind paw. The paw volume was measured by Vernier caliper scale immediately after injection, again after 5 hrs. The percent increase in paw volume (as an index of inflammation) after 5 hour was calculated and reported in Table 4. Comparison of the anti-inflammatory activities exhibited by the test and standard drug is shown in fig 2.

 

 

 

The percent inhibition of rat paw edema was calculated by the following formula-

 

% inhibition = 1- [a-x/b-y] х 100

Where,

a = Paw volume of test group after 5 hrs of injecting carrageenan.

x = Paw volume of test group before injecting carrageenan.

b = Paw volume of control group after 5 hrs of injecting carrageenan.

y= Paw volume of control group before of injecting carrageenan.

 

Table 4: Anti-inflammatory activity of synthesized compounds (IVa-t)

 

 

Fig. 2: Anti-inflammatory activity of synthesized compounds (IVa-t)

 

Note: Anti-inflammatory activities of the test compounds were compared w.r.t control. Data are expressed as % anti-inflammatory activity ± S.E.M. (n = 6) and analyzed by one-way ANOVA followed by Bonferroin t test to determine the significance of the difference between the control group and rats treated with the test compounds. The difference in results were considered significant when P < 0.05. All statistical calculations were carried out using Graph Pad® Prism 5.0 (USA) statistical software.

 

RESULTS AND DISCUSSION:

The 2-Substituted 5-[(2-subtituted-4,5 diphenyl-1H-imidazol-1-yl)methyl]-2,3 dihydro-1,3,4 oxadiazole derivatives were successfully prepared by given scheme and further recrystallized by using ethanol and checked the purity by thin layer chromatographic techniques. The title compounds were further characterized by R_f value, melting point, λ max, FTIR, ¹HNMR and mass spectra. The synthesized compounds could be obtained in good yields with sharp melting points.

 

The structures of synthesized compounds were confirmed on the basis of spectral data. FTIR spectra of all synthesized compounds shows aromatic C=C stretching vibrations at about 1680-1650 cm-1 indicates presence of aromatic ring, absorbance band at the range 1615-1600 cm-1 associated with deformation vibrations of –NH. All compounds shows aromatic CH₂ stretching at about 2980-2930 cm-1, absorbance band at range 1390-1339 cm-1 associated with the C-N stretching vibration. All the compounds shows the absorbance band at about 1298-1240 cm-1 associated with the stretching vibration of C-C bond and also all compounds shows the strong absorbence band at about 1100-1080 cm-1 associated with the stretching vibration of C-O bond.

 

The comp. IV-b, g, l and q show strong band at 3470-3450 cm-1 stretching vibration indicates the presence of –OH group, comp. c, d, h, i, m, n, r and s shows strong band at 1545-1525 cm-1 stretching vibration indicates the presence of –NO₂ group. and comp. IV- e, j, o and t shows strong band at 710-692 cm-1 stretching vibration indicates the presence of –Cl group.

 

The ¹HNMR spectrum of all synthesized compounds exhibited sharp muliplates peak cluster in the range of 6.9 -7.6 ppm indicating the presence of aromatic hydrogen. A sharp singlet peak at 9.9 -10.5 ppm indicating the presence of –NH.

 

The results of analgesic and anti-inflammatory activity of test compounds were given in Table 3 and 4 shows that comp. IV-a, d, f, i, k, m, n, s and t showed significant analgesic and anti-inflammatory activity with compare to standard drugs Tramadol and Indomethacin respectively.

 

CONCLUSION:

A new series of 2-substituted 5-[(2-subtituted-4,5 diphenyl-1H-imidazol-1-yl)methyl]-2,3 dihydro -1,3,4 oxadiazole were synthesized using appropriate synthetic route and screened them for analgesic and anti-inflammatory activity. It can be concluded that, the Comp. IV-a, d, f, i, k, m, n, s and t showed significant analgesic activity with compared to standard drug Tramadol and comp. IV- a, d, f, i, k, n, p, s and t showed the significant anti-inflammatory activity with compared to the standard drug Indomethacin. Thus research work was undertaken for unsubstituted phenyl ring or 3-nitro phenyl ring at 2^nd position of oxadiazole ring shows significant activity whereas –NO₂, -OH and -Cl groups substituted on phenyl ring decreases the analgesic and anti-inflammatory activity. The encouraging results showed may lead to the further development of novel analgesic and anti-inflammatory agent explored further.

 

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Received on 12.06.2012        Modified on 09.07.2012

Accepted on 18.07.2012        © AJRC All right reserved