Abstract
A series of pyridazinone derivatives (19–34) were synthesized with an aim to synthesize safer anti-inflammatory agents. The compounds were evaluated for their anti-inflammatory, analgesic, ulcerogenic and lipid peroxidation (LPO) actions. The percentage inhibition in edema at different time intervals indicated that compounds 20, 26, 28 and 34 exhibited good anti-inflammatory potential, comparable with that of ibuprofen (85.77%) within a range of 67.48–77.23%. The results illustrate that 5-(4-fluoro-benzyl)-3-(4-chloro-phenyl)-1,6-dihydro-6-pyridazinone (26) and 5-(4-chloro-benzyl)-3-(4-chloro-phenyl)-1,6-dihydro-6-pyridazinone (20) showed best anti-inflammatory activity. Furthermore, activity is more in case of chloro substitution as compared with methyl-substitution. The compounds synthesized were also evaluated for their ulcerogenic and LPO action and showed superior gastrointestinal safety profile along with reduction in LPO as compared with that of the ibuprofen.
Introduction
Non-steroidal anti-inflammatory drugs (NSAIDs) are the most commonly prescribed medications in the world for the treatment of pain, fever and inflammation and disorders particularly arthritisCitation1,Citation2. Long-term use of the NSAIDs such as ibuprofen, indomethacin and naproxen exhibit gastric toxicity (gastrointestinal (GI) ulceration, bleeding) and nephrotoxicityCitation3. The search for safer NSAIDs continues with the failure of anticipated ‘Ideal’ anti-inflammatory agents, the coxibs, on long-term usageCitation4,Citation5. Therefore, synthetic approaches based on chemical modification of NSAIDs have been taken with the aim of improving their safety profile.
Pyridazinones have been the subject of intensive synthetic investigations, because they possess a wide spectrum of pharmacological activities. Various 3-(2H)-pyridazinone derivatives have been described and their cardiotonicCitation6,Citation7 anti-secretory and antiulcerCitation8 as well as analgesic and anti-inflammatoryCitation9,Citation10 activities have been investigated. 4-Ethoxy-2-methyl-5-morpholino-3(2H)-pyridazinone (emorfazone) and its derivatives have emerged as being of particular interest. Derivatives of N-substituted-4,6-diaryl-3-pyridazinone have emerged as potential analgesic anti-inflammatory and antipyretic agentsCitation11.
As part of the continuing study for new anti-inflammatory and analgesics in our laboratoriesCitation12,Citation13, a new series of pyridazinone derivatives were synthesized with an aim to obtain safer NSAIDs. The analgesic and anti-inflammatory activities were investigated for the title compounds by the acetic acid-induced writhing test and the carrageenan-induced rat paw edema test, respectively. Lipid peroxidation (LPO) and ulcerogenic actions of some of the selected compounds were also investigated and correlated.
Materials and methods
Chemistry
Melting points were determined in open capillary tubes and are uncorrected. Thin-layer chromatography (TLC) was carried out to monitor the reactions using silica gel (Merck No. 5554). The IR spectra were measured as potassium bromide pellets using a Perkin-Elmer 1725X spectrophotometer. 1H NMR spectra were recorded on Bruker spectropsin DPX-300 MHz in CDCl3; chemical shift (δ) values are reported in parts per million (ppm). The splitting pattern abbreviations are as follows: s, singlet; d, doublet; m, multiplet. Mass spectroscopic analyses for compounds were performed on a JEOL JMS-D 300 instrument. Spectral data are consistent with the assigned structures. The molecular ion for compounds containing chloro-group was calculated according to 35Cl isotope. Elemental analyses were performed on a Perkin-Elmer analyzer and were in range of ±0.4% for each element analyzed (C, H, N). Dry solvents were used throughout.
3-(4-Chloro/methyl benozyl)propionic acid (1,2)
The compounds, 1 and 2, were synthesized according to the reported methodCitation12.
3-Arylidene-5-(4-chloro/methyl phenyl)-2(3H)-furanones (3–18)
Compounds (3–18) were synthesized from 3-(4-chloro/methyl benozyl)propionic acid (1,2) following the literature methodCitation12.
General procedure for the synthesis of 5-(substituted benzyl)-3-aryl-1,6-dihydro-6-pyridazinones (19–34)
2(3H)-Furanones (3–18) (0.005 mole) and hydrazine hydrate (1–2 mL) in n-propanol (5–6 mL) were refluxed for 3 h. After refluxing, reaction mixture was poured onto crushed ice, a precipitate was obtained, which was filtered, dried and recrystallized from methanol to give TLC pure 5-(substituted benzyl)-3-aryl-1,6-dihydro-6-pyridazinone derivatives.
5-Benzyl-3-(4-chlorophenyl)-1,6-dihydro-6-pyridazinone (19)
Yield: 59%, m.p. 174°C. 1H NMR (CDCl3) δ 3.78 (s, 2H, CH2), 7.16 (s, 1H, H-4, pyridazinone ring), 7.14–7.48 (m, 5H, benzyl ring), 7.42 and 7.73 (d each, 2xA2B2, p-substituted phenyl ring), 10.72 (s, 1H, NH). MS: m/z 296(M+). IR (cm−1, KBr): 3186 (NH), 2949 (CH), 1683 (CO), 718 (C–Cl). Anal calcd. for C17H13ClN2O: C, 68.81; H, 4.42; N, 9.44. Found: C, 68.93; H, 4.45; N, 9.43.
5-(4-Chlorobenzyl)-3-(4-chlorophenyl)-1,6-dihydro-6-pyridazinone (20)
Yield: 58%, m.p. 196°C. 1H NMR (CDCl3) δ 3.95 (s, 2H, CH2), 7.11 (s, 1H, H-4, pyridazinone ring), 7.23 (m, 4H, H-2,3,5,6, benzyl ring), 7.32 and 7.41 (d each, 2xA2B2, p-substituted phenyl), 10.97 (s, 1H, NH). MS: m/z 330(M+). IR (cm−1, KBr): 3179 (NH), 2942 (CH), 1688 (CO), 726 (CCl). Anal calcd. for C17H12Cl2N2O: C, 61.65; H, 3.65; N, 8.46. Found: C, 61.55; H, 3.67; N, 8.47.
5-(4-Nitrobenzyl)-3-(4-chlorophenyl)-1,6-dihydro-6-pyridazinone (21)
Yield: 53%, m.p. 197°C. 1H NMR (CDCl3) δ 3.71 (s, 2H, CH2), 6.78 (s, 1H, H-4, pyridazinone ring), 7.37 (m, 4H, H-2,3,5,6, benzyl ring), 7.53 and 7.62 (d each, 2xA2B2, p-substituted phenyl), 10.93 (s, 1H, NH). MS: m/z 341(M+). IR (cm−1, KBr): 3173 (NH), 2936 (CH), 1672 (CO), 707 (CCl). Anal calcd. for C17H12ClN3O3: C, 59.75; H, 3.54; N, 12.30. Found: C, 59.63; H, 3.57; N, 12.31.
5-(4-Hydroxybenzyl)-3-(4-chlorophenyl)-1,6-dihydro-6-pyridazinone (22)
Yield: 57%, m.p. 192°C. 1H NMR (CDCl3) δ 3.59 (s, 2H, CH2), 6.11 (m, 1H, OH), 7.06 (m, 2H, H-2,6, benzyl ring), 7.31 (s, 1H, H-4, pyridazinone ring), 7.47 and 7.71 (d each, 2xA2B2, p-substituted phenyl), 7.49 (m, 2H, H-3,5, benzyl ring), 9.41 (s, 1H, NH). MS: m/z 312(M+). IR (cm−1, KBr): 3178 (NH), 2942 (CH), 1686 (CO), 722 (C–Cl). Anal calcd. for C17H13ClN2O2: C, 65.29; H, 4.19; N, 8.96. Found: C, 65.39; H, 4.17; N, 8.97.
5-(4-Methylbenzyl)-3-(4-chlorophenyl)-1,6-dihydro-6-pyridazinone (23)
Yield: 59%, m.p. 186°C. 1H NMR (CDCl3) δ 2.27 (s, 3H, CH3), 3.51 (s, 2H, CH2), 6.60 (s, 1H, H-4, pyridazinone ring), 7.13 and 7.36 (d each, 2xA2B2, p-substituted benzyl ring), 7.34 (m, 2H, H-3,5, phenyl ring), 7.61 (m, 2H, H-2,4, phenyl ring), 10.93 (s, 1H, NH). MS: m/z 310(M+). IR (cm−1, KBr): 3173 (NH), 2939 (CH), 1684 (CO), 708 (C–Cl). Anal calcd. for C18H15ClN2O: C, 69.57; H, 4.86; N, 9.01. Found: C, 69.53; H, 4.87; N, 9.03.
5-(4-Methoxybenzyl)-3-(4-chlorophenyl)-1,6-dihydro-6-pyridazinone (24)
Yield: 61%, m.p. 169°C. 1H NMR (CDCl3) δ 3.42 (s, 2H, CH2), 3.71 (s, 3H, OCH3), 6.81 (s, 1H, H-4, pyridazinone ring), 7.13 and 7.36 (d each, 2xA2B2, p-substituted benzyl ring), 7.59 (m, 2H, H-3,5, phenyl ring), 7.68 (m, 2H, H-2,4, phenyl ring), 10.73 (s, 1H, NH). MS: m/z 326(M+). IR (cm−1, KBr): 3167 (NH), 3002 (CH), 1675 (CO), 717 (C–Cl). Anal calcd. for C18H15ClN2O2: C, 66.16; H, 4.63; N, 8.57. Found: C, 66.23; H, 4.61; N, 8.55.
5-(4-Hydroxy-3-methoxybenzyl)-3-(4-chlorophenyl)-1,6-dihydro-6-pyridazinone (25)
Yield: 53%, m.p. 191°C. 1H NMR (DMSO) δ 3.48 (s, 2H, CH2), 3.64 (s, 3H, OCH3), 6.53 (s, 1H, H-4, pyridazinone ring), 7.07–7.29 (m, 3H, H-2,5,6, disubstituted benzyl ring), 7.46 and 7.71 (d each, 2xA2B2, p-substituted phenyl ring), 10.92 (s, 1H, NH). MS: m/z 342(M+). IR (cm−1, KBr): 3173 (NH), 2951 (CH), 1680 (CO), 713 (C–Cl). Anal calcd. for C18H15ClN2O3: C, 63.07; H, 4.41; N, 8.17. Found: C, 62.97; H, 4.39; N, 8.19.
5-(4-Fluorobenzyl)-3-(4-chlorophenyl)-1,6-dihydro-6-pyridazinone (26)
Yield: 57%, m.p. 190°C. 1H NMR (CDCl3) δ 3.61 (s, 2H, CH2), 7.05 (s, 1H, H-4, pyridazinone ring), 7.10 and 7.26 (d each, 2xA2B2, p-substituted benzyl ring), 7.41 and 7.60 (d each, 2xA2B2, p-substituted phenyl ring), 11.14 (s, 1H, NH). MS: m/z 314(M+). IR (cm−1, KBr): 3191 (NH), 2944 (CH), 1682 (CO), 719 (C–Cl). Anal calcd. for C17H12ClFN2O: C, 64.87; H, 3.84; N, 8.90. Found: C, 64.93; H, 3.85; N, 8.91.
5-Benzyl-3-(4-methylphenyl)-1,6-dihydro-6-pyridazinone (27)
Yield: 53%, m.p. 168°C. 1H NMR (CDCl3) δ 2.36 (s, 3H, CH3), 3.59 (s, 2H, CH2), 6.86 (s, 1H, H-4, pyridazinone ring), 7.02–7.43 (m, 5H, benzyl ring), 7.46 and 7.79 (d each, 2xA2B2, p-substituted phenyl ring), 8.92 (s, 1H, NH). MS: m/z 276(M+). IR (cm−1, KBr): 3185 (NH), 2952 (CH), 1676 (CO). Anal calcd. for C18H16N2O: C, 78.24; H, 5.84; N, 10.14. Found: C, 78.23; H, 5.87; N, 10.17.
5-(4-Chlorobenzyl)-3-(4-methylphenyl)-1,6-dihydro-6-pyridazinone (28)
Yield: 48%, m.p. 188°C. 1H NMR (CDCl3) δ 2.38 (s, 3H, CH3), 3.94 (s, 2H, CH2), 7.24 (s, 1H, H-4, pyridazinone ring), 7.26 and 7.56 (d each, 2xA2B2, p-substituted benzyl ring), 7.28–7.35 (m, 4H, H-2,3,5,6, phenyl ring), 10.69 (s, 1H, NH). MS: m/z 310(M+). IR (cm−1, KBr): 3174 (NH), 2939 (CH), 1683 (CO), 718 (C–Cl). Anal calcd. for C18H15ClN2O: C, 69.57; H, 4.86; N, 9.01. Found: C, 69.53; H, 4.87; N, 8.99.
5-(4-Nitrobenzyl)-3-(4-methylphenyl)-1,6-dihydro-6-pyridazinone (29)
Yield: 47%, m.p. 189°C. 1H NMR (CDCl3) δ 2.37 (s, 3H, CH3), 3.41 (s, 2H, CH2), 7.13 (s, 1H, H-4, pyridazinone ring), 7.31 and 8.01 (d each, 2xA2B2, p-substituted benzyl ring), 7.48 (m, 2H, H-3,5, phenyl ring), 7.81 (m, 2H, H-2,4, phenyl ring), 11.13 (s, 1H, NH). MS: m/z 321(M+). IR (cm−1, KBr): 3183 (NH), 2948 (CH), 1679 (CO). Anal calcd. for C18H15N3O3: C, 67.28; H, 4.70; N, 13.08. Found: C, 67.23; H, 4.71; N, 13.07.
5-(4-Hydroxybenzyl)-3-(4-methylphenyl)-1,6-dihydro-6-pyridazinone (30)
Yield: 47%, m.p. 196°C. 1H NMR (CDCl3) δ 2.54 (s, 3H, CH3), 3.43 (s, 2H, CH2), 6.40 (s, 1H, H-4, pyridazinone ring), 6.63 (m, 2H, H-2,6, phenyl ring), 6.66 (m, 2H, H-2,6, benzyl ring), 6.79 (m, 2H, H-3,5, phenyl ring), 6.81 (m, 2H, H-3,5, benzyl ring), 12.25 (s, 1H, NH). MS: m/z 291(M+). IR (cm−1, KBr): 3173 (NH), 2957 (CH), 1685 (CO). Anal calcd. for C18H16N2O2: C, 73.96; H, 5.52; N, 9.58. Found: C, 73.98; H, 5.51; N, 9.57.
5-(4-Methylbenzyl)-3-(4-methylphenyl)-1,6-dihydro-6-pyridazinone (31)
Yield: 48%, m.p. 182°C. 1H NMR (CDCl3) δ 2.29 and 2.31 (s, each, 6H, 2xCH3), 3.67 (s, 2H, CH2), 6.51 (s, 1H, H-4, pyridazinone ring), 7.31 and 7.85 (d each, 2xA2B2, p-substituted benzyl ring), 7.37 (m, 2H, H-3,5, phenyl ring), 7.59 (m, 2H, H-2,6, phenyl ring), 10.51 (s, 1H, NH). MS: m/z 289(M+). IR (cm−1, KBr): 3182 (NH), 2940 (CH), 1676 (CO). Anal calcd. for C19H18N2O: C, 78.59; H, 6.25; N, 9.65. Found: C, 78.53; H, 6.27; N, 9.67.
5-(4-Methoxybenzyl)-3-(4-methylphenyl)-1,6-dihydro-6-pyridazinone (32)
Yield: 43%, m.p. 192°C. 1H NMR (CDCl3) δ 2.37 (s, 3H, CH3), 3.67 (s, 3H, OCH3), 3.97 (s, 2H, CH2), 6.79 (s, 1H, H-4, pyridazinone ring), 7.37 and 7.82 (d each, 2xA2B2, p-substituted benzyl ring), 7.49 (m, 2H, H-3,5, phenyl ring), 7.72 (m, 2H, H-2,6, phenyl ring), 11.15 (s, 1H, NH). MS: m/z 305(M+). IR (cm−1, KBr): 3186 (NH), 2944 (CH), 1682 (CO). Anal calcd. for C19H18N2O2: C, 74.49; H, 5.92; N, 9.14. Found: C, 74.53; H, 5.91; N, 9.13.
5-(4-Hydroxy-3-methoxy-benzyl)-3-(4-methylphenyl)-1,6-dihydro-6-pyridazinone (33)
Yield: 51%, m.p. 180°C. 1H NMR (DMSO) δ 2.39 (s, 3H, CH3), 3.25 (s, 3H, OCH3), 3.92 (s, 2H, CH2), 6.82 (s, 1H, H-4, pyridazinone ring), 7.04 (m, 1H, H-6, benzyl ring), 7.25 (m, 2H, H-3,5, phenyl ring), 7.53 (m, 1H, H-2, benzyl ring), 7.68 (m, 2H, H-2,6, phenyl ring), 7.75 (m, 1H, H-5, benzyl ring), 10.73 (s, 1H, NH). MS: m/z 321(M+). IR (cm−1, KBr): 3189 (NH), 2952 (CH), 1687 (CO). Anal calcd. for C19H18N2O3: C, 70.79; H, 5.63; N, 8.69. Found: C, 70.83; H, 5.65; N, 8.67.
5-(4-Fluorobenzyl)-3-(4-methylphenyl)-1,6-dihydro-6-pyridazinone (34)
Yield: 49%, m.p. 174°C. 1H NMR (CDCl3) δ 2.36 (s, 3H, CH3), 3.95 (s, 2H, CH2), 7.01 (s, 1H, H-4, pyridazinone ring), 7.05 and 7.55 (d each, 2xA2B2, p-substituted benzyl ring), 7.21–7.29 (m, 4H, H-2,3,6,5, phenyl ring), 11.42 (s, 1H, NH). MS: m/z 293(M+). IR (cm−1, KBr): 3183 (NH), 2948(CH), 1672 (CO). Anal calcd. for C18H15FN2O: C, 73.45; H, 5.14; N, 9.52. Found: C, 73.43; H, 5.17; N, 9.53.
Pharmacology
The protocol of the animal experiments was approved by the Institutional Animal Ethics Committee. The in-vivo anti-inflammatory activity of the synthesized compounds (19–34) was evaluated by carrageenan-induced rat paw edema method as described by Winter et al.Citation14. Ibuprofen was taken as standard drug for comparison. All the compounds were administered orally and assayed at a dose of 20 mg/kg of body weight. The compounds that exhibited good anti-inflammatory activity (>65%) were further evaluated for their analgesic activity using acetic acid-induced writhing methodCitation15. The compounds that were screened for the analgesic activity were also tested for their ulcerogenic activity by the method reported by Cioli et al.Citation16 and LPO according to the method of Okhawa et al.Citation17. The results of the pharmacological evaluation have been listed in and .
Table 1. Anti-inflammatory activity of the pyridazinone derivatives. 19–34.
Table 2. Analgesic activity along with ulcerogenic and lipid peroxidation effect of the pyridazinone derivatives (20, 26, 28 and 34).
Anti-inflammatory activity
The synthesized compounds were evaluated for their anti-inflammatory activity using carrageenan-induced paw edema method of Winter et al.Citation14. The experiment was performed on Albino rats of Wistar strain of either sex, weighing 180–200 g. The animals were randomly divided into two groups of six each. Group I was kept as control and received only 0.5% carboxymethyl cellulose (CMC) solution. Groups II was kept as standard and received ibuprofen (20 mg/kg, p.o.). Carrageenan solution (0.1% in sterile 0.9% NaCl solution) in a volume of 0.1 mL was injected subcutaneously into the sub-plantar region of the right hind paw of each rat, 30 min after the administration of the test compounds (20 mg/kg) and standard drugs. The paw volume was measured by saline displacement shown on screen of digital Plethysmometer (Ugo Basile) at 2 and 3 h after carrageenan injection. Thus, the edema volume in control group (Vc) and edema volume in groups treated with test compounds (Vt) was measured and the percentage inhibition of edema was calculated using the formula:
Anti-inflammatory activity (% inhibition) = {(Vc − Vt)/Vc} × 100
Analgesic activity
Compounds that showed good anti-inflammatory activity (>65%) were also screened for analgesic activity. Analgesic activity was done by acetic acid induce writhing methodCitation15. Swiss albino mice (25–30 g) of either sex were divided into different groups of six each. A 1% aqueous acetic acid solution (intraperitoneal injection in a volume of 0.1 mL) was used as writhing induced agent. Mice were kept individually in the test cage, before acetic acid injection and habituated for 30 min. Screening of analgesic activity was performed after oral administration of test drugs at a dose of 20 mg/kg. Group I was taken as control and received CMC suspension only, group II received reference drug ibuprofen and rest of the groups were treated with test drugs (20 mg/kg) suspended in 1.0% CMC orally. After 1 h of drug administration 0.10 mL of 1% acetic acid solution was given to mice intraperitoneally. Stretching movements consisting of arching of the back, elongation of body and extension of hind limbs were counted for 5–15 min of acetic acid injection. The analgesic activity was expressed in terms of percentage inhibition.
% Analgesic activity = {(n − n′)/n} × 100
where n is mean number of writhes of control group and n′ the mean number of writhes of test group.
Acute ulcerogenesis
Acute ulcerogenesis test was done according to the study of Cioli et al.Citation16 Albino rats (150–200 g) were divided into different groups consisting of six animals in each group. Ulcerogenic activity was evaluated after oral administration of test compounds or ibuprofen at the dose of 60 mg/kg. Control rats received oral administration of vehicle (suspension of 1% methyl cellulose). Food but not water was removed 24 h before administration of the test compounds. After the drug treatment, the rats were fed with normal diet for 17 h and then killed. The stomach was removed and opened along the greater curvature, washed with distilled water and cleaned gently by dipping in normal saline. The mucosal damage was examined by means of a magnifying glass. For each stomach, the mucosal damage was assessed according to the following scoring system: 0.5: redness, 1.0: spot ulcers, 1.5: hemorrhagic streaks, 2.0: ulcers > 3 but <5, 3.0: ulcers > 5. The mean score of each treated group minus the mean score of control group was regarded as severity index of gastric mucosal damage.
Lipid peroxidation
LPO in the gastric mucosa was determined according to the method of Ohkawa et al.Citation17. After screening for ulcerogenic activity, the gastric mucosa was scraped with two glass slides and 10% of that tissue was homogenized at 10,000g in 1.8 mL of 1.15% ice-cold KCl solution. One millilitre of suspension medium was taken from the supernatant, 0.5 mL of 30% trichloroacetic acid followed by 0.5 mL of 0.8% thiobarbituric acid reagent were added to it. The tubes were covered with aluminium foil and kept in a shaking water bath for 30 min at 80°C. After 30 min, tubes were taken out and kept in ice cold water for 10 min. These were then centrifuged at 3000g for 15 min. The absorbance of supernatant was read at 540 nm at room temperature against the blank on UV spectrophotometer.
The standard curve was used for estimating the concentration of malondialdehyde (MDA) prepared by using 1,1,3,3-tetraethoxypropane (). The results are presented as nanomoles of MDA per milligram of protein ().
Figure 1. Calibration standard curve for TBARS concentration.
Result and discussion
Chemistry
2(3H)-Furanones (3–18) on reaction with hydrazine hydrate in n-propanol gave the title compounds, i.e. 5-(substituted-benzyl)-3-aryl-1,6-dihydro-6-pyridazinone derivatives (19–34). 2(3H)-Furanones (3–18) were prepared using 3-(4-substituted-benzoyl)propionic acid (1–2) following the previously reported methods of modified Perkin’s reaction in higher yieldCitation12. The 3-(4-substituted-benzoyl)propionic acid (1, 2) was synthesized according to Friedal Craft’s acylation reaction condition using substituted benzene ().
Scheme 1. Protocol for synthesis of title compounds.
In the IR spectral data, all the compounds showed peaks each around 3180 (NH), 2940 (CH), 1685 (CO) cm−1. The 1H NMR spectra of the synthesized compounds showed characteristic peaks at appropriate δ values. The CH proton of fourth position of pyridazinone ring appeared as singlet around δ 6.60–7.26. The CH2 proton appeared around δ 3.23–4.47 in aliphatic region. The NH proton appeared as a broad singlet appeared around δ 9.23–12.89. The structure of the compounds was further supported by mass spectral data. The synthesized compounds gave M+ peak in reasonable intensities. The molecular ion or other related ions produced the appropriate isotopic abundances due to the presence of chlorine atom(s).
Pharmacological evaluation
The pharmacological evaluation showed that the compounds are capable anti-inflammatory () and analgesic agents with lesser GI toxicity and reduced LPO ().
The results illustrate that 5-(4-fluoro-benzyl)-3-(4-chloro-phenyl)-1,6-dihydro-6-pyridazinone (26) and 5-(4-chloro-benzyl)-3-(4-chloro-phenyl)-1,6-dihydro-6-pyridazinone (20) showed best anti-inflammatory activity, having maximum percentage inhibition in edema at different time intervals. Their percentage inhibition in edema at different time intervals, i.e. 77.23% (compound 26) and 71.95% (compound 20) was comparable with that of ibuprofen (85.77%). In addition, two more compounds, 28 and 34, showed 67.48 and 68.90% inhibition, respectively. The remaining derivatives too possess anti-inflammatory activity but less than of the standard, ibuprofen.
The anti-inflammatory activity enhanced in the presence of electronegative substitution (chloro) and diminished in the presence of electropositive substitution (methyl) indicating that the activity declines with replacement of electronegative group to electropositive group.
Test compounds that exhibited good anti-inflammatory activity 20, 26, 28 and 34 were further evaluated for their analgesic, ulcerogenic and LPO actions. The results of analgesic activity indicated that compounds 20 and 26 showed 46.83% and 48.97% protection, respectively, against acetic acid-induced writhings and this percentage protection was comparable with that of ibuprofen (61.03%). Compounds 28 and 34 also showed good analgesic activity with 42.12% and 44.22% protection, respectively. According to structure–activity relationship (SAR), it is clear that 5-(4-fluoro-benzyl)-3-(4-chloro-phenyl)-1,6-dihydro-6-pyridazinone (26) and 5-(4-chloro-benzyl)-3-(4-chloro-phenyl)-1,6-dihydro-6-pyridazinone (20) were found to be a good anti-inflammatory agents with significant analgesic activity.
The tested compounds showed low ulcerogenic activity ranging from 0.1 ± 0.1 to 0.2 ± 0.12, whereas the standard drug ibuprofen showed high severity index of 0.8 ± 0.1. The maximum reduction in ulcerogenic activity (0.1 ± 0.1) was found in the compounds 26 and 20. The LPO was measured as nanomoles of MDA per milligram of protein. Ibuprofen exhibited high LPO 0.597 ± 0.007, whereas control group showed 0.239 ± 0.007.
Thus, these compounds showed superior GI safety profile along with reduction in LPO in comparison with ibuprofen. The other tested compounds also exhibited better GI safety profile as compared with the standard drug ibuprofen.
In summary, 5-(4-fluoro-benzyl)-3-(4-chloro-phenyl)-1,6-dihydro-6-pyridazinone (26) and 5-(4-chloro-benzyl)-3-(4-chloro-phenyl)-1,6-dihydro-6-pyridazinone (20) were found to have dual functional, i.e. anti-inflammatory and analgesic properties and hence, can be a promising class of compounds with an interesting pharmacological profile. It is conceivable that these derivatives could be further modified to develop potent and safer anti-inflammatory and analgesic agents. Further studies to acquire more information about quantitative SAR are in progress in our laboratory.
Acknowledgements
The authors thank UGC for financial assistance. Thanks are also due to In-charge animal house, Jamia Hamdard, New Delhi, for providing animals for pharmacological studies.
Declaration of interest
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
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