Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

Synthesis and pharmacological investigation of novel 4-(3-ethylphenyl)-1-substituted-4 H -(1,2,4)triazolo(4,3- a ) quinazolin-5-ones as a new class of H 1 -antihistaminic agents

Synthesis and pharmacological investigation of novel 4-(3-ethylphenyl)-1-substituted-4 H... Acta Pharm. 59 (2009) 97­106 10.2478/v10007-009-0003-1 Short communication VEERACHAMY ALAGARSAMY1,* KUNCHU KAVITHA2 MANI RUPESHKUMAR2 VISWAS RAJA SOLOMON3 JAYA KUMAR1 DINAKARAN SATHESH KUMAR4 HEMANT KUMAR SHARMA5 1 Medicinal Chemistry Research Laboratory MNR College of Pharmacy Fasalwadi, Sangareddy-502294, India 2 Bharathi College of Pharmacy Bharathi Nagar, K. M. Doddi­571422 Mandya (Dist), India 3 Medicinal & Process Chemistry Division, Central Drug Research Institute, Lucknow-226001, India 4 Department of Pharmaceutical Chemistry, Nalanda College of Pharmacy Cheralpally, Nalgonda­508001, India 5 Department of Pharmaceutical Chemistry, Patel College of Pharmacy Bhopal, India A series of novel 4-(3-ethylphenyl)-1-substituted-4H-[1,2,4] triazolo[4,3-a]quinazolin-5-ones (4a-j) were synthesized by the cyclization of 3-(3-ethylphenyl)-2-hydrazino-3H-quinazolin-4-one (3) with various one-carbon donors. The starting material, compound 3, was synthesized from 3-ethyl aniline by a new innovative route with improved yield. When tested for their in vivo H1-antihistaminic activity on conscious guinea pigs, all test compounds protected the animals from histamine induced bronchospasm significantly. Compound 4-(3-ethylphenyl)-1-methyl-4H -[1,2,4]triazolo[4,3-a]quinazolin-5-one (4b) emerged as the most active compound of the series and it is more potent (74.6 % protection) compared to the reference standard chlorpheniramine maleate (71 % protection). Compound 4b shows negligible sedation (10 %) compared to chlorpheniramine maleate (30 %). Therefore compound 4b can serve as the leading compound for further development of a new class of H1-antihistamines. Keywords: quinazolin-5-ones, sedation, H1-antihistaminic agents Accepted January 15, 2009 The first generation antihistamines penetrate the blood brain barrier and also possess anticholinergic properties; this has led to the development of a second generation of H1-antagonists such as terfenadine, cetirizine and astemizole (1). A common feature of the first generation compounds includes two aryl or heteroaryl rings linked to an ali* Correspondence; e-mail: drvalagarsamy@gmail.com phatic tertiary amine via the side chain (diphenhydramine and pheniramine) (2). The second generation compounds (terfenadine and cetirizine) contain many of the structural features of the first generation compounds. The real breakthrough of non-sedative antihistamines came in the early eighties of the twentieth century when modern antihistamines were found to exhibit potent antihistaminic activity without sedative effect (3). Condensed heterocycles containing the new generation of H1-antihistamines (loratadine, azelastine and flazelastine) that do not possess the above mentioned pharmacophore for H1-antihistamines paved the way for the discovery of many novel antihistamines, temelastine (4) and mangostin (5). Quinazolines and condensed quinazolines show excellent antihistaminic activity (6, 7). In continuation, we demonstrated (8, 9) the quinazoline derivatives as potent antihistamines with the least sedation. The present work is an extension of our ongoing efforts towards development and identification of new molecules. Therefore we undertook to synthesize a series of 1,2,4-triazolo-4H-[4,3-a]quinazolin-5-ones containing 3-ethylphenyl substituted at position 4 and alkyl/alicyclic amines substituted at position 1. The synthesized compounds were tested for their in vivo H1-antihistaminic activity on conscious guinea pigs. As sedation is one of the major side effects associated with antihistamines, the test compounds were also evaluated for their sedative potentials by measuring the reduction in locomotor activity using an actophotometer. EXPERIMENTAL Melting points were taken in open capillaries on a Thomas Hoover melting point apparatus (Thomas Hoover, USA) and are uncorrected. IR spectra were recorded in film or in potassium bromide disks on a Perkin-Elmer 398 spectrometer (Perkin-Elmer, USA). 1H spectra were recorded on a DPX-300 MHz Bruker FT-NMR spectrometer (Bruker, USA). Chemical shifts were reported as parts per million (d ppm) using tetramethylsilane (TMS) as an internal standard. Mass spectra were obtained on a Jeol-SX-102 instrument (Jeol, Japan) using fast atom bombardment (FAB positive). Elemental analysis was performed on a Perkin-Elmer 2400 CHN analyzer (Perkin-Elmer, USA); the values were found within the acceptable limits of the calculated values (± 0.4 %). Spectral data (IR, NMR and mass spectra) and elemental analysis data are presented in Tables I and II. The progress of the reaction was monitored on ready-made silica gel plates (Merck, Norway) using chloroform/methanol (9:1) as a solvent system. Iodine was used as a developing agent. All chemicals and reagents used in the syntheses were obtained from Aldrich (USA), Lancaster (USA) or Spectrochem (India). They were used without further purification. Syntheses 3-(3-Ethylphenyl)-2-thioxo-2,3-dihydro-1H-quinazolin-4-one (1). ­ A solution of 3-ethyl aniline (0.02 mol) in dimethyl sulfoxide (10 mL) was stirred vigorously. To this, carbondisulphide (1.6 mL) and aqueous sodium hydroxide 1.2 mL (2 mol L­1) were added dropwise during 30 min under stirring. Dimethyl sulfate (0.02 mol) was added gradually keeping the reaction mixture stirred for 2 h. The reaction mixture was then poured into ice water. The solid obtained was filtered, washed with water, dried and recrystallized from Table I. Physical and analytical data of newly synthesized compounds O N O N N 1­3 R R N N N 4a­j Compd. Molecular formula C16H14N2OS C17H16N2OS C16H16N4O C17H14N4O C18H16N4O C19H18N4O C20H20N4O C18H15ClN4O C22H23N5O C23H25N5O Molecular M.p. (oC) Elemental analysis calcd./found (%) massa Yield (%) C H N 282 296 280 290 304 318 332 338 373 387 389 388 402 273­274 80 162­163 89 213­215 81 245­247 81 263­265 70 212­214 77 221­222 76 274­276 71 212­213 78 251­253 73 198­199 77 231­233 78 271­273 79 68.06 68.12 68.89 68.83 68.55 68.62 70.33 70.30 71.04 71.07 71.68 71.62 72.27 72.24 63.81 63.80 70.76 70.72 71.29 71.36 67.85 67.86 68.02 68.09 68.63 68.68 5.00 5.07 5.44 5.40 5.75 5.78 4.86 4.88 5.30 5.23 5.70 5.74 6.06 6.07 4.46 4.45 6.21 6.27 6.50 6.54 5.95 5.91 6.23 6.26 6.51 6.50 9.92 9.93 9.45 9.47 19.99 19.98 19.30 19.34 18.41 18.40 17.60 17.57 16.86 16.84 16.54 16.57 18.75 18.70 18.07 18.09 17.98 17.93 21.63 21.65 20.88 20.83 1 2 3 4a 4b 4c 4d 4e 4f 4g 4h 4i 4j ­SH ­SCH3 ­NHNH2 ­H ­CH3 ­CH2CH3 ­(CH2)2CH3 ­CH2Cl C22H23N5O2 C22H24N6O CH3 NH C23H26N6O ethanol. Methyl anthranilate (0.01 mol) and the prepared N-(3-ethylphenyl)-methyl dithiocarbamic acid (0.01 mol) were dissolved in ethanol (20 mL). To this, anhydrous potassium carbonate (100 mg) was added and refluxed for 23 h. The reaction mixture was cooled in ice and the solid separated was filtered and purified by dissolving in 10 % alcoholic sodium hydroxide solution and reprecipitated by treating with dilute hydrochloric Table II. IR and NMR spectral data of intermediate and newly synthesized compounds IR (KBr) (cm­1) C=O 1692 1692 1680 C=N ­a ­a ­a Compd. 1 2 3 1H NMR (CDCl3), d (ppm) 1.52­1.64 (t, 3H, CH2CH3), 2.43­2.56 (q, 2H, CH2CH3), 7.15­7.79 (m, 8H, ArH), 10.45 (br s, 1H, NH, D2O exchangeable) 1.25­1.38 (t, 3H, CH2CH3), 2.05­2.17 (q, 2H, CH2CH3), 2.46 (s, 3H, SCH3), 7.33­8.05 (m, 8H ArH) 1.33­1.45 (t, 3H, CH2CH3), 2.75­2.89 (q, 2H, CH2CH3) 5.02 (br s, 2H, NH2 D2O exchangeable), 7.11­7.79 (m, 8H, ArH), 9.53 (br s, 1H, NH D2O exchangeable) 1.01­1.15 (t, 3H, CH2CH3), 2.13­2.26 (q, 2H, CH2CH3), 7.01­7.35 (m, 4H, ArH), 7.54 (s, 1H, ArH), 7.73­8.05 (m, 4H, ArH) 4a 4b 4c 4d 1680 1678 1681 1610 1604 1612 1.23 (s, 3H, CH3), 1.42­1.51 (t, 3H, CH2CH3), 2.85­2.97 (q, 2H, CH2CH3), 7.14­7.63 (m, 8H, ArH) 1.13­1.24 (t, 3H, CH2CH3), 1.44­1.54 (t, 3H, CH2CH3), 2.21­2.33 (q, 3H, CH2CH3), 2.62­2.75 (q, 2H, CH2CH3), 7.05­7.65 (m, 8H, ArH) 0.65­0.73 (t, 2H, CH2CH2CH3), 1.08­1.15 (sext, 2H, CH2CH2CH3), 1.34­1.45 (q, 2H, CH2CH3), 2.42­2.55 (t, 3H, CH2CH3), 2.83­2.94 (t, 3H, CH2CH2CH3), 7.21­7.95 (m, 8H, ArH) 1.04­1.15 (t, 3H, CH2CH3), 2.25­2.36 (q, 2H, CH2CH3), 3.15 (s, 2H, CH2), 7.05­7.66 (m, 8H, ArH) 1.01­1.25 (m, 4H, CH2-pyrrolidinyl), 1.43­1.64 (m, 4H, CH2-pyrrolidinyl), 2.43­2.51 (t, 3H, CH2CH3), 2.72­2.83 (q, 3H, CH2CH3), 3.65 (s, 2H, CH2), 7.22­7.84 (m, 8H, ArH) 0.89­1.09 (m, 6H, CH2-piperidyl), 1.42­1.65 (m, 4H, CH2-piperidyl), 2.33­2.45 (t, 3H, CH2CH3), 2.63­2.78 (q, 2H, CH2CH3), 3.45 (s, 2H, CH2), 7.35­7.76 (m, 8H, ArH) 1.21­1.42 (m, 4H, CH2-morpholinyl), 1.75­1.85 (m, 4H, CH2-morpholinyl), 2.13­2.25 (t, 3H, CH2CH3), 2.51­2.64 (q, 2H, CH2CH3), 3.35 (s, 2H, CH2), 7.11­7.75 (m, 8H, ArH) 0.95­1.13 (m, 4H, CH2-piperazinyl), 1.45­1.66 (m, 4H, CH2-piperazinyl), 2.03­2.15 (t, 3H, CH2CH3), 2.63­2.75 (q, 2H, CH2CH3), 3.75 (s, 2H, CH2), 7.35­7.89 (m, 8H, ArH), 9.57 (s, 1H, NH, D2O exchangeable) 1.01­1.25 (m, 4H, CH2-piperazinyl), 1.44­1.65 (m, 4H, CH2-piperazinyl), 2.11­2.36 (t, 3H, CH2CH3), 2.52­2.66 (q, 2H, CH2CH3), 3.05 (s, 3H, CH3), 3.26 (s, 2H, CH2), 7.34­7.87 (m, 8H, ArH) 4e 4f 4g 4h 4i 4j Not applicable acid. The solid obtained was filtered, washed with water, dried and recrystallized from ethanol. 3-(3-Ethylphenyl)-2-methylsulfanyl-3H-quinazolin-4-one (2). ­ Compound 1 (0.01 mol) was dissolved in 40 mL of 2 % alcoholic sodium hydroxide solution. To this, dimethyl sulfate (0.01 mol) was added dropwise under stirring. The stirring was continued for 1 h, the reaction mixture was then poured into ice water. The solid obtained was filtered, washed with water, dried and recrystallized from the ethanol/chloroform (75:25) mixture. 3-(3-Ethylphenyl)-2-hydrazino-3H-quinazolin-4-one (3). ­ Compound 2 (0.01 mol) was dissolved in ethanol (25 mL). To this, hydrazine hydrate (99 %) (0.1 mol) and anhydrous potassium carbonate (100 mg) were added and refluxed for 38 h. The reaction mixture was cooled and poured into ice water. The solid so obtained was filtered, washed with water, dried and recrystallized from the chloroform/benzene (25:75) mixture. 4-(3-Ethylphenyl)-1-subtituted-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones (4a-e). ­ 3-(4-Ethylphenyl)-2-hydrazino-3H-quinazolin-4-one (3) (0.01 mol) and formic acid (25 mL) were print in a round-bottomed flask and refluxed for 36 h, cooled and poured into ice water. The solid obtained 4a was filtered, washed with water, dried and recrystallized from ethanol. Adopting this procedure, compounds 4b-e were also prepared. 4-(3-Ethylphenyl)-1-subtituted-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-one (4f-j). ­ A mixture of 1-chloromethyl-4-(3-ethylphenyl)-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-one (4e) (0.01 mol) pyrrolidine (0.05 mol) and anhydrous potassium carbonate (100 mg) in dioxane (25 mL) was put in a round bottomed flask and refluxed for 39 h, cooled and poured into ice water. The solid obtained 4f was filtered, washed with water, dried and recrystallized from ethanol/benzene (50:50). Implementing this protocol, compounds 4g-j were also prepared. Pharmacology Animals. ­ Antihistaminic activity was evaluated on male Dunkin Hartley guinea pigs (250­300 g), while sedative-hypnotic activity was tested on albino Swiss mice. The animals were maintained in colony cages at 25 ± 2 °C, relative humidity of 45­55 %, under a 12 h light and dark cycle; they were fed standard animal feed. All animals were acclimatized for a week before the experiment. The Institutional Animal Ethics Committee approved the protocol adopted for the experimentation on animals. Antihistaminic activity. ­ A modification of the method of Van Arman (10) was adopted to determine the antihistaminic potential of the synthesized compounds. Six animals were alloted to each group and were fasted for 12 h. The test compounds and reference standard (chlorpheniramine maleate) were administered orally at a dose of 10 mg kg­1 in 1 % CMC (carboxymethylcelluose) and challenged with histamine aerosol (3 mL of 0.2 % aqueous solution of histamine hydrochloride) in a vaponephrin pocket nebulizer sprayed into a closed transparent cage. The respiratory status reflecting the increasing degree of bronchoconstriction was recorded. The time for the onset of convulsions (preconvulsion) was recorded. Animals remaining stable for more than 6 min were considered protected against histamine-induced bronchospasm. An intraperitoneal injection of chlorpheniramine maleate (Avil, India) at a dose of 25 mg kg­1 was given for the recovery of test animals. Sedative-hypnotic activity. ­ Sedative-hypnotic activity was determined by measuring the reduction in locomotor activity using an actophotometer (11, 12). Six albino Swiss mice were allotted to each group. Basal activity score was taken and then compounds 4a-j and standard chlorpheniramine maleate were administered orally at a dose of 5 mg kg­1 in 1 % CMC. Scores were recorded 1, 2 and 3 h after the drug administration. Statistical analysis. ­ Statistical analysis of the biological activity of the synthesized compounds on animals was evaluated using a one-way analysis of variance (ANOVA). In all cases, posthoc comparisons of the means of individual groups were performed using Tukey's test. All values are expressed as mean ± SD (standard deviation). For statistical analysis, the GraphPad Prism 3.0 version was used. RESULTS AND DISCUSSION Chemistry The key intermediate 3-(3-ethylphenyl)-2-thioxo-2,3-dihydro-1H-quinazolin-4-one (1) was prepared by refluxing methyl anthranilate with 3-ethylphenyl isothiocyanate in ethanol. However, the preparation of 3-ethylphenyl isothiocyanate required for the reaction was a tedious, time consuming process and the yield was also low (60 %). An alternate route was attempted to synthesize compound 1. In this route, 3-ethyl aniline was reacted with carbon disulphide and anhydrous potassium carbonate in acetone to give potassium dithiocarbamate, which was methylated with dimethyl sulfate to afford the dithiocarbamic acid methyl ester, which was refluxed with methyl anthranilate to yield 1. This way of synthesizing 1 suffers from the drawbacks such as the multi-step process, prolonged reaction time (37 h) and low yield (30 %). Hence, improvisation was carried out in this method by using aqueous sodium hydroxide (2 mol L­1) instead of anhydrous K2CO3, and dimethyl sulphoxide (DMSO) (Scheme 1) as a solvent instead of acetone. The use of DMSO as the reaction solvent enhanced the rate of reaction and the use of alkali in higher concentration helped prevent hydrolysis of the intermediate, probably due to less solvation. These modifications not only curtailed the reaction time from 37 to 25 h, but also increased the yield from 30 to 80 %. The product obtained was cyclic and not open-chain thiourea. The structure was confirmed by the IR spectrum, which showed intense peaks at 3216 cm­1 for cyclic thiourea (NH), 1692 cm­1 for carbonyl (C=O) and 1210 cm­1 for thioxo (C=S) stretching. 1H NMR spectrum of 1 showed a triplet at d 1.52­1.64 ppm due to the CH3 group, a quartet at d 2.43­2.56 ppm due to CH2 and a multiplet at d 7.15­7.79 ppm for aromatic (8H) protons and a singlet at d 10.45 ppm indicating the presence of NH. Data from the elemental analyses were found to be in conformity with the assigned structure. Further, the molecular ions recorded in the mass spectrum are also in agreement with the molecular mass of compound 1. 3-(3-Ethylphenyl)-2-methysulfanyl-3H-quinazolin-4-one (2) was obtained by dissolving product 1 in a 2 % alcoholic sodium hydroxide solution and methylating with dimethyl sulfate while stirring at room temperature. The IR spectrum of 2 showed disappearance of NH and C=S stretching signals of cyclic thiourea. It showed a peak for carbonyl (C=O) stretching at 1692 cm­1. The 1H NMR spectrum of compound 2 showed a triplet at d 1.25­1.38 ppm due to CH3, a quartet at d 2.05­2.17 ppm due to CH2, a singlet at d 2.46 ppm due to SCH3 and a multiplet at d 7.33­8.05 ppm due to aromatic (8H) protons. Data from the elemental analyses and the molecular ion recorded in the mass spectrum further confirmed the assigned structure of 2. Nucleophilic displacement of methylthio group of compound 2 with hydrazine hydrate was carried out using ethanol as solvent to afford 3-(3-ethylphenyl)-2-hydrazino102 DMSO NH2 S Na N H S DMS N H O SCH3 CS2/NaOH OCH3 EtOH D NH2 O N N 2 EtOH D SCH3 O NaOH/EtOH DMS N H N S 1 OCH3 NH N H Compd. R NH2NH2·H2O O one carbon donors, D N N R N N O N N 3 NHNH2 4a-j 4a: 4b: 4c: 4d: 4e: 4f: 4g: 4h: 4i: 4j: -H -CH3 -CH2CH3 -(CH2)2CH3 -CH2Cl -pyrrolidinyl -piperidinyl -morpholinyl -piperazinyl -4-methyl piperazinyl Scheme 1 -3H-quinazolin-4-one (3). The required long duration of the reaction (38 h) might be due to the presence of the bulky aromatic ring at position 3, which might have reduced the reactivity of the quinazoline ring system at C-2 position. The formation of 3 was confirmed by the presence of NH and NH2 signals at 3390­3225 cm­1 in the IR spectrum. It also showed a peak for carbonyl (C=O) at 1680 cm­1. The 1H NMR spectrum of compound 3 showed singlets at d 2.46 ppm due to SCH3, a triplet at d 1.33­1.45 ppm due to CH3 group, a quartet at d 2.75­2.89 due to CH2, singlets at d 5.02 ppm and 9.53 ppm due to NH2 and NH respectively, a multiplet at d 7.11­7.77 ppm for aromatic (8H) protons. Data from the elemental analyses were found to be in conformity with the assigned structure of 3. Further, the molecular ion recorded in the mass spectrum is also in agreement with the molecular mass of compound 3. The title compounds were synthesized by cyclization of 3-(3-ethylphenyl)-2-hydrazino-3H-quinazolin-4-one (3) with various one-carbon donors. The 3-(3-ethylphenyl)-2-hydrazino-3H-quinazolin-4-one was synthesized from 3-ethyl aniline by a new innovative route (Scheme 1). The title compounds 4a-j were obtained in fair to good yields through cyclization of 3 with a variety of one-carbon donors such as formic acid, acetic acid, propionic acid, butyric acid and chloroacetyl chloride at reflux. The cyclic product formation is indicated by the disappearance of peaks due to NH and NH2 of the starting compound at 3390­3225 cm­1 in IR spectra of all compounds 4a-e. The 1H NMR spectra of 4f-j showed the absence of NH and NH2 signals. Compounds 4f-j were obtained by the displacement of chlorine of compound 4e with various alicyclic amines such as pyrro103 lidine, piperidine, morpholine, piperazine and 4-methylpiperazine. The IR spectra of compounds 4a-j showed a peak for carbonyl (C=O) around 1680 cm­1. The 1H NMR spectra of compounds 4a-j showed multiplets around d 7.01­8.09 ppm integrating for aromatic protons. Mass spectra of the title compounds are in conformity with the assigned structure and showed molecular ion peaks corresponding to their molecular formula. The M++2 peak was observed in the spectrum of compound 4e, confirming the presence of the chlorine atom in the compound. The relative intensity of this M++2 peak compared to M+ peak is in a ratio of 1:3. The M++2 peak observed in the spectrum of compound 4e disappeared in compounds 4f-j, confirming the displacement of chlorine. In mass spectra of compounds 4a-j, the peak due to 1,2,4-triazolo[4,3-a]quinazoline cation appeared at m/z 168. In addition, a common peak at m/z 144 corresponding to quinazolin-4-one moiety appeared in all mass spectra. Elemental analyses confirmed the elemental composition and purity of the synthesized compounds. Pharmacology Compounds containing the 1,4-disubstituted [1,2,4]triazoloquinazoline ring system (4a-j) were evaluated for their in vivo antihistaminic activity. All the tested compounds were found to exhibit good antihistaminic activity (Table III). Protection data showed that all compounds of the series show significant protection in the range of 70­74 %. Biological studies indicated that different substituents over the first position of the triazoloquinazoline ring exerted varying biological activity. The presence of the methyl group (compound 4b, 74.6 % protection) showed better activity than the unsubstituted comTable III. Antihistaminic and sedative-hypnotic activity of compounds 4a-j CNS depression (%)b 1h 6± 1d 37 ± 2 8 ± 1d 9 ± 2d 11 ± 14 ± 6± 2d 2d 2d 2h 4± 1d 32 ± 2 12 ± 1d 13 ± 2d 15 ± 17 ± 12 ± 2d 2d 2d 3h 4 ± 1d 22 ± 2d 6 ± 2d 9 ± 1d 7 ± 2d 9 ± 2d 6 ± 2d 8 ± 2d 7 ± 2d 9 ± 1d 8 ± 1d 8 ± 1d Compd. Controlc Chlorpheniramine 4a 4b 4c 4d 4e 4f 4g 4h 4i 4j a b Time of onset of convulsion (s) 116 ± 2d Protection (%)a ­ 71 ± 1 72 ± 2 75 ± 2e 74 ± 70 ± 1e 1f 71 ± 2 71 ± 1f 71 ± 2 72 ± 2 73 ± 74 ± 2f 2f 400 ± 10 415 ± 2f 456 ± 3d 445 ± 390 ± 9e 7f 398 ± 7 395 ± 7 403 ± 8 409 ± 7 426 ± 438 ± 6e 5d 8 ± 2d 10 ± 2d 11 ± 10 ± 13 ± 2d 1d 2d 10 ± 1d 11 ± 2d 13 ± 14 ± 12 ± 1d 2d 2d Control: oral dose of 10 mg kg­1 in 1 % CMC. Control: oral dose of 5 mg kg­1 in 1 % CMC. c Control: animals were administered 1 % CMC orally. Significant different relative to chlorpheniramine: d p < 0.0001, e p < 0.001, f p < 0.01. pound (compound 4a, 72.0 % protection). With increased lipophilicity (i.e., ethyl compound 4c, 73.9 % protection) the activity remained but further increase in lipophilicity (i.e., propyl compound 4d, 70.8 % protection) led to a decrease in activity. Replacement of a proton of the methyl group by chlorine (compound 4e, 70.2 % protection) showed a further decrease in activity. Replacement of a proton of the methyl group by alicyclic amines (pyrrolidinyl and piperidinyl compound 4f 70.6 % protection and 4g 71.2 % protection, respectively) showed an increase in activity compared to the chloro substituent. Placement of alicyclic amines with additional hetero atom (morpholinyl compound 4h 71.6 % protection; piperazinyl compound 4i 72.8 % protection and 4-methyl piperazinyl compound 4j 73.5 % protection) led to further increase in activity. As the test compounds could not be converted to water-soluble form, in vitro evaluation for antihistaminic activity could not be performed. The results of sedative-hypnotic activity indicate that all the test compounds exhibited negligible sedation (8­13 %) whereas the reference standard chlorpheniramine maleate showed 30 % sedation. CONCLUSIONS The present study describes the synthesis of a new series of 4-(3-ethylphenyl)-1-substituted-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones (4a-j). The title compounds have exhibited promising antihistaminic activity against histamine-induced bronchospasm on conscious guinea pigs in the in vivo model. Among the series, 4-(3-ethylphenyl)-1-methyl-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-one (4b) was found to be the most active compound. It was more potent than the reference standard chlorpheniramine maleate. Interestingly, compound 4b also showed negligible sedation and could therefore serve as a lead molecule for further modifications to obtain a clinically useful novel class of non-sedating antihistamines. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acta Pharmaceutica de Gruyter

Synthesis and pharmacological investigation of novel 4-(3-ethylphenyl)-1-substituted-4 H -(1,2,4)triazolo(4,3- a ) quinazolin-5-ones as a new class of H 1 -antihistaminic agents

Download PDF
10 pages

Loading next page...
 
/lp/de-gruyter/synthesis-and-pharmacological-investigation-of-novel-4-3-ethylphenyl-1-EfQ8qiJXVG
Publisher
de Gruyter
Copyright
Copyright © 2009 by the
ISSN
1330-0075
eISSN
1846-9558
DOI
10.2478/v10007-009-0003-1
pmid
19304562
Publisher site
See Article on Publisher Site

Abstract

Acta Pharm. 59 (2009) 97­106 10.2478/v10007-009-0003-1 Short communication VEERACHAMY ALAGARSAMY1,* KUNCHU KAVITHA2 MANI RUPESHKUMAR2 VISWAS RAJA SOLOMON3 JAYA KUMAR1 DINAKARAN SATHESH KUMAR4 HEMANT KUMAR SHARMA5 1 Medicinal Chemistry Research Laboratory MNR College of Pharmacy Fasalwadi, Sangareddy-502294, India 2 Bharathi College of Pharmacy Bharathi Nagar, K. M. Doddi­571422 Mandya (Dist), India 3 Medicinal & Process Chemistry Division, Central Drug Research Institute, Lucknow-226001, India 4 Department of Pharmaceutical Chemistry, Nalanda College of Pharmacy Cheralpally, Nalgonda­508001, India 5 Department of Pharmaceutical Chemistry, Patel College of Pharmacy Bhopal, India A series of novel 4-(3-ethylphenyl)-1-substituted-4H-[1,2,4] triazolo[4,3-a]quinazolin-5-ones (4a-j) were synthesized by the cyclization of 3-(3-ethylphenyl)-2-hydrazino-3H-quinazolin-4-one (3) with various one-carbon donors. The starting material, compound 3, was synthesized from 3-ethyl aniline by a new innovative route with improved yield. When tested for their in vivo H1-antihistaminic activity on conscious guinea pigs, all test compounds protected the animals from histamine induced bronchospasm significantly. Compound 4-(3-ethylphenyl)-1-methyl-4H -[1,2,4]triazolo[4,3-a]quinazolin-5-one (4b) emerged as the most active compound of the series and it is more potent (74.6 % protection) compared to the reference standard chlorpheniramine maleate (71 % protection). Compound 4b shows negligible sedation (10 %) compared to chlorpheniramine maleate (30 %). Therefore compound 4b can serve as the leading compound for further development of a new class of H1-antihistamines. Keywords: quinazolin-5-ones, sedation, H1-antihistaminic agents Accepted January 15, 2009 The first generation antihistamines penetrate the blood brain barrier and also possess anticholinergic properties; this has led to the development of a second generation of H1-antagonists such as terfenadine, cetirizine and astemizole (1). A common feature of the first generation compounds includes two aryl or heteroaryl rings linked to an ali* Correspondence; e-mail: drvalagarsamy@gmail.com phatic tertiary amine via the side chain (diphenhydramine and pheniramine) (2). The second generation compounds (terfenadine and cetirizine) contain many of the structural features of the first generation compounds. The real breakthrough of non-sedative antihistamines came in the early eighties of the twentieth century when modern antihistamines were found to exhibit potent antihistaminic activity without sedative effect (3). Condensed heterocycles containing the new generation of H1-antihistamines (loratadine, azelastine and flazelastine) that do not possess the above mentioned pharmacophore for H1-antihistamines paved the way for the discovery of many novel antihistamines, temelastine (4) and mangostin (5). Quinazolines and condensed quinazolines show excellent antihistaminic activity (6, 7). In continuation, we demonstrated (8, 9) the quinazoline derivatives as potent antihistamines with the least sedation. The present work is an extension of our ongoing efforts towards development and identification of new molecules. Therefore we undertook to synthesize a series of 1,2,4-triazolo-4H-[4,3-a]quinazolin-5-ones containing 3-ethylphenyl substituted at position 4 and alkyl/alicyclic amines substituted at position 1. The synthesized compounds were tested for their in vivo H1-antihistaminic activity on conscious guinea pigs. As sedation is one of the major side effects associated with antihistamines, the test compounds were also evaluated for their sedative potentials by measuring the reduction in locomotor activity using an actophotometer. EXPERIMENTAL Melting points were taken in open capillaries on a Thomas Hoover melting point apparatus (Thomas Hoover, USA) and are uncorrected. IR spectra were recorded in film or in potassium bromide disks on a Perkin-Elmer 398 spectrometer (Perkin-Elmer, USA). 1H spectra were recorded on a DPX-300 MHz Bruker FT-NMR spectrometer (Bruker, USA). Chemical shifts were reported as parts per million (d ppm) using tetramethylsilane (TMS) as an internal standard. Mass spectra were obtained on a Jeol-SX-102 instrument (Jeol, Japan) using fast atom bombardment (FAB positive). Elemental analysis was performed on a Perkin-Elmer 2400 CHN analyzer (Perkin-Elmer, USA); the values were found within the acceptable limits of the calculated values (± 0.4 %). Spectral data (IR, NMR and mass spectra) and elemental analysis data are presented in Tables I and II. The progress of the reaction was monitored on ready-made silica gel plates (Merck, Norway) using chloroform/methanol (9:1) as a solvent system. Iodine was used as a developing agent. All chemicals and reagents used in the syntheses were obtained from Aldrich (USA), Lancaster (USA) or Spectrochem (India). They were used without further purification. Syntheses 3-(3-Ethylphenyl)-2-thioxo-2,3-dihydro-1H-quinazolin-4-one (1). ­ A solution of 3-ethyl aniline (0.02 mol) in dimethyl sulfoxide (10 mL) was stirred vigorously. To this, carbondisulphide (1.6 mL) and aqueous sodium hydroxide 1.2 mL (2 mol L­1) were added dropwise during 30 min under stirring. Dimethyl sulfate (0.02 mol) was added gradually keeping the reaction mixture stirred for 2 h. The reaction mixture was then poured into ice water. The solid obtained was filtered, washed with water, dried and recrystallized from Table I. Physical and analytical data of newly synthesized compounds O N O N N 1­3 R R N N N 4a­j Compd. Molecular formula C16H14N2OS C17H16N2OS C16H16N4O C17H14N4O C18H16N4O C19H18N4O C20H20N4O C18H15ClN4O C22H23N5O C23H25N5O Molecular M.p. (oC) Elemental analysis calcd./found (%) massa Yield (%) C H N 282 296 280 290 304 318 332 338 373 387 389 388 402 273­274 80 162­163 89 213­215 81 245­247 81 263­265 70 212­214 77 221­222 76 274­276 71 212­213 78 251­253 73 198­199 77 231­233 78 271­273 79 68.06 68.12 68.89 68.83 68.55 68.62 70.33 70.30 71.04 71.07 71.68 71.62 72.27 72.24 63.81 63.80 70.76 70.72 71.29 71.36 67.85 67.86 68.02 68.09 68.63 68.68 5.00 5.07 5.44 5.40 5.75 5.78 4.86 4.88 5.30 5.23 5.70 5.74 6.06 6.07 4.46 4.45 6.21 6.27 6.50 6.54 5.95 5.91 6.23 6.26 6.51 6.50 9.92 9.93 9.45 9.47 19.99 19.98 19.30 19.34 18.41 18.40 17.60 17.57 16.86 16.84 16.54 16.57 18.75 18.70 18.07 18.09 17.98 17.93 21.63 21.65 20.88 20.83 1 2 3 4a 4b 4c 4d 4e 4f 4g 4h 4i 4j ­SH ­SCH3 ­NHNH2 ­H ­CH3 ­CH2CH3 ­(CH2)2CH3 ­CH2Cl C22H23N5O2 C22H24N6O CH3 NH C23H26N6O ethanol. Methyl anthranilate (0.01 mol) and the prepared N-(3-ethylphenyl)-methyl dithiocarbamic acid (0.01 mol) were dissolved in ethanol (20 mL). To this, anhydrous potassium carbonate (100 mg) was added and refluxed for 23 h. The reaction mixture was cooled in ice and the solid separated was filtered and purified by dissolving in 10 % alcoholic sodium hydroxide solution and reprecipitated by treating with dilute hydrochloric Table II. IR and NMR spectral data of intermediate and newly synthesized compounds IR (KBr) (cm­1) C=O 1692 1692 1680 C=N ­a ­a ­a Compd. 1 2 3 1H NMR (CDCl3), d (ppm) 1.52­1.64 (t, 3H, CH2CH3), 2.43­2.56 (q, 2H, CH2CH3), 7.15­7.79 (m, 8H, ArH), 10.45 (br s, 1H, NH, D2O exchangeable) 1.25­1.38 (t, 3H, CH2CH3), 2.05­2.17 (q, 2H, CH2CH3), 2.46 (s, 3H, SCH3), 7.33­8.05 (m, 8H ArH) 1.33­1.45 (t, 3H, CH2CH3), 2.75­2.89 (q, 2H, CH2CH3) 5.02 (br s, 2H, NH2 D2O exchangeable), 7.11­7.79 (m, 8H, ArH), 9.53 (br s, 1H, NH D2O exchangeable) 1.01­1.15 (t, 3H, CH2CH3), 2.13­2.26 (q, 2H, CH2CH3), 7.01­7.35 (m, 4H, ArH), 7.54 (s, 1H, ArH), 7.73­8.05 (m, 4H, ArH) 4a 4b 4c 4d 1680 1678 1681 1610 1604 1612 1.23 (s, 3H, CH3), 1.42­1.51 (t, 3H, CH2CH3), 2.85­2.97 (q, 2H, CH2CH3), 7.14­7.63 (m, 8H, ArH) 1.13­1.24 (t, 3H, CH2CH3), 1.44­1.54 (t, 3H, CH2CH3), 2.21­2.33 (q, 3H, CH2CH3), 2.62­2.75 (q, 2H, CH2CH3), 7.05­7.65 (m, 8H, ArH) 0.65­0.73 (t, 2H, CH2CH2CH3), 1.08­1.15 (sext, 2H, CH2CH2CH3), 1.34­1.45 (q, 2H, CH2CH3), 2.42­2.55 (t, 3H, CH2CH3), 2.83­2.94 (t, 3H, CH2CH2CH3), 7.21­7.95 (m, 8H, ArH) 1.04­1.15 (t, 3H, CH2CH3), 2.25­2.36 (q, 2H, CH2CH3), 3.15 (s, 2H, CH2), 7.05­7.66 (m, 8H, ArH) 1.01­1.25 (m, 4H, CH2-pyrrolidinyl), 1.43­1.64 (m, 4H, CH2-pyrrolidinyl), 2.43­2.51 (t, 3H, CH2CH3), 2.72­2.83 (q, 3H, CH2CH3), 3.65 (s, 2H, CH2), 7.22­7.84 (m, 8H, ArH) 0.89­1.09 (m, 6H, CH2-piperidyl), 1.42­1.65 (m, 4H, CH2-piperidyl), 2.33­2.45 (t, 3H, CH2CH3), 2.63­2.78 (q, 2H, CH2CH3), 3.45 (s, 2H, CH2), 7.35­7.76 (m, 8H, ArH) 1.21­1.42 (m, 4H, CH2-morpholinyl), 1.75­1.85 (m, 4H, CH2-morpholinyl), 2.13­2.25 (t, 3H, CH2CH3), 2.51­2.64 (q, 2H, CH2CH3), 3.35 (s, 2H, CH2), 7.11­7.75 (m, 8H, ArH) 0.95­1.13 (m, 4H, CH2-piperazinyl), 1.45­1.66 (m, 4H, CH2-piperazinyl), 2.03­2.15 (t, 3H, CH2CH3), 2.63­2.75 (q, 2H, CH2CH3), 3.75 (s, 2H, CH2), 7.35­7.89 (m, 8H, ArH), 9.57 (s, 1H, NH, D2O exchangeable) 1.01­1.25 (m, 4H, CH2-piperazinyl), 1.44­1.65 (m, 4H, CH2-piperazinyl), 2.11­2.36 (t, 3H, CH2CH3), 2.52­2.66 (q, 2H, CH2CH3), 3.05 (s, 3H, CH3), 3.26 (s, 2H, CH2), 7.34­7.87 (m, 8H, ArH) 4e 4f 4g 4h 4i 4j Not applicable acid. The solid obtained was filtered, washed with water, dried and recrystallized from ethanol. 3-(3-Ethylphenyl)-2-methylsulfanyl-3H-quinazolin-4-one (2). ­ Compound 1 (0.01 mol) was dissolved in 40 mL of 2 % alcoholic sodium hydroxide solution. To this, dimethyl sulfate (0.01 mol) was added dropwise under stirring. The stirring was continued for 1 h, the reaction mixture was then poured into ice water. The solid obtained was filtered, washed with water, dried and recrystallized from the ethanol/chloroform (75:25) mixture. 3-(3-Ethylphenyl)-2-hydrazino-3H-quinazolin-4-one (3). ­ Compound 2 (0.01 mol) was dissolved in ethanol (25 mL). To this, hydrazine hydrate (99 %) (0.1 mol) and anhydrous potassium carbonate (100 mg) were added and refluxed for 38 h. The reaction mixture was cooled and poured into ice water. The solid so obtained was filtered, washed with water, dried and recrystallized from the chloroform/benzene (25:75) mixture. 4-(3-Ethylphenyl)-1-subtituted-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones (4a-e). ­ 3-(4-Ethylphenyl)-2-hydrazino-3H-quinazolin-4-one (3) (0.01 mol) and formic acid (25 mL) were print in a round-bottomed flask and refluxed for 36 h, cooled and poured into ice water. The solid obtained 4a was filtered, washed with water, dried and recrystallized from ethanol. Adopting this procedure, compounds 4b-e were also prepared. 4-(3-Ethylphenyl)-1-subtituted-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-one (4f-j). ­ A mixture of 1-chloromethyl-4-(3-ethylphenyl)-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-one (4e) (0.01 mol) pyrrolidine (0.05 mol) and anhydrous potassium carbonate (100 mg) in dioxane (25 mL) was put in a round bottomed flask and refluxed for 39 h, cooled and poured into ice water. The solid obtained 4f was filtered, washed with water, dried and recrystallized from ethanol/benzene (50:50). Implementing this protocol, compounds 4g-j were also prepared. Pharmacology Animals. ­ Antihistaminic activity was evaluated on male Dunkin Hartley guinea pigs (250­300 g), while sedative-hypnotic activity was tested on albino Swiss mice. The animals were maintained in colony cages at 25 ± 2 °C, relative humidity of 45­55 %, under a 12 h light and dark cycle; they were fed standard animal feed. All animals were acclimatized for a week before the experiment. The Institutional Animal Ethics Committee approved the protocol adopted for the experimentation on animals. Antihistaminic activity. ­ A modification of the method of Van Arman (10) was adopted to determine the antihistaminic potential of the synthesized compounds. Six animals were alloted to each group and were fasted for 12 h. The test compounds and reference standard (chlorpheniramine maleate) were administered orally at a dose of 10 mg kg­1 in 1 % CMC (carboxymethylcelluose) and challenged with histamine aerosol (3 mL of 0.2 % aqueous solution of histamine hydrochloride) in a vaponephrin pocket nebulizer sprayed into a closed transparent cage. The respiratory status reflecting the increasing degree of bronchoconstriction was recorded. The time for the onset of convulsions (preconvulsion) was recorded. Animals remaining stable for more than 6 min were considered protected against histamine-induced bronchospasm. An intraperitoneal injection of chlorpheniramine maleate (Avil, India) at a dose of 25 mg kg­1 was given for the recovery of test animals. Sedative-hypnotic activity. ­ Sedative-hypnotic activity was determined by measuring the reduction in locomotor activity using an actophotometer (11, 12). Six albino Swiss mice were allotted to each group. Basal activity score was taken and then compounds 4a-j and standard chlorpheniramine maleate were administered orally at a dose of 5 mg kg­1 in 1 % CMC. Scores were recorded 1, 2 and 3 h after the drug administration. Statistical analysis. ­ Statistical analysis of the biological activity of the synthesized compounds on animals was evaluated using a one-way analysis of variance (ANOVA). In all cases, posthoc comparisons of the means of individual groups were performed using Tukey's test. All values are expressed as mean ± SD (standard deviation). For statistical analysis, the GraphPad Prism 3.0 version was used. RESULTS AND DISCUSSION Chemistry The key intermediate 3-(3-ethylphenyl)-2-thioxo-2,3-dihydro-1H-quinazolin-4-one (1) was prepared by refluxing methyl anthranilate with 3-ethylphenyl isothiocyanate in ethanol. However, the preparation of 3-ethylphenyl isothiocyanate required for the reaction was a tedious, time consuming process and the yield was also low (60 %). An alternate route was attempted to synthesize compound 1. In this route, 3-ethyl aniline was reacted with carbon disulphide and anhydrous potassium carbonate in acetone to give potassium dithiocarbamate, which was methylated with dimethyl sulfate to afford the dithiocarbamic acid methyl ester, which was refluxed with methyl anthranilate to yield 1. This way of synthesizing 1 suffers from the drawbacks such as the multi-step process, prolonged reaction time (37 h) and low yield (30 %). Hence, improvisation was carried out in this method by using aqueous sodium hydroxide (2 mol L­1) instead of anhydrous K2CO3, and dimethyl sulphoxide (DMSO) (Scheme 1) as a solvent instead of acetone. The use of DMSO as the reaction solvent enhanced the rate of reaction and the use of alkali in higher concentration helped prevent hydrolysis of the intermediate, probably due to less solvation. These modifications not only curtailed the reaction time from 37 to 25 h, but also increased the yield from 30 to 80 %. The product obtained was cyclic and not open-chain thiourea. The structure was confirmed by the IR spectrum, which showed intense peaks at 3216 cm­1 for cyclic thiourea (NH), 1692 cm­1 for carbonyl (C=O) and 1210 cm­1 for thioxo (C=S) stretching. 1H NMR spectrum of 1 showed a triplet at d 1.52­1.64 ppm due to the CH3 group, a quartet at d 2.43­2.56 ppm due to CH2 and a multiplet at d 7.15­7.79 ppm for aromatic (8H) protons and a singlet at d 10.45 ppm indicating the presence of NH. Data from the elemental analyses were found to be in conformity with the assigned structure. Further, the molecular ions recorded in the mass spectrum are also in agreement with the molecular mass of compound 1. 3-(3-Ethylphenyl)-2-methysulfanyl-3H-quinazolin-4-one (2) was obtained by dissolving product 1 in a 2 % alcoholic sodium hydroxide solution and methylating with dimethyl sulfate while stirring at room temperature. The IR spectrum of 2 showed disappearance of NH and C=S stretching signals of cyclic thiourea. It showed a peak for carbonyl (C=O) stretching at 1692 cm­1. The 1H NMR spectrum of compound 2 showed a triplet at d 1.25­1.38 ppm due to CH3, a quartet at d 2.05­2.17 ppm due to CH2, a singlet at d 2.46 ppm due to SCH3 and a multiplet at d 7.33­8.05 ppm due to aromatic (8H) protons. Data from the elemental analyses and the molecular ion recorded in the mass spectrum further confirmed the assigned structure of 2. Nucleophilic displacement of methylthio group of compound 2 with hydrazine hydrate was carried out using ethanol as solvent to afford 3-(3-ethylphenyl)-2-hydrazino102 DMSO NH2 S Na N H S DMS N H O SCH3 CS2/NaOH OCH3 EtOH D NH2 O N N 2 EtOH D SCH3 O NaOH/EtOH DMS N H N S 1 OCH3 NH N H Compd. R NH2NH2·H2O O one carbon donors, D N N R N N O N N 3 NHNH2 4a-j 4a: 4b: 4c: 4d: 4e: 4f: 4g: 4h: 4i: 4j: -H -CH3 -CH2CH3 -(CH2)2CH3 -CH2Cl -pyrrolidinyl -piperidinyl -morpholinyl -piperazinyl -4-methyl piperazinyl Scheme 1 -3H-quinazolin-4-one (3). The required long duration of the reaction (38 h) might be due to the presence of the bulky aromatic ring at position 3, which might have reduced the reactivity of the quinazoline ring system at C-2 position. The formation of 3 was confirmed by the presence of NH and NH2 signals at 3390­3225 cm­1 in the IR spectrum. It also showed a peak for carbonyl (C=O) at 1680 cm­1. The 1H NMR spectrum of compound 3 showed singlets at d 2.46 ppm due to SCH3, a triplet at d 1.33­1.45 ppm due to CH3 group, a quartet at d 2.75­2.89 due to CH2, singlets at d 5.02 ppm and 9.53 ppm due to NH2 and NH respectively, a multiplet at d 7.11­7.77 ppm for aromatic (8H) protons. Data from the elemental analyses were found to be in conformity with the assigned structure of 3. Further, the molecular ion recorded in the mass spectrum is also in agreement with the molecular mass of compound 3. The title compounds were synthesized by cyclization of 3-(3-ethylphenyl)-2-hydrazino-3H-quinazolin-4-one (3) with various one-carbon donors. The 3-(3-ethylphenyl)-2-hydrazino-3H-quinazolin-4-one was synthesized from 3-ethyl aniline by a new innovative route (Scheme 1). The title compounds 4a-j were obtained in fair to good yields through cyclization of 3 with a variety of one-carbon donors such as formic acid, acetic acid, propionic acid, butyric acid and chloroacetyl chloride at reflux. The cyclic product formation is indicated by the disappearance of peaks due to NH and NH2 of the starting compound at 3390­3225 cm­1 in IR spectra of all compounds 4a-e. The 1H NMR spectra of 4f-j showed the absence of NH and NH2 signals. Compounds 4f-j were obtained by the displacement of chlorine of compound 4e with various alicyclic amines such as pyrro103 lidine, piperidine, morpholine, piperazine and 4-methylpiperazine. The IR spectra of compounds 4a-j showed a peak for carbonyl (C=O) around 1680 cm­1. The 1H NMR spectra of compounds 4a-j showed multiplets around d 7.01­8.09 ppm integrating for aromatic protons. Mass spectra of the title compounds are in conformity with the assigned structure and showed molecular ion peaks corresponding to their molecular formula. The M++2 peak was observed in the spectrum of compound 4e, confirming the presence of the chlorine atom in the compound. The relative intensity of this M++2 peak compared to M+ peak is in a ratio of 1:3. The M++2 peak observed in the spectrum of compound 4e disappeared in compounds 4f-j, confirming the displacement of chlorine. In mass spectra of compounds 4a-j, the peak due to 1,2,4-triazolo[4,3-a]quinazoline cation appeared at m/z 168. In addition, a common peak at m/z 144 corresponding to quinazolin-4-one moiety appeared in all mass spectra. Elemental analyses confirmed the elemental composition and purity of the synthesized compounds. Pharmacology Compounds containing the 1,4-disubstituted [1,2,4]triazoloquinazoline ring system (4a-j) were evaluated for their in vivo antihistaminic activity. All the tested compounds were found to exhibit good antihistaminic activity (Table III). Protection data showed that all compounds of the series show significant protection in the range of 70­74 %. Biological studies indicated that different substituents over the first position of the triazoloquinazoline ring exerted varying biological activity. The presence of the methyl group (compound 4b, 74.6 % protection) showed better activity than the unsubstituted comTable III. Antihistaminic and sedative-hypnotic activity of compounds 4a-j CNS depression (%)b 1h 6± 1d 37 ± 2 8 ± 1d 9 ± 2d 11 ± 14 ± 6± 2d 2d 2d 2h 4± 1d 32 ± 2 12 ± 1d 13 ± 2d 15 ± 17 ± 12 ± 2d 2d 2d 3h 4 ± 1d 22 ± 2d 6 ± 2d 9 ± 1d 7 ± 2d 9 ± 2d 6 ± 2d 8 ± 2d 7 ± 2d 9 ± 1d 8 ± 1d 8 ± 1d Compd. Controlc Chlorpheniramine 4a 4b 4c 4d 4e 4f 4g 4h 4i 4j a b Time of onset of convulsion (s) 116 ± 2d Protection (%)a ­ 71 ± 1 72 ± 2 75 ± 2e 74 ± 70 ± 1e 1f 71 ± 2 71 ± 1f 71 ± 2 72 ± 2 73 ± 74 ± 2f 2f 400 ± 10 415 ± 2f 456 ± 3d 445 ± 390 ± 9e 7f 398 ± 7 395 ± 7 403 ± 8 409 ± 7 426 ± 438 ± 6e 5d 8 ± 2d 10 ± 2d 11 ± 10 ± 13 ± 2d 1d 2d 10 ± 1d 11 ± 2d 13 ± 14 ± 12 ± 1d 2d 2d Control: oral dose of 10 mg kg­1 in 1 % CMC. Control: oral dose of 5 mg kg­1 in 1 % CMC. c Control: animals were administered 1 % CMC orally. Significant different relative to chlorpheniramine: d p < 0.0001, e p < 0.001, f p < 0.01. pound (compound 4a, 72.0 % protection). With increased lipophilicity (i.e., ethyl compound 4c, 73.9 % protection) the activity remained but further increase in lipophilicity (i.e., propyl compound 4d, 70.8 % protection) led to a decrease in activity. Replacement of a proton of the methyl group by chlorine (compound 4e, 70.2 % protection) showed a further decrease in activity. Replacement of a proton of the methyl group by alicyclic amines (pyrrolidinyl and piperidinyl compound 4f 70.6 % protection and 4g 71.2 % protection, respectively) showed an increase in activity compared to the chloro substituent. Placement of alicyclic amines with additional hetero atom (morpholinyl compound 4h 71.6 % protection; piperazinyl compound 4i 72.8 % protection and 4-methyl piperazinyl compound 4j 73.5 % protection) led to further increase in activity. As the test compounds could not be converted to water-soluble form, in vitro evaluation for antihistaminic activity could not be performed. The results of sedative-hypnotic activity indicate that all the test compounds exhibited negligible sedation (8­13 %) whereas the reference standard chlorpheniramine maleate showed 30 % sedation. CONCLUSIONS The present study describes the synthesis of a new series of 4-(3-ethylphenyl)-1-substituted-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones (4a-j). The title compounds have exhibited promising antihistaminic activity against histamine-induced bronchospasm on conscious guinea pigs in the in vivo model. Among the series, 4-(3-ethylphenyl)-1-methyl-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-one (4b) was found to be the most active compound. It was more potent than the reference standard chlorpheniramine maleate. Interestingly, compound 4b also showed negligible sedation and could therefore serve as a lead molecule for further modifications to obtain a clinically useful novel class of non-sedating antihistamines.

Journal

Acta Pharmaceutica – de Gruyter

Published: Mar 1, 2009

References

  • The pharmacology and use of H1-receptor-antagonist drugs
    F. Simons