Indian Journal of Chemistry Vol. 40B, September 2001 , pp. 8 1 3-816

New antihistaminic agents : Part 6-Synthesis and HI -antihistaminic evaluation of 3- [(N ,N -dialky lamino )alky 1] -6-halo-2-pheny 1.,. 3 ,4-dihydroquinazolin-4(3H)-ones t

S Dev Singh ' , M Bhagavan Raju ' , Rajesh H Bahekar2, K S Rajan2 & A Raghu Ram Rao2* IDepartment of Pharmaceutical Chemistry, V.L. College of Pharmacy, Raichur, 584 10 I, India.

2Medicinal Chemistry Division, University College of Pharmaceutical Sciences, Kakatiya University, Warangal, 506 009, India

Received 2 December /999; accepted (revised) /8 October 2000

Eight new 3-(N,N-dialkylamino)alkyl derivatives of 2-phenyl-3,4-dihydroquinazolin-4(3H)-ones 3a-h have been synthesized as antihistaminic agents. They have been characterized by elemental analyses and spectral (IR, IH NMR and mass) data. The in vitro and in vivo HI-antihistaminic potencies of 3a-h have been evaluated by isolated guinea pig ileum method and histamine chamber method respectively. Among the compounds tested compound 3d is found to be the most potent with the percentage protection (in vivo) 74.77% and IC50 (in vitro) 1 .3 x 10.3 giL.

Quinazolinones are well known for various biological activities. 1 .2 Previously we reported some quinazolinone derivatives as potentially active antihistaminics.3-s In continuation of our work, we report herein the synthesis and antihistaminic activity of some new quinazolinone derivatives 3a-h. Various procedures are found in literature for the synthesis of the quinazoline ring system. Among them, synthesis from 3, I -benzoxazinones is facile and results in higher yields. Synthesis of title compounds 3a-h has been carried out as depicted in Scheme I starting from 3, I -benzoxazinones. The 3, 1 -benzoxazinone was prepared by reported procedures6, which on condensation with various N,N­dialkylaminoalkylamines afforded the title compounds 3 quantitatively .

All of the synthesized compounds were characterized by their physical, analytical and spectral data (Table I). The IR spectra of 3a-h have shown the presence of characteristic absorption peaks 1 670 -1 660 (C=O), 1 590 - 1580 (C=N). The 'H NMR spectra exhibited the expected methylene protons of the side chain (Experimental Section). The mass spectral data indicated stable molecular ion peak for all the compounds and the expected isotopic ion peaks.

Antihistaminic activity The in vitro H ,-antihistaminic activity was carried

out using isolated guinea pig ileum method7•8 and the

tPart of the M. Pharm. Dissertation S. D. Singh, Rajiv Gandhi University of Health Sciences, Bangalore.

x = Br, I; n = 2,3 R = CH3, C2H5, C4H9

Scheme I

details of the procedure have been reported. S The logarithmic doses of the test compounds and their corresponding blockade was graphically presented from which the ICso (the dose corresponding to 50% inhibition of the agonist response) was found out (Table II). Chlorpheniramine maleate was used as standard antihistaminic. It was interesting to observe that all the compounds have shown inhibition to the histaminic contractions. Although some failed to block the response to the agonistic challenge totally, a majority of them could cause 1 00% blockade at higher dose levels. However none of the compounds produced an irreversible blockade. Compound 3d was found to be the most potent one offering ICso of 1 .3xl O-3glL.

For in vivo activity histamine chamber method9.10 was used. Of the series of compounds tested, compOl,mds with three methylene groups (n=3) were found to be more active than those compounds with two (n=2) in general. The increased chain length may be playing a major role in this respect. Compound 3d

8 14 INDIAN J CHEM, SEC. B, SEPTEMBER 2001

Table I-Physical and analytical data of compounds 3a-h Compd R n X Mol. formula m p Yield' Mass Found (Calc.) %

(Mol. Wt.) °C C H N

3a -CH3 3 CI9H:wN3IO 235 87 433 52.57 4.5 1 9.68

[433] (52.66 4.62 9.70)

3b -C2HS 2 C2oiI22N3IO 246 85 447 53.72 5.04 9.59

[447] (53.69 4.92 9.40)

3c -C2HS 3 C2IH24N)IO 232 89 461 54.5 1 5.36 9.05

[461 ] (54.66 5.2 1 9. 1 1 )

3d -C4H9 3 C2sH32N3IO 229 82 5 1 7 57.92 5.93 8.24

[5 17] (58.03 6. 1 8 8. 1 2)

3e -CH3 3 Br C I9H:wN3BrO 169 83 386 59. 1 5 5.3 1 1 0.8 1

[386] (59.07 5. 1 8 1 0.88)

3f -C2Hs 2 Br C2oH22N3BrO 1 97 82 400 59.87 5.43 10.53

[400] (60.00 5.50 10.50)

3g -C2HS 3 Br C2 1H24N3BrO 1 82 8 1 414 60.79 5.77 9.98

[4 14] (60.90 5.80 1 0. 15)

3h -C4H9 3 Br C2SH32N3BrO 175 75 470 63.94 6.59 9.06

[470] (63.83 6.8 1 8.94)

• Recrystallised from cyclohexane : ethyl acetate (2 : 1 )

Table II -Anti histaminic activity of compounds 3a-h Compd R n x in vitro in vivo

ICso' (gIL) Molar Conc. (M) Mean ± S. D. (onset of % Protection convulsions in sec)

3a -CH3 3 1 .6 X 10.3 3 .695 X 1 0-6 955 ± 4.27 73.87

3b -C2HS 2 1 .7 x 10.3 3.803 X 10-6 950 ± 2.38 73.38

3c -C2HS 3 1 .4 x 10.3 3.037 X 10-6 960 ± 5.00 74.61

3d -C4H9 3 1 .3 X 10.3 2.5 15 X 10-6 978 ± 25.8 74.77

3e -CH3 3 Br 1 .6 x 1 0.3 4. 145 X 10-6 948 ± 9.57 72.73

3f -C2HS 2 Br 1 .8 x 10.3 4.500 X 10-6 940 ± 4.78 72.57

3g -C2Hs 3 Br 1.5 x 10.3 3.623 X 10-6 950 ± 9.57 72.97

3h -C4H9 3 Br 1 .4 x 1003 2.979 X 1006 955 ± 5.00 73.38

Control 88.75 ± 4.78

Standards 1 .0 x 10.3 2.567 X 10-6 1 225 ± 26.80 92.80

S Chlorpheniramine maleate was used as standard.

N ICso - inhibitory concentration for 50 % inhibition

Experimental Section was found to exhibit good protection against histamine challenge in guinea pigs, i.e. protection even after 978 sec as against control (88.75 sec).

Further investigations on the possible CNS effects and anticholinergic activity of the test compounds are in progress and the results will be presented elsewhere.

Melting Points were determined in open capillaries using Thermonik Precision Melting Point cum Boiling Point Apparatus, Model C-PMB-2 and are uncorrected. Purity of the compounds were checked by precoated TLC plates (E. Merck Kieselgel 60 F254) . IR spectra were recorded using KBr pellets on a

SINGH et al.: NEW ANTIHISTAMINIC AGENTS: PART 6 8 1 5

Perkin-Elmer 337 Spectrophotometer (vrnax i n cm· I ), IH NMR spectra on a Varian EM-390 90MHz using TMS as internal standard (chemical shifts in � ppm) and mass spectra at (EI-MS) 70 eV on a VG Micromass 7070H instrument. Elemental analyses were carried out using Heraus Carlo Erba 1 1 80 CHN analyzer. Histamine dihydrochloride (used as agonist) was procured from Himedia, Mumbai and chlorpheniramine maleate I.P. (Avil®) from Hoechst, Mumbai was used for the recovery of the test animals after histamine aerosol.

3-(N,N-Dialkylamino)alkyl-6-halo-2-phenyl-3, 4-dihydroquinazolin-4(3H)-one 3a-h: General proce­dure. To a solution of 6-halo-2-phenyl-3 , 1 -benzoxazin-4(3H)-ones (0.01 mole) in dry ethanol (25 mL), N,N-dialkylaminoalkylamine (0.0 1 5 mole) was added dropwise. The reaction mixture was heated under reflux for 2 hr under anhyd. conditions. Excess of the solvent was distilled-off in vacuo and the residue was poured onto crushed ice containing 1 0% HCI with stirring. The resultant product was filtered off, washed extensively with ice cold water, dried and recrystallized from a mixture of cyclohexane and ethyl acetate (2: 1 ) .

3-[2-(N, N-Diethylamino)ethyl]-6-iodo-2-phenyl-3,4-dihydroquinazolin-4(3H)-one 3b: White crystals; Rf : 0.56 (chloroform : methanol, 4.8 : 0.2); IR (KBr): 3262, 1 705, 1 638 (C=O), 1 606, 1 585 (C=N), 108 1 (Ar-I) cm· l ; IH NMR (CDCh): 0 1 . 1 - 1 .3 (t, 6H,CH3-CHr), 2.8-3.0 (q, 4H, CH3-CH2-), 3 .3-3.5 (t, 2H, -CH2-CH2-N-(C2H5)z), 3.9-4. 1 (t, 2H, -CHr CHrN-(C2H5)z), 7.2-8.8 (m, 7H, Aromatic), 8.4 (s, I H, C5-H); MS (mlz, %) : 447 (M+, 1 00%). Anal. Found : C, 52.57; H, 4.5 1 ; N, 9.68. Ca1cd. for C2oH22N3IO : C, 52.66; H, 4.62; N, 9 .70%.

3-[3-(N, N-Dimethylamino)propyl]-6-bromo-2-phenyl-3,4-dihydro- quinazolin-4(3H)-one 3e : White crystals; Rf : 0.48 (chloroform : methanol, 4.8 : 0.2); IR (KBr): 3258, 1 705, 1 646 (C=O), 16 1 1 , 1589 (C=N), 850 cm· l ; IH NMR (CDCh): �1 .7- 1 .9 (pentet, 2H, -CH2-CH2-CH2-N-(CH3)z), 2.9 (s, 6H, -CH3) , 3. 1 -3 .3 (t, 2H, -CHrCHz-CH2-N-(CH3)z), 3 .5-3.7 (t, -CH2-CHrCH2-N-(CH3)z), 7 . 1 -7.8 (m, 7H, Aromatic), 8.3 (s, I H, C5-H); MS (mlz, %) : 386 (M+, 100%). Anal. Found : C, 59. 15 ; H, 5 .3 1 ; N, 10.8 1 . Ca1cd for CI9H2oN3BrO : C, 59.07; H, 5 . 1 8 ; N, 10.88%.

3-[2-(N,N-Diethylamino)ethyl]-6-bromo-2-phenyl-3,4-dihydroquinazolin-4(3H)-one 3f White crystals; Rf : 0.49 (chloroform : methanol, 4.8 : 0.2); IR (KBr): 3260, 1 679 (C=O), 1 6 1 1 , 1 593 (C=N), 1 1 62, 799 cm- I ; IH NMR (CDCh): 0 1 .4- 1 .6 (t, 6H,

CH3-CH2-), 3.0-3.2 (q, 4H, CH3-CH2-), 3 .3-3.5 (t, 2H, -CH2-CH2-N-(C2H5)z), 3 .9-4 . 1 (t, 2H, -CHrCHrN­(C2H5)2), 7 .2-7.9 (m, 7H, Aromatic), 8.3 (s, IH, C5-H); MS (mlz, %) : 400 (M+, 1 00%). Anal. Found : C, 59.87; H, 5 .43; N, 10.53. Calcd. for C2oH25N3BrO : C, 60.00; H, 5.50; N, 10.50%.

Antihistaminic activity Inhibition of histamine-induced isotonic contrac­tions in isolated guinea-pig ileum preparation (in vitro Model)

Guinea pigs of either sex, weighing 250-400g were taken for the experiment. The experimental details have been published and the same method has been followed.5 Taking the logarithmic doses of the test compounds and their corresponding blockade was graphically presented from which the IC50 was found out (Table II). Chlorpheniramine maleate was used as standard antihistaminic agent.

Protection against histamine-induced broncho­spasm on conscious guinea pigs (in vivo Model).

Thirty two healthy adult Hartley guinea pigs of either sex divided into group of 2 animals each weighing around 400 gm, previously fasted for overnight were kept in the histamine chamber, and exposed to aerosol (0.2% aqueous solution of histamine dihydrochloride in a Vaponephrin Pocket Nebulizer) until they collapse. Those that collapse within 2 minutes were revived with fresh air and used for this test. 1 2 hr later, the animals were given an oral dose of test compound suspended in 1 % acacia solution and after 1 hr to allow for absorption, the guinea pigs were exposed to the aerosol. Those that do not collapse within 6 min are deemed protected. Percentage protection has been measured by calculating the time of onset of convulsions (Table II).

Acknowledgement The authors wish to thank the Principals of

University College of Pharmaceutical Sciences, Kakatiya University, Warangal and V L College of Pharmacy, Raichur for providing laboratory facilities and Prof. V. M. Reddy for encouragement.

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8 16 INDIAN J CHEM, SEC. B , SEPTEMBER 2001

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