DESIGN , SYNTHESIS AND EVALUATION OF SOME NOVEL 3-ALLYL-6-IODO-2-SUBSTITUTED THIOQUINAZOLINONE DERIVATIVES FOR ANTICONVULSANT ACTIVITY BY

The urgent demand for the development of new antiepileptic drug with a better efficacy inspired us to design and synthesize a new derivatives of the fused heterocyclic analogs 3-allyl6-iodo-2-(substituted thio)quinazolin-4(3H)-one that prepared and evaluated for their anticonvulsant activity. Compounds 10, 11, 12, 13, 14 and 22 were found to be the most active anticonvulsant of this series. The achieved results proved that the distinctive compounds could be valuable as a model for future devise, acclimatization and investigation to construct more active analogues.


Introduction
Epilepsy is one of the most common neurological disorders, affecting about 1% of the world's population.Much efforts devoted in the recent years for the development of novel therapeutics resulted in the availability of several newer drugs as promising anticonvulsants (Stefan, H.;Feuerstein, T, 2007 , Donner, E. J.;Snead, O. C., 2006).However, the currently available anticonvulsants are effective in reducing the severity and number of seizures in less than 70% of patients.Moreover, their usage is associated with undesirable numerous side effects (Greenwood, R. S., 2000, Namara, M., et al, 2001, Löscher, W.;Schmidt, D., 2002, Bialer, M., et al, 2004).Therefore, continued search for safer and more effective anticonvulsants is urgently necessary.

Experimental
All melting points shown in (table 1) were taken in open capillaries and are uncorrected.
The infrared spectra were recorded on FT/IR-JASCO 4100 using KBr disc technique.
Microanalytical data were conducted on a Perkin-Elmer 2408 analyzer, results are within ± 0.4% of the theoretical values, Thin layer chromatography was performed on Merk 5x10 cm plates, percolated with silica gel GF254 using (EtOAc, hexane 1:10) as solvent system and short wavelength UV light for visualization.All fine chemicals and reagents used were purchased from Aldrich chemical Co. U.S.A. 1 HNMR was recorded on a Bruker 500 MHz spectrophotometer; Chemical shifts are in  (ppm) values downfield from Tetramethyl Siloxane as an internal standard. 13C NMR was recorded on a Bruker 125 MHz spectrophotometer.The mass spectra were measured on Waters Micromass (Water AQUITY UPLC System LCT Premier XE Serial no: KE468).A preliminary screening of the anticonvulsant activity of the study compounds has indicated that some of them exhibit significant activity compared to phenobarbitone as standard drug.The starting material 2-amino-5-iodobenzoic acid (2) was synthesized in 70% yield by adapting a reported procedure (Klemme C. J. and Hunter J. H.1940).

Materials and method
The compounds were tested against pentylenetetrazol-induced convulsions following the method reported by (Soaje-Echaque E, and Lim RKS, 1962) using phenobarbitone sodium as reference drug.Swiss male albino mice (weigh 20-25 g) are randomly divided into 54 groups, 6 mice per each.The test 18 compounds were suspended in saline solution using few drops of tween-80 in a dose of 200, 400 and 800 mg/kg.The test compounds were injected orally using same dosing volume of 0.33 ml.Phenobarbitone sodium (standard anticonvulsant), was given in doses of 6.25, 12.5 and 25 mg/Kg using the same dosing volume.Pentylenetetrazol (100 mg/Kg) was injected i.p. one hour post test compounds or standard injection.The animals were observed for 2 hours.The animal that showed no tonic convulsions within 1 hour after pentylenetetrazol injections were considered to be protected, the percentage protection was calculated per each dose, effective dose (ED 50 ) that protect 50% of animals against pentylentetrazol induced convulsion was then calculated using INSTAT 2 program (philadelphia).The relative potency of the test compounds to phenobarbitone sodium were calculated and used for comparison between compounds under test as shown in table 2.

Conclusion
The present study, new derivatives of 4(3H)-quinazolinones were synthesized and evaluated for their anticonvulsant activity in mice.The results of this study demonstrated that some 3-allyl-6-iodo-2-(substituted thio)quinazolin-4(3H)-one derivatives possess a good anticonvulsant activity, specially, compounds 10, 11, 12, 13, 14 and 22 were equipotent regarding their anticonvulsant potency as they induced 50% protection at dose level of 200 mg/kg.Also, compounds 8, 9, 16, 17, 18 and 19 were equipotent regarding their anticonvulsant potency as they induced 50% protection at dose level of 400 mg/kg.Furthermore, compounds 4, 16 and 21 were equipotent regarding their anticonvulsant potency as they induced 50% protection at dose level of 800 mg/kg.The obtained results showed that compounds 10, 11, 12, 13, 14 and 22 could be useful as a template for future design, modification and investigation to produce more active analogs.

Results and Discussion
Chemistry 5-Iodo-2-aminobenzoic acid (2) was prepared according to a reported procedure (Klemme C. J. and Hunter J. H.1940)

Anticonvulsant activity
The anticonvulsant activities of the new synthesized compounds were evaluated by the use of standard techniques (Krall, R. L, et al, 1987, Poter, R. J, et al, 1984).The preliminary screening was performed at 200-800 mg/kg of all synthesized compounds (4-22) by using of pentylenetetrazole (PTZ) induced seizure as a chemical induction method to generate the convulsion (Vogel, H. G., 2002).
The initial anticonvulsant evaluation showed that compound 20 are inactive; however compounds 10, 11, 12, 13, 14 and 22 were the most active anticonvulsant agents, that caused 50% protection in a dose of 200 mg/Kg body weight while compounds 8, 9, 15, 17, 18 and 19 were moderate activity as anticonvulsant agents caused 50% protection in a dose of 400 mg/Kg, while, compound 2 exhibit 50% protection in a dose between 400 and 800 mg/Kg.On the other hand, compounds 4, 16 and 21 were the least active anticonvulsant caused 50% protection in a dose of 800 mg/Kg; the compound 6 exhibited 16.6 % protections at 800 mg/Kg in comparison to phenobarbitone as standard drug (table 2).

Table 2 :
Screening of anticonvulsant activity of the newly synthesized compounds.