Synthesis and Anticonvulsant Activity of Some Quinazolin-4-(3H)-one Derivatives

A number of 3-substituted-2-(substituted-phenoxymethyl) quinazolin-4(3H)-one derivatives have been synthesized. Their structures have been elucidated on the basis of elemental analyses and spectroscopic studies (IR, 1H-NMR, MS). A preliminary evaluation of the anticonvulsant properties of the prepared compounds has indicated that some of them exhibit moderate to significant activity, compared to a diazepam standard.

In a previous report [18], compounds IIa,b ( Figure 1) were synthesized and tested for their anticonvulsant activity, which was comparable to that of diazepam. As a result, these compounds are potential leads for further design of more active compounds. In this investigation, side chain contraction of II with different pharmacophores groups was applied to prepare 4a,b, 5a-c, 6, 7a-f, 8a-d and 9a,b, in order to further study the effect of these moieties on the anticonvulsant activity.

Results and Discussion
The synthesis of the title compounds 4a,b, 5a-c was carried out as depicted in Scheme 1. Reaction of the un/substituted phenoxyacetyl chlorides 1a-c with methyl anthranilate (2) in dry ether afforded the corresponding methyl 2-(2-(un/substituted phenoxy)acetamido)benzoates 3a-c, which were reacted with guanidine hydrochloride in n-butanol to give the appropriate 2-(substituted phenoxymethyl)-4oxoquinazolin-3(4H)-carboxamides 4a,b. The structures of 4a,b was established through spectroscopic (IR, 1 H-NMR and mass) as well as elemental analyses data. The IR spectra showed the presence of NH and NH 2 bands (3309-3186 cm -1 ), while the 1 H-NMR spectra showed the disappearance of signals corresponding to the methyl ester protons and the presence of NH proton signals that disappeared on deuterium exchange. The mass spectrum of 4a exhibited the molecular ion peak (M + 328), in addition to fragments at m/z 285 [M-C(=NH)NH 2 ] and 251 [M-C(=NH)NH 2 and Cl]. Reaction of 3a-c with hydrazine hydrate under previously described experimental conditions [18,25] yielded 5a-c. The IR spectrum of 5a showed a dramatic lowering in the carbonyl stretching band to 1681 cm -1 , compared to the parent ester (1704 cm -1 ), as well as the appearance of two strong bands corresponding to asymmetric and symmetric NH 2 stretching (3309, 3268 cm -1 ). The 1 H-NMR spectrum lacked the methyl ester protons and displayed the amino protons (5.28 ppm), while the mass spectrum showed the molecular ion peak of the compound (m/z 267), and peaks at m/z 251(M-NH 2 ) and 145 (M-NH 2 and CH 2 OC 6 H 5 ).
Also, 5 reacted with formaldehyde and amines (namely, 2-N-(chlorophenyl)piperazine and 4methoxyaniline) in a Mannich reaction yielding 9a,b (Scheme 2). The IR showed the disappearance of the NH 2 bands together with the presence of NH band (3220 and 3250 cm -1 for 9a and 9b, respectively). The 1 H-NMR of 9b showed the presence of methoxy protons (3.78 ppm) and the methylene protons (1.7 ppm).
The newly synthesized compounds were screened for their anticonvulsant activity by the Maximal Electroshock (MES) induced seizures method [23,24], wherein electroshocks was applied via ear-lip electrodes using diazepam as a reference drug.
Finally, substitution of the 3-amino group with a 3-(4-(2-chlorophenyl)piperazin-1-yl)methylamino one, as in 9a resulted in a mild increase in the activity, while substitution with 3-(4methoxyphenyl)amino (compound 9b) yielded a remarkable increase in the activity. This result indicated that replacement of the COCH 2 group of 8a by a CH 2 NH group as in 9a decreases the activity.

Experimental
General TLC was perfomed on Fluka silica gel on aluminium TLC plates (0.2 mm thickness) with 254 nm fluorescent indicator using ethyl acetate-petroleum ether (5:5) or (6:4) as eluents. All melting points were determined by the open capillary tube method using an IA 9100MK-digital melting point apparatus and are uncorrected. IR spectra were recorded on a Bruker Vector 22 spectrophotometer. 1 H-NMR spectra were recorded on a Varian Mercury VX-300 NMR spectrometer and they were run at 300 MHz in deuterated chloroform (CDCl 3 ) or dimethylsulfoxide (DMSO-d 6 ); the chemical shifts were quoted in δ units and were related to that of the solvents. Mass spectra were recorded on Finnigan MAT, SSQ 7000, mass spectrometer at 70 eV. Elemental Microanalyses were carried out using Heraew and Vario EL III (elemntar), CHNS analyzer at the Microanalytical Center, Cairo University. Compounds 3b,c [12] and 5b,c [18] were prepared according to the reported methods, while compound 5a was prepared by the method of Shishoo et al. [25] but using methyl 2-(2phenoxyacetamido)benzoate (3a) and n-butanol as a solvent.

Synthesis of 2-((2,4-dichlorophenoxy)methyl)-3-hydroxyquinazolin-4(3H)-one (6):
To a solution of 5c (10 mmol) in 1N hydrochloric acid (20 mL), sodium nitrite solution (10%, 10 mL) was added while stirring in an ice bath. The reaction mixture was stirred for an hour then boiled for 5 minutes, cooled and extracted with methylene chloride (3 x 5 mL). The combined organic layers were collected and dried on anhydrous sodium sulfate. The solvent was removed under reduced pressure and the separated solid was crystallized from ethanol-chloroform (

Anticonvulsant activity
Albino mice (purchased from the National Research Centre Animal House) weighing 20-25 gm were kept under hygienic conditions and on standard laboratory diet (diet composition A. O. A. C.: vitamin mix. 1%, mineral mix. 4%, sucrose 20%, cellulose 0.2%, 5% pure casein 10.5%, starch 54.3%) and water was provided ad libitum. Mice were divided into groups of six animals each. The treated groups received the tested compounds intraperitoneally in a dose of 40 mg/kg body weight in DMSO while the control group received DMSO. The standard group received diazepam in a dose of 5 mg/kg. One hour after the injection, electroshock was applied via ear-lip electrodes and generated by a stimulator (Ugo Basile ECT Unit, Pulse generator 57800-001, delivering an alternating 50 Hz current), the stimulus duration was 0.2 second and the end point was tonic hind limb extension. The maximum electro-shock was determined. Then, % protection as well as % potency were calculated according to the following equations: