Synthesis and Analgesic Activity of Some New Pyrazoles and Triazoles Bearing a 6,8-Dibromo-2-methylquinazoline Moiety

2-(6,8-Dibromo-2-methylquinazolin-4-yloxy)-acetohydrazide (4) was prepared by the reaction of 6,8-dibromo-2-methylbenzo-[d][1,3]oxazin-4-one with formamide to afford quinazolinone 2, followed by alkylation with ethyl chloroacetate to give the ester 3. Treatment of ester 3 with hydrazine hydrate and benzaldehyde afforded 4 and styryl quinazoline 5. The hydrazide was reacted with triethyl orthoformate, acetylacetone and ethyl acetoacetate and benzaldehyde derivatives to afford the corresponding pyrazoles 6, 7, 9 and hydrazone derivatives 10a-c. Cyclization of hydrazones 10a-c with thioglycolic acid afforded the thiazole derivatives 11a-c. Reaction of the hydrazide with isothiocyanate derivatives afforded hydrazinecarbothioamide derivatives 12a-c, which cyclized to triazole-3-thiols and thiadiazoles 13a-c and 14a-c, respectively. Fusion of the hydrazide with phthalimide afforded the annelated compound 1,2,4-triazolo[3,4-a]isoindol-5-one (15). The newly synthesized compounds were characterized by their spectral (IR, 1H-, 13C-NMR) data. Selected compounds were screened for analgesic activity.

The synthesis of pyrazolone 6 and pyrazole derivatives 7, as outlined in Scheme 2, involved treating 2-(6,8-dibromo-2-methylquinazolin-4-yloxy)acetohydrazide (4) with triethyl orthoformate and acetyl-acetone, respectively. The IR spectrum of compound 6 showed bands at 3,285, 1,685 cm −1 for NH and C=O functions, while, its 1 H-NMR spectrum showed signals at δ 2.57, 4.83 ppm due to CH 3 and saturated CH in the pyrazolone ring, in addition to a doublet signal at δ 7.50 ppm for the pyrazolone CH=N. The 13 C-NMR spectrum of compound 6 gave signals at δ 22.4 and 82.2 ppm characteristic for CH 3 and OCHCO groups. The structure of compound 7 was corroborated by IR, 1 H-, 13  Treatment of compound 4 with p-substituted benzaldehyde in absolute ethanol afforded benzylidine hydrazide derivatives 10a-c, which were cyclized in the presence of thioglycolic acid to obtain thiazolidine derivatives 11a-c, respectively (Scheme 2). The structure of compounds 10a-c was characterized by the presence of bands between 3,280-3,290 and 1,680-1,685 cm −1 for the amide groups NH and C=O functions. The 1 H-NMR spectra of 10a-c showed a singlet signal at δ 4.95 ppm characteristic for OCH 2 CO, in addition, the important signal at δ 10.2 ppm for the CH=N of the Schiff's base. The signals in the 13 C-NMR spectra of compounds 10a-c confirmed the structures and are mentioned in the Experimental section. Compounds 11a-c showed in their 1 H-NMR spectra characteristic signals at δ 2.85-2.95, 3.67-3.69, and 4.89-4.98 ppm attributed to the CH 3 , CH 2 S and CH 2 O groups, respectively. In addition, signals appearing at δ 5.79-5.92 ppm correspond to the CHAr group in the thiazole ring. The IR spectra of compounds 11a-c showed absorption bands at 3,285-3,310, 1,690-1,695 and 1,680-1,685 cm −1 for NH and 2 C=O groups, while the 13 C-NMR spectrum of compound 11b showed chemical shift signals at δ 23.3, 39.4, 57.7 and 61.9 ppm characteristic for CH 3 , CH 2 S, NCS and CH 2 O groups which confirmed the thiazole ring formation in 11a-c.
Ethyl acetoacetate The new triazole and thiadiazole derivatives 13a,b and 14a,b were obtained from the reactions of the starting hydrazide 4. Reaction of compound 4 with phenyl and cyclohexyl isothiocyanate gave hydrazinecarbothioamide derivatives 12a,b, which was followed by their cyclization using 5% Na 2 CO 3 solution to form 13a,b and with conc. H 2 SO 4 to give 14a,b, as reported in the literature [38] (Scheme 3). Compounds 12a,b were identified by the presence of bands in their IR spectra at 1,235 and 1,220 cm −1 for a C=S group. The structures of 12a,b were also conformed on the basis of their 1 H-NMR spectra and elemental analysis data. The structures of 13a,b were deduced from their correct IR, 1 H-, 13 C-NMR and elemental analysis data. The 1 H-NMR spectrum of compound 13a, for example, showed signals at δ 2.56, 4.95, 13.35 ppm for the CH 3 , CH 2 O and SH groups, while in 13b a multiplet signal at δ 1.22-1.95 ppm for the cyclohexane ring was seen, in addition to signals at 2.51, 4.95 and 13.38 ppm characteristic for CH 3 , CH 2 O and SH groups. In compounds 14a and 14b, the IR spectra gave the absorption bands at 3,280 and 1,618-1620 cm −1 for the NH and C=N groups in the thiadiazole ring. The 1 H-NMR spectrum of compound 14a showed signals at δ 2.56, 4.01 and 4.85 ppm for the CH 3 , NH and CH 2 O groups, in addition to signals at δ 6.50-8.38 for the seven protons of the aromatic ring. The 1 H-NMR spectrum of compound 14b showed signals at δ 1.22-1.95 ppm for the cyclohexane ring, in addition to signals at δ 2.56, 4.08 and 4.98 ppm characteristic for CH 3 , NH and CH 2 O groups. The 13 C-NMR spectra for 13a,b and 14a,b were used to assign the structures. Our research work was finally extended to study the fusion of starting hydrazide 4 with phthalimide to afford 3- The IR spectrum of 15 gave absorption bands at 1,686 and 1,618 cm −1 for C=O and C=N groups. Its 1 H-NMR spectrum showed signals at δ 2.57 and 4.98 ppm for the CH 3 and CH 2 O groups, in addition to a multiplet signal in the aromatic region at δ 7.50-8.35 ppm characteristic of six aromatic protons. Its 13 C-NMR spectrum showed signals at δ 23.2 and 61.9 ppm for the CH 3 and CH 2 O groups, in addition to 17 lines in the sp 2 region which are characteristic for the Ar-C, 4 C=N and C=O groups. The suggested mechanism for formation of compound 15 is given in Scheme 4.

Analgesic Activity
Analgesic activity was examined by using the hot-plate test protocol [40,41]. Sixty Webster mice of both sexes weighting 20-25 g are used for study. All animals were fed diet in pellets following standard good laboratory practices. Mice were maintained under 12 h light/dark cycles with controlled temperature (22 °C). Experiments were performed in accordance with the standard institutional ethical guidelines. After incubation period (one weak) mice were classified into ten groups. One group as negative control received saline, the second group received vehicle (acacia gum) and the third group received valdecoxib (g) as a reference drug, while the other groups received the nine test compounds by subcutaneous infusion (SC administration). Mice were dropped gently in a dry glass beaker of 1 dm 3 capacity maintained at 50-50.5 °C. Normal reaction time in seconds for all mice was determined at time intervals of 10, 30, 60 and 120 minutes, this is the interval extending from the instant the mouse reaches the hot beaker till the animals licks its feet or jump out the beaker (dose 5 mg/kg) [39]. The relative potencies to valdecoxib (g) were then determined (Table 1).

Results
All the tested compounds exhibited more potent analgesic activity than valdecoxib(g) as a reference drug (Table 1). Compounds 7, 13a, 13b, 14a and 14b showed more than twice the activity of Valdecoxib(g) after two hours.

Experimental
Melting points are uncorrected and were recorded in open capillary tubes on a Stuart SMP3 melting point apparatus. Infrared spectra were recorded on a FTIR 1600 spectrophotometer using KBr discs. 1 H and 13 C-NMR spectra were measured on an AC 250 MHz spectrometer. All chemical shifts were reported as δ (ppm) scale using TMS as the standard and coupling-constant values are given in Hz. The solvent for NMR spectra was deuterodimethylsulfoxide. The microanalysis results were within ±0.3% of the calculated values. The pharmacological study was carried out at the National Research Center (Center of Excellence for Advanced Sciences, Cancer Biology Research Laboratory). [1,3]oxazin-4-one (1). 3,5-Dibromo-2-acetamidobenzoic acid (3.50 g) in acetic anhydride (20 mL) was heated on a water bath for 1.5 h, and then left to cool at room temperature to give a pale yellow powder, which was crystallized from ethanol. Yield 95%; m.p.: 140-142 °C. IR    (6). A mixture of 4 (10 mmol) and triethyl orthoformate (16 mL) with a few drops of acetic acid was refluxed for 2 h. After cooling the reaction mixture was poured onto water. The solid obtained was filtered off, dried and crystallized from ethanol to give colorless crystals. Yield 95%; m.p.  (7). A mixture of 4 (10 mmol) and acetylacetone (10 mmol) in acetic acid (10 mL) was refluxed for 6 h. After cooling, the reaction mixture was poured onto ice-water. The colorless powder obtained was crystallized from ethanol. Yield 80%; m.  (8). A mixture of 4 (10 mmol) and ethyl acetoacetate (10 mmol) in acetic acid (10 mL) was refluxed for 5 h, cooled and the reaction mixture was poured onto ice-water to give a colorless powder which was crystallized from ethanol/acetic acid. Yield 75%; m.  (9). A solution of 8 (10 mmol) in sodium hydroxide (10%, 20 mL) was boiled under reflux for 6 h, then the reaction mixture was poured onto ice-water and neutralized with dilute HCl. The solid obtained was collected by filtration, washed with water and crystallized from ethanol. Yield 68%; m.

General Procedure for the Synthesis of Compounds 10a-c
A mixture of 4 (10 mmol) and benzaldehyde derivatives (10 mmol) in absolute ethanol (10 mL) and a few drops of acetic acid was refluxed for 10 h, and the reaction mixture left to cool. The colorless solid was filtered off, and crystallized from ethanol/acetic acid.

General Procedure for the Synthesis of Compounds 11a-c
A mixture of 10a-c (10 mmol) and thioglycolic acid (10 mmol) in dry pyridine (10 mL) was refluxed for 6 h, cooled, and the reaction mixture was poured onto cold dil. HCl. The solid obtained was filtered off, and crystallized from ethanol.

General Procedure for the Synthesis of 13a,b
Compounds 12a,b (1.0 g) were refluxed in 5% Na 2 CO 3 solution (10 mL) for 5 h. The mixture was left to cool, filtered, and the filtrate was acidified with dil. HCl. The solid obtained was filtered off, and crystallized from ethanol to give colorless crystals.