Reactivity of 2-Ethoxyquinazolin- 4-yl hydrazine and its Use in Synthesis of Novel Quinazoline Derivatives of Antimicrobial Activity

The reactions of 2-ethoxy-4-hydrazinoquinazoline 2 with diethyl oxalate and ethyl chloroacetate gave 6-ethoxy-2H-[1,2,4] triazino [4,3-c] quinazoline-3,4-dione 3 and 6-ethoxy-2,3-dihydro-4H-[1,2,4] triazino [4, 3-c] quinazolin-4-one 4 respectively. A series of 5-ethoxy-2-X-[1, 2, 4] triazolo [1, 5-c] quinazolines 5a-d was also produced by reacting 2 with the acid chlorides namely: benzoyl, crotonyl, cinnamyl and 2-furoyl chlorides via Dimroth rearrangement. Also, 2 reacted with ethyl chloroformate giving 6. Condensation of 2 with acetone gave Schiff base 7, and with monosaccharides gave the sugar hydrazones 8a-e which was thereafter acetylated giving the corresponding 9a-e. Cyclization of 8a-e by iron(III) chloride gave triazoloquinazolines 10a-e acyclic C-nucleosides which, by acetylation, afforded 11a-e. All products were confirmed by elemental, IR, MS, and 1H-NMR analysis. Products 8-11 were chosen for biological screening test against gram (+ ive) and gram (- ive) bacteria.

Compound 2 reacted with diethyl oxalate and with ethyl chloroacetate in boiling ethanol to giving products 3 and 4 respectively (Scheme 1). The reaction possibly started with a nucleophilic attack of NH2 of hydrazine moiety on C=O of the ester group through a tetrahedral mechanism intermediate to yield a fleeting acyl derivative followed by 1,3-tautomerism and ring closure via SN2 mechanism.
Compound 2 was reacted with acetone affording derivative 7, whose mass spectrum showed a molecular ion peak at m/z 244,246 whereas the 1 NMR spectrum showed a singlet at δ 2.40 ppm characteristic for CH 3 groups of the hydrazone. A number of sugar hydrazones 8a-e were prepared by condensation of compound 2 with equimolar amounts of D-aldohexoses and D-aldopentoses namely: glucose, galactose, mannose, xylose and arabinose, respectively in boiling ethanol and drops of acetic acid as a catalyst (Scheme 3). Their IR spectra revealed characteristic absorption bands at 3459-3135 cm -1 attributed to OH and NH groups. Acetylation of these hydrazones 8a-e by acetic anhydride in pyridine at room temperature afforded the corresponding per-acetyl products 9a-e, whose IR spectra revealed disappearance of the bands of OH groups and appearance of absorption bands in the carbonyl group frequency region at 1711-1725 cm -1 and 1673 -1692 cm -1 due to the OAc and NAc groups, respectively. The 1 H-NMR spectra showed signals corresponding to O-acetyl groups in addition to NAc groups; whereas no signals could be found for NH groups confirming that per-O-and N-acetylation had taken place. The Scheme 1: synthetic pathway for compounds 3 and 4  R C O C l / C H C l 3 / K 2 C O 3 ; R : -P h ; -C H = C H -C H 3 ; -C H = C H -P h ; f u r a n -2 -y l ;  The mass spectral data of 9e showed a molecular ion peak at m/

Scheme 4: MS data interpretation of compound 9a
The oxidative cyclization of the hydrazones 8a-e with ethanolic iron (III) chloride afforded the triazolo[4, 3-a]quinazolines 10a-e. The oxidation must have taken place by an electrophilic attack of the hard acid site of ferric chloride on the hardest basic site of sugar hydrazones 8a-e followed by an elimination of hydrogen chloride and formation of possibly a nitrilimine that undergoes 1,5-electrocyclization to give 10a-e. The IR spectra showed bands at 3240-3488 cm -1 (OH) and the mass spectral data of 10a showed a molecular ion peak at m/z 364 and 366 and an ion peak at m/z 214 and 216 presumably attributable to the triazoloquinazoline ring (Scheme 5).
The 1 H-NMR spectrum of compound 10c showed a doublet at low field at δ 5.22 ppm assigned to H-1, followed by the rest of the alditol-1-yl chain at higher field. The spectrum of 10e is similar, showing a doublet at low field at δ 5.03 ppm for H-1. Acetylation of 10a-e by acetic anhydride in pyridine at room temperature gave polyacetoxyalkyl derivatives 11a-e, whose IR spectra showed only one absorption band in the C=O frequency region (OA). The OAc groups were confirmed by the 1 H-NMR spectra showing singlets at δ 2.03-2.19. The doublets at δ 5.74-6.02 were attributed to H-1. The mass spectra of products 11b and 11d showed molecular ion peaks at m/z 574, 576 and 501, 503 (Scheme 6) which, on combination with the elemental analysis, led to the assignment of their molecular formulas C 26 H 30 N 4 O 11 and C 23 H 26 N 4 O 9 respectively. In addition, the characteristic fragment at m/z 214,216 was shown attributable to the triazoloquinazoline ring.

Antimicrobial Activity
All compounds were screened for their antimicrobial activity. Compounds 8-11 were tested against gram-positive bacteria Staphylococcus aureus, Streptobacillus moniliformis and Bacillus subtillis and gram-negative bacteria E. coli, Streptobacillus moniliformis and Pseudomonas acru-ginosa species applying the agar plate diffusion method. The screening results (Table 1) indicated that all the tested products exhibited antimicrobial activities against one or more type of bacteria. Almost all triazoloquinazoline products 10a-e and 11a-e showed more inhibition against the gram positive bacteria specially Streptobacillus than the gram negative one.

Experimental
All melting points recorded are uncorrected. The IR spectra were recorded on a Pye Unicam SP1200 spectrophotometer using KBr wafer technique. The 1 H-NMR spectra were determined on a Varian FT-200 or Brucker AC-200 MHz instrument using TMS as an internal standard. Chemical shifts (δ) are expressed in ppm. The mass spectra were determined using MP model NS-5988 and Shimadzu single focusing mass spectrometer (70 eV). All the solvents used were of HPLC/AnalaR grade. All reagents were used as received from Alfa Aesar. An emulsion of 4-chloro-2-ethoxyquinazoline 1 (0.01mol) and hydrazine hydrate (0.05 mol) in benzene (15 mL) was stirred for 2h.The benzene-insoluble gum obtained was treated and washed with water, dried and crystallized from ethanol affording reddish brown crystals of product 2. Evaporation of solvent from the benzene-soluble fraction afforded a residue which was rinsed with water and air dried. Crystallization of the residue from absolute ethanol afforded product 2.

Synthesis of 5-ethoxy-2-substituted[1,2,4]triazolo[1,5-c]quinazoline 5a-d.
To a solution of derivative 2 (0.01mol) in dry chloroform (100 mL) containing anhydrous K 2 CO 3 (1g) the acid chloride namely: benzoyl, crotonyl, cinnamyl and furoyl chlorides (0.015 mol) was added slowly. After the addition was complete, the mixture was stirred at room temperature for 30 min and then heated on a steam bath for1h. The mixture was filtered, evaporated and the crude product was collected and crystallized from the proper solvent affording product 5a-d.

2-ethoxy-4-hydrazinoquinazoline Acetone hydrazone 7.
A solution of crude 2 (0.01 mol) in acetone was left to stand for several days when the solvent had evaporated to give a solid from which the hydrazone 7 (80%) was isolated by chromatography on silica gel (30 g, 2.5% absolute ethanol-chloroform

General procedure for the synthesis of sugar (2-ethoxyquinazolin-4-yl) hydrazones 8a-e.
To a suspension of 2-Ethoxy-4-hydrazinoquinazoline 2 (0.01 mol) in ethanol (30 ml), was added a solution of selected sugar (D-glucose, D-galactose, D-mannose, D-xylose and D-arabinose (0.01 mol)) in water (10 ml) and few drops of glacial acetic acid. The mixture was heated under reflux until reaction was judged complete by TLC (2-6 h). The solid product formed upon cooling was filtered off, washed with the minimum amount of ethanol, dried and finally crystallized from ethanol to afford the corresponding hydrazones 8a-e.

Synthesis of per-O-acetylsugar [1-acetyl-1-(2-ethoxyquinazolin-4-yl)] hydrazones 9a-e.
A cold solution of 8a-e (0.02 mol) in dry pyridine (50 mL) was treated with Ac 2 O (50 mL). The mixture was kept overnight at room temperature, with occasional shaking, and then poured onto crushed ice, and the residue was collected by filtration, washed repeatedly with water, dried and recrystallized from ethanol affording product 9a-e .
1- (D-gluco-pentitol-1-yl)-5-ethoxy[1,2,4] A cold solution of 10a-e (0.002 mol) in dry pyridine (10 mL) was treated with Ac 2 O (6 mL), and the mixture was kept overnight at room temperature, with occasional shaking, and then poured onto crushed ice, and the residue was collected by filtration, washed repeatedly with water, dried and recrystallized from ethanol affording product 11a-e.