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Treatment of 2,3-diaryloxirane-2,3-dicarbonitriles 1a-c with different nitrogen nucleophiles, e.g., hydrazine, methyl hydrazine, phenyl hydrazine, hydroxylamine, thiosemicarbazide, and/or 2-amino-5-phenyl-1,3,4-thiadiazole, afforded pyrazole, isoxazole, pyrrolotriazine, imidazolothiadiazole derivatives 2-5, respectively. Reacting pyrazoles 2a-c with aromatic aldehydes and/or methyl glycinate produced Schiff's bases 7a-d and pyrazolo[3,4-b]-pyrazinone derivative 8, respectively. Treating 7 with ammonium acetate and/or hydrazine hydrate, furnished the imidazolopyrazole and pyrazolotriazine derivatives 9 and 10, respectively. Reaction of 8 with chloroacetic acid and/or diethyl malonate gave tricyclic compound 11 and triketone 12, respectively. On the other hand, compound 1 was reacted with active methylene precursors, e.g., acetylacetone and/or cyclopentanone producing adducts 14a,b which upon fusion with ammonium acetate furnished the 3-pyridone derivatives 15a,b, respectively. Some of newly synthesized compounds were screened for activity against bacterial and fungal strains and most of the newly synthesized compounds showed high antimicrobial activities. The structures of the new compounds were elucidated using IR, 1 H-NMR, 13 C-NMR and mass spectroscopy.

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The present work describes convenient synthesis of the novel Schiff bases 5a and b by reacting phthalazinones 4a and b with 4-methoxybenzaldehyde Reaction of the Schiff bases with phenylisothiocyanate afforded diazetidine derivatives 7a and b. Also, compounds 4a and b reacted with 2-bromoglucoside tetraacetate giving peracetylated N-glycosides 6a and b, which were deacetylated to afford N-glycosylated phthalazinones 8a and b. On the other hand, when compound 3 was treated with POCl 3 /PCl 5 and/or ethyl chloroacetate, chlorophthalazine and ethyl acetate derivatives 9 and 10 were obtained, respectively. Hydrazinolysis of compounds 9 and 10 produced the hydrazino and hydrazide derivatives 11 and 12, respectively. When compound 11 reacted with 2-furanaldehyde, acetic anhydride, and/or carbon disulphide, it gave compounds 13-15, respectively. Treatment of the hydrazide 12 with aromatic aldehydes, acetic anhydride, ethyl acetoacetate, acetyl acetone, ammonium thiocyanate, and/or phthalic anhydride furnished compounds 17-21. Meanwhile, reacting Schiff base 22 with the chlorophthalazine derivative 9 produced compound 23, which on treatment with furoyl chloride produced compound 24. The structures of the novel compounds were confirmed by IR, 1 H-NMR, 13 C-NMR, MS, and elemental analysis. The newly synthesized compounds were tested against Bacillus subtilis and Staphylococcus aureus as Gram-positive bacteria, Escherichia coli and Pseudomonas aurignosa as Gram-negative bacteria, and Candida albicans and Aspergillus niger as fungi strains. Compounds 5a and b, 23, and 24 showed greater antimicrobial activity than the stranded compounds, suggesting that they could be considered as promising antimicrobial agents.Key words phthalazin-1-one; N-glycosylated phthalazinone; Schiff base; diazetedine; antimicrobial activity Phthalazines as N-heterocycles have received considerable attention in the literature as a consequence of their role as pharmacophore.1,2) Recently, they are derived from a wide range of biologically active natural products, troponoid family.3) A novel series of N-substituted-4-phenyl/benzylphthalazin-1-ones, phthalzine-1,4-dione showed antitumor activity. were prepared from the corresponding phthalazinones. Moreover, many substituted and fused phthalazine and phthalzinone derivatives exhibited antimicrobial activity. 23-26)On the basis of the above findings and in continuation of our research interest in the synthesis of novel biologically active heterocycles, [27][28][29][30][31] and with the aim of preparing new derivatives of phthalazine with potential pharmacological activity, we report here the synthesis of novel Schiff bases containing phthalazine moiety, phthalazinone and fused phthalazine derivatives, followed by evaluation of their antimicrobial activity against different strains of bacteria and fungi, where most of synthesized compounds exhibited a moderate to a strong antimicrobial activities. Some of the tested compounds showed antimicrobial activity higher than the reference compounds. Results and D...