Synthesis and Evaluation of Antimicrobial Activity of New Imides and Schiff Bases Derived from Ethyl -4-Amino Benzoate

Abstract

A series of disubstituted 1,3,4-oxadiazole derivatives, including imides and Schiff bases, was achieved from the starting material, ethyl-4-aminobenzoate, which was converted to the corresponding 4-aminobenzohydrazide (1), by its reaction with hydrazine hydrate in absolute ethanol. Two oxadiazole parent nuclei had been synthesized from (1), the first nucleus 5-(4-aminophenyl)-1,3,4-oxadiazol-2-amine(2), and the second is 5-(4-aminophenyl)-1,3,4-oxadiazole-2-thione (3). Compound (2) Obtained from stirring methanolic solution of (1) with cyanogen bromide (CNBr) and sodium bicarbonate (NaHCO3) at RT. While compound (3) was synthesized by refluxing of (1) with CS2 in the presence of (KOH), the produced potassium salt of hydrazide underwent cyclization by acidification with 10% HCl. Meanwhile, the cyclic imides derivatives (4-6) and (10-12) were synthesized by thermal fusion of (2) or (3) with acid anhydrides, While Schiffʼs bases derivatives (7-9) and (13-15) were synthesized by a conventional method involved refluxing of (2) or (3) with different aromatic aldehydes, in acidic medium (using glacial acetic acid). The new derivatives had been tested against three Gram-positive bacteria (Staphylococcus aureus, Micrococcus luteus, and Bacillus pumilus), and two Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli),and two fungal species: (Saccharomyces cerevisiae and Candida albicans). Among the synthesized derivatives, compound (15) displayed a moderate to potent antibacterial activity, against different (Gram- positive and Gram- negative) bacteria, and also showed a slight to moderate antifungal activity.