Microwave synthesis and antibacterial activities of some 2-amino-6-(phenylthio)pyridine-3,5-dicarbonitrile derivatives containing 1,3,4-oxadiazole moiety

5-(4-Aminophenyl)-2-thiol-1,3,4-oxadiazole (3) was synthesized via the reaction of carbon disulfide with 4-aminobenzoyl hydrazide in presence of potassium hydroxide in absolute ethanol. Compound 3 was converted to the corresponding diazonium salt which was introduced in coupling reaction with alkaline solution of 2-hydroxybenzaldehyde as coupling reagent to give azooxadiazole derivative (4) containing aldehyde group. The resulting aldehyde (4) was then introduced in condensation reactions with the aromatic Thiophenol derivatives including using microwave irradiation technique in absolute ethanol to produce ten 2-amino-4-(2-hydroxy-5-((4-(5-mercapto-1,3,4-oxadiazol-2-yl)phenyl)diazenyl)phenyl)-6-(phenylthio)pyridine-3,5-dicarbonitrile derivatives (5a-j), respectively in vitro Antibacterial activity of the target compounds were investigated using two types of bacteria, Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative). The results indicated that the newly synthesized 2-amino-4-(2-hydroxy-5-((4-(5-mercapto-1,3,4-oxadiazol-2-yl)phenyl) diazenyl)phenyl)-6-(phenylthio)pyridine-3,5-dicarbonitrile derivatives (compounds 5d and 5f) showed enhanced activity against Gram-negative bacteria when compared with that of the control drug (gentamycin).