| Summary: | A series of 3-substituted 6-methoxy-1H-pyrazolo [3,4-b]quinoline derivatives was synthesized by treating 6-methoxy-1H-pyrazolo[3,4-b]quinolin-3-amine (6) with different acid anhydrides including succinic anhydride, maleic anhydride and phthalic anhydride. Also, a series of 3-heteroaryl-2-chloro-6-methoxyquinolines was prepared through 1,3-dipolar cycloaddition of different bi-nucleophiles including hydrazine hydrate, hydroxylamine hydrochloride, thiourea, guanidine hydrochloride, urea and metformin hydrochloride to the chalcone derivative 3-(2-chloro-6-methoxyquinolin-3-yl)-1-(4-methoxyphenyl)prop-2-en-1-one. Structural identifications of all products were reported and the new compounds were screened for their in vitro antimicrobial activity against Streptococcus pneumonia and Bacillus subtilis as examples for Gram-positive bacteria, Pseudomonas aeruginosa and Escherichia coli as examples for Gram-negative bacteria, and Aspergillus fumigatus, Syncephalastrum racemosum, Geotriucum candidum and Candida albicans as representative examples of fungi. The majority of tested compounds showed moderate activities against a wide range of the selected organisms. Among the tested compounds, pyrimidine derivatives 16 and 17 showed the highest antimicrobial activity against gram-positive strains while the highest activity against E. coli as example for Gram-negative strains was observed in the case of 11 and 17. Compounds 14 and 17 were found to be extremely potent against three of the selected fungal strains.
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