Novel biologically active pyridine derivatives: Synthesis, structure characterization, in vitro antimicrobial evaluation and structure-activity relationship

Abstract

The rate of microbial resistance has continued to rise significantly as the availability of new antibiotics has declined. A new series of pyridine and thienopyridine derivatives were designed, synthesized and tested as antimicrobial agents. The reaction of 4-bromo acetophenone and vetraldehyde (3,4-dimethoxy benzaldehyde) in ethanol and sodium hydroxide solution afforded the corresponding chalcone which was used as a suitable precursor to prepare a new series of pyridine derivatives. The treatment of the latter chalcone with 2-cyanothioacetamide afforded the corresponding pyridinethione which was used as a precursor to synthesize the targeted thienopyridine derivatives in good to excellent yield by the reaction with 2-chloro-N-arylacetamide derivatives, α-haloketones, methyl iodide or chloroacetonitrile in one or two steps. The structure of the synthesized compounds was confirmed chemically by their preparations with other pathways and their spectral data. The newly synthesized pyridine and thienopyridine derivatives exhibited good to strong antimicrobial activity against microbial strains E. coli, B. mycoides and C. albicans. With maximal antimicrobial activity against B. mycoides (33 mm) and C. albicans (29 mm), respectively, compounds 12a and 15 demonstrated the highest inhibition zone. Compound 12a prevented the growth of E. coli, at MIC level of 0.0195 mg/mL, and B. mycoides and C. albicans at MIC level below than 0.0048 mg/mL, respectively. Additionally, compound 15 prevented the visible growth of E. coli, B. mycoides, and C. albicans at MIC values of >0.0048, 0.0098, and 0.039 mg/mL, respectively. The relation between the chemical structure of the synthesized pyridine and thienopyridine compounds and their antimicrobial properties was discussed in the SAR study.