Photochemistry of nitro-substituted (E)-2-azachalcones with theoretical calculations and biological activities

Four new stereoselective dimerization products (4a–c, 5) of m- and p-nitro-substituted (E)-2-azachalcones (2 and 3) were synthesized and tested for antimicrobial and antioxidant activities. Compounds 1–3 showed very good antimicrobial activities against all the tested microorganisms, Escherichia coli, Yersinia pseudotuberculosis, Pseudomonas aeruginosa, Bacillus cereus, Listeria monocytogenes, Staphylococcus aureus, Enterococcus faecalis, and Candida albicans. Five of the compounds tested were radical scavengers with 50% scavenging concentration (SC50) values between 0.130 and 2.047 mg/mL. The monomeric o-nitro-substituted (E)-2-azachalcone (1) showed the highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity with the SC50 value of 0.130 mg/mL. Compound 3 was prooxidant and compound 4b was inactive in DPPH test. The higher antimicrobial activity of compound 1 was paralleled with its higher antioxidant activity, which makes it potential agent for the cure of bacterial infections concurrent with oxidative stress.The theoretical calculations based on transition state structures were made to obtain possible photochemical dimerization products of compounds 1–3. The expected dimeric products from calculations coincided with those experimentally produced.