Synthesis of N-alkyl derivatives and photochemistry of nitro (E)-3-azachalcones with theoretical calculations and biological activities

Three new N-alkyl substituted nitro (E)-3-azachalconium bromides (4–6) and two new stereoselective dimerization products (7 and 8) of o-, m-, and p-nitro substituted (E)-3-azachalcones were synthesized and tested for antimicrobial and antioxidant activities. Compounds 4–6 showed very good antimicrobial activities against Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, Staphylococcus aureus, Bacillus cereus, and Candida tropicalis and no activity against Klebsiella pneumoniae and Yersinia pseudotuberculosis. The monomers of o-, m-, and p-nitro substituted (E)-3-azachalcones (1–3) and their N-alkyl derivatives (4–6) showed good DPPH radical scavenging activity with IC50 values in the range of 0.25–0.90 mg/mL. The dimerization product 8 showed the highest activity among the eight compounds synthesized, while compound 7 was inactive in DPPH test. Compounds 4 and 8 showed similar antioxidant activity as the standard antioxidants Trolox® and Vitamin C.The possible photochemical dimerization products of compounds 1–3 were calculated theoretically based on transition state structures. The experimentally obtained β-truxinic type dimers were also the expected products from transition state energy calculations.