Synthesis, antimicrobial activity and molecular modeling study of 3-(5-amino-(2H)-1,2,4-triazol-3-yl]-naphthyridinones as potential DNA-gyrase inhibitors.

Four series of triazolylnaphthyridinone derivatives were synthesized as structural surrogates of nalidixic acid. The targeted derivatives involve: 3-(5-acylamino-2H-1,2,4-triazol-3-yl)-naphtyridin-4-ones 6(a-e); 3-(5-benzylidineamino-2H-1,2,4-triazol-3-yl)-naphthyridin-4-ones 8(a-g) and their 6-bromonaphthyridin-4-one analogs 7(a-e); 9(a-g). The synthesized compounds were evaluated In vitro for their antimicrobial activity against selected resistant strains of G+ve, G-ve, and Mycobacterium phlei. The results revealed remarkable selectivity, of the tested compounds, against Bacillus subtilis and Aggregatibacter actinomycetemcomitans, which are resistant to nalidixic acid. The growth inhibition zones were ranging from 20 to 40 mm at 10 mg/ml and the respective MIC-values ∼3.68-6.3 µM. The results illustrate that the 6-bromo derivatives 7(a-e) and 9(a-g) were more potent than the non-brominated counterparts 6(a-e) and 8(a-e) respectively. Inhibition of E. coli DNA-gyrase supercoiling activity is also evaluated. The 5-(4-methoxybanzamido)-triazolyl-6-bromonaphthyridinone (7e) exhibits IC50 = 1.94 μg/ml, which is comparable to that of nalidixic acid (IC50: 1.74 μg/ml). In addition, the most prominent IC50-values are displayed by: (7a;IC50: 2.77 μg/ml); (8g; IC50: 3.78 μg/ml); and (9d;IC50: 3.21 μg/ml). Molecular docking to the active site of DNA-gyrase cleavage complex of Acinetobacter baumannii (PDB code: 2xkk) co-crystallized with moxifloxacin revealed similar binding modes in addition to new interactions. Assessment of drug-likeness characteristics illustrate that the synthesized compounds showed agreement to Lipinski's and Veper's parameters. The study could offer an exceptional framework that may lead to the discovery of new potent antimicrobial agents.