Dual Inhibitory Activity of 1-ethyl-3-(4-(hydrazinecarbonyl)-phenyl)urea Derivatives Against DNA Gyrase and Topoisomerase IV of Streptococcuspneumoniae as Antibacterial Agents

Introduction: DNA gyrase and topoisomerase IV (Topo IV) are essential bacterial enzymes absent in higher eukaryotes, making them attractive antibacterial drug targets. The rising prevalence of multidrug-resistant Streptococcus pneumoniae underscores the urgent need for novel therapeutic agents targeting these enzymes. Methods: We designed fifteen novel 1-ethyl-3-(4-(hydrazinecarbonyl)-phenyl)urea derivatives using an in silico approach, followed by chemical synthesis and structural characterization (¹H NMR, ¹³C NMR, HRMS). The compounds were evaluated for inhibitory activity against S. pneumoniae DNA gyrase, Topo IV, and their ATPase domains, along with antibacterial activity (MIC assay) and cytotoxicity in HepG2 cells. Results: All synthesized compounds inhibited the tested enzymes, with compounds 18GP06-15 and 18GP06-08 showing the most potent and balanced dual inhibition (IC₅₀ = 0.511 and 0.555 μM against DNA gyrase; IC₅₀ = 9.24 and 8.64 μM against Topo IV). These compounds also exhibited strong activity against Gyrase B ATPase (IC₅₀ = 0.49 and 0.51 μM) and moderate inhibition of Topo IV ATPase (IC₅₀ = 3.12 and 3.99 μM). Antibacterial assays revealed MIC values ranging from 1.1 to 7.8 μg/mL, with 18GP06-15 being the most potent (MIC = 1.1 μg/mL), comparable to doxycycline (MIC = 1 μg/mL). None of the compounds showed significant cytotoxicity against HepG2 cells (IC₅₀ = 63.11–67.83 μM) compared to cisplatin (IC₅₀ = 6.41 μM). Discussion: The study demonstrated that ethylurea–hydrazine hybrids effectively inhibit both DNA gyrase and Topo IV, suggesting potential as dual-target antibacterial agents. Structure– activity relationship (SAR) analysis indicated that aliphatic linkers at the R position enhanced potency compared to aromatic substituents. Compounds 18GP06-15 and 18GP06-08 emerged as promising leads, showing strong enzyme inhibition, favorable antibacterial activity, and minimal cytotoxicity. Conclusion: Compounds 18GP06-15 and 18GP06-08 exhibited potent dual inhibitory activity against S. pneumoniae DNA gyrase and Topo IV, with low cytotoxicity. These findings support their potential as lead candidates for further optimization in the development of novel antibacterial agents.