Emerging Piperazine Derivatives: Synthesis, Characterization, Biological Evaluation, Molecular Docking, and ADMET In...

Antimicrobial resistance (AMR) is a major global concern, with pathogens such as E. coli, B. subtilis, P. aeruginosa, and S. aureus showing increasing resistance to conventional antibiotics. Piperazine, a six-membered heterocyclic scaffold, is widely used in drug design due to its flexibility and diverse biological activities.

A new series of piperazine derivatives was synthesized with aromatic and heterocyclic substituents. The compounds were characterized using spectroscopic and physicochemical techniques. Their antibacterial activity was evaluated in vitro against Gram-positive and Gram-negative bacteria using the cup-plate method, with ciprofloxacin employed as the standard reference drug. Molecular docking studies and in silico ADME/Tox analyses were performed to assess protein binding, pharmacokinetic properties, and toxicity. Based on the results, a structure-activity relationship (SAR) analysis was also carried out.

Among the synthesized derivatives, compound 13 exhibited the most potent broad-spectrum antibacterial activity, showing maximum inhibition against Bacillus subtilis (21.3 mm) along with notable activity against Escherichia coli and Staphylococcus aureus. Molecular docking studies revealed strong binding affinity toward DHFR from S. aureus (-10.60 kcal/mol) and ankyrin repeat protein from B. subtilis (-9.02 kcal/mol). Additionally, in silico ADME/Tox predictions suggested favorable oral bioavailability, low toxicity risk, and minimal inhibition of CYP enzymes. The SAR analysis showed that piperazine derivatives containing well-placed electron-withdrawing groups and balanced physicochemical properties displayed improved antibacterial activity, with compound 13 emerging as the most potent due to its strong molecular interactions.

SAR analysis indicated that electron-withdrawing substituents on the piperazine core enhanced antibacterial potency. The combination of structural modification, strong protein binding, and favorable pharmacokinetic properties explains the superior activity of compound 13.

Compound 13 emerges as a promising broad-spectrum antibacterial agent. The study demonstrates the potential of SAR-guided piperazine derivatives for developing novel antibacterial therapeutics and supports further in vivo evaluation and structural optimization.