Ferrocenyl-Based Acetylaniline Derivatives as Novel DNA Gyrase Inhibitors: Integrated Experimental and Computational Insights for Antibacterial Drug Design

Abstract

This thesis presents the design, synthesis, physicochemical characterisation, and comprehensive in silico evaluation of a series of ferrocenyl acetylaniline derivatives (FcMe2Ac, FcMe3Ac, and FcMe4Ac), with particular emphasis on elucidating the relationships between molecular structure, electronic properties, and interaction behaviour toward bacterial DNA gyrase, a key enzymatic target in antibacterial drug discovery. The target compounds were synthesised via a nucleophilic substitution strategy, yielding the desired regioisomers in moderate to high yields (48–80%) with good reproducibility. Structural confirmation was achieved through complementary spectroscopic techniques, including FT-IR, UV–Visible spectroscopy, and one- and two-dimensional NMR analyses. FT-IR spectra displayed characteristic bands corresponding to N–H stretching (~3290–3445 cm⁻¹) and carbonyl functionalities (~1647–1651 cm⁻¹), while UV–Visible spectra revealed absorption maxima in the range of 259–432 nm, attributed to π→π* transitions within the aromatic system and metal-centred d–d transitions. NMR data confirmed the expected molecular architecture, with distinctive signals corresponding to the ferrocenyl unit (~4.1–4.3 ppm) and aromatic protons (~6.6–7.8 ppm). Electrochemical characterisation by cyclic voltammetry demonstrated a quasi-reversible Fe(II)/Fe(III) redox process for all derivatives, with formal potentials ranging from 43.9 to 57.5 mV. The observed peak separations (ΔEp = 87.8–115 mV) and near-unity current ratios confirmed quasi-reversible behaviour. Diffusion coefficients (1.11 × 10⁻⁷–5.74 × 10⁻⁷ cm²·s⁻¹) and heterogeneous electron-transfer rate constants (0.14 × 10⁻³–0.62 × 10⁻³ cm·s⁻¹) indicated that both transport and kinetic properties are strongly influenced by substitution pattern. Density functional theory calculations provided detailed insight into the electronic structure, revealing HOMO energies between −5.83 and −5.68 eV and HOMO–LUMO gaps of 3.99–4.29 eV, indicative of moderate chemical stability and controlled reactivity. Global reactivity descriptors confirmed this behaviour, with hardness values ranging from 1.995 to 2.143 eV and electrophilicity indices up to 3.519 eV. The progressive increase in dipole moment (3.82–5.12 D) reflects enhanced molecular polarity across the series. Molecular docking studies targeting the ATP-binding domain of DNA gyrase (GyrB) demonstrated favourable binding affinities (−7.34 to −8.58 kcal·mol⁻¹), with FcMe4Ac exhibiting the strongest interaction. Binding mode analysis revealed stabilisation within the ATP-binding