Fluoroquinolones have been studied for more than half a century. Since the 1960s, four generations of these synthetic antibiotics have been created and successfully introduced into clinical practice. However, they are still of interest for medicinal chemistry due to the wide possibilities for chemical modification, with subsequent useful changes in the pharmacokinetics and pharmacodynamics of the initial molecules. This review summarizes the chemical and pharmacological results of fluoroquinolones hybridization by introducing different heterocyclic moieties into position 3 of the core system. It analyses the synthetic procedures and approaches to the formation of heterocycles from the fluoroquinolone carboxyl group and reveals the most convenient ways for such procedures. Further, the results of biological activity investigations for the obtained hybrid pharmacophore systems are presented. The latter revealed numerous promising molecules that can be further studied to overcome the problem of resistance to antibiotics, to find novel anticancer agents and more.

Among all modern antibiotics, fluoroquinolones are well known for their broad spectrums of activity and efficiency toward microorganisms and viruses. However, antibiotic resistance is still a problem, which has encouraged medicinal chemists to modify the initial structures in order to combat resistant strains. Our current work is aimed at synthesizing novel hybrid derivatives of ciprofloxacin and norfloxacin and applying docking studies and biological activity evaluations in order to find active promising molecules. We succeeded in the development of a synthetic method towards 1,2,3-triazole-substituted ciprofloxacin and norfloxacin derivatives. The structure and purity of the obtained compounds were confirmed by ¹H NMR, ¹³C NMR, ¹⁹F NMR, LC/MS, UV-, IR- spectroscopy. Docking studies, together with in vitro research against Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, Bacillus subtilis ATCC 6633, Pseudomonas aeruginosa ATCC 27853, Candida albicans NCTC 885-653 revealed compounds in which activity exceeded the initial molecules.

The title compound, C₂₄H₂₆N₂O₄S, can be obtained via two synthetic routes. According to our investigations, the most suitable way is by the reaction of ethyl 2-bromoacetate with sodium tosylsulfinate in dry DMF. It was crystallized from methanol into the monoclinic P2₁/n space group with a single molecule in the asymmetric unit. Hirshfeld surface analysis was performed to define the hydrogen bonds and analysis of the two-dimensional fingerprint plots was used to distinguish the different types of interactions. Two very weak non-classical C—H...O hydrogen bonds were found and the contributions of short contacts to the Hirshfeld surface were determined. Molecules form an isotropic network of intermolecular interactions according to an analysis of the pairwise interaction energies. A molecular docking study evaluated the interactions in the title compound with the active centers of macromolecules of bacterial targets (Staphylococcus aureus DNA Gyrase PDB ID: 2XCR, Mycobacterium tuberculosis topoisomerase II PDB ID: 5BTL, Streptococcus pneumoniae topoisomerase IV PDB ID: 4KPF) and revealed high affinity towards them that exceeded the reference antibiotics of the fluoroquinolone group.

The current situation in medicine and pharmacy still requires the time and effort of medicinal chemists, who must develop new synthetic approaches and create promising molecules that can turn into novel antimicrobials. Due to the problem of resistance to well-known antibiotics combined with the occurrence of new diseases that we observe, we can be sure that this research is going to be in demand. However, not always searching for a totally new molecule seems to be a good idea. The structural modification and hybridization of once efficient agents is also logical and actually has already provided us with many generations of antibiotics. Therefore, our scientific team has been working with fluoroquinolones with the aim of conducting docking studies, modifying them, and then studying the biological activity of the obtained compounds. In the first stage of the research, we conducted docking studies and then started to work on ciprofloxacin and norfloxacin, only modifying their C-7 position. The introduction of a 1,2,3-triazole moiety as a result of a convenient synthetic procedure led to new molecules for which moderate antimicrobial and antifungal activities were revealed. Furthermore, the C-3 position was modified with an arylsulfonyl moiety with parallel modifications of N-1 and C-7. For now, synthetic procedures have been developed for the similar transformation and biological activity of the obtained compounds that are under study.