Structure-Activity Relationship of Ciprofloxacin towards S-Spike Protein of SARS-CoV-2: Synthesis and In-Silico Evaluation.

The recent outbreak of the coronavirus (COVID-19) pandemic, caused by the SARS-CoV-2 virus, has posed serious threats to global health systems. Although several directions have been put by the WHO for effective treatment, use of antibiotics, particularly ciprofloxacin, in suspected and acquired Covid-19 patients has raised an even more serious concern of antibiotic resistance. Ciprofloxacin has been reported to inhibit entry of SARS-CoV-2 into the host cells via interacting with the spike (S) protein. However, a proper structure-activity relationship study of ciprofloxacin with the S-protein is lacking, which inhibits researchers from developing a more potent fluoroquinolone analogue, specific for inhibition of SARS-CoV-2 viral entry. Herein, in order to have a structure-activity relationship study, we have accomplished a short and convergent synthesis of different derivatives of ciprofloxacin and a detailed in-silico study using molecular docking to explore the interactions of the derivatives with S-protein. The ADMET studies also indicated the drug likeliness and nontoxicity of the derivatives. Furthermore, the molecular dynamics simulation approach was used to study the dynamical behavior after the best docked derivative binds to the protein, and the MM-PBSA approach was adopted to calculate the binding energies. This has led to a derivative that has higher interactions with the S-protein compared to ciprofloxacin, without hampering the dynamics of the interactions. The strong affinity of compound 5 with the SARS-CoV-2 spike RBD protein was further evaluated experimentally using biolayer interferometry (BLI). Furthermore, molecular docking and molecular dynamics simulation were extended to evaluate its binding with the mutated variants Delta and Omicron. We anticipate that the current study could lead to an alternative therapeutic viral inhibitor with a better efficacy than ciprofloxacin.