BISMUTH-BASED BICYCLIC PEPTIDE INHIBITORS TARGETING MAIN PROTEASE OF SARS-COV-2

Author

• Funsho Sarah Afolabi, Kennesaw State UniversityFollow

Semester of Graduation

Spring 2026

Degree Type

Thesis

Degree Name

Masters in Chemical Sciences

Department

Department of Chemistry and Biochemistry

Committee Chair/First Advisor

Dr. Mohammad A. Halim

Second Advisor

Dr. Masafumi Yoshinaga

Third Advisor

Dr. Madalynn Marshall

Abstract

The emergence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus and the resultant COVID-19 disease represent the foremost public health crisis of this century, exerting a profound impact on the global economy, human health and lives. The main protease (Mpro) is a vital protease that facilitates viral replication. Inhibition of this viral protease enzyme blocks the formation of functional viral proteins required for the viral life cycle. Peptide therapeutics are very attractive as they are highly selective, have good tolerability, and have fewer adverse effects. However, they aren’t without limitations, which include poor metabolic stability, membrane permeability, and oral bioavailability. Bicycling has been found to overcome these limitations. The Temporin-like peptide (TLP) has been previously studied by our group and found to effectively inhibit the main protease. In this study, TLP analogs containing three cysteines have been synthesized and used for Bismuth-based bicyclic analogs. The inhibitory effect of the Bismuth-based analogs on the activity of the main protease has been analyzed using FRET and LC-MS-based assays. Bi-3CTLP1 showed IC₅₀ values of 11.47 µM in FRET and 13.61 µM in LCMS assays, respectively, whereas Bi-3CTLP2 demonstrated IC50 values of 12.99 µM in FRET and 18.04 µM in LCMS. The kinetics results showed that the velocity of the product formation significantly decreased and revealed that Bi-3CTLP1 peptide can act as a noncompetitive inhibitor, which can bind to free enzyme and the enzyme-substrate complex. Moreover, bicyclic peptides showed strong intestinal stability up to the incubation period of four hours.