Analysis of the Lipophilicity and HSA Binding Profile of Biologically Relevant 2‐Mercaptobenzoic Acid Derivatives

One of the key factors determining a compound's distribution, metabolism, and therapeutic properties is its binding affinity to human serum albumin (HSA). This study investigated the binding interaction between potential biologically active S-alkyl (methyl-[L1], ethyl-[L2], propyl-[L3], butyl-[L4], and benzyl-[L5]) derivatives of 2-mercaptobenzoic acid and HSA using various spectroscopic methods and molecular docking simulations. The protonation constants (β_n) of the investigated ligands were determined potentiometrically in aqueous solutions, whereas their lipophilicity was assessed using different experimental methods and software packages. An increase in the absorption intensity of HSA upon interaction with the investigated compounds indicates static quenching and the formation of a complex between HSA and the ligands. The incorporation of alkyl groups into the ligand molecules results in a slight increase in the protonation constants of the tested compounds, as well as an enhancement lipophilicity compared to 2-mercaptobenzoic acid. In silico analyses demonstrated that multiple amino acid residues are crucial for the binding process in Sudlow site I, situated within subdomain IIA, with salt bridges being the predominant interaction.