Quinazoline derivatives as novel bacterial sphingomyelinase enzyme inhibitors

Bacillus cereus sphingomyelinase C (B. cereus SMase), which plays a crucial role in bacterial virulence, has emerged as a new therapeutic target for treating opportunistic infections caused by this pathogen. It also shares catalytic domain similarity with human neutral sphingomyelinase 2 (nSMase2), which is implicated in Alzheimer's disease. In this study, a series of quinazoline derivatives were synthesized and evaluated for their inhibition of B. cereus SMase, electric eel acetylcholinesterase (EeAChE), and equine butyrylcholinesterase (eqBuChE). Moreover, the antibacterial, anti-hemolytic and metal chelation properties of the selected compounds were determined. Among the synthesized compounds, 6-chloro-2-thioxo-2,3-dihydroquinazolin-4(1H)-one (compound 4) and 6-fluoro-2-thioxo-2,3-dihydroquinazolin-4(1H)-one (compound 5) exhibited promising inhibition of B. cereus SMase, with IC₅₀ values of 6.43 and 6.50 µM, respectively. The mode of inhibition of compound 4 was determined as mixed-type inhibition by enzyme kinetic study. In addition, compounds 4 and 5 showed 59.50% and 51.66% eqBuChE inhibition at 50 µM concentration, respectively. Furthermore, compound 4 reduced B. cereus-induced hemolysis on sheep erythrocytes and able to form a complex with Cu²⁺ in ligand:metal ratio of 2:1. Additionally, cambinol, an inhibitor of both nSMase2 and B. cereus SMase, was found to exhibit inhibitory activity against eqBuChE, with IC₅₀ value of 7.40 µM. The biological data were also supported by the results of molecular docking studies and in-silico physicochemical properties/ADME predictions of the selected compounds were determined.