PDE5-IN-6c is a potent and selective phosphodiesterase 5A1 (PDE5A1) inhibitor with the potential to inhibit Alzheimer's disease (AD). PDE5-IN-6c exhibits an excellent in vitro IC50 (0.056 nM), demonstrating its potent inhibitory activity. PDE5-IN-6c has improved water solubility, making it a more attractive drug candidate.