Design synthesis and evaluation of usnic acid derivatives as multi-target drugs for Alzheimer's disease

The pathogenesis of AD is complex, and existing clinical drugs only alleviate symptoms and are difficult to block the course of the disease. Although UA has neuroprotective activities such as antioxidant and anti-inflammatory properties, its anti-AD activity is severely restricted by drug defects such as a single target and insufficient blood-brain barrier permeability. Therefore, this study takes UA as the lead compound, designs and synthesizes 38 UA derivatives, systematically evaluates their anti-AD biological activity, and aims to screen for multifunctional anti AD lead compounds. Among them, the lead compound S12 exhibited exceptional activity, with an EC₅₀ value of 1.24 μM representing a 17.9-fold improvement in potency relative to the parent compound. Furthermore, WB assays were conducted to elucidate the underlying mechanism of action of this compound. The results revealed that compound S12 exerts anti-AD activity through the synergistic modulation of multiple signaling pathways: it inhibits activation of the MAPK and NF-κB pathways, as well as aberrant phosphorylation of tau protein; concurrently, it downregulates BACE1 expression to reduce Aβ production, and suppresses activation of the Bax/Bcl-2 pathway thereby inhibiting caspase-1 activation and ultimately confers neuroprotective, anti-AD effects. The apparent permeability coefficient of compound S12 across an in vitro (BBB) model was determined to be 7.66 × 10^-6 cm/s, confirming its ability to effectively cross the BBB. Further pharmacological evaluation demonstrated that S12 exerted a potent ameliorative effect on learning and memory deficits in an AD mouse model. In vivo toxicity assessment, no gross or histopathological abnormalities were observed in the major organs, including the heart, liver, spleen, and kidneys. Moreover, S12 significantly attenuated neuronal pathological injury in the hippocampus of Aβ-induced AD model mice, underscoring its robust neuroprotective activity. In conclusion, compound S12 demonstrates robust efficacy in ameliorating learning and memory deficits, enhancing blood-brain barrier permeability, and exerting anti-AD activity. Accordingly, it represents a highly promising multifunctional therapeutic candidate for the treatment of AD.