New racemic annulated pyrazolo[1,2-b]phthalazines as tacrine-like AChE inhibitors with potential use in Alzheimer's disease.

A novel series of tacrine-like compounds 7a-u possessing a fused pyrazolo[1,2-b]phthalazine structure were designed and synthesized as potent and selective inhibitors of AChE. The in-vitro biological assessments demonstrated that several compounds had high anti-AChE activity at nano-molar level. The more promising compound 7l with IC50 of 49 nM was 7-fold more potent than tacrine and unlike tacrine, it was highly selective against AChE over BuChE. The cell-based assays against hepatocytes (HepG2) and neuronal cell line (PC12) revealed that 7l had significantly lower hepatotoxicity compared to tacrine, with additional neuroprotective activity against H2O2-induced damage in PC12 cells. This compound could also inhibit AChE-induced and self-induced Aβ peptide aggregation. The advantages including synthetic accessibility, high potency and selectivity, low toxicity, adjunctive neuroprotective and Aβ aggregation inhibitory activity, make this compound as a new multifunctional lead for Alzheimer's disease drug discovery.