Tacrines as Therapeutic Agents for Alzheimer's Disease. IV. The Tacripyrines and Related Annulated Tacrines

Notwithstanding the clinical use of tacrine was hampered by severe hepatotoxicity, tacrine still remains a reference scaffold in the search for new efficient drugs for Alzheimer's disease therapy. In this account we summarize the efforts toward the development and characterization of non-hepatotoxic tacripyrines and related tacrine analogues resulting from the substitution of the benzene ring by a 1,4-dihydropyridine, a 1,2,3,4-tetrahydropyrimidine or a pyridone nucleus. These efforts have successfully led to the identification of a number of promising hits endowed with interesting multifunctional profiles. These include the 4′-metoxytacripyrine (S)-ITH122, able to target cholinesterases (ChEs), beta-amyloid (Aβ) and Ca2+ channels, the racemic 3′-methoxytacripyrimidine EB65F2, the first fully balanced micromolar inhibitor of ChEs and Ca2+ channels, and tacripyrine (−)-SCR1693 a GSK-3β (enzyme involved in tau phosphorylation) inhibitor able to also lower Aβ production in N2a cells.