Design, Synthesis and Molecular Modeling Study of Radiotracers Based on Tacrine and Its Derivatives for Study on Alzheimer’s Disease and Its Early Diagnosis

From 1993 to 2013, tacrine was an approved drug for Alzheimer’s disease. Due to its strong inhibitory properties towards cholinesterase, tacrine causes an increase in the level of the neurotransmitter acetylcholine in the cholinergic system of the central nervous system. This work presents a review of articles in which tacrine or its derivatives labeled with the radionuclides 3H, 11C, 14C, 123I, 99mTc and 68Ga were used as vectors in radiotracers dedicated to the diagnosis of Alzheimer’s disease. The possibility of clinical applications of the obtained radiopreparations was assessed by analyzing their physicochemical properties, ability to cross the blood–brain barrier and the level of uptake in the brain. Based on these data, it was shown that radiopreparations based on the tacrine molecule or its very close analogues retain the ability to cross the blood–brain barrier, while radiopreparations containing a more modified tacrine molecule (connected via a linker to a radionuclide chelator) lose this ability. This is probably the result of the addition of a chelator, which significantly increases the size of the radiopreparation and reduces its lipophilicity. Computer docking studies of tacrine derivatives and/or radiopreparations showed how these compounds bind to the active sites of acetyl- and butyrylcholinesterase.