Multipotent drugs with cholinergic and neuroprotective properties for the treatment of Alzheimer and neuronal vascular diseases. I. Synthesis, biological assessment, and molecular modeling of simple and readily available 2-aminopyridine-, and 2-chloropyridine-3,5-dicarbonitriles

The synthesis, molecular modeling, and pharmacological analysis of new multipotent simple, and readily available 2-aminopyridine-3,5-dicarbonitriles (3-20), and 2-chloropyridine-3,5-dicarbonitriles (21-28), prepared from 2-amino-6-chloropyridine-3,5-dicarbonitrile (1) and 2-amino-6-chloro-4- phenylpyridine-3,5-dicarbonitrile (2) is described. The biological evaluation showed that some of these molecules were modest inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), in the micromolar range. The 2-amino (3, 4), and 2-chloro derivatives 21-23, 25, 26 were AChE selective inhibitors, whereas 2-amino derivatives 5, 14 proved to be selective for BuChE. Only inhibitor 24 was equipotent for both cholinesterases. Kinetic studies on compound 23 showed that this compound is a mixed-type inhibitor of AChE showing a K_i of 6.33 μM. No clear SAR can be obtained form these data, but apparently, compounds bearing small groups such as the N,N′-dimethylamino or the pyrrolidino, regardless of the presence of a 2-amino, or 6-chloro substituent in the pyridine ring, preferentially inhibit AChE. Molecular modeling on inhibitors 4, 5, 22, and 23 has been carried out to give a better insight into the binding mode on the catalytic active site (CAS), and peripheral anionic site (PAS) of AChE. The most important differences in the observed binding relay on the modifications of the group at C2, as the amino group forms two hydrogen bonds that direct the binding mode, while in the case of compounds with a chlorine atom, this is not possible. The neuroprotective profile of these molecules has been investigated. In the LDH test, only compounds 26, 3, 22, and 24 showed neuroprotection with values in the range 37.8-31.6% in SH-SY5Y neuroblastoma cells stressed with a mixture of oligomycin-A/rotenone, but in the MTT test only compound 17 (32.9%) showed a similar profile. Consequently, these compounds can be considered as attractive multipotent therapeutic molecules on two key pharmacological receptors playing key roles in the progress of Alzheimer, that is, cholinergic dysfunction and oxidative stress, and neuronal vascular diseases.