Flexible 1-[(2-aminoethoxy)alkyl]-3-ar(o)yl(thio)ureas as novel acetylcholinesterase inhibitors. Synthesis and biochemical evaluation.

A series of flexible 1-(2-aminoethoxy)-3-ar(o)yl(thio)ureas was synthesized and assessed for antiacetylcholinesterase activity. This series was designed in order to optimize the spacer length linking the two pharmacophoric moieties, i.e., the basic nitrogen and the ar(o)yl(thio)-urea unit, and to test compounds with greater conformational flexibility. Thus, the replacement of the previously described spacer, 4-piperidinylethyl, by a linear ethoxyethyl chain gave compounds of slightly comparable potency, providing that they were correctly substituted. The results show that this new flexible spacer is compatible with high inhibitory activities. The optimal chain length corresponds to five methylene groups, allowing an efficient interaction between the two pharmacophoric units and the two reported hypothetical enzyme hydrophobic binding sites. Moreover, the initially optimized benzyl group, attached to the basic nitrogen, was found to be advantageously replaced by a cyclohexyl group, showing that an aromatic residue does not represent a prerequisite for activity.