The exploration of 1,2,3,4,5,6-hexahydroazepino[4,3-b]indole derivatives as selective butyrylcholinesterase inhibitors

The role of butyrylcholinesterase (BChE) in the progression of Alzheimer’s disease (AD) has recently become more crucial (1). It is known that in healthy human brain acetylcholinesterase (AChE) predominates over BChE activity, but, as AD progresses, The levels of AChE in the brain decrease by as much as 90%, whilst the levels of BChE, Mainly in the G1 form (i.e., globular form of monomer structure), increase (2,3). This suggests that the inhibition of BChE may be useful in ameliorating the cholinergic transmission, which likely worsen in AD due to the BChE increased activity (4). As a matter of fact, in the AD brain, selective BChE inhibitors, such as tricyclic cymserine Analogs (1,5), have been demonstrated to have beneficial effects in vivo, probably by recovering cholinergic activity and/or by restoring AChE:BChE activity ratios to the levels observed in the healthy brain. Some years ago, we reported the ChE inhibition activity of novel annulated (e.g., pyrrole- and indole-fused) tetrahydroazocines, which showed AChE selectivity (6). Herein, we explore the ChE inhibition activity of a large series of 1,2,3,4,5,6-hexahydroazepino[4,3-b]ndole derivatives, some of which proved to be potent and selective BChE inhibitors. In particular, the lactam derivative 2 was highly active against BChE, with a subnanomolar IC50 Value. Synthesis, enzyme inhibition data and SARs are presented and discussed.