Synthesis and biological evaluation of (-)- and (+)-debromoflustramine B and its analogues as selective butyrylcholinesterase inhibitors

A series of pyrrolidinoindolines have been synthesized as debromoflustramine B (4a) analogues for their evaluation as cholinesterase inhibitors. Structure-activity studies of this series revealed the Optimum pharmacophoric elements required for activity and resulted in the discovery of selective butyrylcholinesterase inhibitors with micromolar potency. Biological testing demonstrated that (-)-4a was 7500 times more potent than its enantiomer (+)-4b. The most active inhibitor against BChE in the series was demethyldebromoflustramine B (5a), with an IC50 value of 0.26 mu M. X-ray crystallography of 15 and docking studies of selected compounds into human BChE (PDB 1POI) are presented. Molecular modeling studies showed that pi-hydrogen bond, classical hydrogen bond, and cation-pi interactions are critical for optimum potency.