Aminonaphthoquinone Mannich Bases Derived from Lawsone and Their Copper(II) Complex Derivatives: Synthesis and Potential Cholinesterase Inhibitors as Identified by On-flow Assay

A new series of Mannich bases derived from 2-hydroxy-1,4-naphthoquinone (lawsone), substituted benzaldehydes and two primary amines, and their Cu complexes were synthesized and evaluated for their potential as selective cholinesterase inhibitors (ChEIs). Immobilized capillary enzyme reactors (ICERs) bearing butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) were used not only for the on-flow screening assay but also for determining the inhibitory potency and equilibrium binding constants of the lead inhibitors. Eight copper complexes were identified and characterized as potent reversible and selective ChEIs with inhibitory potencies (IC50) and constants of inhibition (Ki) ranging from 1.24 to 11.5 μmol L−1. One of the compounds was particularly promising, showing IC50 and Ki values of 1.24 ± 0.01 and 1.06 ± 0.01 μmol L−1, respectively, for huAChE. These values were lower than those for the standard inhibitor galanthamine (IC50 = 206 ± 30.0 and Ki = 126 ± 18.0 μmol L−1). Even though, it is showing noncompetitive inhibition of huAChE and linear mixed-type inhibition of eeAChE. These complexes showed a promising cholinesterase inhibitory activity and can be used as model inhibitors.