Design, synthesis and pharmacological evaluation of hybrid molecules out of quinazolinimines and lipoic acid lead to highly potent and selective butyrylcholinesterase inhibitors with antioxidant properties

A set of hybrid molecules were synthesized out of lipoic acid, alpha,omega-diamines of different lengths serving as spacers, and cholinesterase (ChE) inhibiting [2,1-b]quinazolinimines. Depending on the length of the alkylene spacer the amide hybrids are inhibitors of acetylcholinesterase (AChE) with inhibitory activities of 0.5-4.6 mu M and inhibitors of butyrylcholinesterase (BChE) with activities down to 5.7 nM, therefore greatly exceeding the inhibitory activities of the parent quinazolinimines by factors of up to 1000. Due to increasing activity at BChE with increasing length of the alkylene spacer similar to 100-fold selectivity toward BChE is reached with a hepta- and an octamethylene spacer. Kinetic measurements reveal competitive and reversible inhibition of both ChEs by the hybrids. Furthermore, cell viability and antioxidant activity (using the ORAC-fluorescein assay) of several hybrids were evaluated, showing cytotoxicity at concentrations from 3.7 to 10.2 mu M and antioxidant properties are in the range of 0.4-0.8 Trolox equivalents (lipoic acid = 0.6). (C) 2008 Elsevier Ltd. All rights reserved.