A codrug of the anti-Alzheimer drug tacrine and the natural product silibinin was synthesized. The codrug’s biological and pharmacological properties were compared to an equimolar mixture of the components. The compound showed potent acetyl- and butyrylcholinesterase inhibition. In a cellular hepatotoxicity model, analyzing the influence on viability and mitochondria of hepatic stellate cells (HSC), the toxicity of the codrug was markedly reduced in comparison to that of tacrine. Using a neuronal cell line (HT-22), a neuroprotective effect against glutamate-induced toxicity could be observed that was absent for the 1:1 mixture of components. In subsequent in vivo experiments in rats, in contrast to the effects seen after tacrine treatment, after administration of the codrug no hepatotoxicity and no induction of the cytochrome P450 system were noticed. In a scopolamine-induced cognitive impairment model using Wistar rats, the codrug was as potent as tacrine in reversing memory dysfunction. The tacrine–silibinin codrug shows high AChE and BChE inhibition, neuroprotective effects, lacks tacrine’s hepatotoxicity in vitro and in vivo, and shows the same pro-cognitive effects in vivo as tacrine, being superior to the physical mixture of tacrine and silibinin in all these regards.

Tri- and tetracyclic nitrogen-bridgehead compounds were designed and synthesized to yield micromolar cholinesterase (ChE) inhibitors. Structure–activity relationships identified potent compounds with butyrylcholinesterase selectivity. These compounds were selected as starting points for the design and synthesis of carbamate-based (pseudo)irreversible inhibitors. Compounds with superior inhibitory activity and selectivity were obtained and kinetically characterized also with regard to the velocity of enzyme carbamoylation. Structural elements were identified and introduced that additionally showed neuroprotective properties on a hippocampal neuronal cell line (HT-22) after glutamate-induced intracellular reactive oxygen species generation. We have identified potent and selective pseudoirreversible butyrylcholinesterase inhibitors that release reversible inhibitors with neuroprotective properties after carbamate transfer to the active site of cholinesterases.Keywords: Alzheimer's disease; butyrylcholinesterase; carbamates; neuroprotection

The spacer structure of homobivalent quinazolinimes acting as potent acetyl-(AChE)- and butyrylcholinesterase (BChE) inhibitors was chemically modified introducing tertiary amine and acyl-amide moieties, and the activities at both ChEs were evaluated. Molecular docking was applied to explain the data and probe the capacity of the mid-gorge site of both ChEs. The novel spacer structures considerably alter the biological profile of bivalent quinazolinimines with regard to both inhibitory activity and selectivity. Mutual interaction of binding to the various sites of the enzymes was further investigated by applying also different spacer lengths and ring sizes of the alicycle of the tricyclic quinazolinimines. In order to achieve selectivity toward BChE and to improve inhibitory activities, the spacer structure was optimized and identified a highly potent and selective BChE inhibitor.