Donepezil-d4 (hydrochloride) is the deuterium labeled Donepezil hydrochloride. Donepezil Hydrochloride (E2020) is a reversible, selective AChE inhibitor with an IC50 of 6.7 nM for AChE activity. Donepezil shows high selectivity for AChE over BuChE[1]. Donepezil exhibits neuroprotective effect on Aβ42 neurotoxicity[2].