The identification of small molecule aminoimidazoles as potent and selective human β- secretase inhibitors is reported. These analogues demonstrate low nannomolar potency for BACE1 in a FRET assay, exhibit comparable activity in a cell-based (ELISA) assay, and show> 100× selectivity for the other structurally related aspartyl proteases BACE2, cathepsin D, renin, and pepsin. Our design strategy was supported by molecular modeling studies ...