cis-(1S,2R) isomer 6 exhibited the most potent BACE1 inhibitory activity among them. X-ray structure analysis of the complex of 6 and BACE1 revealed that its unique binding mode is due to the apparent CH−π interaction between the rigid cyclopropane ring and the Tyr71 sidechain. A derivatization study using 6 as a lead molecule led to the development of highly potent inhibitors in which the structure–activity