A Brain-Penetrant and Bioavailable Pyrazolopiperazine BACE1 Inhibitor Elicits Sustained Reduction of Amyloid β In Vivo

[Image: see text] We recently disclosed a set of heteroaryl-fused piperazine inhibitors of BACE1 that combined nanomolar potency with good intrinsic permeability and low Pgp-mediated efflux. Herein we describe further work on two prototypes of this family of inhibitors aimed at modulating their basicity and reducing binding to the human ether-a-go-go-related gene (hERG) channel. This effort has led to the identification of compound 36, a highly potent (hAβ42 cell IC(50) = 1.3 nM), cardiovascularly safe, and orally bioavailable compound that elicited sustained Aβ(42) reduction in mouse and dog animal models.