Inhibitors of BACE for treating Alzheimer's disease: a fragment-based drug discovery story.

Several fragment-based methods have been applied to the discovery of new lead sources for inhibitors of BACE1, an important therapeutic target for Alzheimer's disease. Among the most common fragment hits were various amidine-containing molecules in which the amidine engaged in discrete H-bond donor-acceptor interaction with the BACE1 catalytic dyad. Structure and medicinal chemistry knowledge-based optimization with emphasis on ligand efficiency resulted in identification of a key pharmacophore comprising a non-planar cyclic amidine scaffold directly attached to a phenyl group projecting into S1. This key pharmacophore is a common feature of known clinical candidates and has dominated the recent patent literature. A structural comparison of the non-planar cyclic amidine motif with other BACE1 pharmacophores highlights its uniqueness and distinct advantages.