Structural Design, Solid-Phase Synthesis and Activity of Membrane-Anchored β-Secretase Inhibitors on Aβ Generation from Wild-Type and Swedish-Mutant APP

Covalent coupling of β‐secretase inhibitors to a raftophilic lipid anchor via a suitable spacer by using solid‐phase peptide synthesis leads to tripartite structures displaying substantially improved inhibition of cellular secretion of the β‐amyloid peptide (Aβ). Herein, we describe a series of novel tripartite structures, their full characterization by NMR spectroscopy and mass spectrometry, and the analysis of their biological activity in cell‐based assays. The tripartite structure concept is applicable to different pharmacophores, and the potency in terms of β‐secretase inhibition can be optimized by adjusting the spacer length to achieve an optimal distance of the inhibitor from the lipid bilayer. A tripartite structure containing a transition‐state mimic inhibitor was found to be less potent on Aβ generation from Swedish‐mutant amyloid precursor protein (APP) than from the wild‐type protein. Moreover, our observations suggest that specific variants of Aβ are generated from wild‐type APP but not from Swedish‐mutant APP and are resistant to β‐secretase inhibition. Efficient inhibition of Aβ secretion by tripartite structures in the absence of appreciable neurotoxicity was confirmed in a primary neuronal cell culture, thus further supporting the concept. Anchoring of β‐secretase inhibitors to the lipid raft domains of the cell membrane by using a spacer‐linked dihydrocholesterol leads to tripartite structures with substantially improved efficacy. The concept is applicable to different pharmacophores (a–i; e shown in picture) and the best spacer lengths are in the range of 35–89 Å. Moreover, significant differences were demonstrated in the Aβ‐peptide secretion from wild‐type(wt) versus Swedish(sw)‐mutant APP. The present results provide a basis for the development of potential new drugs for the treatment of Alzheimer's disease.