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J Med Chem. 2016 Apr 14;59(7):3231-48. doi: 10.1021/acs.jmedchem.5b01995. Epub 2016 Mar 22.

Structure-Based Design of an Iminoheterocyclic β-Site Amyloid Precursor Protein Cleaving Enzyme (BACE) Inhibitor that Lowers Central Aβ in Nonhuman Primates.

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Department of Global Chemistry, ‡Department of Neuroscience, §Department of Safety Assessment and Laboratory Animal Research, ∥Department of Discovery Pharmaceutical Sciences, and ⊥Department of Pharmacokinetics, Pharmacodynamics, and Drug Metabolism, Merck Research Laboratories , 2015 Galloping Hill Road, Kenilworth, New Jersey 07033, United States.


We describe successful efforts to optimize the in vivo profile and address off-target liabilities of a series of BACE1 inhibitors represented by 6 that embodies the recently validated fused pyrrolidine iminopyrimidinone scaffold. Employing structure-based design, truncation of the cyanophenyl group of 6 that binds in the S3 pocket of BACE1 followed by modification of the thienyl group in S1 was pursued. Optimization of the pyrimidine substituent that binds in the S2'-S2″ pocket of BACE1 remediated time-dependent CYP3A4 inhibition of earlier analogues in this series and imparted high BACE1 affinity. These efforts resulted in the discovery of difluorophenyl analogue 9 (MBi-4), which robustly lowered CSF and cortex Aβ40 in both rats and cynomolgus monkeys following a single oral dose. Compound 9 represents a unique molecular shape among BACE inhibitors reported to potently lower central Aβ in nonrodent preclinical species.

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