Optimization of Hydroxyethylamine Transition State Isosteres as Aspartic Protease Inhibitors by Exploiting Conformational Preferences

NMR conformational analysis of a hydroxyethylamine peptide isostere developed as an aspartic protease inhibitor shows that it is a flexible architecture. Cyclization to form pyrrolidines, piperidines, or morpholines results in a preorganization of the whole system in solution. The resulting conformation is similar to the conformation of the inhibitor in the active site of BACE-1. This entropic gain results in increased affinity for the enzyme when compared with the acyclic system. For morpholines <b>27</b> and <b>29</b>, the combination of steric and electronic factors is exploited to orient substituents toward S1, S1′, and S2′ pockets both in the solution and in the bound states. These highly preorganized molecules proved to be the most potent compounds of the series. Additionally, the morpholines, unlike the pyrrolidine and piperidine analogues, have been found to be brain penetrant BACE-1 inhibitors

Optimization of Hydroxyethylamine Transition State Isosteres as Aspartic Protease Inhibitors by Exploiting Conformational Preferences

NMR conformational analysis of a hydroxyethylamine peptide isostere developed as an aspartic protease inhibitor shows that it is a flexible architecture. Cyclization to form pyrrolidines, piperidines, or morpholines results in a preorganization of the whole system in solution. The resulting conformation is similar to the conformation of the inhibitor in the active site of BACE-1. This entropic gain results in increased affinity for the enzyme when compared with the acyclic system. For morpholines <b>27</b> and <b>29</b>, the combination of steric and electronic factors is exploited to orient substituents toward S1, S1′, and S2′ pockets both in the solution and in the bound states. These highly preorganized molecules proved to be the most potent compounds of the series. Additionally, the morpholines, unlike the pyrrolidine and piperidine analogues, have been found to be brain penetrant BACE-1 inhibitors

Discovery of (1<i>S</i>,2<i>R</i>,3<i>S</i>,4<i>S</i>,5<i>R</i>,6<i>R</i>)‑2-Amino-3-[(3,4-difluorophenyl)sulfanylmethyl]-4-hydroxy-bicyclo[3.1.0]hexane-2,6-dicarboxylic Acid Hydrochloride (LY3020371·HCl): A Potent, Metabotropic Glutamate 2/3 Receptor Antagonist with Antidepressant-Like Activity

As part of our ongoing efforts to identify novel ligands for the metabotropic glutamate 2 and 3 (mGlu_2/3) receptors, we have incorporated substitution at the C3 and C4 positions of the (1<i>S</i>,2<i>R</i>,5<i>R</i>,6<i>R</i>)-2-amino-bicyclo­[3.1.0]­hexane-2,6-dicarboxylic acid scaffold to generate mGlu_2/3 antagonists. Exploration of this structure–activity relationship (SAR) led to the identification of (1<i>S</i>,2<i>R</i>,3<i>S</i>,4<i>S</i>,5<i>R</i>,6<i>R</i>)-2-amino-3-[(3,4-difluorophenyl)­sulfanylmethyl]-4-hydroxy-bicyclo­[3.1.0]­hexane-2,6-dicarboxylic acid hydrochloride (LY3020371·HCl, <b>19f</b>), a potent, selective, and maximally efficacious mGlu_2/3 antagonist. Further characterization of compound <b>19f</b> binding to the human metabotropic 2 glutamate (hmGlu₂) site was established by cocrystallization of this molecule with the amino terminal domain (ATD) of the hmGlu₂ receptor protein. The resulting cocrystal structure revealed the specific ligand–protein interactions, which likely explain the high affinity of <b>19f</b> for this site and support its functional mGlu₂ antagonist pharmacology. Further characterization of <b>19f</b> in vivo demonstrated an antidepressant-like signature in the mouse forced-swim test (mFST) assay when brain levels of this compound exceeded the cellular mGlu₂ IC₅₀ value