ABSTRACT
Selective N-methyl-d-aspartate receptor subunit 2B (NR2B) antagonists show potential as analgesic drugs, and do not cause side effects associated with non-selective N-methyl-d-aspartate (NMDA) antagonists. Using a scaffold-hopping approach, we previously identified isoxazole derivative 4 as a potent selective NR2B antagonist. In this study, further scaffold hopping of isoxazole derivative 4 and optimization of its pharmacokinetic profile led to the discovery of the orally bioavailable compound 6v. In a rat study of analgesia, 6v demonstrated analgesic effects against neuropathic pain.
Subject(s)
Analgesics/chemical synthesis , Analgesics/pharmacology , Drug Design , Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors , Analgesics/chemistry , Analgesics/pharmacokinetics , Animals , Male , Molecular Structure , Rats , Rats, Sprague-Dawley , Structure-Activity RelationshipABSTRACT
Accumulation of Aß peptides is a hallmark of Alzheimer's disease (AD) and is considered a causal factor in the pathogenesis of AD. ß-Secretase (BACE1) is a key enzyme responsible for producing Aß peptides, and thus agents that inhibit BACE1 should be beneficial for disease-modifying treatment of AD. Here we describe the discovery and optimization of novel oxazine-based BACE1 inhibitors by lowering amidine basicity with the incorporation of a double bond to improve brain penetration. Starting from a 1,3-dihydrooxazine lead 6 identified by a hit-to-lead SAR following HTS, we adopted a p Ka lowering strategy to reduce the P-gp efflux and the high hERG potential leading to the discovery of 15 that produced significant Aß reduction with long duration in pharmacodynamic models and exhibited wide safety margins in cardiovascular safety models. This compound improved the brain-to-plasma ratio relative to 6 by reducing P-gp recognition, which was demonstrated by a P-gp knockout mouse model.
Subject(s)
Amyloid Precursor Protein Secretases/antagonists & inhibitors , Amyloid beta-Peptides/metabolism , Aspartic Acid Endopeptidases/antagonists & inhibitors , Oxazines/chemistry , Peptide Fragments/metabolism , Protease Inhibitors/chemistry , Protease Inhibitors/pharmacology , ATP Binding Cassette Transporter, Subfamily B/genetics , ATP Binding Cassette Transporter, Subfamily B/metabolism , ATP Binding Cassette Transporter, Subfamily B, Member 1/genetics , ATP Binding Cassette Transporter, Subfamily B, Member 1/metabolism , Amyloid Precursor Protein Secretases/chemistry , Animals , Aspartic Acid Endopeptidases/chemistry , Brain/drug effects , Brain/metabolism , Crystallography, X-Ray , Dogs , Drug Design , ERG1 Potassium Channel/metabolism , Guinea Pigs , Humans , Madin Darby Canine Kidney Cells , Mice, Inbred C57BL , Mice, Knockout , Oxazines/pharmacology , Protease Inhibitors/pharmacokinetics , Structure-Activity RelationshipABSTRACT
NR2B subunit containing N-methyl-d-aspartate (NMDA) receptor is an attractive target for chronic pain due to its involvement in disease states and its limited distribution in the central nervous system. Cyclohexanol-based leads 6a and 6c were identified as potent NR2B-selective NMDA antagonists utilizing a scaffold hopping approach. Further optimization of this series through replacement of the amide in the leads with an isoxazole and efforts to optimize the pharmacokinetic profiles led to the discovery of orally available brain penetrants 7k and 7l, which demonstrated analgesic activity in the mouse formalin test at early and late phases.
