Design, Synthesis, and Biological Evaluation of Novel Spiro Imidazobenzodiazepines to Identify Improved Inhaled Bronchodilators.

Novel gamma-aminobutyric acid receptor (GABA A R) ligands structurally related to imidazobenzodiazepine MIDD0301 were synthesized using spiro-amino acid N-carboxyanhydrides (NCAs). These compounds demonstrated increased resistance to phase 2 metabolism and avoided the formation of a 6H isomer. Compound design was guided by molecular docking using the available crystal structure of the α 1 β 3 γ 2 GABA A R and correlated with in vitro binding data. The carboxylic acid containing GABA A R ligands have high aqueous solubility, low permeability, and low cell toxicity. The inability of GABA A R ligands to cross the blood-brain barrier was confirmed in vivo by the absence of sensorimotor inhibition. Pharmacological activities at lung GABA A Rs were demonstrated by ex vivo relaxation of guinea pig airway smooth muscle and reduction of methacholine-induced airway hyperresponsiveness (AHR) in conscious mice. We identified bronchodilator 5c with an affinity of 9 nM for GABA A Rs that was metabolically stable in the presence of human and mouse microsomes.