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

Novel gamma-aminobutyric acid receptor (GABAR) 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 αβγ GABAR and correlated with in vitro binding data. The carboxylic acid containing GABAR ligands have high aqueous solubility, low permeability, and low cell toxicity. The inability of GABAR ligands to cross the blood-brain barrier was confirmed in vivo by the absence of sensorimotor inhibition. Pharmacological activities at lung GABARs 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 with an affinity of 9 nM for GABARs that was metabolically stable in the presence of human and mouse microsomes.