Allyl m-Trifluoromethyldiazirine Mephobarbital: An Unusually Potent Enantioselective and Photoreactive Barbiturate General Anesthetic
journal contributionposted on 26.07.2012, 00:00 by Pavel Y. Savechenkov, Xi Zhang, David C. Chiara, Deirdre S. Stewart, Rile Ge, Xiaojuan Zhou, Douglas E. Raines, Jonathan B. Cohen, Stuart A. Forman, Keith W. Miller, Karol S. Bruzik
We synthesized 5-allyl-1-methyl-5-(m-trifluoromethyl-diazirynylphenyl)barbituric acid (14), a trifluoromethyldiazirine-containing derivative of general anesthetic mephobarbital, separated the racemic mixture into enantiomers by chiral chromatography, and determined the configuration of the (+)-enantiomer as S by X-ray crystallography. Additionally, we obtained the 3H-labeled ligand with high specific radioactivity. R-(−)-14 is an order of magnitude more potent than the most potent clinically used barbiturate, thiopental, and its general anesthetic EC50 approaches those for propofol and etomidate, whereas S-(+)-14 is 10-fold less potent. Furthermore, at concentrations close to its anesthetic potency, R-(−)-14 both potentiated GABA-induced currents and increased the affinity for the agonist muscimol in human α1β2/3γ2L GABAA receptors. Finally, R-(−)-14 was found to be an exceptionally efficient photolabeling reagent, incorporating into both α1 and β3 subunits of human α1β3 GABAA receptors. These results indicate R-(−)-14 is a functional general anesthetic that is well-suited for identifying barbiturate binding sites on Cys-loop receptors.