Conformationally restricted leukotriene receptor antagonists: [(octahydro-2-oxo-7-tetradecylidene-2H-1-benzopyran-8-yl)thio]ace tic acids.

[(Octahydro-2-oxo-7-tetradecylidene-2H-1-benzopyran-8-yl)thio]acet ic acid (MDL 43,291) is a novel leukotriene (LT) receptor antagonist. It is a competitive antagonist of LTD4 (pA2 = 6.7) and LTE4 (pA2 = 6.7) and an apparent noncompetitive inhibitor of LTC4 ('pseudo' pA2 = 6.8) in the longitudinal muscle of the guinea pig ileum. At concentrations that effectively antagonize peptidoleukotriene-induced contractions, MDL 43,291 does not antagonize histamine, carbachol or substance P. In vivo, 10-30 mg/kg MDL 43,291, given intravenously, effectively inhibits increases in insufflation pressure induced by 100 ng/kg i.v. LTD4. This compound is a prototype of a novel class of leukotriene receptor antagonists that may be useful in the treatment of bronchial asthma and related disorders.