Development of a novel series of styrylquinoline compounds as high- affinity leukotriene D4 receptor antagonists: Synthetic and structure- activity studies leading to the discovery of (±)-3-[[[3-[2-(7-chloro-2- quinolinyl)-(E)-ethenyl]phenyl][[3-(dimethylamino)-3- oxopropyl]thio]methyl]thio]propionic acid

Article abstract of DOI:10.1021/jm00099a011

Based on LTD₄ receptor antagonist activity of 3-(2-quinolinyl-(E)- ethenyl)pyridine (2) found in broad screening, structure-activity studies were carried out which led to the identification of 3-[[[3-[2-(7-chloro-2- quinolinyl)-(E)-ethenyl]phenyl][[3-(dimethylamino)-3- oxopropyl]thio]methyl]thio]propionic acid (1, MK-571) as a potent and orally active LTD₄ receptor antagonist. These studies demonstrated that a phenyl ring could replace the pyridine in 2 without loss of activity, that 7-halogen substitution in the quinoline group was optimal for binding, that the (E)- ethenyl linkage was optimal, that binding was enhanced by incorporation of a polar acidic group or groups in the 3-position of the aryl ring, and that two acidic groups could be incorporated via a dithioacetal formed from thiopropionic acid and the corresponding styrylquinoline 3-aldehyde to yield compounds such as 20 (IC₅₀ = 3 nM vs [³H]LTD₄ binding to the guinea pig lung membrane). It was found that one of the acidic groups could be transformed into a variety of the amides without loss of potency and that the dimethylamide 1 embodied the optimal properties of intrinsic potency (IC₅₀ = 0.8 nM on guinea pig lung LTD₄ receptor) and oral in vivo potency in the guinea pig, hyperreactive rat, and squirrel monkey. The evolution of 2 to 1 involves the increase of >6000-fold in competition for [³H]LTD₄ binding to guinea pig lung membrane and a >40-fold increase in oral activity as measured by inhibition of antigen-induced dyspnea in hyperreactive rats.