1,4-Dihydropyridines as Antagonists of Platelet Activating Factor. 1. Synthesis and Structure-Activity Relationships of 2-(4-Heterocyclyl)phenyl Derivatives

Article abstract of DOI:10.1021/jm00095a005

A novel class of 2-(4-heterocyclylphenyl)-1,4-dihydropyridines (2-38) possessing antagonist activity against platelet activating factor (PAF) was prepared by the Hantzsch synthesis from a variety of ethyl 4'-heterocyclic-substituted benzoylacetates, aryl or heteroaryl aldehydes, and substituted 3-aminocrotonamides or 3-aminocrotonate esters.Structure-activity relationships were evaluated where PAF antagonist activity was measured in vitro by determining the concentration of compound (IC50) required to inhibit the PAF-induced aggregation of rabbit washed platelets,and in vivo by determining the oral dose (ED50) which protected mice from a lethal injection of PAF.The nature of the substituent at the dihydropyridine 2-position was found to be important for both in vitro and in vivo activity, whereas there was greater flexibility for structural variation at the 4- and 5-positions.The most potent compound was 4-(2-chlorophenyl)-1,4-dihydro-3-(ethoxycarbonyl)-6-methyl-2-<4-(2-methylimidazo<4,5-c>pyrid-1-yl)phenyl>-5-pyridine (17, UK-74,505), IC50 = 4.3 nM, ED50 = 0.26 mg/kg po, which was found to be approximately 33 times more potent in vitro (rabbit platelet aggregation) and about 8 times more potent in vivo (murine lethality) than WEB2086.Compound 17 also exhibited a long duration of action in the dog (inhibition of PAF-induced whole blood aggregation ex vivo was maintained for > 24 h following a single oral dose of 75 μg/kg) and was highly selective as a PAF antagonist, showing only weak affinity (IC50 = 6600 nM) for the <3H>nitrendipine binding site.As a result of its high oral potency, selectivity, and duration of action, UK-74,505 has been selected for clinical evaluation.