CALCIUM-ANTAGONISM AND CALMODULIN-ANTAGONISM OF ELNADIPINE DERIVATIVES - COMPARATIVE SAR

The Ca2+-antagonistic properties of elnadipine derivatives have been quantified by means of binding experiments in bovine cerebral cortex membranes using H-3-nitrendipine. Competition experiments have shown a 308-fold concentration range of K(i)-values (2.9 x 10(-10) to 8.9 x 10(-8)) for elnadipine derivatives and a eudismic ratio for elnadipine and its (+)-enantiomer of 448. Calmodulin (CaM)-antagonistic properties have been measured in the test system of CaM-stimulated phosphodiesterase. The concentration range of IC50 values only amounts to 9 (5 x 10(-7) to 4.5 x 10(-6) M). In contrast to Ca2+-antagonism, enantioselectivity of CaM-inhibition by elnadipine is negligible. CaM-antagonistic potency of elnadipine derivatives is diminished by a factor of 10 to 5000 as compared to their Ca2+-antagonistic potency. The following conclusions regarding structural determinants of Ca2+- and CaM-antagonistic properties can be made: lipophilic substituents of the oxadiazole in 5-position of the dihydropyridine (DHP) ring increase the CaM-antagonistic and decrease the Ca2+-antagonistic potency: correspondingly the unsubstituted compound is the strongest Ca2+- and the weakest CaM-antagonist; 1,3,4-oxadiazole substitution is superior to 1,2,4-oxadiazole as regards Ca2+- and CaM-antagonistic potency.