The chemistry and biological activity of derivatives of strophanthidin

Cardiotonic steroids: correlation of sodium-potassium adenosine triphosphate inhibition and ion transport in vitro with inotropic activity and toxicity in dogs

1. A new series of cardiotonics based on five steroid nuclei has been evaluated for inhibition of Na-+/K-+-ATPase and Rb uptake by red blood cells, and for inotropic activity and toxicity in dogs. Structure-activity relationships are discussed. 2. The in vitro tests can be used satisfactorily to predict inotropic activity, but not toxicity or therapeutic ratio. 3. Although compounds with greatly improved therapeutic ratios relative to ouabain and tolusin have been obtained, they proved to be strongly emetic in the conscious dog.

Structure-activity relationships of several cardiotonic steroids with respect to inhibition of ion transport in frog muscle

Cesium uptake by sodium-loaded frog sartorius muscles was inhibited 100% by 10(-6)M ouabain and 10(-6)M cymarin. The doses for 50% inhibition of cesium uptake by five cardiotonic aglycones were 1.5 x 10(-6)M for strophanthidin, 2 x 10(-7)M for telocinobufagin, 1.6 x 10(-6) for digitoxigenin, 2.4 x 10(-6)M for periplogenin, and 6.3 x 10(-6)M for uzarigenin. Because of the limited solubility of sarmentogenin the maximum concentration studied was 2 x 10(-6)M which inhibited cesium uptake about 36%. Inhibition of cesium uptake by cymarin was not reversed during a 3.5 hr incubation in fresh solution while the muscles treated with ouabain and strophanthidin recovered partly during this time. Cymarin was a more potent inhibitor of sodium efflux than strophanthidin and periplogenin was less potent. Increased cesium ion concentration in the external solution decreased the strophanthidin inhibition of cesium uptake but 25 mM cesium did not overcome the inhibition by 10(-8)-10(-6)M strophanthidin. Increased potassium ion concentration in the external solution decreased but did not completely overcome inhibition of sodium efflux by strophanthidin. It is concluded that potassium or cesium ions do not compete with these drugs for a particular site on the ion transport complex. The same structural features of the drugs are necessary for inhibition of ion transport in frog muscle as are required for inhibition of ion transport in other tissues, inhibition of sodium-potassium-stimulated ATPases, and toxicity to animals.

Hellebrigenin 3-haloacetates: potent site-directed alkylators of transport adenosinetriphosphatase

Hellebrigenin, which diflers from strophanthidin only in its lactone ring, has 30 times the affinity of strophanthidin for the brain (Na + K)-activated adenosinetriphosphatase. Hellebrigenin 3-acetate and hellebrigenin 3,5-diacetate are about three times more potent toward this enzyme than hellebrigenin is. The 3-iodoacetate and 3-bromoacetate of hellebrigenin were synthesized and were highly potent irreversible inhibitors of the enzyme. The iodoacetate was 20 times more potent than the bromoacetate, as expected from the superior alkylating power of iodoacetate as compared to bromoacetate. The irreversible inhibition of the enzyme by hellebrigenin 3-bromoacetate and by strophanthidin 3-bromoacetate paralleled the affinities of the nonesterified steroids for reversible inhibition; this is further strong evidence for the site-directed alkylation of the (Na + K)-activated sinetriphosphatase by the haloacetate derivatives of the cardiotonic steroids.