Studies on cardioactive steroids. I. Structure-activity relationships on the isolated atrium

Cardenamides from Cardenolides: Cardiac and Anticancer Activities

Two ways are shown to transform cardioactive cardenolides into cardenamides [17β-(5-oxo-2,5-dihydropyrrol-3-yl)-5β,14β-androstane derivatives], and their derivatives by replacement of their ring oxygen by N-R. Cardioactivity is strongly decreased by this transformation. The comparatively easily accessible 21-oxocardenamides [17β-(2-maleimidyl)steroids] are strongly thiol reactive and show remarkable anticancer activity.

Comparative studies of some semisynthetic K-strophanthins with natural cardiac glycosides

In this study the pharmacological effects of seven semisynthetic cardenolides have been investigated and compared with those of 11 natural cardiac glycosides. These compounds are of different potency on electrically driven isolated guinea-pig atria. Their concentration response curves showed different slopes, which could be an indication of varying therapeutic range. The pharmacodynamics of these compounds on isolated guinea-pig atria are in good correlation with the data obtained from binding studies on guinea-pig ventricular homogenate as well as that obtained from comparative experiments on Na+,K+-ATPase activity inhibition.

Synthesis and biological activity of some cardiotonic compounds related to gitoxigenin

The four diastereomeric 3,16-diacetates 6, 9, 10 and 11 were prepared from gitoxin 1 by the routes shown in Schemes 1 and 2 and tested for inotropic activity in the isolated guinea-pig atrial preparation. In line with earlier findings in the digitoxigenin series, derivatives with a 3 alpha-acetoxy function, viz 9 and 10, possessed high biological activity.

Synthesis and biological activity of some 3-amino compounds related to digoxigenin

3 alpha-Amino 1a and 3 beta-amino 1b analogues of digoxigenin 14 and their 12 beta-acetate derivatives 2a and 2b were prepared and tested for inotropic activity in the isolated guinea-pig atrial preparation. The 3 alpha-amino compounds were inactive whereas the 3 beta-amino compounds showed comparable activity to their 3 beta-hydroxy counterparts. The replacement of the 17 beta-butenolide ring by other ring systems was investigated. Compounds with a 3'-furyl ring, 9b and 16 were found to possess appreciable activity. A compound with a 4'-pyridazinyl ring 13b exhibited weak activity, whereas the isomeric butenolide compound 11b proved inactive. N-monomethylation of the amine 2b reduced activity and N-dimethylation abolished activity. Acetylation of the 12 beta-hydroxyl function gave less active compounds.

Investigation into the species-specific deacylation of penta-acetyl-gitoxin

Penta-acetyl-gitoxin (PAG) shows species-specific deacylation to 16-acetyl-gitoxin (16 AG; I and III) or gitoxin (II and IV) by homogenates of liver and intestinal mucosa of man (I), rabbit (II), guinea-pig (III) and rat (IV), whereas it is degraded into tri- and tetra-acetates by homogenates of guinea-pig myocardium as well as by human blood and serum. The identity of the principal and chloroform-extractable metabolities in human urine after PAG administration with 16-AG has been demonstrated by mass spectrometry.

Correlation between inhibition of (Na+, K+)-membrane-ATPase and positive inotropic activity of cardenolides in isolated papillary muscles of guinea pig

Concentrations of 17 cardenolides, cardenolide glucuronides and sulfates producing half-maximal inhibition of (Na+, K+)-membrane-ATPase from different organs and animal species were determined in vitro. In addition the concentrations that increased the contractility of guinea pig isolated papillary muscles to a particular level were investigated. Comparisons between ATPase-inhibiting and positive inotropic cardiac activities showed extensive parallelism: the correlation coefficients after log/log transformation were between 0.92 and 0.97. The same close correlations are found if dissociation constants of cardenolide receptor complexes and concentrations causing 86Rb-uptake inhibition in human erythrocytes are examined. The concentrations necessary for inhibition of (Na+, K+)-membrane-ATPase of the guinea pig heart and the concentrations required to achieve a defined positive inotropic effect in guinea pig papillary muscle showed a log/log correlation coefficient of 0.97 (P less than 0.001). In both tests the potencies covered more than three orders of magnitude. The results support Repke's hypothesis on the digitalis receptor.

Pharmacokinetic investigations in man of two acetyl derivatives of 16alpha-gitoxin

3H-16-acetyl-16alpha-gitoxin or 3H-penta-acetyl-16alpha-gitoxin were injected iv or administered po to 15 volunteers and 3 patients. The elimination half-life and excretion in urine within 4 days were estimated as a percentage of the administered radioactivity, and metabolic studies on the fate of the administered glycosides were performed. In volunteers the following results were obtained: 3H-16-acetyl-16alpha-gitoxin 1 mg iv.: 50 +/- 11 h, 28.3 +/- 4.1%; 3H-16-acetyl-16alpha-gitoxin 1mg po: 48 +/- 8 h, 25.4 +/- 2.8%; 3H-penta-acetyl-16alpha-gitoxin 2 mg po: 51 +/- 12 h, 20.7 +/- 3.2%, respectively. In 3 patients with a cannulated bile duct 9.9% (mean) of the administered 3H-16-acetyl-16alpha-gitoxin was excreted. By comparison of the radioactivity excreted in urine following the 2 routes of 16-acetate administration, the percentage absorption was calculated to be 88.5%. In serum and urine 16-acetyl-16alpha-gitoxin and 16alpha-gitoxin were found as possible metabolites of both glycosides, in the ratio of 75-85:15-25, and both metabolites were also found in bile. Within 16 h after penta-acetate administration, two additional metabolites (bis-acetyl-derivatives of 16alpha-gitoxin) were detected in serum and urine within 16 h after administration of penta-acetate.