Alberto Cerri

A series of 5-substituted (3aS,7aR)-7a-methylperhydroinden-3a-ol derivatives bearing a 1(S)-(ω-aminoalkoxy)iminoalkyl or -alkenyl substituent was synthesized, starting from the Hajos−Parrish ketol 47, as simplified analogues of very potent 17β-aminoalkyloximes with digitalis skeleton, previously reported. The target compounds were evaluated in vitro for displacement of the specific [³H]ouabain binding from the dog kidney Na⁺,K⁺-ATPase receptor. Some of them revealed IC₅₀ values in the micromolar range. The most active compounds possess a cyclohexyl group in the 5(S) position and in position 1(S) the same aminoalkyloxime groups already reported for the digitoxigenin-like series in position 17β. Although the ring conformation of these derivatives was comparable to that of uzarigenin, the binding affinities of the most active ones were 4/8-fold lower in comparison to that standard. Three compounds among those with the highest affinities were assayed in vitro for their inotropic activity on an electrically driven guinea pig left atrium and were found to be less potent than both digoxin, the most widely used inotropic agent, and the corresponding digitalis 17β-aminoalkyloximes.

The synthesis and binding affinities to the digitalis Na⁺,K⁺-ATPase receptor of a series of 3β,14β-dihydroxy-5β-androstane and 3β-hydroxy-14-oxoseco-D-5β-androstane derivatives bearing a 17α-(aminoalkoxy)imino chain are reported; some derivatives were also studied for their inotropic activity. Our recently proposed model of interaction of molecules with the digitalis receptor was used to design these compounds. On that basis, the possibility to design novel potent inhibitors of Na⁺,K⁺-ATPase without being constrained by the stereochemistry of the classical digitalis skeleton in the D-ring region was predicted. The binding affinities of the most potent compounds in the two series, (EZ)-17α-{2-[(2-aminoethoxy)imino]ethyl}-5β-androstane-3β,14β-diol (6f) and (EZ)-3β-hydroxy-17α-{2-[(2-aminoethoxy)imino]ethyl}-14,15-seco-5β-androstan-14-one (24c) are higher than that of the potent natural compound digitoxigenin, despite the unusual α-exit of the substituent in position 17 of 6f or the disruption of the D-ring in 24c. These results further support the validity of our recently proposed model of binding at the digitalis receptor. Results of the inotropic tests on guinea pig atrium deserve further investigation on the pharmacological profile of these derivatives.

A series of digitalis-like compounds with a 17-aminoalkoxyiminoalkyl or -alkenyl substituent was synthesized and evaluated for inhibition of Na⁺,K⁺-ATPase and for inotropic activity. The highest inhibition was found with compounds having the substituent in configuration 17β and the amino group at a distance of 6 or 7 bonds from C(17) of the digitoxigenin skeleton. The presence of the oxime function strengthens the interaction with the receptor, more if α,β-unsaturated, thus mimicking the electronic situation of the unsaturated lactone in natural digitalis compounds. The most active compounds showed Na⁺,K⁺-ATPase inhibitory potencies (IC₅₀) 17−25 times higher than the standards digitoxigenin and digoxin and 3−11 times higher inotropic potencies (EC₅₀) in isolated guinea pig left atria. These features are supported by a molecular model suggesting the possible interactions of the groups described above with particular amino acid residues in the H1−H2 domains of Na⁺,K⁺-ATPase. Some interactions are the classical ones already described in the literature; a new, very strong interaction of the basic group with the Cys138 was found and adds new possibilities to design compounds interacting with this region of the receptor. The most interesting compounds were also studied in vivo in the anesthetized guinea pig for evaluating their inotropic effect versus the lethal dose. Compounds 9 and 12 showed a slightly higher safety ratio than digoxin and deserve further evaluation.