17β-O-Aminoalkyloximes of 5β-Androstane-3β,14β-diol with Digitalis-like Activity:  Synthesis, Cardiotonic Activity, Structure−Activity Relationships, and Molecular Modeling of the Na⁺,K⁺-ATPase Receptor

Abstract

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 17beta 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 alpha,beta-unsaturated, thus mimicking the electronic situation of the unsaturated lactone in natural digitalis compounds. The most active compounds showed Na(+),K(+)-ATPase inhibitory potencies (IC(50)) 17-25 times higher than the standards digitoxigenin and digoxin and 3-11 times higher inotropic potencies (EC(50)) 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.

Novel analogues of Istaroxime, a potent inhibitor of Na+,K+-ATPase: Synthesis, structure–activity relationship and 3D-quantitative structure–activity relationship of derivatives at position 6 on the androstane scaffold

“…(E,Z)-3-(2-Aminoethoxyimino)-6-methyleneandrostane-17-one hydrochloride (1) Prepared in 90% yield from 6-methyleneandrostane-3,17-dione 61 and 2-aminoethoxyamine dihydrochloride. 26 …”

Elucidation of the Na+, K+-ATPase digitalis binding site

“…Furthermore, significant reduction in the binding affinity of ouabain [13][14][15][16][17][18] has been demonstrated subsequent to the alteration of individual residues in the TM5-TM6 loop (e.g., L793, T797); in the TM7-TM8 loop (e.g., R880); and other residues in the TM4, TM7 and TM10 segments [13][14][15][16][17][18]. Repke et al [19] and Cerri et al [20] have proposed as an alternative hypothesis that ouabain binds within the membrane along the TM1 and TM2 segments of two juxtaposed a-subunits of a dimeric (ab) 2 protomer, but this model is inconsistent with much of the mutational data, and with both our recent 3D-quantitative structure-activity relationship (3D-QSAR) model developed using comparative molecular field analysis (CoMFA) of cardiotonic steroid inhibition of ATPase activity [21], and solid-state NMR results obtained using ouabain derivatives [22].…”

Hydroxylamines and Oximes: Biological Properties and Potential Uses as Therapeutic Agents

“…−C=N−) 179 . This modification reduced 200-fold (IC 50 = 100 μM) the inhibition of Na + , K + -ATPase by digoxin (IC 50 = 0.5 μM).…”

“…Oximes (and their O-ether derivatives) of furan and thiophene 194 , pyridine 195 , indole and isatin 196 , pyrrole 197 and quinoline 198 are characterized by vasodilating and cardiotonic activities, and they were proposed as potential anticoagulant and antihypertensive drugs. O-aminoalkyl oximes with structures resembling that of digitogenin were reported as potential substitutes for the digitalis cardiac glycosides in the treatment of congestive heart failure 179,199 . Another O-aminoalkyl oxime, bimoclomol maleate, is considered to be a promising drug for treatment of abnormal vascular reactivity 186 .…”