Chemical synthesis of the cardiotonic steroid glycosides and related natural products.

The active components from the extracts of Digitalis, cardiotonic steroid glycosides, have been ingested by humans for more than 200 years as a medicinal therapy for heart failure and abnormal heart rhythms. The positive inotropic activity of the cardiotonic steroids that mediates clinically useful physiological effects in patients has been attributed largely to a high affinity inhibitory interaction with the extracellular surface of the membrane-bound sodium pump (Na(+)/K(+)-ATPase). However, previously unrecognized intracellular signaling pathways continue to be uncovered. This Review examines both partial and de novo synthetic approaches to the medicinally important and structurally captivating cardenolide and bufadienolide steroid families, with an emphasis on the stereocontrolled construction of the pharmacophoric aglycone (genin) framework.

Digitalis-like compounds: synthesis and biological evaluation of seco-D and D-homo derivatives.

The synthesis of seco-D and D-homo digitalis derivatives, from the carda-14,20(22)-dienolide 1, is described. Selective ozonolysis gave the seco-D 14-ketoaldehyde 2a. Modification of the two carbonyl groups and of the alpha, beta-unsaturated lactone ring of the seco-D 14-ketoaldehyde 2a allowed preparation of derivatives with a broad range of binding affinity to the Na+, K(+)-ATPase receptor. Some of the seco-D derivatives (10, 11b, and 13b) showed a binding affinity similar to that of digitoxigenin, demonstrating that the D-ring is not essential for recognition by the digitalis receptor. In the class of D-homo derivatives the highest binding value, about 15 times lower than that of digitoxigenin, was that of the C/D cis compound 29b; the C/D trans analog 28b showed a 7-fold decrease in binding affinity, indicating that the C/D configuration plays an important role in D-homo derivatives as in the classical digitalis compounds.

Structure-activity relationships of synthetic digitoxigenyl glycosides.

Antiviral, cytotoxic and anti-ATPase activities of 14 synthetic digitoxigenyl glycosides were compared with each other. The activities of those containing gentiobioside and melibioside were much weaker than the others. On the other hand, the three activities were highly correlated with each other.

[Studies on cardiac ingredients of plants. VIII. Preparation of nitrates of proscillaridin and their pharmacological activities].

To reduce the vascular contracting effect of the cardiac glycoside, proscillaridin (1), all kinds of its nitrates were prepared by utilizing effectively an isopropylidene function as a protective group. The pharmacological activities of proscillaridin nitrates were evaluated by the use of isolated guinea-pig papillary muscle preparations and Na+,K(+)-adenosine triphosphatase preparations from the dog kidney. Furthermore, the effect for smooth muscle using the helical strips isolated from 13-week old spontaneously hypertensive rat was examined. The positive inotropic effects and Na+, K(+)-adenosine triphosphatase inhibition activities of mononitrates (6, 9, 15) and dinitrates (3, 4, 5) were a little less potent than 1, but those of trinitrate (2) were much reduced. Every nitrate did not exhibited a vascular contracting effect but a relaxing effect. Among them, the vascular relaxing effects of 2',3'-dinitrate (3) and 2',4'-dinitrate (4) were more potent than those of the other nitrates.

Cardiac glycosides. 6. Gitoxigenin C16 acetates, formates, methoxycarbonates, and digitoxosides. Synthesis and Na+,K+-ATPase inhibitory activities.

A series of 17 gitoxigenin 16 beta-formates, acetates, and methoxycarbonates was synthesized, including their 3 beta-acetates, formates, and digitoxosides. A 16 beta-formate group was generally found to increase activity 30 times, a 16 beta-acetate group 9-12 times, while a 16 beta-methoxycarbonate decreased activity by two-thirds. 3 beta-Formates and acetates had little effect on activity by themselves, but sometimes reduced the activity-increasing properties of 16 beta-formates and acetates. A 3 beta-digitoxoside increases the activity of gitoxigenin by 15 times, but the effect is less if the 16 beta-group is esterified. And finally, a 16-one decreases activity dramatically. These data suggest an important role for C16 esters and possibly the presence of a separate binding site on Na+,K+-ATPase corresponding to the cardenolide C16 position.

Cardenolide analogues. 14. Synthesis and biological activity of glucosides of C17 beta-modified derivatives of digitoxigenin.

An improved method for the synthesis of cardiac glycosides was used to prepare 3 beta-glucosides of digitoxigenin derivatives in which the 17 beta side chain was CH=CHX (X = COOH, CONH2, COCH3, CN, or COOR). We compared the inotropic activity of the compounds with that of digitoxigenin glucoside using guinea pig left atria. All compounds were active except for the acid (7) and the amide (8). The inactivity of the amide, in spite of its favorable shape and high capacity for forming intermolecular hydrogen bonds, is incompatible with some previous structure-activity relationship theories. Of the active genins, glucosidation enhanced activity by a factor of about 2. All glucosides, including those with high potency, showed rapid onset and offset of action. The stepwise fall in potency that occurred when the ester group (CH=CHCOOR) was increased in bulk supported previous suggestions that the portion of the digitalis receptor that interacts with the C17 side chain lies within a cleft.