Cardenolides cardiac

Digitoxigenin glycoside) (cardenolide, cardiac glycoside) D. viridifbra (Scrophulariaceae) [leaf] toxic]... 

When used at room temperature in the presence of an active platinum catalyst in an inert solvent, e.g., acetone or ethyl acetate, oxygen will oxidize nonhindered, saturated hydroxyl groups and exposed allylic alcohols. This reagent has found extensive use in sugar chemistry and is particularly suited for the selective oxidation of either 3a- or 3j -alcohols of steroids. Other hydroxyl groups on the steroid skeleton are much less sensitive to oxidation. As a result, this reaction has been used extensively in research on polyhydroxy cardiac-active principles, e.g., the cardenolides and bufadienolides, where the 3-hydroxyl group is easily oxidized without extensive oxidation or dehydration of other hydroxyl groups. The ordinarily difficult selective oxidation of the... 

Na+/K+-ATPase. Figure 2 Specific Inhibitors of Na+/K+-ATPase. (a) Endogenous cardiac glycosides identified in mammals. Substances with a 5-membered lactone at position C17 of the steroid moiety are referred to as cardenolides, those with a 6-membered lactone as bufadienolides. (b) Palytoxin (C P NsO ) produced by corals of the genus Palythoa. 

If 50% of Europeans with essential hypertension are affected by this disease because of an elevated secretion of endogenous ouabain, then there might be a chance to block its interaction at the cardiac glycoside binding site of Na+/K+-ATPase and thus lower blood pressure. This therapeutic approach seems to be successfiil. Recent studies provide evidence that the cardenolide analogue Rostafuroxin (PST 2238 Fig. 4) at very low concentrations can overcome the ouabain-induced tise of hypertension in experimental animals [6]. This compound has recently entered the phase I of clinical trials and is certainly a prototype of a new class of antihypertensive drugs. 

A classical example of sequestration is the monarch butterfly Danaus plexip-pus (Danainae) which feeds on leaves oiAsclepias curassavica (Asclepiadaceae) and sequesters cardenolides such as calotropin (158) (Fig. 29). This molecule was shown to afford the butterfly an efficient protection against birds [150-152]. It was also demonstrated that its resistance to cardiac glycosides is due to a single amino acid mutation in the ouabain-binding site of the Na+/K+ ATPase [153,154]. 

FIGURE 11.7 Cardiac glycosides consist of a sugar, a steroid skeleton, and a lactone ring. A five-membered lactone ring as here occurs in the cardenolide type. 

Cardiac glycosides are medicinally important steroids. Cardenolides are used in heart therapy, as emetics, diuretics, and purgatives. They affect the Na+/K+-ATPase and are very toxic at high doses. 

Types of Cardiac Glycoside. Three groups of plants produce cardenolides the Digitalis species, growing in temperate climates the Strophanthus species, of tropical provenance and Scilla (sea onion or squill), a Mediterranean plant. 

N.A. Convallaria majalis L. C. sepium L. Cardiac glycosides, cardenolides, convallotoxin, convalloside, convallatoxol, flavonoid glycosides." Affect in heart failure, regulate heart beat, lower blood pressure. 

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