Digitalis glycosides structure

The three most important groups of steroids are the sterols, bile acids, and steroid hormones. Particularly in plants, compounds with steroid structures are also found that are notable for their pharmacological effects—steroid alkaloids, digitalis glycosides, and saponins. 

Other classes of proteins that have been clearly identified as drug receptors include enzymes, which may be inhibited (or, less commonly, activated) by binding a drug (eg, dihydrofolate reductase, the receptor for the antineoplastic drug methotrexate) transport proteins (eg, Na+/K+ ATPase, the membrane receptor for cardioactive digitalis glycosides) and structural pro-teins (eg, tubulin, the receptor for colchicine, an anti-inflammatory agent). 

Milrinone is a member of a new class of bipyridine inotropic/vasodilator agents with phosphodiesterase inhibitor activity. It is a positive inotrope and vasodilator, with little chronotropic activity, different in structure and mode of action from either the digitalis glycosides or catecholamines (see also Figures 23 and 42). 

Diverse plants (A) are sources of sugar-containing compounds (glycosides) that also contain a steroid ring (structural formulas, p. 133) and augment the contractile force of heart muscle (B) cardiotonic glycosides, cardiosteroids, or digitalis."... 

The positive benefits of extracts of two species of Digitalis purpurea (foxglove and lanata) were recognized long before the active constituents were isolated and structurally characterized. The cardiac glycosides, which include digoxin, digitoxin, and deslanoside, exert a powerful and selective positive inotropic action on the cardiac muscle (see Chapter 35). 

From Strophanthus gratus a crystalline glycoside, ouabain, has been obtained. It was so named because it was first isolated from the root and bark of the Ouabaio tree, which is the source of an arrow poison used by the Somalis of East Africa. Because of its well-defined physical characteristics and crystalline structure, ouabain, C29H44012, served for a time as a standard in the U.S. for the assay of the digitalis group of drugs. 

Figure 6.8. Digitalis (foxglove) glycosides, a Mode of action. The drags inhibit the Na /K -ATP ase. The increased intracellular sodium concentration will reduce the activity of the Na /Ca antiport system and therefore lead to an increase of intracellular Ca and augment myofilament contraction, b Structures.

Figure 6.5 Structures of cardiac glycosides mentioned in the text and cardenolide esters and glycosides produced by biotransformation. Formation of the sugar side chain of Digitalis cardenolides.

---