The cardiac glycosides are pharmaceutically potential drug groups that are available to medicine today for the treatment of congestive heart failure. Clinically availabilities are derived from the leaves and seeds of plant in the genera Digitalis and Strophanthus. In vitro culture, regeneration, and production of Digitalis (foxglove) cardenolides and other secondary metabolites were reviewed in detail ().
Strophanthus, belonging to the family Apocynaceae (the dogbane family), is from the Greek meaning “a turn or twist” and “a flower” and refers to the twisted lobes of the corolla. About 40 species of Strophanthus native to Africa and Asia, chiefly tropical, are perennial trees, shrubs or climbers up to 3 m tall. The leaves are feathery or leathery and opposite. The cymose inflorescence is terminal. Members of this genus have a variety of fragrant flowers, ranging in color from white, through the yellows and reds, to purple. The calyxes is glandular, the corolla funnel-shaped, with five lobes tapering into attenuated, long tails. The two carpeled ovaries develop into capsular fruits having two diverging free follicles, which enclose the hairy seeds. Strophanthus seeds have long been used by the native Africans in the preparation of arrow poisons ().
The flowering of Strophanthus gratus grown in the greenhouse can be seen in site. A large number of cardiac glycosides have been isolated from Strophanthus plants (), and highly oxygenated aglycones in comparison with Digitalis cardenolides are characteristic of Strophanthus cardenolides (). Strophanthus gratus, found in western tropical Africa from Sierra Leone to the Congo, contains 4-8% G-strophanthin (ouabain) in the seeds. Its chemical structure is 3p-(α-L-rhamnopyranosyloxy)-1β,5, 11α,14,19-pentahydroxy-5β,14β-card-20(22)-enolide octahydrate (Fig. 3) and this compound is the most polar of the commonly used cardiac glycosides. The seeds of Strophanthus kombe, native to central and eastern Africa, mainly Mozambique, Northern Rhodesia, Nyasaland, and Tanzania, provide the precursor for semisynthetic compound acetylstrophanthidin. Both of these compounds are of clinical interest because of their rapid onset of action and the relatively rapid offset of effect when they are administered intravenously (). In biochemical studies, ouabain is well known as a specific inhibitor of Na+, K+-ATPase.
G-Strophanthin (ouabain) obtained from the seeds of Strophanthus gratus or from the wood of Acokanthera schimperi or A. ouabaio (Apocynaceae) is official in the pharmacopoeias of many countries; Argentina, Austria, Belgium, Czechoslovakia, Egypt, France, West Germany, Italy, Japan, Mexico, The Netherlands, Scandinavia, Poland, Romania, Spain, Switzerland, and Turkey (all 8 H2O); Portugal (9 H2O). Additionally, proprietary names and manufacturers for commerical use are as follows; g-Strofantin (DAK, Denmark, Sweden); Ouabaine Aguettant (France); Ouabaine Arnaud (Gamaprod, Australia; Nativelle, France; Lipomed, United Kingdom, The Netherlands, Spain); Purostrophan (KaliChemie, West Germany); Strodival (Herbert, West Germany); Strophoperm (West Germany) ().
In order to obtain Strophanthus cardenolides, we continue fundamental studies using plant cell and tissue cultures. No cardenolides were detected by TLC analysis of extracts of the calli derived from Strophanthus gratus, Strophanthus amboensis, Strophanthus intermedius, and Strophanthus divaricatus. Moreover, cardenolide production could not be observed by bio-transformation of progesterone, a precursor of cardenolides, with these suspension cultures, similarly using cultured cells of Digitalis purpurea ().
In this chapter, we describe the biotransformation of digitoxigenin (1), a precursor of cardiac glycosides, by cell suspension cultures of Strophanthus gratus (), Strophanthus amboensis (), Strophanthus intermedium (), and Strophanthus divaricatus () and cardiac glycosides from the regenerated plants of Strophanthus divaricatus through the calli under controlled culture conditions ().
Selections from the book: “Medicinal and Aromatic Plants IV”, 1993.