Cardiac glycosides biosynthesis

Seidel, S., Kreis, W. and Reinhard, E. (1990) A5-3fJ-Hydroxysteroid dehydrogenase/ A5-A4-ketosteroid isomerase (3fJ-HSD) a possible enzyme of cardiac glycoside biosynthesis, in cell cultures and plants of Digitalis lanata EHRH. Plant Cell Rep., 8, 621-4. 

Natural products are generally classified by a number of criteria functional, structural and biosynthetic. Despite the reservations expressed above, certain functional subdivisions are useful in certain applications. Such terms as antibiotics, hormones or cardiac glycosides are commonly used. The grouping of natural products on the basis of common carbon skeletons is perhaps the most attractive for the chemist. The realization that many natural products fall into distinct structural groups which could be, at least formally, derived from much simpler molecules was an important development in that it led to the proposal of speculative biogenetic hypotheses which were largely responsible for stimulating the rapid development of the field of biosynthesis. However, such an approach is not entirely satisfactory since it is now clear that many compounds which are of similar structural types are derived by quite different routes in vivo. 

Keywords biosynthesis cardiac glycosides ecdysteroids metabolic pathways phylogeny pregnanes saponins secondary metabolites withanolides... 

Biochemistry of Sterols, Cardiac Glycosides, Brassinosteroids, Phytoecdysteroids 309 6.2.1 Biosynthesis... 

Plant sterols are products of primary metabolism, but they may also be regarded as direct precursors of many secondary plant metabolites, such as the cardiac glycosides, saponins and steroid alkaloids. All of the compounds mentioned share the same basic skeleton therefore, the accumulation of a particular compound can only be achieved if (1) enzymes with a high degree of substrate specificity are involved in their biosynthesis, (2) metabolites can be channelled efficiently to the respective pathways and (3) products can be transported, sequestered and/or stored in specific compartments. 

The biosynthesis of the Cja-bufadienolides, aglycones of the cardiac glycosides, e.g. hellibrigenin (III) is not known. 

GERSHENZON, J., KREIS, W., Biosynthesis of monoterpenes, sesquiterpenes, diterpenes, sterols, cardiac glycosides and steroid saponins, in Biochemistry of Plant Secondary Metabolism, Annual Plant Reviews, Vol. 2 (Wink, M., ed,), Sheffield Academic Press, Sheffield. 1992, pp. 222-299. 

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