Of cardenolide

Nelson, C. J., Seiber, J. N., and Brower, L. P. (1981). Seasonal and intraplant variation of cardenolide content in the California milkweed, A5c/ep/(M eriocarpa, and implications for plant defense. Jowrna/ of ChemicalEcobgy 7,981-1010. 

Glycoside diversification also has occurred in the coevolution of monarch butterflies and milkweeds (7). It may be desirable to relate the toxicity of cardenolides to the hydrolytic capabilities of susceptible and nonsusceptible insects. Cardenolides from Rsclepias species can be hydrolyzed by 3-glucosidases present in the plant (6), yet specialized Danans species are able to sequester these compounds, a process wh ich requires control of hydrolysis. 

Structure-Activity Correlations. The structure-activity relationships of cardenolides have been thoroughly investigated, and have undergone considerable revision on the basis of crystallographic work and potential energy calculations. The correlations are summarized as follows ... 

Analyses of cardenolide processing in the arctlld, Cycnla inopinatus, and the monarch, Danaus plexippus, demonstrate that each species has evolved distinctive physiological mechanisms for manipulating the medley of allelochemlcs that are internally omnipresent (26). 

Larvae of Inoplnatus emerge as major sequestrators of cardenolides primarily because their hemolymph, which is present in a relatively large volume, effectively sequesters high concentrations of polar cardenolides (26). Cardenolide excretion largely reflects loss of these steroids as components of the larval exuviae, the concentration of these compounds becoming relatively stable after pupal ecdysis. These steroids are ubiquitously distributed in the adult moth, having been derived primarily from the rich cardenolide pool in the larval blood. 

Nishio, S. "The Fates and Adaptive Signficance of Cardenolides Sequestered by Larvae of Danaus plexippus (L.) and Cycnia inopinatus (Hy. Edwards)" Ph. D. Thesis, University of Georgia, 1980. 

Synthetic methods for 2(5jF/)-furanones have been developed in the preparation of cardenolides (65MI31200). The ketone (171) when reacted with lithium ethoxyacetylide gives the carbinol (172) which undergoes acid catalyzed rearrangement to the a,/3-unsaturated ester (173). Allylic oxidation of (173) with selenium dioxide under mild conditions gives digitoxigenin acetate (174) (Scheme 38). 

Because a substantial excess of the halide is used in the Koenigs-Knorr synthesis of cardenolides, it is usually difficult, if not impossible, to secure the acylated intermediate in crystalline form. Hence, Reichstein nd coworkers18 introduced a procedure whereby the whole of the products arising from the coupling reaction are saponified, employing a solution of potassium hydrogen carbonate in aqueous methanol. This modified transesterification procedure renders all extraneous carbohydrate materials water-soluble the methanol is removed by evaporation, leaving an aqueous solution from which the (deacylated) cardenolide may be obtained by... 

Of the sixteen isomeric aldohexoses, only D-glucose has been found as a carbohydrate component of cardenolides. It generally occurs in combination with other sugars, and rarely are cardenolides found in which a d-glucose residue is joined directly to the aglycon moiety.6 Prior to the work... 

Pyranosyl moiety Formula of cardenolide LD/Vmole References... 

---