Cardenolides, synthetic

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 of this transformation, cardiac aglycons and cardenolides should not be exposed to alkalinity greater than that provided by aqueous bicarbonate solution. The use of the Zempl6n procedure88 for the saponification of O-acylated cardenolides is likewise hazardous, although Elderfield and coworkers12 18 were successful in deacetylating their synthetic cardenolides with barium methoxide in methanol. 

A clue to a possibly correct assessment of the conformations of a-L- and of jS-D-cardenolides is provided by the infrared absorption spectra2 of the a-L-rhamnoside [evomonoside (10)3 and the synthetic a-D-rhamnoside (27) of digitoxigenin (1). The two spectra are so similar that only on very close scrutiny can minor differences be observed indeed, they are almost superposable. This fact suggested that the vibrational characteristics of the two molecules are nearly identical. Their structures might, then, be represented as shown, in which both have equivalent conformations. It is... 

This volume contains two chapters which update topics presented in earlier ones. The chemistry of the deoxy sugars has been expanded considerably since the review in Volume 8 by Overend and Stacey (Birmingham), as is attested by the chapter by Hanessian (Ann Arbor). The article on synthetic cardenolides, or cardiac glycosides, by Zorbach and Bhat (Georgetown) is an extension of related topics previously reviewed by Elderfield (Volume 1) and by Reichstein and Weiss (Volume 17). 

Steroids, which are a class of compounds that occur in nature and in synthetic products, have a cyclopen-tanoperhydrophenanthrene skeleton. The carbon atoms and rings are labeled according to the scheme shown in Fig. 1. The following classes of compounds belongs to steroids sterols, bile acids, cardenolides, androgens, estrogens, corticosteroids, steroid sa-pogenins, steroid alkaloids, ecdysteroids, and vitamin D. 

D-Oleandrose (38) has so far only been isolated from the digitanol glycoside lanafolein, but never from a cardenolide. With the exception of L-acofriose (27), L-acovenose (31), and L-diginose (42), all of these sugars have been prepared synthetically. A glycoside from Beaummtia grandiflora contains L-cymarose, which was recently obtained crystalline. 

The gross biological activity of various classes of steroids has been briefly reviewed and their action at cellular and molecular levels discussed. The texts of the Plenary Lectures presented at the Sixth International Symposium on The Chemistry of Natural Products have been published these include papers on steroidal alkaloids and sapogenins, " synthetic cardenolides, mass spectrometry of steroids, photochemical transformations of steroids which have preparative value, and new methods of specific fluorination of steroids. A series of graduate lectures on selected topics has appeared. ... 

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