Fluorinated steroids, biological selectivity

Fluorinated Steroids. The fluorination of steroids has been known to have profound effects on biological activity since the early work of Fried (40). Fluorinated steroids have been described in other reviews (111). The use of fluorination as a tool to enhance biological selectivity and to improve the utility of a biologically active material has been clearly demonstrated in studies of vitamin D. ... 

The tertiary fluorination reaction is general even for complex steroid molecules. By selecting the correct electron-withdrawing substituent in various places, one can substitute almost any tertiary hydrogen of the skeleton. Consecutive dehydrofluorination produces double bonds serving as entry for constructing biologically important steroids.41 Thus it is possible to introduce fluorine at positions 9, 14, 17, and more, see 11, 12 and 13, respectively. 

The fluorination of 12, easily prepared from the corresponding triketo steroid, with an equimolar amount of 1 (Scheme 2) shows the remarkable ability of 1 to distinguish di-substituted from tri-substituted enol silyl ethers. The 9a-fluoro steroid 13 is produced in 51% yield (78% based on recovered triketo steroid) and the combined yield of the other fluorinated products is only 4.6%.17 it thus is apparent that 1 reacts almost exclusively with the trisubstituted enol ether moiety. The new, selective direct fluorination at the 9a-position holds considerable promise as a means to prepare biologically important 9a-fiuoro steroids.18... 

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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