Description
The syntheses of steroids substituted with perfluoroalkyl, perfluoroalkanoyloxy, and perfluoroalkenyloxy groups are described. These compounds are intended as co-emulsifying agents with Pluronic F-68 or phospholipid emulsifiers for perfluorinated compounds (PFC} in water. A brief review of synthetic blood, concept of emulsification, and our choice of ideal PFC for the synthetic blood studies is also presented. Steroids substituted with perfluoroalkyl groups at C-3, C-7, and C-20 positions were synthesized by coupling perfluoroalkyl copper reagents with steroidal bromides, and reacting perfluoroalkyl Grignards with steroidal ketones. Mono-, bis-, and tris-perfluorooctanoyloxy derivatives of sterols and bile acids were synthesized by employing 4-dimethylaminopyridine-catalyzed perfluoroacylation. In the absence of 4-dimethylaminopyridine a much slower reaction occurred, and in case of bile acids the C-12 hydroxyl group did not react. The synthesis of C-23 hydroxylated tris-(perfluorooctanoyloxy)-substituted bile acid derivative was achieved by first acylating the hydroxyl groups of 3a,7a- 12a-trihydroxy-24-nor-5f3-chol-22-ene, and then hydro borating the double bond in the side-chain. Perfluoroalkenyl ethers of sterols were prepared by the base-catalyzed addition/elimination reaction of sterols with perfluoroalkenes. Best results were obtained when n-butyllithium was used as a base; only perfluoro-trans-l alkenyl-1-oxy steroids were obtained. C-23 and C-24 hydroxylated bis- and tris-perfluoroalkenyloxy derivatives of bile acids were synthesized by two methods. In the first method the C-24 hydroxyl group of 5f3-cholan-3a,7a,12a,24-tetrol was selectively protected with tert-butyldiphenylsilyl chloride. The unsubstituted hydroxyl groups were then deprotonated with n-butyllithium and reacted with perfluoro alkene to give perfluoroalkoxy substitution on the steroid ring. In the second method the hydroxyl groups of 3a,7a,12a-trihydroxy-5f3-chol-22-ene (or 3a,12a-dihydroxy- 24-nor-5f3-chol-22-ene) were first deprotonated with n-butyllithium and then reacted with perfluoroalkenes. The C-22 double bond was then hydroborated to give C-23 hydroxylated perfluoroalkenyloxy bile acid derivatives. Steroids with one perfluoroalkyl, perfluoroalkenyloxy or perfluoroalkanoyloxy group are soluble to the extent of 40-100 mg per 4 gm (2 mL) of 1-bromoperfluorooctane. The solubilities of similarly substituted bis- and tris substituted compounds are in excess of 2 gm per 4 gm of 1-bromoperfluorooctane.
