Remote functionalization of litho-cholic acid

Abstract

A remote photochemical functionalization of 3$\alpha$-acetylated lithocholic acid ester of p-hydroxy benzophenone (I) and m-benzoyl-2-methyl phenyl acetic acid ester of lithochloate (II) was attempted. The compound (I) was prepared through the reaction of p-hydroxy benzophenone with 3$\alpha$-acetylated lithocholic acid using N,N``dimethyl-carbodiimide (DCC) as a coupling reagent and dimethyl amino pyridine (DMAP) as a catalyst. Compound (II) was prepared through the reaction of m-benzoyl-2-methyl phenyl acetic acid chloride with lithocholate. The purified cyclohexane and/or benzene solution of (I) and (II) were irradiated with 350 nm UV light. The photoproduct mixtures were checked by thin layer chromatography and separated into several fractions by silica gel column chromatography. The NMR spectrum of each fraction was obtained and examined. The major photo-reaction was not the expected intramolecular reaction occurring by the intramolecular hydrogen abstraction by benzophenone moiety but intermolecular reactions such as photoreaction with solvent, impurities in the solvent, and decomposition of the steroid, etc.. No useful compound was obtained by this method.