Synthesis and 29-14C-labeling of 3α,7α,12α-trihydroxy-27-carboxymethyl-5β-cholestan-26-oic acid. A bile acid occurring in peroxisomal diseases

Abstract The synthesis and 14 -labeling of 3α,7α,12α-trihydroxy-27-carboxymethyl-5-β-cholestan-26-oic acid by two different approaches is described. One of them involves chain elongation of cholic acid via Wittig-Horner condensation of its formylated 24-aldehyde with tetraethyl phosphonoglutarate. The resulting cholestenoate, on deprotection and hydrogenation, affords the unusual C 29 bile acid in good yield. An alternative procedure consists in a malonic ester synthesis starting from the formulated 24-alcohol which, after conversion into a mesylate, is reacted with sodium salt of 2-carboethoxy-γ-butyrolactone. Alkaline hydrolysis, decarboxylation, esterification with diazomethane and selective tosylation of the newly introduced primary hydroxyl function give a C 28 precursor, which is easily chain-elongated into a labeled or unlabeled C 29 bile acid by reaction with cyanide and hydrolysis. Due to easy lactonization of some of the C 28 intermediates, the latter method provides a better way for introducing a C-29 label than the sequence usually employed for carboxyl labeling of bile acids and consisting in a decarboxylative halogenation of the parent acid followed by substitution of the norhalogenide with [ 14 C]cyanide and hydrolysis. The structure of the synthesized acid or its dimethyl ester is confirmed by 13 C nuclear magnetic resonance spectroscopy and mass spectrometry, and is also shown by gas liquid chromatography to be identical with an authentic sample of biosynthesis C 29 dioic bile acid extracted from body fluids of Zellweger patients.