Journal of Lipid Research, Vol 32, 1381-1387, Copyright © 1991 by Lipid Research, Inc.
Stereospecific synthesis and two-dimensional 1H-NMR investigation of isoursocholic acid
B Dayal and G Salen
Department of Medicine, UMDNJ-New Jersey Medical School, Newark 07103.
This report describes the chemical synthesis of isoursocholic acid (3 beta,
7 beta, 12 alpha-trihydroxy-5 beta-cholanoic acid) from its corresponding 3
alpha-analog. The method consists of refluxing a mixture of ursocholic
acid, triphenylphosphine, and diethyl azodicarboxylate in benzene solution
with an acid such as formic acid. The sterically pure ester (3
beta-formate) so formed after saponification with LiOH-aqueous methanol
then allowed an easy access to the epimer of the starting acid. Large scale
preparative separation and purification of the final product and synthetic
intermediates were accomplished by flash column chromatography of their
methyl ester derivatives. Structural assignment of the isourscholic acid
molecule was confirmed by complete analysis of proton NMR spectra using 2-D
NMR correlation experiments which rigorously established the (3 beta/3
alpha) and (7 beta/7 alpha) hydroxyl configurations in the isoursocholic
and ursocholic acids. It is suggested that the isoursocholic acid will be
useful as a reference compound and as a substrate in studies dealing with
the hepatic inversion of the 3 beta- hydroxy group.
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