Synthesis of 5beta-cholestane-3alpha, 7alpha, 12alpha, 25-tetrol and 5beta-cholestane-3alpha, 7alpha, 245, 25-pentol.

This paper describes syntheses of 5beta-cholestane-3alpha, 7alpha, 12alpha, 25-tetrol and 5beta-cholestane-3alpha, 7alpha, 12alpha, 24xi, 25-pentol which give higher yields than previously published methods. In addition, 5beta-cholestane-3alpha, 7alpha, 12alpha, 24xi, 25-pentol was synthesized by a different procedure, namely via performic acid oxidation of the correspinding unsaturated triol, which gave a lower yield but avoided the formation of 5beta-cholestane-3alpha, 7alpha, 12alpha, 25, 26-pentol, which normally tends to contaminate the final product. Structures were confirmed by gas-liquid chromatography, infrared-, proton magnetic resonance- and mass spectrometry, 5beta-Cholestane-3alpha, 7alpha, 12alpha, 25-tetrol and 5beta-cholestane-3alpha, 7alpha, 12alpha, 24xi, 25-pentol were required for in vivo and in vitro studies of the (hypothetical) 25-hydroxylation pathway of cholic acid biosynthesis.     

Identification of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25,26-hexol in human urine

A new bile alcohol, 5 beta-cholestanehexol, was identified in the urine of healthy humans as the glucuronide. The bile alcohol glucuronide fraction was isolated by an ion exchange chromatography on piperidinohydroxypropyl Sephadex LH-20. After enzymatic hydrolysis, the bile alcohols were converted into trimethylsilyl ether derivatives and analyzed by a combination of gas-liquid chromatography and mass spectrometry. The major bile alcohol was 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25-pentol. As minor constituents the following C26 and C27 bile alcohols were identified: 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25,26-hexol, 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25-pentol, 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,26-pentol, 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25,26-pentol. In addition to these bile alcohols, a new bile alcohol was identified as a sixth component of the urinary bile alcohols. The structure was assigned as (24S)-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25,26-hexol by the direct comparison of mass spectral data and chromatographic properties with synthetic standard. The average daily excretion of the new bile alcohol was 28.6 micrograms and 3.0% of the total bile alcohols. The presence of 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25-pentol and 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25,26-hexol suggests that 26-hydroxylation of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25-pentol is most likely for the biosynthesis of this new bile alcohol.     

Configurational assignment of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 23, 25-pentol excreted by patients with cerebrotendinous xanthomatosis (a circular dichroism study).

The absolute configuration of the C27 pentahydroxy bile alcohol present in bile and feces of two patients with cerebrotendinous xanthomatosis (CTX) was determined by circular dichroism (CD) spectroscopy. Under anhydrous conditions CD spectra of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 23, 25-pentol in the presence of Eu (fod) 3[tris (1, 1, 1, 2, 2, 3, 3-hepta fluoro-7, 7-dimethyl-octane-4, 6-dionato) europium (III)] exhibited a large induced split Cotton effect at ca. 310 nm. From the induced circular dichroism of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 23, 25-pentol with Eu(fod) 3 it was concluded that the CTX bile alcohol has the 1, 3 glycol structure with carbon 23 having the R configuration. This information will be useful in elucidating a structural mechanism for the conversion of 5 beta-cholestranepentols into bile acids in man and rat.     

Structural and biosynthetic studies of a principal bile alcohol, 27-nor-5beta-cholestane-3alpha,7alpha,12alpha,24,25-pentol, in human urine

The stereochemistry at C-24 and C-25 of 27-nor-5beta-cholestane-3alpha,7alpha,12alpha,24 ,25-pentol, a principal bile alcohol in human urine, and its biosynthesis are studied. Four stereoisomers of the C(26)-24,25-pentols were synthesized by reduction with LiAlH(4) of the corresponding epoxides prepared from (24S)- or (24R)-27-nor-5beta-cholest-25-ene-3alpha, 7alpha,12alpha,24-tetrol. The stereochemistries at C-25 were deduced by comparison of the C(26)-24,25-pentols with the oxidation products of (24Z)-27-nor-5beta-cholest-24-ene-3alpha,7alpha, 12alpha-triol with osmium tetraoxide. On the basis of this assignment, the principal bile alcohol excreted into human and rat urine was determined to be (24S,25R)-27-nor-5beta-cholestane-3alpha,7alpha, 12alpha,24,25-pentol, accompanied by a lesser amount of (24R, 25R)-isomer. To elucidate the biosynthesis of the C(26)-24,25-pentol, a putative intermediate, 3alpha,7alpha, 12alpha-trihydroxy-27-nor-5beta-cholestan-24-one, derived from 3alpha,7alpha, 12alpha-trihydroxy-24-oxo-5beta-cholestanoic acid by decarboxylation during the side-chain oxidation of 3alpha,7alpha, 12alpha-trihydroxy-5beta-cholestanoic acid, was incubated with rat liver homogenates. The 24-oxo-bile alcohol could be efficiently reduced to yield mainly (24R)-27-nor-5beta-cholestane-3alpha,7alpha, 12alpha,24-tetrol. If a 25R-hydroxylation of the latter steroid occurs, it should lead to formation of (24S,25R)-C(26)-24,25-pentol. Now it has appeared that a major bile alcohol excreted into human urine is (24S,25R)-27-nor-5beta-cholestane-3alpha,7alpha, 12alpha, 24, 25-pentol, which might be derived from 3alpha,7alpha, 12alpha-trihydroxy-27-nor-5beta-cholestan-24-one via (24R)-27-nor-5beta-cholestane-3alpha, 7alpha,12alpha,24-tetrol.     

Absolute configuration at carbon 23 of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,23,25-pentol excreted by patients with cerebrotendinous xanthomatosis

Absolute configuration at C-23 of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,23,25-pentol, one of the bile alcohols isolated from the patients with cerebrotendinous xanthomatosis, was unequivocally determined as 23S by conversion of a key intermediate, (23S)-5 beta-cholest-25-ene-3 alpha,7 alpha,12 alpha,23-tetrol to either the bile alcohol of known absolute configuration, (23R)-5 beta-cholestane-3 alpha,7 alpha,12 alpha,23-tetrol, or the naturally occurring 23,25-pentol.     

Synthesis of 3 alpha,7 alpha,12 alpha,25-tetrahydroxy-5 beta-cholestan-24-one, an intermediate in the 25-hydroxylation pathway of cholic acid biosynthesis from cholesterol

This paper describes the chemical synthesis of 3 alpha,7 alpha,12 alpha,25-tetrahydroxy-5 beta-cholestan-24-one via selective oxidation of 5 beta-cholestane-3 alpha,7 alpha,12 alpha, 24 xi,25-pentol with silver carbonate on celite. The structure of this 24-keto bile alcohol was confirmed by gas-liquid chromatography and mass spectrometry. Synthesis of this compound via pyridinium chlorochromate oxidation of the triacetoxy derivative of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24 xi,25-pentol followed by saponification further established its structure. 3 alpha,7 alpha,12 alpha,25-Tetrahydroxy-5 beta-cholestan-24-one was required for the in vivo and in vitro studies of side-chain oxidation and cleavage in the 25-hydroxylation pathway of cholic acid biosynthesis.     

Synthesis and structure of 26 (or 27)-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24S,25 xi-pentol isolated from the urine and feces of a patient with sitosterolemia and xanthomatosis

The urine and feces of a patient with the rare inherited lipid storage disease, sitosterolemia and xanthomatosis, were analyzed. Substantial quantities of C26-bile alcohol, 26 (or 27)-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24S,25 xi-pentol along with 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24-tetrol, 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25-tetrol, 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24R,25-pentol, and 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25,26-pentol were found. The structure of the C26-bile alcohol was confirmed by direct comparison (gas-liquid chromatography-mass spectrometry and thin-layer chromatography) with a standard sample synthesized from cholic acid. The configurational assignment at C-24 was determined by lanthanide-induced circular dichroism Cotton effect measurements. The increased excretion of these C26- and C27-bile alcohols suggests an abnormality of bile acid biosynthesis in this disease.     

Configuration at C-25 in 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25,26-pentol excreted by patients with cerebrotendinous xanthomatosis: circular dichroism and 13C-NMR studies

The configuration at C-25 in 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha,25,26-pentol isolated from the bile and feces of patients with cerebrotendinous xanthomtosis (CTX) was determined from the lanthanide-induced circular dichroism (CD) Cotton effects and 13C-NMR measurements. Under anhydrous conditions, CD spectra of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha,25,26-pentol in the presence of Eu(fod)3 exhibited a large induced negative Cotton effect at 320 nm. On the basis of the empirical rule (primary-tertiary-alpha-diols) in which R compounds have positive Cotton effects and S compounds have negative Cotton effects at 320 nm, it was concluded that 25,26-pentol has the 1,2,glycol structure with C-25 having the S-configuration. This assignment was based upon comparison with model compounds, 25(R and S),26-dihydroxy cholesterols and 25(R and S),26-dihydroxy cholecalciferols whose single-crystal X-ray structure and 13C-NMR studies have been performed. It is suggested that these data may be helpful to clarify the stereospecificity of the hydroxylation of the terminal methyl group of the cholesterol side chain in CTX.     

Identification of 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24 xi, 25 xi,26-hexol and partial characterization of the bile alcohol profile in urine

The nature of the bile alcohols present in urine of an infant with neonatal cholestasis has been investigated. Urine was extracted with Sep-Pak C18 cartridges and a glucuronide fraction was isolated by ion exchange chromatography on Lipidex-DEAP. Following enzymatic hydrolysis and purification on Lipidex-DEAP, the bile alcohols were isolated by high performance liquid chromatography. Fourteen compounds were studied by a combination of microchemical reactions and capillary column gas-liquid chromatography-mass spectrometry. Both C26 and C27 bile alcohols were present. Among the former, three additional isomers of the previously identified 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24 xi,25 xi-pentol were detected. A new C26 bile alcohol, 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24 xi,25 xi,26 -hexol, was identified, and a 27-norcholestane-pentolone with hydroxyl groups at C-24 and C-25 and a keto group in the ring system was partially characterized. The C27 bile alcohols consisted of cholestanepentols, -tetrolones, and -pentolones. 5 beta-Cholestane-3 alpha,7 alpha,12 alpha,25,26-pentol (5 beta-bufol), one of its isomers and an isomer of cholestane-3,7,12,24,26-pentol were present. Two cholestanetetrolones and two cholestanepentolones having the keto group in the ring system were partially characterized. The hydroxyl groups in the side chain of the tetrolones were at C-24,26 and C-25,26, respectively, whereas the pentolones had hydroxyl groups at C-24,25 and C-25,26, respectively. The excretion of glucuronidated bile alcohols in urine is suggested to reflect an alternative metabolism of intermediates in the normal biosynthesis of bile acids.     

Chemical synthesis of 5beta-cholestane-3alpha, 7alpha, 24, 25-tetrol and its metabolism in the perfused rabbit liver

5beta-[G-3H]Cholestane-3alpha, 7alpha, 24xi, 25-tetrol (IV) was synthesized via dehydration and peroxidation of 5beta-[G-3H]cholestane-3alpha, 7alpha, 25-triol. Following perfusion of the labeled compound in the isolated rabbit liver, the bile alcohol and bile acid metabolites secreted into the bile were identified by a combination of thin layer chromatography, gas-liquid chromatography, and gas-liquid chromatography/mass spectrometry. The following bile alcohols were tentatively identified: 5beta-cholest-23-ene-3alpha, 7alpha, 25-triol, 5beta-cholest-25-ene-3alpha, 7alpha, 12alpha, 24xi-tetrol, and 5beta-cholestane-3alpha, 7alpha, 12alpha, 24xi, 25-pentol. The amount of administered tetrol recovered unchanged ranged from 1 to 88%. Cholic acid was the major product, but limited amounts of chemodeoxycholic acid were also formed. The 24-hydroxyl group in the steroid side chain did not prevent 12alpha-hydroxylation.     

Identification of new bile alcohols, 5 beta-cholestane-3 alpha,7 alpha,24,26-tetrol, 5 beta-cholestane-3 alpha,7 alpha,25,26-tetrol, and 5 beta-cholestane-3 alpha,7 alpha,26,27-tetrol in human gallbladder bile

The nature of cholestanetetrols present as the glucurono-conjugates in human gallbladder bile was studied. Glucurono-conjugated bile alcohols were isolated by ion exchange chromatography and, after enzymatic hydrolysis, were fractionated by reversed phase partition chromatography to give a fraction containing tetrahydroxy bile alcohols which was analyzed by gas-liquid chromatography and mass spectrometry. Along with the three previously identified bile alcohols, 5 alpha- and 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha,24-tetrols, and 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha,26-tetrol, three new cholestanetetrols, possessing two hydroxyl groups in the ring system and two in the side chain, were detected in the tetrahydroxy bile alcohol fraction. These new bile alcohols were identified as 5 beta-cholestane-3 alpha, 7 alpha,24,26-tetrol, 5 beta-cholestane-3 alpha, 7 alpha,25,26-tetrol, and 5 beta-cholestane-3 alpha, 7 alpha,26,27-tetrol by direct comparison of their gas-liquid chromatographic behaviors and mass spectral data with those of authentic standards prepared from chenodeoxycholic acid by partial synthesis.     

Identifications of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 23 beta-tetrol, 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 24 alpha-tetrol, and 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 24 beta-tetrol in cerebrotendinous xanthomatosis

The bile alcohols present in the feces of a patient with cerebrotendinous xanthomatosis were studied. Three bile alcohols which are different from any known natural bile alcohol were isolated as minor components of the fecal bile alcohol fraction. The structures of these compounds were established as 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 23 beta-tetrol, 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 24 alpha-tetrol, and 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 24 beta-tetrol by comparison with synthetic samples.     

C26-analogs of naturally occurring bile alcohols-II. Preparation of 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,23-tetrols (23R and 23S) and 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,26-tetrols (25R and 25S) by a hydroboration procedure

A convenient procedure for the synthesis of 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,23-tetrol (23R and 23S) and 24-nor-5 beta-cholestane-3 alpha,7 alpha,12alpha,26-tetrol (25R and 25S) starting from 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,25-tetrol was developed. Dehydration of 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha, 25-tetrol with glacial acetic acid and acetic anhydride yielded a mixture of 24-nor-5 beta-cholest-23-ene-3 alpha,7 alpha,12 alpha-triol and the corresponding delta 25 compound. Hydroboration and oxidation of the mixture of unsaturated nor-triols resulted in the formation of 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,23-tetrols (23R and 23S) and 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,26-tetrols (25R and 25S). In addition, smaller amounts of 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,22 xi-tetrol and 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol were also obtained. The C26 bile alcohols epimeric at C-23 and C-25 were resolved by analytical and preparative TLC and characterized by gas-liquid chromatography and mass spectrometry. Provisional assignment of the configurations of the C-23 and C-25 hydroxyl groups were made on the basis of molecular rotation differences. These C26 alcohols will be used to test the stereospecificity of the hepatic enzymes that promote oxidation of the cholesterol side chain.     

Identification of (22R)-3 alpha,7 alpha,12 alpha,22- and (23R)-3 alpha,7 alpha,12 alpha,23-tetrahydroxy-5 beta-cholestanoic acids in urine from a patient with Zellweger's syndrome

The nature of two novel C27 bile acids present as the taurine conjugates in urine from a patient with Zellweger's syndrome was studied. Bile acids conjugated with taurine were isolated from unconjugated and glycine-conjugated bile acids by means of ion-exchange chromatography. After alkaline hydrolysis of the taurine conjugates, the hydrolysate was acidified and extracted with ether; the extract was again subjected to ion-exchange chromatography to separate neutral from acidic compounds. The neutral fraction, which consisted mainly of two steroidal lactones, was treated with lithium aluminum hydride, and the reduction products were identified as (22R)-5 beta-cholestane-3 alpha,7 alpha,12 alpha,22,26-pentol and (23R)-5 beta-cholestane-3 alpha,7 alpha,12 alpha,23,26-pentol by direct comparison of their gas-liquid chromatographic behaviors and mass spectral data with those of chemically synthesized authentic samples. Thus, the chemical structure of two native bile acids present in urine from a patient with Zellweger's syndrome should be formulated as (22R)-3 alpha,7 alpha,12 alpha,22-tetrahydroxy-5 beta-cholestanoic acid and (23R)-3 alpha,7 alpha,12 alpha,12 alpha,23-tetrahydroxy-5 beta-cholestanoic acid, respectively.     

Bile alcohol profiles in bile, urine, and feces of a patient with cerebrotendinous xanthomatosis

Bile alcohols in bile, urine, and feces of a patient with cerebrotendinous xanthomatosis have been analyzed by a combination of capillary gas-liquid chromatography and mass spectrometry after fractionation into groups according to mode of conjugation. The presence of at least 18 bile alcohols, which were excreted mainly as glucurono-conjugates in bile and urine, and as unconjugated forms in feces, was demonstrated. The following bile alcohols were identified with certainty by direct comparison with reference compounds: 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol; (23R)-5 beta-cholestane-3 alpha,7 alpha,12 alpha,23-tetrol; 5 alpha- and 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24-tetrols; 5 alpha- and 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25-tetrols; 27-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25-pentol; (22R)-5 beta-cholestane-3 alpha,7 alpha,12 alpha,22,25-pentol; (23R)- and (23S)-5 beta-cholestane-3 alpha,7 alpha, 12 alpha,23,25-pentols; 3 alpha,12 alpha,25-trihydroxy-5 beta-cholestane-7-one; (24R)- and (24S)-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25-pentols; 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25,26-pentol. Although the bile alcohol profile in urine was quite different from those in bile and feces, the determination of urinary bile alcohols as well as of biliary and fecal bile alcohols could be used for diagnosis of cerebrotendinous xanthomatosis.     

New bile alcohols--synthesis of 5beta-cholestane-3alpha, 7alpha, 25-triol and 5beta-cholestane-3alpha, 7alpha, 25-24 (14C)-triol.

5beta-Cholestane-3alpha, 7alpha, 25-triol and 5beta-cholestane-3alpha, 7alpha, 25-24(14-C)-triol were synthesized from 3alpha, 7alpha-dihydroxy-5beta-cholanoic acid (chenodeoxycholic acid). Chenodeoxycholic acid was converted to the diformoxy derivative (II) using formic acid. Reaction of II with thionyl chloride yielded the acid chloride which was treated with diazomethane (CH-2-N-2 or 14-CH-2-N-2) to produce 3alpha, 7alpha-diformoxy-24-oxo-25-diazo-25-homocholane (III, A or B). 25-Homochenodeoxycholic acid (IV, A or B) was formed from III by means of the Wolff rearrangement of the Arndt-Eistert synthesis. The methyl ester of V (A or B) was treated with methyl magnesium iodidi in ether to provide the desired triol, VI (A and B). The triol was identified by mass spectrometry and elemental analysis and was characterized by thin-layer and gas-liquid chromatography. The 3alpha, 7alpha, 25-triol is of possible significance as an intermediate in the pathway of bile acid formation from cholesterol.     

Identification of 5 β-cholestane-3 α, 7 α, 12 α, 25, 26-pentol in cerebrotendinous xanthomatosis

An unrecognized pentahydroxy bile alcohol has been isolated from the bile and feces of patients with cerebrotendinous xanthomatosis (CTX). Its structure, 5 β-cholestane-3 α, 7 α, 12 α, 25, 26-pentol has been deduced by spectroscopic methods and confirmed by comparison with a synthetic analog.     

Radioimmunoassay of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25-tetrol 3-glucuronide in serum of patients with cerebrotendinous xanthomatosis.

A rapid, convenient, and specific radioimmunoassay for 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25-tetrol has been developed. Specific antiserum was obtained from rabbits immunized by the bile alcohol-bovine serum albumin conjugate, which was coupled by an (O-carboxymethyl)oxime bridge at the C-3 position. The assay produces values for serum concentrations of bile alcohol glucuronides in patients with cerebrotendinous xanthomatosis.     

Metabolism of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 26-tetrol and 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 25-tetrol into cholic acid in normal human subjects.

Side chain oxidation and cleavage of precursors in cholic acid synthesis is thought to involve initial hydroxylation at either position 25 or 26 of the side chain. Therefore, the conversion of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 26-tetrol and 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 25-tetrol into cholic acid was studied in normal subjects after single intravenous injections of these labeled alcohols. Eighty-six percent and 82% of 5 beta-cholestane, 3 alpha, 7 alpha, 12 alpha, 26-tetrol was converted into cholic acid in two subjects, respectively. However, only 14 and 16% of the injected 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 25-tetrol was converted into cholic acid in two subjects, respectively. Thus, this study indicates that 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 25-tetrol is an inefficient substrate for cholic acid biosynthesis in man and that the major route of cholic acid synthesis probably involves the 26-hydroxylated intermediate.     

Absolute configuration of pentahydroxy bile alcohols excreted by patients with cerebrotendinous xanthomatosis: a circular dichroism study

The absolute configurations of the C27 pentahydroxy bile alcohols present in bile and feces of two patients with cerebrotendinous xanthomatosis (CTX) were determined by circular dichroism (CD) spectroscopy. The CD spectra of 5beta-cholestane-3alpha,7alpha,12alpha,24alpha,25-pentol in the presence of Eu(fod)3 [tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dionato) europium (III)] exhibited a negative Cotton effect and was assigned to 24R absolute configuration. Conversely, 5beta-cholestane-3alpha,7alpha,12alpha,24beta,25-pentol showed a strong positive Cotton effect and was assigned the 24S configuration. These assignments were based upon comparison with a model compound, 5-cholestene-3beta,24(R),25-triol, whose single-crystal X-ray structure has been determined. The importance of these data is to establish a structural mechanism for the conversion of 5beta-cholestane-3alpha,7alpha,12alpha,24S,25-pentol rather than 5beta-cholestane-3alpha,7alpha,12alpha,24R,25-pentol into cholic acid in man as well as in animals.