Improved synthesis of 5 beta-cholestane-3 alpha,7 alpha,12 alpha, 26(27)-tetrol isomers from cholic acid

Synthesis of a mixture of the 25(R) and 25(S) isomers of 5 beta-cholestane-3 alpha,7 alpha,12 alpha, 26(27)-tetrol from cholic acid in four steps, including a Wittig reaction, is described.     

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.     

Conversion of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 26-tetrol into 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid by rabbit liver mitochondria

Rabbit liver mitochondria in the presence of NAD+ were found to catalyze the conversion of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 26-tetrol into 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid. The peroxisomal fraction did not catalyze the reaction. Sonication of the mitochondria or dialysis overnight against a hypotonic buffer increased the rate of oxidation twofold. Most of the enzyme activity was recovered in the supernatant fraction after centrifugation at 100,000xg of sonicated mitochondria. 4-Heptylpyrazole, an inhibitor of cytosolic ethanol dehydrogenase, inhibited the mitochondrial formation of 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid by 70%. Disulfiram, an inhibitor of cytosolic acetaldehyde dehydrogenase, did not inhibit the reaction. The role of the mitochondrial dehydrogenase system in bile acid biosynthesis is discussed.     

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.     

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.     

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.     

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.     

Formation of cholic acid via 3 alpha, 7 alpha,12 alpha-trihydroxy-5 beta-cholestan-26-oic acid in the dog.

The proposed cholic precursor, 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-[3H]cholestan-26-oic acid, and [14C]cholesterol were infused intravenously at a constant rate into two dogs for 25 days. If the specific activities of trihydroxy[3H]cholestanoic acid and [3H]cholic acid will be equal after an isotopic steady-state is achieved. The specific activities of [14C]deoxycholic acid (formed from [14C]cholic acid) isolated in the stool of these two dogs were equal the last four days of the infusion indicating that labeled deoxycholic acid (and presumably labeled cholic acid) was in an isotopic steady-state. However, the specific activities of trihydroxy[3H]cholestanoic acid were 3.3 and 5.7 times greater than the specific activities of [3H]cholic acid, respectively. These data suggest that either an alternate route of cholic acid synthesis exists exclusive of trihydroxycholestanoic acid or that an isotopic steady state of trihydroxycholestanoic acid cannot be reached during an infusion of labeled trihydroxycholestanoic acid.     

Identification of pentahydroxy bile alcohols in cerebrotendinous xanthomatosis: characterization of 5beta-cholestane-3alpha, 7alpha, 12alpha, 24xi, 25-pentol and 5beta-cholestane-3alpha, 7alpha, 12alpha, 23xi, 25-pentol.

This paper describes studies dealing with the nature of the C27 pentahydroxy bile alcohols present in the bile and feces of two patients with cerebrotendinous xanthomatosis (CTX). The presence of a bile alcohol having the structure 5beta-cholestane-3alpha,7alpha,12alpha,24alpha,25-pentol was confirmed by separation of the two 24-hydroxy epimers of 5beta-cholestane-3alpha,7alpha,12alpha,24,25-pentol and characterization of the dpimers by gas-liquid chromatography and infrared and mass spectrometry. Tentative assignment of the 24alpha and 24beta configuration was made on the basis of molecular rotation differences. A second major bile alcohol excreted by the CTX subjects was 5beta-cholestane-3alpha,7alpha,12alpha,23xi,25-pentol. Its structure was determined by infrared spectrometry, proton magnetic resonance spectrometry, and mass spectrometry because a reference compound was not available.     

Oxidation of 5 beta-cholestane-3 alpha,7 alpha, 12 alpha-triol into 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid by cytochrome P-450(26) from rabbit liver mitochondria

The mitochondrial cytochrome P-450(26), previously shown to catalyze 26-hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol, was found to convert this substrate also into 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid. The formation of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid increased with increasing incubation time and enzyme concentration. Addition of NAD+ to the incubation mixture did not increase the formation of the acid. Incubation with 5 beta-cholestane-3 alpha,7 alpha,12 alpha,26-tetrol, cytochrome P-450(26), ferredoxin, ferredoxin reductase and NADPH resulted in one major product, 3 alpha,7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid. The cytochrome P-450 required both ferredoxin, ferredoxin reductase and NADPH for activity. NADPH could not be replaced by NAD+ or NADP+.     

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.     

Formation of cholic acid from 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid in human skin fibroblasts.

Whether 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) was converted into cholic acid in human skin fibroblasts was examined. THCA was incubated with subcellular fractions of cultured skin fibroblasts in the presence of NAD+, ATP, CoA, and Mg2+. The reaction products were analyzed by thin-layer chromatography and high-performance liquid chromatography after p-bromophenacyl ester derivatization. The highest specific activity was found in the light mitochondrial fraction (2.71 nmol/mg protein/h). The specific activity was about 9-fold higher than that in heavy mitochondrial fraction. The peroxisomal fraction prepared from the light mitochondrial fraction by sucrose gradient centrifugation was also able to catalyze the conversion of THCA into cholic acid. The specific activity in this fraction was a further 2.2-fold higher than that in the light mitochondrial fraction. These results suggest that cultured human skin fibroblasts are able to convert THCA into cholic acid, and that the activity exists in peroxisomes.     

The metabolism of 3alpha, 7alpha, 12alpha-trihydroxy-5beta-cholestan-26-oic acid into cholic: an enzyme assay using homogenates of human liver.

An enzyme assay was developed to measure the conversion of the bile acid precursor, 3alpha, 7alpha, 12alpha-trihydroxy-5beta-cholestan-26-oic acid (THCA), into cholic acid using homogenates of human liver biopsies. The average rate of metabolism of THCA into cholic acid was found to be 3.9 +/- 0.5 (+/- 1 SD) pmoles of cholic acid formed/mg liver/minute in twelve normal liver biopsies. This assay system can be used to determine if the syndrome of neonatal cholestasis associated with a metabolic block in the conversion of THCA into cholic acid is transmitted as a genetic trait.     

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.     

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.     

Stereoselective synthesis of (24R and 24S) 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25-pentols and (25R and 25S) 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25,26-pentols using a modified osmium-catalyzed Sharpless asymmetric dihydroxylation process.

Described herein are the stereoselective syntheses of the (24R, 24S) and (25R, 25S) isomers of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,25-pentols and 5 beta-cholestane-3 alpha,7 alpha,12 alpha,25,26-pentols by using a modified osmium-catalyzed Sharpless asymmetric dihydroxylation process. Also presented herein are the results of lanthanide-induced CD Cotton effect measurements and 1H- and 13C-nuclear magnetic resonance studies of (24R, 24S) and (25R, 25S)-5 beta-cholestanepentols and their derivatives. These compounds were required to study the biosynthesis of cholic acid from cholesterol.     

Biosynthesis of cholic acid in rat liver. 24-Hydroxylation of 3alpha, 7alpha, 12alpha-trihydroxy-5beta-cholestanoic acid.

Conversion of 3alpha, 7alpha, 12alpha-trihydroxy-5beta-[7beta-3H]cholestanoic acid into 3alpha, 7alpha, 12alpha, 24-tetrahydroxy-5beta-cholestanoic acid in rat liver was catalyzed either by the mitochondrial fraction fortified with the 100,000 times g supernatant fluid or the microsomal fraction fortified with 100,000 times g supernatant fluid and ATP. The microsomal system was more active than the mitochondrial system. With the microsomal system the rate of reaction was considerably faster with free 3alpha, 7alpha, 12alpha-trihydroxy-5beta-cholestanoic acid as substrate than with the corresponding coenzyme A ester. Addition of coenzyme A inhibited the activity. Addition of cofactors other than ATP and coenzyme A did not markedly influence the reaction. The 100,000 times g supernatant fluid could be substituted with a protein fraction obtained by ammonium sulfate precipitation and Sephadex chromatography of the 100,000 times g supernatant fluid. The reaction was not catalyzed by a mixed function oxidase since there was no incorporation of 18O into the product when the reaction was performed in an atmosphere containing 18O2. On the other hand, oxygen may be obligatory since there was almost complete inhibition when the reaction was performed in an atmosphere consisting of nitrogen. Carbon monoxide did not inhibit the reaction. One atom of deuterium was incorporated into the product when the reaction was performed in a medium containing deuterated water. It was concluded that microsomal 24-hydroxylation of 3alpha, 7alpha, 12alpha-trihydroxy-5beta-cholestanoic acid involves the combined action of a desaturase and a hydratase. The reaction catalyzed by the hydratase appears to be stereospecific since the 24alpha epimer of 3alpha, 7alpha,12alpha-trihydroxy-5beta-cholestanoic acid was the predominant product. In contrast to the microsomal system, the mitochondrial system was not stimulated by the addition of ATP and was not inhibited by coenzyme A. The coenzyme A ester of 3alpha, 7alpha, 12alpha-trihydroxy-5beta-cholestanoic acid was 24-hydroxylated more efficiently than the free acid.