Metabolism of (24R and 24S)-27-nor-24-methyl-3α,7α-dihydroxy-5β-cholestan-26-oic acids and 27-nor-3α,7α-dihydroxy-5β-cholestan-26-oic acid in guinea pigs

[7β-³H]-(24R and 24S)-27-nor-24-methyl-3α,7α-dihydroxy-5β-cholestan-26-oic acids and [7β-³H]-27-nor-3α,7α-dihydroxy-5β-cholestan-26-oic acid (C₂₇ and C₂₆ bile acids having the same nuclear configuration as cheno-deoxycholic acid and its precursor, 3α,7α-dihydroxy-5β-cholestan-26-oic-acid) were synthesized and administered intraperitoneally to bile fistula guinea pigs. The biliary bile acids formed were hydrolyzed and analyzed by thin layer chromatography, and the metabolites were identified by the inverse isotope dilution method. The results showed that both (24R and 24S)-27-nor-24-methyl-3α,7α-dihydroxy-5β-cholestan-26-oic acids were not metabolized by the liver and were excreted unchanged as their taurine and glycine conjugates whereas 27-nor-3α,7α-dihydroxy-5β-cholestan-26-oic acid was converted to chenodeoxycholic acid.     

Chemical synthesis of the (25R)- and (25S)-epimers of 3α,7α,12α-trihydroxy-5α-cholestan-27-oic acid as well as their corresponding glycine and taurine conjugates

The (25R)- and (25S)-epimers of C₂₇ 3α,7α,12α-trihydroxy-5α-cholestan-27-oic acid as well as their corresponding N-acylamidate conjugates with glycine or taurine were prepared starting from cholic acid in 14 steps. The principal reactions involved were (1) reduction of a key intermediary C₂₄allo-cholic acid performate with NaBH₄/triethylamine/ethyl chloroformate, (2) iodination of the resulting 3,7,12-triformyloxy-5α-cholan-24-ol with I₂/triphenylphosphine; (3) nucleophilic substitution of the iodo derivative with diethylmethyl malonate/NaH; and (4) hydrolysis of the resulting 3,7,12-triformyloxy-25-methyl-26,27-diethyl ester with KOH, followed by decarboxylation of the geminal dicarboxylic acid with LiCl. N-Acylamidation of the resulting (25R)/(25S)-3α,7α,12α-trihydroxy-5α-cholestan-27-oic acid mixture with glycine or taurine afforded the corresponding epimeric mixtures of the glycine and taurine conjugates. The (25R)- and (25S)-epimers of the three variants of unconjugated and conjugated 3α,7α,12α-trihydroxy-5α-cholestan-27-oic acid were efficiently separated by HPLC on a reversed-phase C₁₈ column and their structural characteristics, particularly the chiral center at C-25, delineated using ¹H and ¹³C NMR. These synthetic compounds should be useful as authentic reference standards for establishing their presence in bile as well as being useful in studies on the biosynthesis of allo-bile acids from cholesterol.     

Improved synthesis of 3α,7α,12α,24ξ -tetrahydroxy-5 β -cholestan-26-oic acid

This paper describes three simple and short methods for the conversion of cholic acid into cholylaldehyde with protected hydroxyl groups. The first method involves lithium aluminum hydride reduction of the tetrahydropyranyl ether of methyl cholate and oxidation of the resulting primary alcohol with pyridinium chlorochromate. The second method employs diborane for the reduction of the -COOH group to the -CH₂OH group, while the third method involves the reduction of 3α, 7α, 12α -triformyloxy-5β -cholan-24-oic acid (as the acid chloride) directly into 3α, 7α, 12α -triformyloxy-5β -cholan-24-al with TMA-ferride (tetramethylammonium hydridoirontetracarbonyl). The aldehyde obtained by any of the above methods underwent smooth Reformatsky reaction with ethyl α -bromopropionate to yield 3α, 7α, 12α, 24ξ -tetrahydroxy-5β -cholestan-26-oic acid.     

7β,12β-dihydroxy-5β-cholan-24-oic acid as an internal standard for quantitative determination of bile acids by gas chromatography

In order to find an artificial internal standard compound for quantitative determination of bile acids by gas chromatography, 7α,12α-,7α, 12β-, 7β,12α- and 7β,12β-dihydroxy-5β-cholan-24-oic acids were chemically synthesized with cholic acid (1) as the first starting material. The gas chromatographie retention time of 7β,12β-dihydroxy-5β-cholan-24-oic acid (ββ-isomer) was more different from that of natural bile acids than the other isomers. Moreover, ββ-isomer was extracted in the same fraction as the bile acids from urine, and no urinary substance had the same retention time as ββ-isomer. No artifact was produced from ββ-isomer during the analysis procedure. It was concluded that the ββ-isomer is an internal standard compound with certain advantages for the quantitative determination of bile acids in urine by gas chromatography, irrespective of the recovery rate during the analysis procedure.     

Synthesis and absolute configuration at C-23 of [23R and 23S]-3α, 7α, 23-trihydroxy-5β-cholan-24-oic and [23R and 23S]-3α, 7α, 12α, 23-tetrahydroxy-5β-cholan-24-oic acids

A synthesis of /23R and 23S/-3α, 7α, 23-trihydroxy-5β-cholan-24-oic acids is described. Lithium enolate of completely protected starting chenodeoxycholic acid was directly hydroxylated at C-23 by the oxidoperoxymolybdenum /hexamethylphosphoric triamide/ /pyridine/ complex. The resulting derivatives containing hydroxyl group at C-23 were separated by liquid column chromatography and their configurations at C-23 were assigned by molecular rotation as well as circular dichroism measurements. In a similar way /23R and 23S/-3α, 7α, 12α, 23-tetrahydroxy-5β-cholan-24-oic acids were prepared and their structures identified.Synthetic compounds of the 23R configuration proved to be identical with the bile acids previously isolated from seal bile.     

Metabolism of 3α, 7α-dihydrexy-7β-methyl-5β-cholanoic acid and 3α,7β-dihydroxy-7α-methyi-5β-cholanoic acid in hamsters

The metabolic fate of the bile add analogs, 3α,7α-dihydroxy-7β-methyl-5β-cholanoic acid and 3α,7β-dihydroxy-7α-methyl-5β-cholanoic acid, was investigated and compared with that of chenodeoxycholic acid in hamsters. Both bile acid analogs were absorbed rapidly from the intestine and excreted into bile at similar to that of chenodeoxycholic acid. In the strain of hamster studied, the biliary bile were conjugated with both glycine and taurine. After continuous intravenous infusion, chenodeoxycholic acid the analogs became the major bile acid constituents in bile. After oral administration of a single dose of these compounds, fecal analysis revealed the existence of unchanged material (25–35%) as well as considerable amounts of metabolites (65–75%). The major metabolites excreted into feces were more polar than the starting material and were tentatively identified as trifaydroxy-7-methyl compounds by radioactive thin-layer chromatography. However, monohydroxy compounds were also found in the fecal extracts. These results show that chenodeoxycholic acid and ursodeoxycholic acid with a methyl group at the 7-position are resistant to bacterial 7-dehydroxylation than the normally occurring bile acids and that a certain proportion of these analogs is hydroxylated to give the corespondiag trihydroxy compound(s), In a control experiment, about 5% of administered chenodeoxychoulic acid was metabolized to a trihydroxy feile acid, but most of the compound (95%) was transformed into lithocholic acid.     

Chenodeoxycholic acid synthesis in the hamster: A metabolic pathway via 3β, 7α-dihydroxy-5-cholen-24-oic acid

The quantitative significance of the metabolism of 3β, 7α-dihydroxy-5-cholen-24-oic acid to chenodeoxycholic acid was evaluated in the hamster. A precursor-product relationship was established in this species by the finding that intravenous administration to an animal previously given cholesterol-4-¹⁴C caused a significant reduction in the specific activity of chenodeoxycholic acid. Administration of 12.9 μmole of the precursor was followed by a 10-fold increase in chenodeoxycholic acid excretion although the predominant excretory pathway was via biliary excretion as a monosulfate. The data indicate that synthesis of bile acid from cholesterol via the intermediate 3β, 7α-dihydroxy-5-cholen-24-oic acid can be a quantitatively important pathway.     

Synthesis, aggregation behavior and cholesterol solubilization studies of 16-epi-pythocholic acid (3α,12α,16β-trihydroxy-5β-cholan-24-oic acid)

Synthesis, aggregation behavior and in vitro cholesterol solubilization studies of 16-epi-pythocholic acid (3α,12α,16β-trihydroxy-5β-cholan-24-oic acid, EPCA) are reported. The synthesis of this unnatural epimer of pythocholic acid (3α,12α,16α-trihydroxy-5β-cholan-24-oic acid, PCA) involves a series of simple and selective chemical transformations with an overall yield of 21% starting from readily available cholic acid (CA). The critical micellar concentration (CMC) of 16-epi-pythocholate in aqueous media was determined using pyrene as a fluorescent probe. In vitro cholesterol solubilization ability was evaluated using anhydrous cholesterol and results were compared with those of other natural di- and trihydroxy bile acids. These studies showed that 16-epi-pythocholic acid (16β-hydroxy-deoxycholic acid) behaves similar to cholic acid (CA) and avicholic acid (3α,7α,16α-trihydroxy-5β-cholan-24-oic acid, ACA) in its aggregation behavior and cholesterol dissolution properties.     

Transformation of lithocholic acid to a new bile acid, 3α, 15β-dihydroxy-5β-cholanic acid by Cunninghamella blakesleeana ST-22

Summary A fungus identified as Cunninghamella blakesleeana (Lendner) can carry out 15-hydroxylation of lithocholic acid to a new bile acid (3,15-dihydroxy-5-cholanic acid). By optimizing the fermentation conditions, the amount of the product increased from 0.17 g/l to 1.2 g/l. Hydrophilicity measurements and in vitro cholesterol solubilization tests showed that 3, 15-dihydroxy-5-cholanic acid was as effective as ursodeoxycholic acid in cholesterol solubilization.Abbreviations LCA lithocholic acid (3-hydroxy-5-cholanic acid) - 3, 15-DHC (3, 15-dihydroxy-5-cholanic acid) - DMSO dimethyl sulfoxide - CHES 2-[N-cyclohexylamino]ethanesulfonic acid     

Synthesis of 3α,7α-dihydroxy-5β-androstan-17-one

A short and efficient method for the stereospecific synthesis of 3α,7α-dihydroxy-5β-androstan-17-one was accomplished from the readily available 4-androstene-3,17-dione. Key steps are the stereospecific and selective epoxidation of 4,6-androstadiene-3,17-dione, followed by hydrogenations with carefully selected reagents, solvents and reaction conditions.     

Extending SAR of bile acids as FXR ligands: discovery of 23-N-(carbocinnamyloxy)-3α,7α-dihydroxy-6α-ethyl-24-nor-5β-cholan-23-amine

Within our efforts in the discovery of novel potent and selective ligands for the FXR receptor, 23-N-(carbocinnamyloxy)-3α,7α-dihydroxy-6α-ethyl-24-nor-5β-cholan-23-amine was synthesized and evaluated for its ability to activate and modulate the biological response of the receptor. Alphascreen and RT-PCR revealed that the 6α-ethyl-24-norcholanyl-23-amine derivate behaves as full FXR agonist endowed with high binding affinity and efficacy, representing a promising lead candidate for further optimization. In addition, docking studies provide new insights into the molecular basis governing the partial and full agonist activity at FXR.     

Bile acids. LXIV. Synthesis of 5α-cholestane-3α,7α,25-triol and esters of new 5α-bile acids

Interest in the structural requirements of a sterol or bile acid for maximal activity by an hepatic microsomal steroid 12α-hydroxylase prompted the preparation of 5α-cholestane-3α, 7α, 25-triol and 5α-analogs of 3α, 7α-dihydroxy-5β-cholane-24-carboxylic acid. Methyl 3α, 7α-dihydroxy-5β-cholane-24-carboxylate derived from methyl chenodeoxycholate via the Arndt-Eistert reaction was allomerized with Raney nickel in boiling p-cymene to provide a number of products of which methyl 3,7-dioxo-5β- and 5α-cholane-24-carboxylates, methyl 3-oxo-7α-hydroxy-5β-and 5α-cholane-24-carboxylates, were identified. Reduction with K-Selectride of methyl 3-oxo-7α-hydroxy-5β-cholane-24-carboxylate, provided a high yield of methyl 3α, 7α-dihydroxy-5α-cholane-24-carboxylate. Treatment of this ester with an excess of methyl magnesium iodide afforded 5α-cholestane-3α, 7α, 25-triol. The products were characterized by thin-layer and gas liquid chromatography, proton resonance, infrared and mass spectrometry.     

Identification and characterization of two bile acid coenzyme A transferases from Clostridium scindens, a bile acid 7α-dehydroxylating intestinal bacterium

The human bile acid pool composition is composed of both primary bile acids (cholic acid and chenodeoxycholic acid) and secondary bile acids (deoxycholic acid and lithocholic acid). Secondary bile acids are formed by the 7α-dehydroxylation of primary bile acids carried out by intestinal anaerobic bacteria. We have previously described a multistep biochemical pathway in Clostridium scindens that is responsible for bile acid 7α-dehydroxylation. We have identified a large (12 kb) bile acid inducible (bai) operon in this bacterium that encodes eight genes involved in bile acid 7α-dehydroxylation. However, the function of the baiF gene product in this operon has not been elucidated. In the current study, we cloned and expressed the baiF gene in E. coli and discovered it has bile acid CoA transferase activity. In addition, we discovered a second bai operon encoding three genes. The baiK gene in this operon was expressed in E. coli and found to encode a second bile acid CoA transferase. Both bile acid CoA transferases were determined to be members of the type III family by amino acid sequence comparisons. Both bile acid CoA transferases had broad substrate specificity, except the baiK gene product, which failed to use lithocholyl-CoA as a CoA donor. Primary bile acids are ligated to CoA via an ATP-dependent mechanism during the initial steps of 7α-dehydroxylation. The bile acid CoA transferases conserve the thioester bond energy, saving the cell ATP molecules during bile acid 7α-dehydroxylation. ATP-dependent CoA ligation is likely quickly supplanted by ATP-independent CoA transfer.     

Synthesis of (4-C)-labeled and non-labeled 3β,15α-dihydroxy-5-pregnen-20-one and 3β,15α-dihydroxy-5-androsten-17-one

The synthesis of labeled and non-labeled 3β,15α-dihydroxy-5-pregnen-20-one (V) and 3β, 15α-dihydroxy-5-androsten-17-one (XI) is described. Treatment of 15α-hydroxy-4-pregnene-3,20-dione (I) with acetic anhydride and acetyl chloride gave 3,15α-diacetoxy-3,5-pregnadien-20-one (II). The enol acetate (II) was ketalized by a modification of the general procedure to yield 3,15α-diacetoxy-3,5-pregnadien-20-one cyclic ethylene ketal (III) which was then reduced with NaBH₄ and LiAlH₄ to give 3β, 15α-dihydroxy-5-pregnen-20-one cyclic ethylene ketal (IV). Cleavage of the ketal group of IV gave V. Similarly, XI was prepared by starting with 15α-hydroxy-4-androstene-3,17-dione (VII). The (4-¹⁴C)-3β,15α-dihydroxy-5-pregnen-20-one was prepared by a modification of the above procedure in that the enol acetate (II)was directly reduced with NaBH₄ and LiAlH₄ to yield 5-pregnene-3β,15α,20β-triol (XIII) which was then oxidized enzymatically with 20β-hydroxysteroid dehydrogenase to V.     

C-19-steroid 7α-hydroxylation by rat testes. isolation and identification of: 7α, 17β-dihydroxy-5α-androstan-3-one, 5α-androstan-3α,7α,17β-triol and 5α-androstane-3β,7α, 17β-triol

From incubations of testosterone with rat testicular homogenates in the presence of a NADPH-generating system, the following 7α-hydroxylated metabolites could be isolated and identified: 7α,17β-dihydroxy-4-androsten-3-one (7α-hydroxy-testosterone), 7α-17β-dihydroxy-5α-androstan-3-one (7α-hydroxy-Dht), 5α-androstan-3α,7α,17β-triol (7α-hydroxy-3α-A'DIOL) and 5α-androstane-3β,7α,l7β-triol (7α-hydroxy-3β-A'DIOL). To our knowledge this is the first demonstration of the formation of 5α-reduced-7α-hydroxylated metabolites of testosterone in the male gonad. These 5α-reduced-7α-hydroxylated metabolites could also be isolated after incubations of 5α-androstane-3α,17β-diol (3α-A'D10L) with testicular homogenates in the presence of a NADPH-generating system.Measured as the sum of 7α-hydroxy-testosterone, 7α-hydroxy-Dht. 7α-hydroxy-3α-A'DIOL and 7α-hydroxy-3β-A'DIOL formed using testosterone as substrate, total 7α-hydroxylase activity was six times higher in testes of mature rats than in testes from animals 23 days old. With 3α-A'DIOL as substrate total 7α-hydroxylase in the mature testis was about three times greater than in the sexually immature testis.     

Synthesis and anti-glioma activity of 25(R)-spirostan-3β,5α,6β,19-tetrol

Malignant gliomas are common and aggressive brain tumours in adults. The rapid proliferation and diffuse brain migration are the main obstacles to successful treatment. Here, we show 25(R)-spirostan-3β,5α,6β,19-tetrol, a polyhydroxy steroid, is capable of suppressing proliferation and migration of C6 malignant glioma cells in a concentration-dependent manner. The compound 25(R)-spirostan-3β,5α,6β,19-tetrol was synthesised by seven steps starting from diosgenin in 8.55% overall yield. The structures of the synthetic compounds were characterised by infrared (IR), ¹H nuclear magnetic resonance (NMR), ¹³C NMR spectra and EA.     

Synthesis and acetylcholinesterase inhibitory activity of 2β,3α-disulfoxy-5α-cholestan-6-one

Disodium 2β,3α-dihydroxy-5α-cholestan-6-one disulfate (8) has been synthesized using cholesterol (1) as starting material. Sulfation was performed using trimethylamine-sulfur trioxide complex in dimethylformamide as the sulfating agent. The acetylcholinesterase inhibitory activity of compound 8 was evaluated and compared to that of disodium 2β,3α-dihydroxy-5α-cholestane disulfate (10) and diols 7 and 9. Compounds 8 and 10 were active with IC(50) values of 14.59 and 59.65 μM, respectively. Diols 7 and 9 showed no inhibitory activity (IC(50)>500 μM).     

Microbiological degradation of bile acids. Ring a cleavage and 7α,12α-dehydroxylation of cholic acid by Arthrobacter simplex

The metabolism of cholic acid by Arthrobacter simplex was investigated. This organism effected both ring a cleavage and elimination of the hydroxyl groups at C-7 and C-12 and gave a new metabolite, (4R)-4-[4alpha-(2-carboxyethyl)-3aalpha-hexahydro-7abeta-methyl-5-oxoindan-1beta-yl]valeric acid, which was isolated and identified through its partial synthesis. A degradative pathway of cholic acid into this metabolite is tentatively proposed, and the possibility that the proposed pathway could be extended to the cholic acid degradation by other microorganisms besides A. simplex is discussed. The possibility that the observed reactions in vitro could occur during the metabolism of bile acids in vivo is considered.     

Quantification of urinary 3α,21-dihydroxy-5β-pregnan-20-one and 5-pregnene-3β, 20α-diol by mass fragmentography

A sensitive and accurate method is described for measuring urinary corticosteroids by gas chromatography-mass spectroscopy (GC-MS). Using single peak monitoring (mass fragmentography) and electron impact ionization, the acetates of 3α,21-dihydroxy-5β-pregnan-20-one (tetrahydrodeoxycorticoster-one) and 5-pregnene-3β,20α-diol were estimated with deuterio-acetate carriers as recovery markers. With this technique, the coefficient of variation did not exceed 3% for GC-MS analyses of the urinary corticosteroid samples by single peak monitoring. An evaluation of the trimethylsilyl ether derivatives of the two steroids by chemical ionization was also made. Secretion rates determined for deoxycorticos-terone derived from specific activities of urinary tetrahydrodeoxycorticosterone and excretion levels of 5-pregnene-3β,20α-diol were slightly lower than those obtained by other methods.