Improved Chemical Synthesis, X‐Ray Crystallographic Analysis, and NMR Characterization of (22R)‐/(22S)‐Hydroxy Epimers of Bile Acids

Abstract

We report an improved synthesis of the (22R)- and (22S)-epimers of 3α,7α,12α,22-tetrahydroxy-5β-cholan-24-oic acid and 3α,7α,22-trihydroxy-5β-cholan-24-oic acid from cholic acid (CA) and chenodeoxycholic acid (CDCA), respectively. The principal reactions involved were as follows: (1) oxidative decarboxylation of the bile acid peracetates with lead tetraacetate, and (2) subsequent Reformatsky reaction of the 23,24-dinor-22-aldehydes with ethyl bromoacetate in the presence of activated Zn as a catalyst with the reaction temperature maintained precisely at 75 °C. The absolute configuration of the chiral center at C-22 of each epimer was established by single-crystal X-ray diffraction data using its ethyl ester-peracetate derivative. The (1)H- and (13)C-NMR spectra that permit the (22R)- and (22S)-epimers to be distinguished are reported as well as the specific (1)H shift effects induced by C(5)D(5)N. Bile acids having hydroxyl groups at C-22 are present in a variety of animal biles, previously have been difficult to identify, and are known to have distinctive physicochemical and biological properties.

Chemical Synthesis of the Epimeric (23R)‐ and (23S)‐Fluoro Derivatives of Bile Acids via Horner–Wadsworth–Emmons Reaction

“…2, the synthetic routes to key intermediates (6a and 6b) from primary bile acids (2a and 2b) are essentially the same as those reported previously [14]. Thus, treatment of 2a and 2b with acetic anhydride and 4-dimethylaminopyridine resulted in the formation of the peracetate derivatives (3a and 3b), which in turn were transformed into the C 23 24-nor-22-enes (4a and 4b) by the side chain degradation with lead tetraacetate [(AcO) 4 Pb] and cuprous acetate [(AcO) 2 Cu] in boiling pyridine [15,16].…”

“…The crystals contain about 1.5 molecule of water per molecule of 1b-S, likely from methanol used for recrystallization that had not been dried prior to use. Thus, the X-ray analysis provided directly the absolute configuration at C-23, in analogy with hydroxylated derivatives epimeric at C-23, C-25, C-22/C-25 or C-24/C-25 of bile acids and bile alcohols [14,[21][22][23][24], and conclusive evidence for the stereochemical assignment of 1b-S as the (23S)-configuration, which was the secondary-eluted peak in Fig. 3 (2); 1b-R was therefore assigned as (23R).…”

Isolation and Identification of a Urinary Biomarker for Lung Cancer: 27-Nor-5β-Cholestane-3α,7α,12α,24R,25S Pentol Glucuronide and Its Deuterated Analog

“…(3 R ,5 S ,7 R ,8 R ,9 S ,10 S ,12 S ,13 R ,14 S ,17 R )-17-((2 R ,5 R ,6 S )-5,6-bis(benzyloxy)hept-3-en-2-yl)-10,13-dimethylhexadecahydro-1H-cyclopenta[a]phenanthrene-3,7,12-triyl triacetate ( 10a ). Olefins 4 [ 25 , 26 , 27 , 28 ] (0.15 g, 0.31 mmol) and 5a (0.434 g, 1.55 mmol) were dissolved in 5.0 mL of benzene and degassed with argon for 5.0 min. Hoveyda-Grubb’s 2nd generation catalyst (97.0 mg, 10 mol%) was added to the mixture and refluxed under argon for 20 h. The crude reaction mixture was adsorbed onto 5.0 g of silica gel and dried under vacuum.…”

“…13 ((((2S,3S)-pent-4-ene-2,3-diyl)bis(oxy))bis(methylene))dibenzene (5d) 1 H NMR (400 MHz, CDCl 3 ) δ 7.34-7.08 (m, 10H), 5.75 (ddd, J = 16.7, 10.9, 7.5 Hz, 1H), 5.30-5.17 (m, 2H), 4.57 (d, J = 12.2 Hz, 3H), 4.35 (d, J = 12.0 Hz, 1H), 3.77 (ddt, J = 7.5, 5.8, 1.0 Hz, 1H), 3.66-3.48 (m, 1H), 1.08 (d, J = 6.4 Hz, 3H). 13 Olefins 4 [25][26][27][28] (0.15 g, 0.31 mmol) and 5a (0.434 g, 1.55 mmol) were dissolved in 5.0 mL of benzene and degassed with argon for 5.0 min. Hoveyda-Grubb's 2nd generation catalyst (97.0 mg, 10 mol%) was added to the mixture and refluxed under argon for 20 h. The crude reaction mixture was adsorbed onto 5.0 g of silica gel and dried under vacuum.…”