Synthesis of biliverdin and bilirubin 1-O-acyl-β-d-glucopyranuronic acids

Abstract

Biliverdin and bilirubin mono- and di-beta-glucuronides were prepared by nucleophilic substitution of the 1-O-mesyl derivative of alpha-ethoxyethyl-protected glucuronic acid (compound II) with the tetrabutylammonium salts of biliverdin and bilirubin. Removal of the acetal-protecting groups by mild acid treatment yielded biliverdin glucuronides, which were reduced to bilirubin glucuronides. Depending on reaction conditions the pure beta-anomers or mixtures highly enriched in the beta-anomers were obtained. The biliverdin and bilirubin glucuronides were identical with pigments derived from bile. They were characterized as the IX alpha isomers and the beta-anomers by alkaline hydrolysis, n.m.r. spectroscopy, hydrolysis with beta-glucuronidase and conversion into dipyrrolic azopigments. Model reactions of the 1-O-mesylate (II) with other nucleophiles also were performed, i.e. the acetate anion and various alcohols.

Potential bile acid metabolites. 24. An efficient synthesis of carboxyl‐linked glucosides and their chemical properties

“…Since the carboxyl-linked glucosides of bile acids are susceptible to both hydrolysis and transesterification in alcoholic solvents, particular caution should therefore be paid in the isolation and purification processes. 1 H NMR spectra provided confirmatory evidence for the structures of individual acyl glucosides (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). The resonance positions of 18-, 19-, and 21-methyl protons, as well as methine protons at C-3, C-6, C-7, or C-12, are essentially unchanged compared to those observed for the corresponding unconjugated bile acids.…”

“…Previous syntheses of acyl glucuronides have required multiple steps with several protections and deprotections, resulting in low overall yields (23)(24)(25)(26). A feasible, shorter method, however, has recently been reported for the preparation of acyl glucuronides, all of which are produced in a condensation reaction between carboxylic acids and a protected glucuronic acid derivative in the presence of diisopropyl-(or diethyl)-azodicarboxylate and triphenylphosphine as coupling agents (27,28).…”

“…( (24). This was recrystallized from EtOAc as a colorless amorphous solid; yield, 85%; mp, 164-166°C.…”

“…Normal-phase thin-layer chromatography (TLC) of the free 1-O-acyl-β-D-glucosides of bile acids (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28) was performed on a precoated silica gel plate (E. Merck, Darmstadt, Germany) using chloroform/methanol/acetic acid (24:6:3, by vol; solvent system A) or EtOAc/acetic acid (9:1, vol/vol; solvent system B) mixtures as the developing solvents. Reversed-phase TLC was carried out on precoated C 18 silica gel plates (E. Merck) using a developing mixture of methanol/ water (19:1, vol/vol; solvent system C).…”

“…1 H nuclear magnetic resonance (NMR) spectra were obtained on a JEOL JNM-EX 270 FT NMR instrument (Tokyo, Japan) at 270 MHz, with CDCl 3 , CDCl 3 containing 20% dimethylsulfoxide (DMSO)d 6 or CD 3 OD containing 0.1% Me 4 Si as the solvent; chemical shifts are expressed as δ ppm relative to Me 4 Si. High-resolution mass spectra (HR-MS) were obtained on a JEOL JMS-LCmate double focusing magnetic mass spectrometer equipped with an electrospray ionization (ESI) probe under the positive ion mode (PIM) [M + Na] + for benzyl ester derivatives (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) or negative ion mode (NIM) [M − H] − for free esters (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). For reference compounds, polypropylene glycol (50 ppm) in methanol for 1 and 2, or polyethyleneglycol (50 ppm) in methanol for 3-14 was used in PIM; and sodium trifluoroacetate (200 ppm) and sodium acetate (40 ppm) in methanol for 15 and 16, or polyethyleneglycol sulfate (50 ppm) in methanol for 17-28 was used in NIM.…”