Glucuronide and sulfate conjugates of ICI 182,780, a pure anti-estrogenic steroid. Order of addition, catalysis and substitution effects in glucuronidation

Glucuronidated Flavonoids in Neurological Protection: Structural Analysis and Approaches for Chemical and Biological Synthesis

Both plant and mammalian cells express glucuronosyltransferases that catalyze glucuronidation of polyphenols such as flavonoids and other small molecules. Oral administration of select polyphenolic compounds leads to the accumulation of the corresponding glucuronidated metabolites at μM and sub-μM concentrations in the brain, associated with amelioration of a range of neurological symptoms. Determining the mechanisms whereby botanical extracts impact cognitive wellbeing and psychological resiliency will require investigation of the modes of action of the brain-targeted metabolites. Unfortunately, many of these compounds are not commercially available. This article describes the latest approaches for the analysis and synthesis of glucuronidated flavonoids. Synthetic schemes include both standard organic synthesis, semisynthesis, enzymatic synthesis and use of synthetic biology utilizing heterologous enzymes in microbial platform organisms.

Synthesis of Glycosides of Glucuronic, Galacturonic and Mannuronic Acids: An Overview

Uronic acids are carbohydrates present in relevant biologically active compounds. Most of the latter are glycosides or oligosaccharides linked by their anomeric carbon, so their synthesis requires glycoside-bond formation. The activation of this anomeric center remains difficult due to the presence of the electron-withdrawing C-5 carboxylic group. Herein we present an overview of glucuronidation, mannuronidation and galacturonidation reactions, including syntheses of prodrugs, oligosaccharides and stereochemical aspects.

Identification of some benproperine metabolites in humans and investigation of their antitussive effect

AIM

To identify 4 unknown metabolites of benproperine (BPP, 1) in human urine after a po dose, and to investigate the antitussive effect of monohydroxylate metabolites.

METHODS

The putative metabolite references were prepared using chemical synthesis. Their structures were identified using 1H and 13C nuclear magnetic resonance, and mass spectrometry. The metabolites in human urine were separated and assayed using liquid chromatography-ion trap mass spectrometry (LC/MS/MS), and further confirmed by comparison of their mass spectra and chromatographic retention times with those of synthesized reference substances. The antitussive effects of metabolites were evaluated on coughs induced by 7.5% citric acid in conscious guinea pigs.

RESULTS

1-[1-Methyl-2-[2-(phenylmethyl)phenoxy]-ethyl]-4-piperidinol (2), 1-[1-methyl-2-[2-(phenylmethyl)phenoxy] ethyl]-3-piperidinol (3) and their glucuronides 4 and 5 were obtained from chemical synthesis. Four urinary metabolites in human urine showed peaks with the same chromatographic retention times and mass spectra in LC/MS/MS as synthetic substances 2, 3, 4 and 5. Phosphates of compounds 2 and 3 prolonged the latency of cough and reduced the number of coughs during the 3 min test using citric acid, but did not reduce the number of coughs during the 5 min immediately after the test in conscious guinea pigs.

CONCLUSION

Compounds 2, 3, 4, and 5 were identified as the metabolites of BPP in human urine. Among them, compounds 2 and 3 are inactive in the antitussive effect.

Glucuronidation of steroidal alcohols using iodosugar and imidate donors

We report a study of the glucuronidation of a number of important steroidal secondary alcohols. The alcohols studied are androsterone 7, epiandrosterone 8, 17-acetoxy-androstane-3alpha,17beta-diol 9, 11alpha-hydroxyprogesterone 10, and 3-benzoylestradiol 11. These were first glucuronidated using the Schmidt trichloroacetimidate method with variations in acyl substituent (viz. derivatives 2 and 3), Lewis acid catalyst and order of addition. The results are contrasted with those obtained using our recently described glycosyl iodide donor 4, catalysed either by N-iodosuccinimide (NIS) or various metal salts.

Synthesis and analysis of conjugates of the major vitamin E metabolite, alpha-CEHC

Glucuronide and sulphate conjugates of 2,5,7,8-tetramethyl-2-(2'-carboxyethyl)-6-hydroxychroman (alpha-CEHC), the major metabolite of alpha-tocopherol (vitamin E), have been synthesized and used for the first direct analysis of conjugated urinary vitamin E metabolites. The metabolites of vitamin E (alpha-tocopherol) could be useful as markers of the function(s) of vitamin E in vivo. A number of methods have been described for the analysis of urinary vitamin E metabolites but these have relied on either acid or enzymatic deconjugation of the metabolites prior to analysis by high performance liquid chromatography or gas chromatography/mass spectrometry. These methods have provided useful information about the amount and types of metabolites excreted in the urine but suffer from a number of disadvantages. Deconjugation has been shown to produce artifacts as a result of the conversion of alpha-CEHC to alpha-tocopheronolactone and the efficiency of deconjugation is also difficult to assess. Methods that allow the direct measurement of the conjugated metabolites would overcome these problems and would also substantially reduce the preparation and analysis time. Here we describe the use of conjugated standards to characterize alpha-CEHC conjugates in human urine by tandem mass spectrometry (MS-MS). The future use of MS-MS to measure urinary vitamin E metabolites is also discussed.

Chemical synthesis and characterization of conjugates of a novel catechol-O-methyltransferase inhibitor

BIA 3-202, 1-(3,4-dihydroxy-5-nitrophenyl)-2-phenylethanone 3, is a novel, reversible, and tight-binding peripheral inhibitor of the enzyme catechol-O-methyltransferase (COMT), which is currently under clinical evaluation for the treatment of Parkinson's disease as an adjunct to current L-Dopa/peripheral decarboxylase inhibitor therapy. Chemically pure, well-characterized reference standards of conjugates of 3 were required for investigation of the routes of metabolism in several animal species (including humans) and for pharmacokinetic studies. The lack of suitable literature precedents for efficient, regioselective synthesis of nitrocatechol conjugate metabolites prompted us to develop efficient and highly selective chemical preparations of O-glucuronide and O-sulfate conjugates of 3 such that multigram quantities of excellent purity can now be conveniently synthesized. It is anticipated that these procedures could be applied to the synthesis of conjugates of other COMT inhibitors, also based on the 3-nitrocatechol pharmacophore.