Synthesis of urine drug metabolites: glucuronic acid glycosides of phenol intermediates

The investigation of drug metabolism requires substantial amount of metabolites. Isolation from urine is tedious, therefore, the material obtained by synthesis is preferred. Substantial amounts of three tentative drug metabolites, phenolic glucuronides, have been prepared using easily available glycosyl donors. The final products [3(2-N-methyl-N-isopropylaminoethoxy)phenyl] beta-D-glucopyranosiduronic acid, 4-amino-3,5-dimethylphenyl beta-D-glucopyranosiduronic acid and [2(S)-propanoyl-6-O-naphthyl] beta-D-glucopyranuronic acid are useful as, for example, reference material in metabolite investigations.

Synthesis and Reactivity of Some 6-Substituted-2,4-dimethyl-3-pyridinols, a Novel Class of Chain-Breaking Antioxidants

The synthesis and study of a series of 6-substituted-2,4-dimethyl-3-pyridinols having interesting antioxidant properties is reported. The general synthetic strategy leading to the compounds involved a low-temperature aryl bromide-to-alcohol conversion as the last step. 2,4-dimethyl-3-pyridinol (1a), 2,4,6-trimethyl-3-pyridinol (1b), and 2,4-dimethyl-6-(dimethylamino)-3-pyridinol (1d) were thus prepared from the corresponding 3-bromopyridine precursor. The methoxy derivative 2,4-dimethyl-6-(methoxy)-3-pyridinol (1c) was also prepared by an alternate route via a Baeyer-Villiger reaction on the substituted benzaldehyde precursor. Novel bicyclic pyridinols 2 and 3 required prior construction of the ring structure. Thus, 2 was prepared by the use of a 6-step intramolecular Friedel-Crafts strategy, and 3 required an 11-step sequence with a thermolytic intramolecular inverse-demand Diels-Alder reaction between a pyrimidine ring and an alkyne as the key step. Basicities of the pyridinols approached physiological pH with increasing electron density in the ring. Pyridinols 1a-d were found to be indefinitely stable to air oxidation while 2 and 3 decomposed upon extended exposure to the atmosphere. The reactivities of the pyridinols toward chain-carrying peroxyl radicals in homogeneous organic solution were examined by studying the kinetics of radical-initiated styrene autoxidations under controlled conditions. These experiments revealed that some of the newly synthesized pyridinols are the most effective phenolic chain-breaking antioxidants reported to date.

Sugar-substituted 2-azetidinone cholesterol absorption inhibitors: enhanced potency by modification of the sugar

A glucuronide conjugate of the potent 2-azetidinone cholesterol absorption inhibitor Sch 58235 was synthesized to confirm the structure of a metabolite isolated from in vivo sources. A series of 2-azetidinone glycosides was prepared via Schmidt trichloroimidate methodology. Enhanced cholesterol absorption inhibition was achieved by modification of the sugar moiety.

Sugar-substituted 2-azetidinones as cholesterol absorption inhibitors

The asymmetric synthesis of a glucuronide conjugate of the 2-azetidinone cholesterol absorption inhibitor Sch 48461 was accomplished to confirm the structure of a metabolite isolated from in vivo sources. Key features of this article include the asymmetric synthesis of 2-azetidinones by Evan's chiral oxazolidinone methodology and glucuronide formation by a Mitsunobu protocol.

Direct detection of the internal acyl migration reactions of benzoic acid 1-O-acylglucuronide by 13C-labeling and nuclear magnetic resonance spectroscopy

1-O-Acyl-beta-D-glucopyranuronates can undergo irreversible binding to proteins mainly through internal acyl migration reactions, which may have toxicological significance. A new method based on the 13C-labeling and nuclear magnetic resonance (NMR) spectroscopy has been developed to study the reactivity of the 1-O-acyl-beta-D-glucopyranuronate of benzoic acid. In phosphate buffer (pH 7.4) solution at 37 degrees C, the glucuronide showed apparent first-order degradation kinetics (T1/2, 125 min), and concurrent and sequential appearance of 2-, 3- and 4-O-acyl isomers as both alpha- and beta-anomers was observed. The isomeric glucuronides were identified by two-dimensional NMR of the reaction mixture. The direct approach using 13C-labeling and NMR could also provide insights into the reactivities of other labile drug acylglucuronides and their isomeric glucuronides.

Development of a simple liquid chromatographic method for the separation of mixtures of positional isomers and anomers of synthetic 2-, 3- and 4-fluorobenzoic acid glucuronides formed via acyl migration reactions

Many drugs containing carboxylate groups form beta-1-O-acyl glucuronides as their major phase II metabolites in vivo. These ester glucuronides are potentially reactive due to the susceptibility of the acyl group to nucleophilic reactions resulting in hydrolysis, acyl migration or covalent adduct formation. In the present study, a number of synthetic fluorobenzoic acid glucuronide conjugates were chosen as models for chromatographic studies. A high-performance liquid chromatography method is presented for the simultaneous determination of the 1-, 2-, 3- and 4-positional isomers of the acyl glucuronides, and their alpha- and beta-anomers for the 2-, 3- and 4-fluorobenzoic acids as well as each aglycone formed as a result of hydrolysis. The same elution order was found for the acyl migrated glucuronide isomers of the three fluorobenzoic acids in their equilibrium mixtures. The alpha-4-O-acyl isomer eluted first followed by the beta-4-O-acyl isomer, then the beta-1-O-acyl, the beta-3-O-acyl, the alpha-3-O-acyl, the alpha-2-O-acyl and finally the beta-2-O-acyl isomer eluted. The method was used to determine the overall degradation rates, the acyl migration rates and the hydrolysis rates of 1-O-(2-fluorobenzoyl)-beta-D-glucopyranuronic acid 1-O-(3-fluorobenzoyl)-beta-D-glucopyranuronic acid and 1-O-(4-flurobenzoyl)-beta-D-glucopyranuronic acid in a buffer system pH 7.4 at 25 degrees C. It was found that the order of beta-1-glucuronide acyl migration rates was 2-fluorobenzoyl > 3-fluorobenzoyl > 4-fluorobenzoyl. Both the acyl migration rates and the elution order were interpreted in terms of electronic effect of the fluorine substituent on the carbonyl carbon.

Biotransformation of mianserin in laboratory animals and man

1. The biotransformation and excretion of the antidepressant mianserin were studied after oral administration of the labelled drug to rats, mice, rabbits, guinea pigs and humans. Mianserin was well absorbed and almost completely metabolized in all five species. 2. Major metabolic pathways of mianserin were p-oxidation of the N-substituted aromatic ring followed by conjugation, and oxidation and demethylation of the N-methyl moiety, followed by conjugation. Direct conjugation of the N-methyl moiety was observed as a metabolic pathway specific for man. 3. Conjugated metabolites were isolated by h.p.l.c. and identified by 1H-n.m.r. and FAB spectrometry. Novel metabolites such as an N-O-glucuronide in the guinea pig and an N-sulphonate in rat and guinea pig, were identified using these techniques. A quaternary N-glucuronide was found only in man.

A review of the methods of chemical synthesis of sulphate and glucuronide conjugates

1. Methods for the synthesis of drug conjugates with sulphuric acid have been reviewed. 2. Some analytical methods are presented for the analysis of sulphate conjugates. 3. The synthesis of several types of N, O and C beta-D-glucuronides is reviewed. Different beta-coupling reactions of protected glucuronides are presented. 4. Application of n.m.r. and mass spectrometry to the analysis of beta-D-glucuronides is discussed.

A mass spectrometric approach to the identification of conjugated drug metabolites

For the identification of intact underivatized drug conjugates, the mass spectrometric technique of choice is fast atom bombardment (FAB); the combined use of both positive and negative ion FAB usually provides information on the molecular mass and nature of conjugates under study, while the number of exchangeable hydrogen atoms can be determined using trideuterated glycerol as the FAB-matrix. Electron impact and desorption chemical ionization spectra can be used to study the aglycone part of the conjugated metabolites. With this approach metabolites conjugated with glucuronic acid, sulphuric acid and amino acids have been identified. The identification was supported by analysis of reference compounds, prepared by chemical synthesis. The examples given are selected from current metabolism studies on drug candidates in development within Organon's research.