Structural evaluation of the glucuronides of morphine and formoterol using chemical derivatization with 1,2-dimethylimidazole-4-sulfonyl chloride and liquid chromatography/ion trap mass spectrometry

Advancing structural elucidation of conjugation drug metabolites in metabolite profiling with novel electron-activated dissociation

RATIONALE

This study focuses on the advantage of using the novel electron-activated dissociation (EAD) technology on the QTOF system for structural elucidation of conjugation metabolites. In drug metabolite identification, conceptual "boxes" are generally used to represent potential sites of modifications, which are proposed based on MS/MS data. Electron-activated dissociation (EAD) provides unique fragmentation patterns, potentially allowing for more precise localization of the metabolic modification sites compared to CID, particularly for conjugations.

METHOD

Known compounds were incubated with rat liver microsomes in the presence of nicotinamide adenine dinucleotide phosphate (NADPH), uridine dihosphate-glucuronic acid (UDPGA), and glutathione. Conjugation metabolites were analyzed using the QTOF system. High-resolution MS/MS spectra were collected using EAD and CID fragmentations along with TOF MS full scan for tested drugs and metabolites. Fragmentation patterns were compared to evaluate their efficiency in structural elucidation.

RESULTS

Metabolite profiling identified conjugation metabolites (glucuronides and GSH adducts), using characteristic mass shifts. A comparison of EAD and CID fragmentation revealed EAD-specific fragments for most conjugates. EAD was able to break the relatively stable bonds on parent drug motifs while keeping relatively weak conjugation bonds intact, despite the generally low intensity of EAD. EAD effectively narrowed the conceptual "box" representing modification sites, providing more definitive information on conjugation sites and facilitating the structural elucidation of conjugated metabolites.

CONCLUSION

EAD is a powerful tool for metabolite profiling in drug development, particularly for identifying conjugation sites. EAD-enabled MS/MS spectra offer a greater variety of signature fragments compared to CID, resulting in more comprehensive and unique structural information for metabolic modification analysis. Overall, EAD, complementary to CID, has the potential to narrow down potential modification sites, significantly enhancing the precision of conjugation metabolite structure elucidation.

Glucuronidation Pathways of 5- and 7-Hydroxypropranolol: Determination of Glucuronide Structures and Enzyme Selectivity

Propranolol, a non-selective beta-blocker medication, has been utilized in the treatment of cardiovascular diseases for several decades. Its hydroxynaphthyl metabolites have been recognized to possess varying degrees of beta-blocker activity due to the unaltered side-chain. This study achieved the successful separation and identification of diastereomeric glucuronic metabolites derived from 4-, 5-, and 7-hydroxypropranolol (4-OHP, 5-OHP, and 7-OHP) in human urine. Subsequently, reaction phenotyping of 5- and 7-hydroxypropranolol by different uridine 5'-diphospho-glucuronosyltransferases (UGTs) was carried out, with a comparison to the glucuronidation of 4-hydroxypropranolol (4-OHP). Among the 19 UGT enzymes examined, UGT1A1, UGT1A3, UGT1A7, UGT1A8, UGT1A9, UGT1A10, UGT2A1, and UGT2A2 were found to be involved in the glucuronidation of 5-OHP. Furthermore, UGT1A6 exhibited glucuronidation activity towards 7-OHP, along with the aforementioned eight UGTs. Results obtained by glucuronidation of corresponding methoxypropranolols and MS/MS analysis of 1,2-dimethylimidazole-4-sulfonyl (DMIS) derivatives of hydroxypropranolol glucuronides suggest that both the aromatic and aliphatic hydroxy groups of the hydroxypropranolols may be glucuronidated in vitro. However, the analysis of human urine samples collected after the administration of propranolol leads us to conclude that aromatic-linked glucuronidation is the preferred pathway under physiological conditions.

Application of microfluidic technologies in forensic analysis

The application of microfluidic technology in forensic medicine has steadily expanded over the last two decades due to the favorable features of low cost, rapidity, high throughput, user-friendliness, contamination-free, and minimum sample and reagent consumption. In this context, bibliometric methods were adopted to visualize the literature information contained in the Science Citation Index Expanded from 1989 to 2022, focusing on the co-occurrence analysis of forensic and microfluidic topics. A deep interpretation of the literature was conducted based on co-occurrence results, in which microfluidic technologies and their applications in forensic medicine, particularly forensic genetics, were elaborated. The purpose of this review is to provide an impartial evaluation of the utilization of microfluidic technology in forensic medicine. Additionally, the challenges and future trends of implementing microfluidic technology in forensic genetics are also addressed.

Simultaneous measurement of free and conjugated estrogens in surface water using capillary liquid chromatography tandem mass spectrometry

Given detrimental impacts induced by estrogens at trace level, determination of them is significant but challenging due to their low content in environmental samples and inherent weak ionisation. A modified derivatisation-based methodology was applied for the first time to detect estrogen in free and conjugated forms including some isomers simultaneously using liquid chromatography tandem mass spectrometry (LC-MSn). Derivatisation reaction with previously used 1,2-dimethyl-1H-imidazole-5-sulphonyl chloride allowed significant increase of mass spectrometric signal of analytes and also provided distinctive fragmentation for their confirmation even in complicated matrix. Then satisfactory recovery (>75%) for the majority of analytes was achieved following optimisation of solid phase extraction (SPE) factors. The linearity was validated over a wide concentration with the correlation coefficient around 0.995. The repeatability of this methodology was also confirmed via the intra-day and inter-day precision and was less than 11.73%. Validation of method quantification limits (MQLs) for all chosen estrogens was conducted using 1000 mL surface water, ranging from 7.0 to 132.3 pg L-1. The established methodology was applied to profile presence of targeted estrogens in natural surface water samples. Out of the ten compounds of interest, three free estrogens (E1, E2, E3) and two sulphate estrogens (E1-3S and E2-3S) were found over their MQLs, being in the range of 0.05-0.32 ng L-1.

Options of the Main Derivatization Approaches for Analytical ESI and MALDI Mass Spectrometry

The inclusion of preliminary chemical labeling (derivatization) in the analysis process by such powerful and widespread methods as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is a popular and widely used methodological approach. This is due to the need to remove some fundamental limitations inherent in these powerful analytic methods. Although a number of special reviews has been published discussing the utilization of derivatization approaches, the purpose of the present critical review is to comprehensively summarize, characterize and evaluate most of the previously developed and practically applied, as well as recently proposed representative derivatization reagents for ESI-MS and MALDI-MS platforms in their mostly sensitive positive ion mode and frequently hyphenated with separation techniques. The review is focused on the use of preliminary chemical labeling to facilitate the detection, identification, structure elucidation, quantification, profiling or MS imaging of compounds within complex matrices. Two main derivatization approaches, namely the introduction of permanent charge-fixed or highly proton affinitive residues into analytes are critically evaluated. In situ charge-generation, charge-switch and charge-transfer derivatizations are considered separately. The potential of using reactive matrices in MALDI-MS and chemical labeling in MS-based omics sciences is given.

Differentiation of Deprotonated Acyl-, N-, and O-Glucuronide Drug Metabolites by Using Tandem Mass Spectrometry Based on Gas-Phase Ion-Molecule Reactions Followed by Collision-Activated Dissociation

Glucuronidation, a common phase II biotransformation reaction, is one of the major in vitro and in vivo metabolism pathways of xenobiotics. In this process, glucuronic acid is conjugated to a drug or a drug metabolite via a carboxylic acid, a hydroxy, or an amino group to form acyl-, O-, and/or N-glucuronide metabolites, respectively. This process is traditionally thought to be a detoxification pathway. However, some acyl-glucuronides react with biomolecules in vivo, which may result in immune-mediated idiosyncratic drug toxicity (IDT). In order to avoid this, one may attempt in early drug discovery to modify the lead compounds in such a manner that they then have a lower probability of forming reactive acyl-glucuronide metabolites. Because most drugs or drug candidates bear multiple functionalities, e.g., hydroxy, amino, and carboxylic acid groups, glucuronidation can occur at any of those. However, differentiation of isomeric acyl-, N-, and O-glucuronide derivatives of drugs is challenging. In this study, gas-phase ion-molecule reactions between deprotonated glucuronide metabolites and BF₃ followed by collision-activated dissociation (CAD) in a linear quadrupole ion trap mass spectrometer were demonstrated to enable the differentiation of acyl-, N-, and O-glucuronides. Only deprotonated N-glucuronides and deprotonated, migrated acyl-glucuronides form the two diagnostic product ions: a BF₃ adduct that has lost two HF molecules, [M - H + BF₃ - 2HF]^-, and an adduct formed with two BF₃ molecules that has lost three HF molecules, [M - H + 2BF₃ - 3HF]^-. These product ions were not observed for deprotonated O-glucuronides and unmigrated, deprotonated acyl-glucuronides. Upon CAD of the [M - H + 2BF₃ - 3HF]^- product ion, a diagnostic fragment ion is formed via the loss of 2-fluoro-1,3,2-dioxaborale (MW of 88 Da) only in the case of deprotonated, migrated acyl-glucuronides. Therefore, this method can be used to unambiguously differentiate acyl-, N-, and O-glucuronides. Further, coupling this methodology with HPLC enables the differentiation of unmigrated 1-β-acyl-glucuronides from the isomeric acyl-glucuronides formed upon acyl migration. Quantum chemical calculations at the M06-2X/6-311++G(d,p) level of theory were employed to probe the mechanisms of the reactions of interest.

Phenol-selective mass spectrometric analysis of jet fuel

A bromobenzyl charged tag selectively reacts with key contaminants in jet fuel to provide charged ethers that are readily detectable by ESI-MS.

Evaluation of the metabolism, bioactivation and pharmacokinetics of triaminopyrimidine analogs toward selection of a potential candidate for antimalarial therapy

1. During the course of metabolic profiling of lead Compound 1, glutathione (GSH) conjugates were detected in rat bile, suggesting the formation of reactive intermediate precursor(s). This was confirmed by the identification of GSH and N-acetylcysteine (NAC) conjugates in microsomal incubations. 2. It was proposed that bioactivation of Compound 1 occurs via the formation of a di-iminoquinone reactive intermediate through the involvement of the C-2 and C-5 nitrogens of the pyrimidine core. 3. To further investigate this hypothesis, structural analogs with modifications at the C-5 nitrogen were studied for metabolic activation in human liver microsomes supplemented with GSH/NAC. 4. Compounds 1 and 2, which bear secondary nitrogens at the C-5 of the pyrimidine core, were observed to form significant amounts of GSH/NAC-conjugates in vitro, whereas compounds with tertiary nitrogens at C-5 (Compound 3 and 4) formed no such conjugates. 5. These observations provide evidence that electron/hydrogen abstraction is required for the bioactivation of the triaminopyrimidines, potentially via a di-iminoquinone intermediate. The lack of a hydrogen and/or steric hindrance rendered Compound 3 and 4 incapable of forming thiol conjugates. 6. This finding enabled advancement of compound 4, with a desirable potency, safety and PK profile, as a lead candidate for further development in the treatment of malaria.

Multiple stage MS in analysis of plasma, serum, urine and in vitro samples relevant to clinical and forensic toxicology

This paper reviews MS approaches applied to metabolism studies, structure elucidation and qualitative or quantitative screening of drugs (of abuse) and/or their metabolites. Applications in clinical and forensic toxicology were included using blood plasma or serum, urine, in vitro samples, liquids, solids or plant material. Techniques covered are liquid chromatography coupled to low-resolution and high-resolution multiple stage mass analyzers. Only PubMed listed studies published in English between January 2008 and January 2015 were considered. Approaches are discussed focusing on sample preparation and mass spectral settings. Comments on advantages and limitations of these techniques complete the review.

Measurement of Estradiol in Human Serum by LC-MS/MS Using a Novel Estrogen-Specific Derivatization Reagent

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method is described that employs a novel derivatization reagent for the measurement of serum estradiol (E2), with simultaneous analysis of underivatized testosterone (T) and dihydrotestosterone (DHT). The main advantage of the new derivatization reagent 1,2-dimethylimidazole-5-sulfonyl chloride is its analyte-specific fragmentation that enables monitoring of confirmatory mass transitions with high sensitivity. The reaction mixture can be analyzed without additional purification steps using a 9.5 min gradient run, and sensitive detection is achieved with a triple quadrupole mass spectrometer using atmospheric pressure photoionization. Method validation was performed with human serum samples, including a comparison with a standard LC-MS/MS method using 120 samples from a clinical study, and analysis of certified E2 serum reference materials BCR-576, BCR-577, and BCR-578. The lower limits of quantification for E2, T, and DHT were 0.5 pg/mL, 25 pg/mL, and 0.10 ng/mL, respectively, from a 200-μL sample. Validation results indicated good accuracy and agreement with established, conventional LC-MS/MS assays, demonstrating suitability for analysis of samples containing E2 in the low pg/mL range, such as serum from men, children, and postmenopausal women.

A rapid and specific derivatization procedure to identify acyl-glucuronides by mass spectrometry

A simple procedure is described to identify acyl-glucuronides by coupled liquid chromatography/mass spectrometry after derivatization to a hydroxamic acid with hydroxylamine. The reaction specificity obviates the need for isolation of the acyl-glucuronide from an extract. Glucuronides derived from carbamic acids, and alkyl- and aromatic amines, are inert to the derivatization reaction conditions, making the hydroxamic acid derivative a fingerprint for acyl-glucuronides.

In vitro formation of phase I and II metabolites of propranolol and determination of their structures using chemical derivatization and liquid chromatography-tandem mass spectrometry

Derivatization with 1,2-dimethylimidazole-4-sulfonyl chloride (DMISC) has been successfully used as a tool to differentiate between aromatic and aliphatic O-glucuronides of hydroxypropranolol. The analyses were performed with liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) with both a triple quadrupole and an ion trap instrument. Hydroxylated forms of propranolol can be glucuronidated in aliphatic as well as aromatic positions. These isoforms are not distinguishable by tandem MS alone, as they both initially lose 176 Da, i.e. monodehydrated glucuronic acid, giving back the aglycone. Two in vitro systems were set up for the production of propranolol metabolites. The obtained isomers of 4'-hydroxypropranolol glucuronide were determined to correspond to one aliphatic and one aromatic form, using chemical derivatization with DMISC and LC-MS(n). DMISC was shown to react with the secondary amine in the case where the naphtol was occupied by the glucuronyl moiety, resulting in a different fragmentation pattern compared with that of the aliphatic glucuronide, where the naphtol group was accessible to derivatization.