NMR spectrometry isotopic fingerprinting: A tool for the manufacturer for tracking Active Pharmaceutical Ingredients from starting materials to final medicines

NMR-Based Method for Intramolecular 13C Distribution at Natural Abundance Adapted to Small Amounts of Glucose

Quantitative nuclear magnetic resonance (NMR) for isotopic measurements, known as irm-NMR (isotope ratio measured by NMR), is well suited for the quantitation of ¹³C-isotopomers in position-specific isotope analysis and thus for measuring the carbon isotope composition (δ¹³C, mUr) in C-atom positions. Irm-NMR has already been used with glucose after derivatization to study sugar metabolism in plants. However, up to now, irm-NMR has exploited a "single-pulse" sequence and requires a relatively large amount of material and long experimental time, precluding many applications with biological tissues or extracts. To reduce the required amount of sample, we investigated the use of 2D-NMR analysis. We adapted and optimized the NMR sequence so as to be able to analyze a small amount (10 mg) of a glucose derivative (diacetonide glucofuranose, DAGF) with a precision better than 1 mUr at each C-atom position. We also set up a method to correct raw data and express ¹³C abundance on the usual δ¹³C scale (δ-scale). In fact, due to the distortion associated with polarization transfer and spin manipulation during 2D-NMR analyses, raw ¹³C abundance is found to be on an unusual scale. This was compensated for by a correction factor obtained via comparative analysis of a reference material (commercial DAGF) using both previous (single-pulse) and new (2D) sequences. Glucose from different biological origins (CO₂ assimilation metabolisms of plants, namely, C₃, C₄, and CAM) was analyzed with the two sequences and compared. Validation criteria such as selectivity, limit of quantification, precision, trueness, and robustness are discussed, including in the framework of green analytical chemistry.

A NIR, 1H-NMR, LC-MS and chemometrics pilot study on the origin of carvedilol drug substances: a tool for discovering falsified active pharmaceutical ingredients

Falsification of drugs, entailing the use of drug substances from unknown unapproved suppliers, is one of the main concerns for the quality of medicines. Therefore, traceability of active ingredients represents an effective tool to fight the illegal trade of medicinal products. In this view, the present pilot study explores the profile of carvedilol active ingredients and possible differences related to the origin. Sixteen samples were examined by near-infrared spectroscopy (NIR), proton nuclear magnetic resonance (¹H-NMR spectrometry) and liquid chromatography mass spectrometry (LC-MS) Q-TOF and the data were analysed by principal component analysis (PCA), cluster analysis and PLSDA discriminant analysis. The results evidenced that the combined information from the three techniques gave good classification of the samples neatly distinguishing the APIs from European countries from the APIs manufactured out of Europe. In particular, NIR spectroscopy provided effective separation between European and non-European manufacturers and ¹H-NMR or LC-MS added specific information related to the separation. Concerning LC-MS Q-TOF, the analysis of multiple isobaric peaks proved to be highly predictive of the drug substance origin and emerged as a promising tool in the field of medicine traceability.

European fingerprint study on omeprazole drug substances using a multi analytical approach and chemometrics as a tool for the discrimination of manufacturing sources

Like drug products, Active Pharmaceutical Ingredients (APIs) are subject to substandard and falsification issues, which represent a threat to patient health. In order to monitor the quality of drug substances and prevent the use of non-compliant APIs, Official Medicine Control Laboratories work together in a European network developing coordinated strategies and programmes. The API working group proposed a market surveillance study on omeprazole and omeprazole magnesium with the objectives of controlling the pharmaceutical quality of samples, checking compliance with the monographs of the European Pharmacopoeia, and collecting analytical fingerprints that could be further used to differentiate manufacturing sources for future authenticity investigations. The study described in this article reports the analysis carried out by 7 European laboratories on 28 samples from 11 manufacturers with 5 analytical techniques (related substances with HPLC, residual solvents with GC-MS, near infrared spectroscopy, proton nuclear magnetic resonance spectroscopy and X-ray powder diffractometry). The large amount of resulting analytical data were centralized and treated with two chemometric methods: Principal Component Analysis and Hierarchical Clustering Analysis. Data were analyzed separately and in combination (data fusion), allowing us to conclude that NMR and XRPD were suitable to differentiate samples originating from 9 out of 11 manufacturers. Analytical fingerprints associated with chemometrics were demonstrated to be a valuable methodology to discriminate manufacturers of omeprazole and omeprazole magnesium APIs and detect future substandard and falsified APIs.

Source Attribution of the Chemical Warfare Agent Soman Using Position-Specific Isotope Analysis by 2H NMR Spectroscopy: From Precursor to Degradation Product

Position-specific isotope analysis (PSIA) by NMR spectroscopy is a technique that provides quantitative isotopic values for every site—a so-called isotopic fingerprint—of a compound of interest. The isotopic fingerprint can be used to link samples with a common origin or to attribute a synthetic chemical to its precursor source. Despite PSIA by NMR being a powerful tool in chemical forensics, it has not yet been applied on chemical warfare agents (CWAs). In this study, different batches of the CWA Soman were synthesized from three distinctive pinacolyl alcohols (PinOHs). Prior to NMR analysis, the Soman samples were hydrolyzed to the less toxic pinacolyl methylphosphonate (PMP), which is a common degradation product. The PinOHs and PMPs were applied to PSIA by ²H NMR experiments to measure the isotopic distribution of naturally abundant ²H within the pinacolyl moiety. By normalizing the ²H NMR peak areas, we show that the different PinOHs have unique intramolecular isotopic distributions. This normalization method makes the study independent of references and sample concentration. We also demonstrate, for the first time, that the isotopic fingerprint retrieved from PSIA by NMR remains stable during the production and degradation of the CWA. By comparing the intramolecular isotopic profiles of the precursor PinOH with the degradation product PMP, it is possible to attribute them to each other.

Protein NMR of biologicals: analytical support for development and marketed products

Application of NMR spectroscopy to derive in-depth characterization of structure and dynamical properties of biomolecules is well established nowadays in many laboratories. Most of these methods rest on the availability of protein labeled with stable isotopes like ¹³C and ¹⁵N. In this report examples are presented on the application of NMR spectroscopic methods to characterize biopharmaceutical proteins in cases no isotope labeled material are available. This is typically found in protein samples used in the development of formulations and production processes. Another important focus of this report is the application of NMR methodology in the field of counterfeit drugs of biologicals and biosimilars. Especially here, NMR does offer relevant structural and quantitative data due to the high versatility of the NMR equipment. An excurse regarding the high medical relevance for a detailed spectroscopic analysis of counterfeits will be presented.

NMR-based isotopic and isotopomic analysis

Molecules exist in different isotopic compositions and most of the processes, physical or chemical, in living systems cause selection between heavy and light isotopes. Thus, knowing the isotopic fractionation of the common atoms, such as H, C, N, O or S, at each step during a metabolic pathway allows the construction of a unique isotope profile that reflects its past history. Having access to the isotope abundance gives valuable clues about the (bio)chemical origin of biological or synthetic molecules. Whereas the isotope ratio measured by mass spectrometry provides a global isotope composition, quantitative NMR measures isotope ratios at individual positions within a molecule. We present here the requirements and the corresponding experimental strategies to use quantitative NMR for measuring intramolecular isotope profiles. After an introduction showing the historical evolution of NMR for measuring isotope ratios, the vocabulary and symbols - for describing the isotope content and quantifying its change - are defined. Then, the theoretical framework of very accurate quantitative NMR is presented as the principle of Isotope Ratio Measurement by NMR spectroscopy, including the practical aspects with nuclei other than ²H, that have been developed and employed to date. Lastly, the most relevant applications covering three issues, tackling counterfeiting, authentication, and forensic investigation, are presented, before giving some perspectives combining technical improvements and methodological approaches.

Forensic application of position-specific isotopic analysis of trinitrotoluene (TNT) by NMR to determine 13C and 15N intramolecular isotopic profiles

2,4,6-trinitrotoluene (TNT) is a molecule which is easily identified with current instrumental techniques but it is generally impossible to distinguish between sources of the same substance (TNT). To overcome this difficulty, we present a multi stable isotope approach using isotope ratio monitoring by mass spectrometry (irm-MS) and Nuclear Magnetic Resonance spectrometry (irm-NMR). In the one hand, irm-MS provides bulk isotopic composition at natural abundance in ¹³C and ¹⁵N. The range of variation between samples is rather small particularly for ¹³C. In the other hand, irm-¹³C NMR and irm-¹⁵N NMR enable the determination of positional intramolecular ¹³C/¹²C ratios (δ¹³C_i) and ¹⁵N/¹⁴N ratios (δ¹⁵N_i) with high precision that lead to larger variation between samples. The present work reports an application of the recent methodology using irm-¹⁵N NMR to determine position-specific ¹⁵N isotope content of TNT. The interest of this methodology is compared to irm-¹³C NMR and irm-MS (¹³C and ¹⁵N) in terms of TNT samples discrimination. Thanks to the use of irm-NMR the results show a unique isotopic fingerprint for each TNT which enable origin discrimination between the samples without ambiguity.

Position-specific 15 N isotope analysis in organic molecules: A high-precision 15 N NMR method to determine the intramolecular 15 N isotope composition and fractionation at natural abundance

The position-specific ¹⁵ N isotope content in organic molecules, at natural abundance, is for the first time determined by using a quantitative methodology based on ¹⁵ N Nuclear Magnetic Resonance (NMR) spectrometry. ¹⁵ N NMR spectra are obtained by using an adiabatic "Full-Spectrum" INEPT sequence in order to make possible ¹⁵ N NMR experiments with a high signal-to-noise ratio (>500), to reach a precision with a standard deviation below 1‰ (0.1%). This level of precision is required for observing small changes in ¹⁵ N content associated to ¹⁵ N isotope effects. As an illustration, the measurement of an isotopic enrichment factor ε for each ¹⁵ N isotopomer is presented for 1-methylimidazole induced during a separation process on a silica column. The precision expressed as the long-term repeatability of the methodology is good enough to evaluate small changes in the ¹⁵ N isotope contents for a given isotopomer. As observed for ¹³ C, inverse and normal ¹⁵ N isotope effects occur concomitantly, giving access to new information on the origin of the ¹⁵ N isotope effects, not detectable by other techniques such as isotope ratio measured by Mass Spectrometry for which bulk (average) values are obtained.

Position-Specific Carbon Stable Isotope Ratios by Proton NMR Spectroscopy

Carbon stable isotopes provide insights into the origin and synthesis pathway of an organic molecule, and hence, contribute information that is fundamental to understanding chemical, physiological, and ecological processes. Organic carbon ¹³C/¹²C isotope ratios are commonly obtained as whole-molecule averages or as measurements of bulk samples. In contrast, position-specific isotope analysis (PSIA) provides isotope ratios for the individual carbons within a molecule, providing additional information that is masked by traditional analytical techniques. Here we introduce a ¹H NMR method for determining position-specific ¹³C/¹²C ratios within organic molecules. A peak shape superposition procedure is used to bypass the need for traditional peak integration, by exploiting relationships among the shapes of ¹H and ¹³C satellite peaks in ¹H NMR spectra. The method also has a significant sensitivity advantage over NMR methods that utilize direct detection of ¹³C. Furthermore, we demonstrate that isotope standard materials (such as those obtainable from U.S. Geological Survey) are indispensable in calibrating an NMR instrument, in order to obtain accurate isotope ratio results. Our analytical approach was applied to organic molecules of different complexity and origin, including ethanols, propionic acids, and thymidine. Results verify that chemically identical molecules from different sources can have different intramolecular isotope distributions; hence position-specific ¹³C/¹²C ratios provide an isotopic fingerprint of an organic molecule. Position-specific information for the nucleoside thymidine, where five of eight carbon positions were measured, is significant because its complexity would make it a difficult target for PSIA by mass spectrometry. The ¹H NMR method is complementary to other methods of PSIA, and will make ¹³C/¹²C PSIA employable to a wider range of organic molecules.

The new face of isotopic NMR at natural abundance

The most widely used method for isotope analysis at natural abundance is isotope ratio monitoring by Mass Spectrometry (irm-MS) which provides bulk isotopic composition in ² H, ¹³ C, ¹⁵ N, ¹⁸ O or ³⁴ S. However, in the 1980s, the direct access to Site-specific Natural Isotope Fractionation by Nuclear Magnetic Resonance (SNIF-NMR^TM ) was immediately recognized as a powerful technique to authenticate the origin of natural or synthetic products. The initial - and still most popular - application consisted in detecting the chaptalization of wines by irm-² H NMR. The approach has been extended to a wide range of methodologies over the last decade, paving the way to a wide range of applications, not only in the field of authentication but also to study metabolism. In particular, the emerging irm-¹³ C NMR approach delivers direct access to position-specific ¹³ C isotope content at natural abundance. After highlighting the application scope of irm-NMR (² H and ¹³ C), this article describes the major improvements which made possible to reach the required accuracy of 1‰ (0.1%) in irm-¹³ C NMR. The last part of the manuscript summarizes the different steps to perform isotope analysis as a function of the sample properties (concentration, peak overlap) and the kind of targeted isotopic information (authentication, affiliation). Copyright © 2016 John Wiley & Sons, Ltd.

Enhanced forensic discrimination of pollutants by position-specific isotope analysis using isotope ratio monitoring by (13)C nuclear magnetic resonance spectrometry

In forensic environmental investigations the main issue concerns the inference of the original source of the pollutant for determining the liable party. Isotope measurements in geochemistry, combined with complimentary techniques for contaminant identification, have contributed significantly to source determination at polluted sites. In this work we have determined the intramolecular (13)C profiles of several molecules well-known as pollutants. By giving additional analytical parameters, position-specific isotope analysis performed by isotope ratio monitoring by (13)C nuclear magnetic resonance (irm-(13)C NMR) spectrometry gives new information to help in answering the major question: what is the origin of the detected contaminant? We have shown that isotope profiling of the core of a molecule reveals both the raw materials and the process used in its manufacture. It also can reveal processes occurring between the contamination site 'source' and the sampling site. Thus, irm-(13)C NMR is shown to be a very good complement to compound-specific isotope analysis currently performed by mass spectrometry for assessing polluted sites involving substantial spills of pollutant.

A retro-biosynthetic approach to the prediction of biosynthetic pathways from position-specific isotope analysis as shown for tramadol

Tramadol, previously only known as a synthetic analgesic, has now been found in the bark and wood of roots of the African medicinal tree Nauclea latifolia. At present, no direct evidence is available as to the biosynthetic pathway of its unusual skeleton. To provide guidance as to possible biosynthetic precursors, we have adopted a novel approach of retro-biosynthesis based on the position-specific distribution of isotopes in the extracted compound. Relatively recent developments in isotope ratio monitoring by (13)C NMR spectrometry make possible the measurement of the nonstatistical position-specific natural abundance distribution of (13)C (δ(13)Ci) within the molecule with better than 1‰ precision. Very substantial variation in the (13)C positional distribution is found: between δ(13)Ci = -11 and -53‰. Distribution is not random and it is argued that the pattern observed can substantially be interpreted in relation to known causes of isotope fractionation in natural products. Thus, a plausible biosynthetic scheme based on sound biosynthetic principals of precursor-substrate relationships can be proposed. In addition, data obtained from the (18)O/(16)O ratios in the oxygen atoms of the compound add support to the deductions made from the carbon isotope analysis. This paper shows how the use of (13)C NMR at natural abundance can help with proposing a biosynthetic route to compounds newly found in nature or those difficult to tackle by conventional means.

Real-time oil-saturation monitoring in rock cores with low-field NMR

Nuclear magnetic resonance (NMR) provides a powerful suite of tools for studying oil in reservoir core plugs at the laboratory scale. Low-field magnets are preferred for well-log calibration and to minimize magnetic-susceptibility-induced internal gradients in the porous medium. We demonstrate that careful data processing, combined with prior knowledge of the sample properties, enables real-time acquisition and interpretation of saturation state (relative amount of oil and water in the pores of a rock). Robust discrimination of oil and brine is achieved with diffusion weighting. We use this real-time analysis to monitor the forced displacement of oil from porous materials (sintered glass beads and sandstones) and to generate capillary desaturation curves. The real-time output enables in situ modification of the flood protocol and accurate control of the saturation state prior to the acquisition of standard NMR core analysis data, such as diffusion-relaxation correlations. Although applications to oil recovery and core analysis are demonstrated, the implementation highlights the general practicality of low-field NMR as an inline sensor for real-time industrial process control.