Journal of Pharmaceutical and Biomedical Analysis 101 (2014) 102–122 Contents lists available at ScienceDirect Journal of Pharmaceutical and Biomedical Analysis j ournal homepage: www.elsevier.com/locate/jpba Review Pharmaceutical impurities and degradation products: Uses and applications of NMR techniques ∗ Rubén M. Maggio, Natalia L. Calvo, Silvana E. Vignaduzzo, Teodoro S. Kaufman Instituto de Química Rosario (IQUIR, CONICET–UNR) and Área Análisis de Medicamentos, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, Rosario S2002LRK, Argentina a r a t b i c s t l e i n f o r a c t Article history: Current standards and regulations demand the pharmaceutical industry not only to produce highly pure Received 25 February 2014 drug substances, but to achieve a thorough understanding of the impurities accompanying their manufac- Received in revised form 11 April 2014 tured drug substances and products. These challenges have become important goals of process chemistry Accepted 12 April 2014 and have steadily stimulated the search of impurities after accelerated or forced degradation procedures. Available online 24 April 2014 As a result, impurity profiling is one of the most attractive, active and relevant fields of modern pharmaceutical analysis. This activity includes the identification, structural elucidation and quantitative Keywords: determination of impurities and degradation products in bulk drugs and their pharmaceutical formula- NMR spectroscopy tions. Pharmaceutical impurities LC–NMR Nuclear magnetic resonance (NMR) spectroscopy has evolved into an irreplaceable approach for phar- Structural elucidation maceutical quality assessment, currently playing a critical role in unequivocal structure identification Qualitative and quantitative analysis as well as structural confirmation (qualitative detection), enabling the understanding of the underlying mechanisms of the formation of process and/or degradation impurities. NMR is able to provide qualitative information without the need of standards of the unknown com- pounds and multiple components can be quantified in a complex sample without previous separation. When coupled to separative techniques, the resulting hyphenated methodologies enhance the analytical power of this spectroscopy to previously unknown levels. As a result, and by enabling the implementa- tion of rational decisions regarding the identity and level of impurities, NMR contributes to the goal of making better and safer medicines. Herein are discussed the applications of NMR spectroscopy and its hyphenated derivate techniques to the study of a wide range pharmaceutical impurities. Details on the advantages and disadvantages of the methodology and well as specific challenges with regards to the different analytical problems are also presented. © 2014 Elsevier B.V. All rights reserved. Contents 1. Introduction . 103 1.1. Pharmaceutical impurities and approaches to their modern quality control . 103 1.2. NMR spectroscopy . 104 1.2.1. NMR spectroscopy as an analytical tool: Advantages and disadvantages . 104 1.2.2. NMR spectroscopy and qualitative pharmaceutical analysis . 104 1.2.3. NMR spectroscopy and quantitative pharmaceutical analysis: qNMR. 104 1.2.4. Hyphenated NMR techniques . 105 2. NMR-assisted Identification/structure elucidation and quantitation of related impurities . 106 2.1. Process-related impurities . 106 2.1.1. Impurities resulting from isolation in naturally occurring APIs . 106 ∗ Corresponding author. Tel.: +54 341 4370477x118; fax: +54 341 4370477x118. E-mail address: [email protected] (T.S. Kaufman). http://dx.doi.org/10.1016/j.jpba.2014.04.016 0731-7085/© 2014 Elsevier B.V. All rights reserved. R.M. Maggio et al. / Journal of Pharmaceutical and Biomedical Analysis 101 (2014) 102–122 103 2.1.2. Impurities in synthetic active pharmaceutical ingredients . 107 2.1.3. Process impurities: Geometric and conformational isomers . 108 2.1.4. Process impurities: Positional and functional group isomers . 109 2.1.5. Process impurities: Configurational isomers. Epimers and enantiomers; NMR determination of enantiomeric purity . 110 2.1.6. Genotoxic, toxic and mutagenic impurities . 110 2.1.7. Organic volatile impurities (residual solvents) and other accompanying impurities . 112 2.2. Degradation products. 112 2.2.1. Impurities resulting from degradation of synthetic APIs . 112 2.2.2. Impurities resulting from degradation of natural product APIs. 114 2.3. Miscellaneous impurities . 115 2.3.1. Impurities and degradation products related to excipients. 115 2.3.2. Leaching impurities . 116 2.3.3. Interaction products . 116 3. Other NMR active nuclei . 116 4. Conclusions and perspectives . 117 Acknowledgements . 117 Appendix A. Acronyms, abbreviations and their definitions, regarding NMR experiments . 117 References . 117 1. Introduction with an excipient and/or immediate container closure system [21]. 1.1. Pharmaceutical impurities and approaches to their modern In addition, in current pharmaceutical development processes, quality control impurities in the API have identification and qualification thresh- olds of 0.10 and 0.15% respectively, for doses of the API up to 2 g/day The quality assurance and quality control of active pharma- [20] and many recent publications reflect interest in compounds ceutical ingredients (APIs) and excipients are major issues in ranging from 0.01 to 0.1%. pharmaceutical analysis, which intend to prevent damages to the Reliable assessment of drug purity in accordance with these patients. Quality control methods are regulated in the pharma- stringent standards requires the use of state of the art validated copeias and other documents, which are continuously revised in analytical methods, increasingly sensitive detections, and mainly order to keep updated drugs, excipients, and also their methods for an analyst prepared to critically interpret the results. analysis. Furthermore, internationally agreed recommendations, The available tools for impurity profiling have already been such as those issued by the International Conference on Harmo- reviewed [22]. Reversed-phase liquid chromatography (RP–LC) is nization (ICH) are steadily moving pharmaceutical analysis beyond still the primary method for analyte separation toward impurity compendial requirements, with the advantage of the most mod- profiling of drugs. However, an increasing number of examples ern analytical technologies [1]. Pharmaceutical impurities are the show the usefulness of both nuclear magnetic resonance (NMR) unwanted chemicals that remain with the API, develop during for- spectroscopy and mass spectrometry (MS) as additional tools for mulation, or upon degradation of both API and drug products. Their the detection and quantitation of difficult to solve impurity chal- presence, even in small amounts, might influence the efficacy and lenges. safety of the pharmaceutical products; therefore, drug purity has When employed as stand-alone techniques, NMR and MS offer a always been associated to drug quality. high degree of orthogonality and complementarity [23]. In partic- The evolution of chemical knowledge and the advent of ular, NMR spectroscopy is relevant because it can simultaneously increasingly sensitive and selective analytical methods have been and selectively detect multiple components in a sample, even with- continuously stimulating the interest in the determination of drug out their physical separation. purity and the impurities themselves in both, natural and synthetic Mass spectrometric studies can provide structure-rich informa- products. This is in line with the policy of the pharmaceutical indus- tion of organic compounds, even those found at trace impurity try, which has always demanded that the API should be as pure as levels, with small amounts of sample. When hyphenated with an LC possible. The number of recently published books [2], book chapters separation, and when electro-spray (ESI) or atmospheric-pressure [3–6] and papers on the subject demonstrate the increasing impor- chemical ionization (APCI) are used, MS provides very impor- tance of pharmaceutical impurities [7–11] and impurity profiling tant information about the molecular weights (especially when [12–16]. These and other [17–19] publications also reflect the con- implemented in high-resolution mode) of the chromatographed tinued interest of the regulatory authorities, industry and scientists compounds. It can also provide the structure (through the frag- in these areas. mentation pattern).