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Zacharias NM, Ornelas A, Lee J, Hu J, Davis JS, Uddin N, Pudakalakatti S, Menter DG, Karam JA, Wood CG, Hawk ET, Kopetz S, Vilar E, Bhattacharya PK, Millward SW. Real‐Time Interrogation of Aspirin Reactivity, Biochemistry, and Biodistribution by Hyperpolarized Magnetic Resonance Spectroscopy. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201812759] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Niki M. Zacharias
- Department of Cancer Systems Imaging The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
- Department of Urology The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - Argentina Ornelas
- Department of Cancer Systems Imaging The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - Jaehyuk Lee
- Department of Cancer Systems Imaging The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - Jingzhe Hu
- Department of Cancer Systems Imaging The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - Jennifer S. Davis
- Department of Epidemiology The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - Nasir Uddin
- Department of Cancer Systems Imaging The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - Shivanand Pudakalakatti
- Department of Cancer Systems Imaging The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - David G. Menter
- Department of Gastrointestinal Medical Oncology The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - Jose A. Karam
- Department of Urology The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - Christopher G. Wood
- Department of Urology The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - Ernest T. Hawk
- Department of Clinical Cancer Prevention The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - Scott Kopetz
- Department of Gastrointestinal Medical Oncology The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - Eduardo Vilar
- Department of Gastrointestinal Medical Oncology The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
- Department of Clinical Cancer Prevention The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - Pratip K. Bhattacharya
- Department of Cancer Systems Imaging The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
| | - Steven W. Millward
- Department of Cancer Systems Imaging The University of Texas MD Anderson Cancer Center 1515 Holcombe Blvd. Houston TX 77030 USA
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Zacharias NM, Ornelas A, Lee J, Hu J, Davis JS, Uddin N, Pudakalakatti S, Menter DG, Karam JA, Wood CG, Hawk ET, Kopetz S, Vilar E, Bhattacharya PK, Millward SW. Real-Time Interrogation of Aspirin Reactivity, Biochemistry, and Biodistribution by Hyperpolarized Magnetic Resonance Spectroscopy. Angew Chem Int Ed Engl 2019; 58:4179-4183. [PMID: 30680862 DOI: 10.1002/anie.201812759] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Revised: 01/21/2019] [Indexed: 12/21/2022]
Abstract
Hyperpolarized magnetic resonance spectroscopy enables quantitative, non-radioactive, real-time measurement of imaging probe biodistribution and metabolism in vivo. Here, we investigate and report on the development and characterization of hyperpolarized acetylsalicylic acid (aspirin) and its use as a nuclear magnetic resonance (NMR) probe. Aspirin derivatives were synthesized with single- and double-13 C labels and hyperpolarized by dynamic nuclear polarization with 4.7 % and 3 % polarization, respectively. The longitudinal relaxation constants (T1 ) for the labeled acetyl and carboxyl carbonyls were approximately 30 seconds, supporting in vivo imaging and spectroscopy applications. In vitro hydrolysis, transacetylation, and albumin binding of hyperpolarized aspirin were readily monitored in real time by 13 C-NMR spectroscopy. Hyperpolarized, double-labeled aspirin was well tolerated in mice and could be observed by both 13 C-MR imaging and 13 C-NMR spectroscopy in vivo.
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Affiliation(s)
- Niki M Zacharias
- Department of Cancer Systems Imaging, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA.,Department of Urology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - Argentina Ornelas
- Department of Cancer Systems Imaging, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - Jaehyuk Lee
- Department of Cancer Systems Imaging, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - Jingzhe Hu
- Department of Cancer Systems Imaging, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - Jennifer S Davis
- Department of Epidemiology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - Nasir Uddin
- Department of Cancer Systems Imaging, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - Shivanand Pudakalakatti
- Department of Cancer Systems Imaging, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - David G Menter
- Department of Gastrointestinal Medical Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - Jose A Karam
- Department of Urology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - Christopher G Wood
- Department of Urology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - Ernest T Hawk
- Department of Clinical Cancer Prevention, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - Scott Kopetz
- Department of Gastrointestinal Medical Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - Eduardo Vilar
- Department of Gastrointestinal Medical Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA.,Department of Clinical Cancer Prevention, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - Pratip K Bhattacharya
- Department of Cancer Systems Imaging, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
| | - Steven W Millward
- Department of Cancer Systems Imaging, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX, 77030, USA
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Glöggler S, Wagner S, Bouchard LS. Hyperpolarization of amino acid derivatives in water for biological applications. Chem Sci 2015; 6:4261-4266. [PMID: 29218193 PMCID: PMC5707458 DOI: 10.1039/c5sc00503e] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2015] [Accepted: 05/07/2015] [Indexed: 12/20/2022] Open
Abstract
We report on the successful synthesis and hyperpolarization of N-unprotected α-amino acid ethyl propionate esters and extensively, on an alanine derivative hyperpolarized by PHIP (4.4 ± 1.0% 13C-polarization), meeting required levels for in vivo detection. Using water as solvent increases biocompatibility and the absence of N-protection is expected to maintain biological activity.
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Affiliation(s)
- S Glöggler
- Department of Chemistry and Biochemistry , University of California at Los Angeles , Los Angeles , California 90095-1569 , USA .
| | - S Wagner
- Biomedical Imaging Research Institute , Cedars Sinai Medical Center , 8700 Beverly Blvd, Davis Building G149E , Los Angeles , California 90048-1804 , USA
| | - L-S Bouchard
- Department of Chemistry and Biochemistry , University of California at Los Angeles , Los Angeles , California 90095-1569 , USA .
- California NanoSystems Institute , 570 Westwood Plaza, Building 114 , Los Angeles , California 90095-1569 , USA
- Department of Bioengineering , University of California at Los Angeles , 420 Westwood Plaza, RM 5121 Engineering V, P.O. Box 951600 , Los Angeles , California 90095-1569 , USA
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Fekete M, Bayfield O, Duckett SB, Hart S, Mewis RE, Pridmore N, Rayner PJ, Whitwood A. Iridium(III) hydrido N-heterocyclic carbene-phosphine complexes as catalysts in magnetization transfer reactions. Inorg Chem 2013; 52:13453-61. [PMID: 24215616 PMCID: PMC3850244 DOI: 10.1021/ic401783c] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Indexed: 11/28/2022]
Abstract
The hyperpolarization (HP) method signal amplification by reversible exchange (SABRE) uses para-hydrogen to sensitize substrate detection by NMR. The catalyst systems [Ir(H)2(IMes)(MeCN)2(R)]BF4 and [Ir(H)2(IMes)(py)2(R)]BF4 [py = pyridine; R = PCy3 or PPh3; IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene], which contain both an electron-donating N-heterocyclic carbene and a phosphine, are used here to catalyze SABRE. They react with acetonitrile and pyridine to produce [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4 and [Ir(H)2(NCMe)(py)(IMes)(PCy3)]BF4, complexes that undergo ligand exchange on a time scale commensurate with observation of the SABRE effect, which is illustrated here by the observation of both pyridine and acetonitrile HP. In this study, the required symmetry breaking that underpins SABRE is provided for by the use of chemical inequivalence rather than the previously reported magnetic inequivalence. As a consequence, we show that the ligand sphere of the polarization transfer catalyst itself becomes hyperpolarized and hence that the high-sensitivity detection of a number of reaction intermediates is possible. These species include [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4, [Ir(H)2(MeOH)(py)(IMes)(PPh3)]BF4, and [Ir(H)2(NCMe)(py)2(PPh3)]BF4. Studies are also described that employ the deuterium-labeled substrates CD3CN and C5D5N, and the labeled ligands P(C6D5)3 and IMes-d22, to demonstrate that dramatically improved levels of HP can be achieved as a consequence of reducing proton dilution and hence polarization wastage. By a combination of these studies with experiments in which the magnetic field experienced by the sample at the point of polarization transfer is varied, confirmation of the resonance assignments is achieved. Furthermore, when [Ir(H)2(pyridine-h5)(pyridine-d5)(IMes)(PPh3)]BF4 is examined, its hydride ligand signals are shown to become visible through para-hydrogen-induced polarization rather than SABRE.
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Affiliation(s)
- Marianna Fekete
- Department of Chemistry, Centre for Hyperpolarization
in Magnetic Resonance, University of York, York Science Park, York, YO10 5NY, U.K.
| | - Oliver Bayfield
- Department of Chemistry, Centre for Hyperpolarization
in Magnetic Resonance, University of York, York Science Park, York, YO10 5NY, U.K.
| | - Simon B. Duckett
- Department of Chemistry, Centre for Hyperpolarization
in Magnetic Resonance, University of York, York Science Park, York, YO10 5NY, U.K.
| | - Sam Hart
- Department of Chemistry, Centre for Hyperpolarization
in Magnetic Resonance, University of York, York Science Park, York, YO10 5NY, U.K.
| | - Ryan E. Mewis
- Department of Chemistry, Centre for Hyperpolarization
in Magnetic Resonance, University of York, York Science Park, York, YO10 5NY, U.K.
| | - Natalie Pridmore
- Department of Chemistry, Centre for Hyperpolarization
in Magnetic Resonance, University of York, York Science Park, York, YO10 5NY, U.K.
| | - Peter J. Rayner
- Department of Chemistry, Centre for Hyperpolarization
in Magnetic Resonance, University of York, York Science Park, York, YO10 5NY, U.K.
| | - Adrian Whitwood
- Department of Chemistry, Centre for Hyperpolarization
in Magnetic Resonance, University of York, York Science Park, York, YO10 5NY, U.K.
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Glöggler S, Colell J, Appelt S. Para-hydrogen perspectives in hyperpolarized NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 235:130-142. [PMID: 23932399 DOI: 10.1016/j.jmr.2013.07.010] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Revised: 07/11/2013] [Accepted: 07/15/2013] [Indexed: 06/02/2023]
Abstract
The first instance of para-hydrogen induced polarization (PHIP) in an NMR experiment was serendipitously observed in the 1980s while investigating a hydrogenation reaction (Seldler et al., 1983; Bowers and Weitekamp, 1986, 1987; Eisenschmid et al., 1987) [1-4]. Remarkably a theoretical investigation of the applicability of para-hydrogen as a hyperpolarization agent was being performed in the 1980's thereby quickly providing a theoretical basis for the PHIP-effect (Bowers and Weitekamp, 1986) [2]. The discovery of signal amplification by a non-hydrogenating interaction with para-hydrogen has recently extended the interest to exploit the PHIP effect, as it enables investigation of compounds without structural alteration while retaining the advantages of spectroscopy with hyperpolarized compounds [5]. In this article we will place more emphasis of the future applications of the method while only briefly discussing the efforts that have been made in the understanding of the phenomenon and the development of the method so far.
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Affiliation(s)
- Stefan Glöggler
- Department of Chemistry and Biochemistry, University of California, 607 Charles E Young Drive East, Young Hall 2056, Los Angeles, CA 90095, USA.
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Green RA, Adams RW, Duckett SB, Mewis RE, Williamson DC, Green GGR. The theory and practice of hyperpolarization in magnetic resonance using parahydrogen. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2012; 67:1-48. [PMID: 23101588 DOI: 10.1016/j.pnmrs.2012.03.001] [Citation(s) in RCA: 253] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2012] [Accepted: 03/05/2012] [Indexed: 05/03/2023]
Affiliation(s)
- Richard A Green
- Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom
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Duckett SB, Mewis RE. Application of parahydrogen induced polarization techniques in NMR spectroscopy and imaging. Acc Chem Res 2012; 45:1247-57. [PMID: 22452702 DOI: 10.1021/ar2003094] [Citation(s) in RCA: 169] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Magnetic resonance provides a versatile platform that allows scientists to examine many different types of phenomena. However, the sensitivity of both NMR spectroscopy and MRI is low because the detected signal strength depends on the population difference that exists between the probed nuclear spin states in a magnetic field. This population difference increases with the strength of the interacting magnetic field and decreases with measurement temperature. In contrast, hyperpolarization methods that chemically introduce parahydrogen (a spin isomer of hydrogen with antiparallel spins that form a singlet) based on the traditional parahydrogen induced polarization (PHIP) approach tackle this sensitivity problem with dramatic results. In recent years, the potential of this method for MRI has been recognized, and its impact on medical diagnosis is starting to be realized. In this Account, we describe the use of parahydrogen to hyperpolarize a suitable substrate. This process normally involves the introduction of a molecule of parahydrogen into a target to create large population differences between nuclear spin states. The reaction of parahydrogen breaks the original magnetic symmetry and overcomes the selection rules that prevent both NMR observation and parahydrogen/orthohydrogen interconversion, yielding access to the normally invisible hyperpolarization associated with parahydrogen. Therefore the NMR or MRI measurement delivers a marked increase in the detected signal strength over the normal Boltzmann-population derived result. Consequently, measurements can be made which would otherwise be impossible. This approach was pioneered by Weitekamp, Bargon, and Eisenberg, in the late 1980s. Since 1993, we have used this technique in York to study reaction mechanisms and to characterize normally invisible inorganic species. We also describe signal amplification by reversible exchange (SABRE), an alternative route to sensitize molecules without directly incorporating a molecule of parahydrogen. This approach widens the applicability of PHIP methods and the range of materials that can be hyperpolarized. In this Account we describe our parahydrogen studies in York over the last 20 years and place them in a wider context. We describe the characterization of organometallic reaction intermediates including those involved in catalytic reactions, either with or without hydride ligands. The collection of spectroscopic and kinetic data with rapid inverse detection methods has proved to be particularly informative. We can see enhanced signals for the organic products of catalytic reactions that are linked directly to the catalytic intermediates that form them. This method can therefore prove unequivocally that a specific metal complex is involved in a catalytic cycle, thus pinpointing the true route to catalysis. Studies where a pure nuclear spin state is detected show that it is possible to detect all of the analyte molecules present in a sample using NMR. In addition, we describe methods that achieve the selective detection of these enhanced signals, when set against a strong NMR background such as that of water.
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Affiliation(s)
- Simon B. Duckett
- Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom
| | - Ryan E. Mewis
- Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom
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Tang JA, Gruppi F, Fleysher R, Sodickson DK, Canary JW, Jerschow A. Extended para-hydrogenation monitored by NMR spectroscopy. Chem Commun (Camb) 2011; 47:958-60. [DOI: 10.1039/c0cc03421e] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Approaches for the rapid identification of drug metabolites in early clinical studies. Bioanalysis 2011; 3:197-213. [DOI: 10.4155/bio.10.186] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Understanding the metabolism of a novel drug candidate in drug discovery and drug development is as important today as it was 30 years ago. What has changed in this period is the technology available for proficient metabolite characterization from complex biological sources. High-efficiency chromatography, sensitive MS and information-rich NMR spectroscopy are approaches that are now commonplace in the modern laboratory. These advancements in analytical technology have led to unequivocal metabolite identification often being performed at the earliest opportunity, following the first dose to man. For this reason an alternative approach is to shift from predicting and extrapolating possible human metabolism from in silico and nonclinical sources, to actual characterization at steady state within early clinical trials. This review provides an overview of modern approaches for characterizing drug metabolites in these early clinical studies. Since much of this progress has come from technology development over the years, the review is concluded with a forward-looking perspective on how this progression may continue into the next decade.
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Looking back through the MIST: a perspective of evolving strategies and key focus areas for metabolite safety analysis. Bioanalysis 2010; 2:1235-48. [DOI: 10.4155/bio.10.71] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The publication of the US FDA MIST guidance document in 2008 reignited the debate around the most appropriate strategies to underwrite metabolite safety for novel compounds. Whilst some organizations have suggested that the guidelines necessitate a paradigm shift to more thorough metabolite analysis during early development, an evaluation of historical practices shows that the principles of the guidelines have always largely underpinned metabolism studies within the pharmaceutical industry. Therefore, it is argued that existing practices, when coupled to appropriate emerging analytical tools and a case-by-case consideration of the relevance of the generated metabolism data in terms of structure, physicochemisty, abundance and activity, represent a fit-for-purpose approach to metabolite-safety assessments.
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Roth M, Koch A, Kindervater P, Bargon J, Spiess HW, Münnemann K. (13)C hyperpolarization of a barbituric acid derivative via parahydrogen induced polarization. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 204:50-55. [PMID: 20207180 DOI: 10.1016/j.jmr.2010.01.016] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2009] [Revised: 01/29/2010] [Accepted: 01/30/2010] [Indexed: 05/28/2023]
Abstract
Significant (13)C NMR signal enhancement by a factor of 5000 of a barbituric acid derivative (5-methyl-5-propenyl-barbituric acid) via parahydrogen induced polarization is presented. This hyperpolarization is achieved by hydrogenating 5-methyl-5-propargyl-barbituric acid with 98% enriched para-H(2) under elevated temperature and pressure and transferring the initially created (1)H hyperpolarization with an INEPT-derived pulse sequence to (13)C. The polarization can be selectively transferred to different carbons in the barbituric acid derivative by applying different pulse delays in the INEPT pulse sequence. These results demonstrate the potential of using hyperpolarized barbituric acid derivatives as "active" contrast agents in MRI and visualizing their pharmacokinetics in vivo.
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Affiliation(s)
- Meike Roth
- Max-Planck-Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany
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Abstract
HPLC detector technology has advanced dramatically over the past 20 years, with a range of highly sensitive and specific detectors becoming available. What is still missing from the bioanalyst’s armoury, however, is a highly sensitive detector that gives an equimolar response independent of the compound. This would allow for quantification of compounds without the requirement for a synthetic standard or a radiolabeled analogue. In particular, such a detector applied to metabolism studies would establish the relative significance of the various metabolic routes. The recently issued US FDA guidelines on metabolites in safety testing (MIST) focus on the relative quantitation of human metabolites being obtained as soon as feasible in the drug-development process. In this article, current detector technology is reviewed with respect to its potential for quantitation without authentic standards or a radiolabel and put in the context of the MIST guidelines. The potential for future developments are explored.
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Gutmann T, Sellin M, Breitzke H, Stark A, Buntkowsky G. Para-hydrogen induced polarization in homogeneous phase—an example of how ionic liquids affect homogenization and thus activation of catalysts. Phys Chem Chem Phys 2009; 11:9170-5. [DOI: 10.1039/b908198d] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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