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Chiu KY, Ai Y, Tanim-Ai Hassan M, Li X, Gunawardena HP, Chen H. Standards-Free Absolute Quantitation of Oxidizable Glycopeptides by Coulometric Mass Spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2024. [PMID: 38815255 DOI: 10.1021/jasms.4c00052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2024]
Abstract
Currently, glycopeptide quantitation is mainly based on relative quantitation due to absolute quantitation requiring isotope-labeled or standard glycopeptides which may not be commercially available or are very costly and time consuming to synthesize. To address this grand challenge, coulometric mass spectrometry (CMS), based on the combination of electrochemistry (EC) and mass spectrometry (MS), was utilized to quantify electrochemically active glycopeptides without the need of using standard materials. In this study, we studied tyrosine-containing glycopeptides, NYIVGQPSS(β-GlcNAc)TGNL-OH and NYSVPSS(β-GlcNAc)TGNL-OH, and successfully quantified them directly with CMS with a discrepancy of less than 5% between the CMS measured amount and the theoretical amount. Taking one step further, we applied this approach to quantify glycopeptides generated from the digestion of NIST mAb, a monoclonal antibody reference material. Through HILIC column separation, five N297 glycopeptides resulting from NIST mAb tryptic digestion were successfully separated and quantified by CMS for an absolute amount without the use of any standard materials. This study indicates the potential utility of CMS for quantitative proteomics research.
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Affiliation(s)
- Kai-Yuan Chiu
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, United States
| | - Yongling Ai
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, United States
| | - Md Tanim-Ai Hassan
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, United States
| | - Xuanwen Li
- Analytical Research & Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Harsha P Gunawardena
- The Janssen Pharmaceutical Companies of Johnson & Johnson, Springhouse, Pennsylvania 19002, United States
| | - Hao Chen
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, United States
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FNU PIJ, Tanim-Al-Hassan M, Yaroshuk T, Ai Y, Chen H. Absolute Quantitation of Peptides and Proteins by Coulometric Mass Spectrometry After Derivatization. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 2024; 495:117153. [PMID: 38009161 PMCID: PMC10673616 DOI: 10.1016/j.ijms.2023.117153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2023]
Abstract
Peptide/protein quantitation using mass spectrometry (MS) is advantageous due to its high sensitivity. Traditional absolute peptide quantitation methods rely on making calibration curves using peptide standards or isotope-labelled peptide standards, which are expensive and take time to synthesize. A method which can eliminate the need for using standards would be beneficial. Recently, we developed coulometric mass spectrometry (CMS) which can be used to quantify peptides that are oxidizable (e.g., those containing tyrosine or tryptophan), without using peptide standard. The method is based on electrochemical oxidation of peptides followed by MS to measure the oxidation yield. However, it cannot be directly used to quantify peptides without oxidizable residues. To extend this method for quantifying peptides/proteins in general, in this study, we adopted a derivatization strategy, in which a target peptide is first tagged with an electroactive reagent such as monocarboxymethylene blue NHS ester (MCMB-NHS ester), followed with quantitation by CMS. To illustrate the power of this method, we have analyzed peptides MG and RPPGFSPFR. The quantification error was less than 5%. Using RPPGFSPFR as an example, the quantitation sensitivity of the technique was found to be 0.25 pmol. Furthermore, we also used the strategy to quantify proteins cytochrome C and β-casein with an error of 2-26%.
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Affiliation(s)
- Praneeth Ivan Joel FNU
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark, NJ, 07102, USA
| | - Md. Tanim-Al-Hassan
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark, NJ, 07102, USA
| | - Timothy Yaroshuk
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark, NJ, 07102, USA
| | - Yongling Ai
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark, NJ, 07102, USA
| | - Hao Chen
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark, NJ, 07102, USA
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Li X. Recent applications of quantitative mass spectrometry in biopharmaceutical process development and manufacturing. J Pharm Biomed Anal 2023; 234:115581. [PMID: 37494866 DOI: 10.1016/j.jpba.2023.115581] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Revised: 06/27/2023] [Accepted: 07/12/2023] [Indexed: 07/28/2023]
Abstract
Biopharmaceutical products have seen rapid growth over the past few decades and continue to dominate the global pharmaceutical market. Aligning with the quality by design (QbD) framework and realization, recent advances in liquid chromatography-mass spectrometry (LC-MS) instrumentation and related techniques have enhanced biopharmaceutical characterization capabilities and have supported an increased development of biopharmaceutical products. Beyond its routine qualitative characterization, the quantitative feature of LC-MS has unique applications in biopharmaceutical process development and manufacturing. This review describes the recent applications and implications of the advancement of quantitative MS methods in biopharmaceutical process development, and characterization of biopharmaceutical product, product-related variants, and process-related impurities. We also provide insights on the emerging applications of quantitative MS in the lifecycle of biopharmaceutical product development including quality control in the Good Manufacturing Practice (GMP) environment and process analytical technology (PAT) practices during process development and manufacturing. Through collaboration with instrument and software vendors and regulatory agencies, we envision broader adoption of phase-appropriate quantitative MS-based methods for the analysis of biopharmaceutical products, which in turn has the potential to enable manufacture of higher quality products for patients.
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Affiliation(s)
- Xuanwen Li
- Analytical Research and Development, MRL, Merck & Co., Inc., 126 E. Lincoln Avenue, Rahway, NJ 07065, USA.
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Yao H, Sherer EC, Lu M, Small J, Martin GE, Lam YH, Chen Q, Helmy R, Liu Y, Chen H. One-Step Regio- and Stereoselective Electrochemical Synthesis of Orexin Receptor Antagonist Oxidative Metabolites. J Org Chem 2022; 87:15011-15021. [PMID: 36322780 PMCID: PMC10512451 DOI: 10.1021/acs.joc.2c01311] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Synthesis of drug metabolites, which often have complex structures, is an integral step in the evaluation of drug candidate metabolism, pharmacokinetic (PK) properties, and safety profiles. Frequently, such synthetic endeavors entail arduous, multiple-step de novo synthetic routes. Herein, we present the one-step Shono-type electrochemical synthesis of milligrams of chiral α-hydroxyl amide metabolites of two orexin receptor antagonists, MK-8133 and MK-6096, as revealed by a small-scale (pico- to nano-mole level) reaction screening using a lab-built online electrochemistry (EC)/mass spectrometry (MS) (EC/MS) platform. The electrochemical oxidation of MK-8133 and MK-6096 was conducted in aqueous media and found to produce the corresponding α-piperidinols with exclusive regio- and stereoselectivity, as confirmed by high-resolution nuclear magnetic resonance (NMR) characterization of products. Based on density functional theory (DFT) calculations, the exceptional regio- and stereoselectivity for this electrochemical oxidation are governed by more favorable energetics of the transition state, leading to the preferred secondary carbon radical α to the amide group and subsequent steric hindrance associated with the U-shaped conformation of the cation derived from the secondary α-carbon radical, respectively.
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Affiliation(s)
- Huifang Yao
- Department of Pharmacokinetics, Pharmacodynamics and Drug Metabolism, MRL, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
| | - Edward C. Sherer
- Analytical Research and Development, MRL, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
| | - Mei Lu
- Department of Chemistry & Biochemistry, Ohio University, Athens, OH 45701, USA
| | - James Small
- Analytical Research and Development, MRL, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
| | - Gary E. Martin
- Analytical Research and Development, MRL, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
| | - Yu-hong Lam
- Computational and Structural Chemistry, MRL, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
| | - Qinghao Chen
- Process Research and Development, MRL, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
| | - Roy Helmy
- Department of Pharmacokinetics, Pharmacodynamics and Drug Metabolism, MRL, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
| | - Yong Liu
- Analytical Research and Development, MRL, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065, USA
| | - Hao Chen
- Department of Chemistry & Biochemistry, Ohio University, Athens, OH 45701, USA
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark, NJ 07102, USA
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Ai Y, Gunawardena HP, Li X, Kim YI, Dewald HD, Chen H. Standard-Free Absolute Quantitation of Antibody Deamidation Degradation and Host Cell Proteins by Coulometric Mass Spectrometry. Anal Chem 2022; 94:12490-12499. [PMID: 36018377 PMCID: PMC10492508 DOI: 10.1021/acs.analchem.2c02709] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Proteomic absolute quantitation strategies mainly rely on the use of synthetic stable isotope-labeled peptides or proteins as internal standards, which are highly costly and time-consuming to synthesize. To circumvent this limitation, we recently developed a coulometric mass spectrometry (CMS) approach for absolute quantitation of proteins without the use of standards, based on the electrochemical oxidation of oxidizable surrogate peptides, followed by mass spectrometry measurement of the peptide oxidation yield. Previously, CMS was only applied for single-protein quantitation. In this study, first, we demonstrated absolute quantitation of multiple proteins in a mixture (e.g., β-lactoglobulin B, α-lactalbumin, and carbonic anhydrase) by CMS in one run, without using any standards. The CMS quantitation result was validated with a traditional isotope dilution method. Second, CMS can be used for absolute quantitation of a low-level target protein in a mixture; for instance, 500 ppm of PLBL2, a problematic host cell protein (HCP), in the presence of a highly abundant monoclonal antibody (mAb) was successfully quantified by CMS with no use of standards. Third, taking one step further, this study demonstrated the unprecedented quantitative analysis of deamidated peptide products arising from the mAb heavy chain deamidation reaction. In particular, absolute quantitation of the deamidation succinimide intermediate which had not been performed before due to the lack of standard was conducted by CMS, for the first time. Overall, our data suggest that CMS has potential utilities for quantitative proteomics and biotherapeutic drug discovery.
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Affiliation(s)
- Yongling Ai
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, United States
| | - Harsha P Gunawardena
- Janssen Research & Development, The Janssen Pharmaceutical Companies of Johnson & Johnson, Spring House, Pennsylvania 19477, United States
| | - Xuanwen Li
- Analytical Research & Development, Merck & Co., Inc., 2000 Galloping Hill Road, Kenilworth, New Jersey 07033, United States
| | - Yong-Ick Kim
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, United States
| | - Howard D Dewald
- Department of Chemistry and Biochemistry, Ohio University, Chemistry Building, 133 University Terrace, Athens, Ohio 45701, United States
| | - Hao Chen
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, United States
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Wang Q, Liu Z, Liu Y, Chen H. Absolute Quantitation of N-Nitrosamines by Coulometric Mass Spectrometry without Using Standards. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2022; 33:875-884. [PMID: 35446584 PMCID: PMC9119692 DOI: 10.1021/jasms.2c00064] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Carcinogenic N-nitrosamines were recently found in the sartan family of drugs and caused many drug recalls. Both of their detection and quantification are therefore important. Methods reported for N-nitrosamine quantitation rely on the use of standards and are just applicable to simple N-nitrosamines. There is an urgent need to quantify N-nitrosamines derived from drugs with a complicated structure that lack standards. To tackle the issue, this study describes a novel absolute quantitation strategy for N-nitrosamines using coulometric mass spectrometry (CMS) without standards. In our approach, N-nitrosamine is first converted into electrochemically active hydrazine via zinc reduction under acidic condition and the resulting hydrazine can then be easily quantified using CMS. To validate our method, six simple N-nitrosamines, N-nitrosodiethylamine (NDEA), N-nitroso-4-phenylpiperidine (NPhPIP), N-nitrosodiphenylamine (NDPhA), N-nitrosodibutylamine (NDBA), N-nitrosodipropylamine (NDPA), and N-nitrosopiperidine (NPIP), were chosen as test samples, and they all were quantified with excellent measurement accuracy (quantitation error ≤1.1%). Taking this one step further, as a demonstration of the method utility, a drug-like N-nitrosamine, (R)-N-(2-(6-chloro-5-methyl-1'-nitroso-2,3-dihydrospiro[indene-1,4'-piperidin]-3-yl)propan-2-yl)acetamide (VII), was also synthesized and successfully quantified using our method at 15 ppb level in a complex formulation matrix, following solvent extraction, N-nitrosamine isolation, and reductive conversion. Because of the feature of requiring no standards, CMS provides a simple and powerful approach for N-nitrosamine absolute quantitation and has great potential for analysis of other drug impurities or metabolites.
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Affiliation(s)
- Qi Wang
- Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, United States
| | - Zhijian Liu
- Department of Process Research and Development, Merck Research Laboratories, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Yong Liu
- Analytical Research and Development, Merck Research Laboratories, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Hao Chen
- Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, United States
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Li Y, Zhou B, Wang K, Zhang J, Sun W, Zhang L, Guo Y. Powerful Steroid-Based Chiral Selector for High-Throughput Enantiomeric Separation of α-Amino Acids Utilizing Ion Mobility-Mass Spectrometry. Anal Chem 2021; 93:13589-13596. [PMID: 34597017 DOI: 10.1021/acs.analchem.1c02691] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Stereospecific recognition of amino acids (AAs) plays a crucial role in chiral biomarker-based diagnosis and prognosis. Separation of AA enantiomers is a long and tedious task due to the requirement of AA derivatization prior to the chromatographic or electrophoretic steps which are also time-consuming. Here, a mass-tagged chiral selector named [d0]/[d5]-estradiol-3-benzoate-17β-chloroformate ([d0]/[d5]-17β-EBC) with high reactivity and good enantiomeric resolution in regard to AAs was developed. After a quick and easy chemical derivatization step of AAs using 17β-EBC as the single chiral selector before ion mobility-mass spectrometry analysis, good enantiomer separation was achieved for 19 chiral proteinogenic AAs in a single analytical run (∼2 s). A linear calibration curve of enantiomeric excess was also established using [d0]/[d5]-17β-EBC. It was demonstrated to be capable of determining enantiomeric ratios down to 0.5% in the nanomolar range. 17β-EBC was successfully applied to investigate the absolute configuration of AAs among peptide drugs and detect trace levels of d-AAs in complex biological samples. These results indicated that [d0]/[d5]-17β-EBC may contribute to entail a valuable step forward in peptide drug quality control and discovering chiral disease biomarkers.
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Affiliation(s)
- Yuling Li
- State Key Laboratory of Organometallic Chemistry and National Center for Organic Mass Spectrometry in Shanghai, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032, China
| | - Bowen Zhou
- State Key Laboratory of Organometallic Chemistry and National Center for Organic Mass Spectrometry in Shanghai, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032, China
| | - Keke Wang
- Shimadzu Research Laboratory (Shanghai) Co. Ltd., Shanghai 201206, China
| | - Jing Zhang
- State Key Laboratory of Organometallic Chemistry and National Center for Organic Mass Spectrometry in Shanghai, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032, China
| | - Wenjian Sun
- Shimadzu Research Laboratory (Shanghai) Co. Ltd., Shanghai 201206, China
| | - Li Zhang
- State Key Laboratory of Organometallic Chemistry and National Center for Organic Mass Spectrometry in Shanghai, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032, China
| | - Yinlong Guo
- State Key Laboratory of Organometallic Chemistry and National Center for Organic Mass Spectrometry in Shanghai, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032, China
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8
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Ai Y, Zhao P, FNU PIJ, Chen H. Absolute Quantitation of Tryptophan-Containing Peptides and Amyloid β-Peptide Fragments by Coulometric Mass Spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2021; 32:1771-1779. [PMID: 34101439 PMCID: PMC8925997 DOI: 10.1021/jasms.1c00121] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Isotope-labeled internal standards are routinely used for mass spectrometry (MS)-based absolute quantitation. However, syntheses of isotope-labeled peptides are time-consuming and costly. To tackle this issue, we recently developed a coulometric mass spectrometric (CMS) approach for absolute quantitation without the use of standards, based on the electrochemical oxidation of cysteine or tyrosine-containing peptides followed by mass spectrometric measurement of the oxidation yield. To further expand the utility of this method, herein we present the CMS method for absolute quantitation of peptides based on tryptophan electrochemical oxidation. Several tryptophan-containing peptides, such as WGG, WQPPRARI, WAGGDASGE, RTRPLWVRME, and KVPRNQDWL, were successfully quantified with a quantification error ranging from -4.5 to +4.3%. Furthermore, this quantitation approach is also applicable to protein, in which protein can be digested and a surrogate peptide can be selected for quantification to reflect the amount of the parent protein, as exemplified by CMS analysis of peptide GITWK from cytochrome c. The CMS result agreed well with the traditional isotope dilution method, with only a small difference of 3.5%. In addition, CMS was used to successfully quantify amyloid beta (Aβ) peptide fragments (up to 28 amino acid residues) based on tyrosine oxidation. The validity of the CMS method for peptide and protein absolute quantitation without using isotope-labeled peptide standards would greatly facilitate proteomics research.
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Affiliation(s)
| | | | | | - Hao Chen
- Corresponding Author: Hao Chen - Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, New Jersey, USA 07102
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9
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Kang A, Ryu J, Lee J, Kim S, Lee CY, Yun WS. Calibration curve-free electrochemical quantitation by micro-nano multi-scale gap devices. Mikrochim Acta 2021; 188:200. [PMID: 34041606 DOI: 10.1007/s00604-021-04861-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2021] [Accepted: 05/13/2021] [Indexed: 12/25/2022]
Abstract
Quantitation without relying on the calibration curve has long been an issue of overcoming analytical problems accompanied with the inherent limitations of the calibration curve fitting errors. Here, we report on a calibration curve-free method for electrochemical quantitation based on a multi-scale gap device (MGD). The MGD is an integrated device having a series of interdigitated electrodes (IDE) with micro-to-nano gap distances. The device shows a gap-dependent redox current of the analyte when subjected to the electrochemical cycling between the two facing electrodes of its componential IDEs. Based on the fact that the current increases as the gap distance decreases, the analyte concentration could be directly estimated: the rate of increase in the current was directly proportional to the analyte concentration. The calibration curve was not necessary for the quantitation. The accuracy of this MGD approach was better than that of an IDE collection of the same gap distance, which was deteriorated at the larger gap distances particularly. The MGD-based quantitation of dopamine, potassium ferricyanide, and aminophenol was demonstrated in a relatively broad range of concentrations (100 nM-5 mM).
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Affiliation(s)
- Aeyeon Kang
- Department of Chemistry, Sungkyunkwan University, Suwon, 16419, South Korea
| | - Jiho Ryu
- Department of Chemistry, Sungkyunkwan University, Suwon, 16419, South Korea
| | - Jisu Lee
- Department of Chemistry, Sungkyunkwan University, Suwon, 16419, South Korea
| | - Seunghun Kim
- Department of Chemistry, Sungkyunkwan University, Suwon, 16419, South Korea
| | - Cho Yeon Lee
- Nano/Bio Fusion Technology Research Center, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Wan Soo Yun
- Department of Chemistry, Sungkyunkwan University, Suwon, 16419, South Korea.
- Nano/Bio Fusion Technology Research Center, Sungkyunkwan University, Suwon, 16419, Republic of Korea.
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10
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Wang Q, Wang Q, Zhang Y, Mohamed YM, Pacheco C, Zheng N, Zare RN, Chen H. Electrocatalytic redox neutral [3 + 2] annulation of N-cyclopropylanilines and alkenes. Chem Sci 2020; 12:969-975. [PMID: 34163863 PMCID: PMC8179209 DOI: 10.1039/d0sc05665k] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Although synthetic organic electrochemistry (EC) has advanced significantly, net redox neutral electrosynthesis is quite rare. Two approaches have been employed to achieve this type of electrosynthesis. One relies on turnover of the product by the reactant in a chain mechanism. The other involves both oxidation on the anode and reduction on the cathode in which the radical cation or the radical anion of the product has to migrate between two electrodes. Herein, a home-built electrochemistry/mass spectrometry (EC/MS) platform was used to generate an N-cyclopropylaniline radical cation electrochemically and to monitor its reactivity toward alkenes by mass spectrometry (MS), which led to the discovery of a new redox neutral reaction of intermolecular [3 + 2] annulation of N-cyclopropylanilines and alkenes to provide an aniline-substituted 5-membered carbocycle via direct electrolysis (yield up to 81%). A chain mechanism, involving the regeneration of the substrate radical cation and the formation of the neutral product, is shown to be responsible for promoting such a redox neutral annulation reaction, as supported by experimental evidence of EC/MS.
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Affiliation(s)
- Qi Wang
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology Newark New Jersey 07102 USA
| | - Qile Wang
- Department of Chemistry and Biochemistry, University of Arkansas Fayetteville Arkansas 72701 USA
| | - Yuexiang Zhang
- Department of Chemistry and Biochemistry, Ohio University Athens Ohio 45701 USA
| | - Yasmine M Mohamed
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology Newark New Jersey 07102 USA
| | - Carlos Pacheco
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology Newark New Jersey 07102 USA
| | - Nan Zheng
- Department of Chemistry and Biochemistry, University of Arkansas Fayetteville Arkansas 72701 USA
| | - Richard N Zare
- Department of Chemistry, Stanford University Stanford California 94305-5080 USA
| | - Hao Chen
- Department of Chemistry & Environmental Science, New Jersey Institute of Technology Newark New Jersey 07102 USA
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