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Noki S, de la Torre BG, Albericio F. Safety-Catch Linkers for Solid-Phase Peptide Synthesis. Molecules 2024; 29:1429. [PMID: 38611709 PMCID: PMC11012524 DOI: 10.3390/molecules29071429] [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: 02/27/2024] [Revised: 03/18/2024] [Accepted: 03/20/2024] [Indexed: 04/14/2024] Open
Abstract
Solid-phase peptide synthesis (SPPS) is the preferred strategy for synthesizing most peptides for research purposes and on a multi-kilogram scale. One key to the success of SPPS is the continual evolution and improvement of the original method proposed by Merrifield. Over the years, this approach has been enhanced with the introduction of new solid supports, protecting groups for amino acids, coupling reagents, and other tools. One of these improvements is the use of the so-called "safety-catch" linkers/resins. The linker is understood as the moiety that links the peptide to the solid support and protects the C-terminal carboxylic group. The "safety-catch" concept relies on linkers that are totally stable under the conditions needed for both α-amino and side-chain deprotection that, at the end of synthesis, can be made labile to one of those conditions by a simple chemical reaction (e.g., an alkylation). This unique characteristic enables the simultaneous use of two primary protecting strategies: tert-butoxycarbonyl (Boc) and fluorenylmethoxycarbonyl (Fmoc). Ultimately, at the end of synthesis, either acids (which are incompatible with Boc) or bases (which are incompatible with Fmoc) can be employed to cleave the peptide from the resin. This review focuses on the most significant "safety-catch" linkers.
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Affiliation(s)
- Sikabwe Noki
- Peptide Science Laboratory, School of Chemistry and Physics, University of KwaZulu-Natal, Westville, Durban 4000, South Africa;
- KwaZulu-Natal Research Innovation and Sequencing Platform (KRISP), School of Laboratory Medicine and Medical Sciences, College of Health Sciences, University of KwaZulu-Natal, Durban 4041, South Africa
| | - Beatriz G. de la Torre
- KwaZulu-Natal Research Innovation and Sequencing Platform (KRISP), School of Laboratory Medicine and Medical Sciences, College of Health Sciences, University of KwaZulu-Natal, Durban 4041, South Africa
| | - Fernando Albericio
- Peptide Science Laboratory, School of Chemistry and Physics, University of KwaZulu-Natal, Westville, Durban 4000, South Africa;
- CIBER-BBN, Networking Centre on Bioengineering, Biomaterials, and Nanomedicine, Department of Organic Chemistry, University of Barcelona, 08028 Barcelona, Spain
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2
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Duengo S, Muhajir MI, Hidayat AT, Musa WJA, Maharani R. Epimerisation in Peptide Synthesis. Molecules 2023; 28:8017. [PMID: 38138507 PMCID: PMC10745333 DOI: 10.3390/molecules28248017] [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] [Received: 08/31/2023] [Revised: 10/11/2023] [Accepted: 10/23/2023] [Indexed: 12/24/2023] Open
Abstract
Epimerisation is basically a chemical conversion that includes the transformation of an epimer into another epimer or its chiral partner. Epimerisation of amino acid is a side reaction that sometimes happens during peptide synthesis. It became the most avoided reaction because the process affects the overall conformation of the molecule, eventually even altering the bioactivity of the peptide. Epimerised products have a high similarity of physical characteristics, thus making it difficult for them to be purified. In regards to amino acids, epimerisation is very important in keeping the chirality of the assembled amino acids unchanged during the peptide synthesis and obtaining the desirable product without any problematic purification. In this review, we report several factors that induce epimerisation during peptide synthesis, including how to characterise and affect the bioactivities. To avoid undesirable epimerisation, we also describe several methods of suppressing the process.
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Affiliation(s)
- Suleman Duengo
- Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran, Sumedang 45363, West Java, Indonesia; (S.D.); (M.I.M.); (A.T.H.)
- Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Negeri Gorontalo, Gorontalo 96128, North Sulawesi, Indonesia;
| | - Muhamad Imam Muhajir
- Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran, Sumedang 45363, West Java, Indonesia; (S.D.); (M.I.M.); (A.T.H.)
| | - Ace Tatang Hidayat
- Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran, Sumedang 45363, West Java, Indonesia; (S.D.); (M.I.M.); (A.T.H.)
- Central Laboratory, Universitas Padjadjaran, Sumedang 45363, West Java, Indonesia
| | - Weny J. A. Musa
- Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Negeri Gorontalo, Gorontalo 96128, North Sulawesi, Indonesia;
| | - Rani Maharani
- Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Padjadjaran, Sumedang 45363, West Java, Indonesia; (S.D.); (M.I.M.); (A.T.H.)
- Central Laboratory, Universitas Padjadjaran, Sumedang 45363, West Java, Indonesia
- Research Collaboration Centre for Theranostic Radiopharmaceutical, National Research and Innovation Agency (BRIN), Sumedang 45363, West Java, Indonesia
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3
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Mthembu SN, Chakraborty A, Schönleber R, Albericio F, de la Torre BG. Solid-Phase Synthesis of C-Terminus Cysteine Peptide Acids. Org Process Res Dev 2022. [DOI: 10.1021/acs.oprd.2c00321] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Sinenhlanhla N. Mthembu
- Peptide Science Laboratory, School of Chemistry and Physics, University of KwaZulu-Natal, Westville, Durban 4000, South Africa
- KwaZulu-Natal Research Innovation and Sequencing Platform (KRISP), School of Laboratory Medicine and Medical Sciences, College of Health Sciences, University of KwaZulu-Natal, Durban 4041, South Africa
| | - Amit Chakraborty
- Peptide Science Laboratory, School of Chemistry and Physics, University of KwaZulu-Natal, Westville, Durban 4000, South Africa
| | | | - Fernando Albericio
- Peptide Science Laboratory, School of Chemistry and Physics, University of KwaZulu-Natal, Westville, Durban 4000, South Africa
- CIBER-BBN, Networking Centre on Bioengineering, Biomaterials and Nanomedicine, and Department of Organic Chemistry, University of Barcelona, Barcelona 08028, Spain
- Institute for Advanced Chemistry of Catalonia (IQAC-CSIC), 08034 Barcelona, Spain
| | - Beatriz G. de la Torre
- Peptide Science Laboratory, School of Chemistry and Physics, University of KwaZulu-Natal, Westville, Durban 4000, South Africa
- KwaZulu-Natal Research Innovation and Sequencing Platform (KRISP), School of Laboratory Medicine and Medical Sciences, College of Health Sciences, University of KwaZulu-Natal, Durban 4041, South Africa
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4
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Sánchez-Campillo I, Miguel-Gracia J, Karamanis P, Blanco-Canosa JB. A versatile o-aminoanilide linker for native chemical ligation. Chem Sci 2022; 13:10904-10913. [PMID: 36320694 PMCID: PMC9491214 DOI: 10.1039/d2sc04158h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2022] [Accepted: 08/25/2022] [Indexed: 12/04/2022] Open
Abstract
Chemical protein synthesis (CPS) is a consolidated field founded on the high chemospecificity of amide-forming reactions, most notably the native chemical ligation (NCL), but also on new technologies such as the Ser/Thr ligation of C-terminal salicylaldehyde esters and the α-ketoacid-hydroxylamine (KAHA) condensation. NCL was conceptually devised for the ligation of peptides having a C-terminal thioester and an N-terminal cysteine. The synthesis of C-terminal peptide thioesters has attracted a lot of interest, resulting in the invention of a wide diversity of different methods for their preparation. The N-acylurea (Nbz) approach relies on the use of the 3,4-diaminobenzoic (Dbz–COOH) and the 3-amino-(4-methylamino)benzoic (MeDbz–COOH) acids; the latter disclosed to eliminate the formation of branching peptides. Dbz–COOH has been also used for the development of the benzotriazole (Bt)-mediated NCL, in which the peptide–Dbz–CONH2 precursor is oxidized to a highly acylating peptide–Bt–CONH2 species. Here, we have brought together the Nbz and Bt approaches in a versatile linker, the 1,2-diaminobenzene (Dbz). The Dbz combines the robustness of MeDbz–COOH and the flexibility of Dbz–COOH: it can be converted into the Nbz or Bt C-terminal peptides. Both are ligated in high yields, and the reaction intermediates can be conveniently characterized. Our results show that the Bt precursors have faster NCL kinetics that is reflected by a rapid transthioesterification (<5 min). Taking advantage of this major acylating capacity, peptide–Bt can be transselenoesterified in the presence of selenols to afford peptide selenoesters which hold enormous potential in NCL. Peptide–(o-aminoanilides) prepared on a solid phase yield peptide–Nbz and peptide–Bt. Both undergo thioesterification in the presence of thiols, as well as selenoesterification in peptide–Bt. They are readily used in NCL for protein synthesis.![]()
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Affiliation(s)
- Iván Sánchez-Campillo
- Institute for Advanced Chemistry of Catalonia (IQAC-CSIC) Jordi Girona 18-26 08034 Barcelona Spain
| | - Judit Miguel-Gracia
- Institute for Advanced Chemistry of Catalonia (IQAC-CSIC) Jordi Girona 18-26 08034 Barcelona Spain
| | - Periklis Karamanis
- Dept. of Chemistry "G. Ciamician", University of Bologna Via Selmi 2 40126 Bologna Italy
| | - Juan B Blanco-Canosa
- Institute for Advanced Chemistry of Catalonia (IQAC-CSIC) Jordi Girona 18-26 08034 Barcelona Spain
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Abstract
A growing theme in chemistry is the joining of multiple organic molecular building blocks to create functional molecules. Diverse derivatizable structures—here termed “scaffolds” comprised of “hubs”—provide the foundation for systematic covalent organization of a rich variety of building blocks. This review encompasses 30 tri- or tetra-armed molecular hubs (e.g., triazine, lysine, arenes, dyes) that are used directly or in combination to give linear, cyclic, or branched scaffolds. Each scaffold is categorized by graph theory into one of 31 trees to express the molecular connectivity and overall architecture. Rational chemistry with exacting numbers of derivatizable sites is emphasized. The incorporation of water-solubilization motifs, robust or self-immolative linkers, enzymatically cleavable groups and functional appendages affords immense (and often late-stage) diversification of the scaffolds. Altogether, 107 target molecules are reviewed along with 19 syntheses to illustrate the distinctive chemistries for creating and derivatizing scaffolds. The review covers the history of the field up through 2020, briefly touching on statistically derivatized carriers employed in immunology as counterpoints to the rationally assembled and derivatized scaffolds here, although most citations are from the past two decades. The scaffolds are used widely in fields ranging from pure chemistry to artificial photosynthesis and biomedical sciences.
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Arbour CA, Mendoza LG, Stockdill JL. Recent advances in the synthesis of C-terminally modified peptides. Org Biomol Chem 2020; 18:7253-7272. [PMID: 32914156 PMCID: PMC9508648 DOI: 10.1039/d0ob01417f] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/10/2023]
Abstract
C-Terminally modified peptides are important for the development and delivery of peptide-based pharmaceuticals because they impact peptide activity, stability, hydrophobicity, and membrane permeability. Additionally, the vulnerability of C-terminal esters to cleavage by endogenous esterases makes them excellent pro-drugs. Methods for post-SPPS C-terminal functionalization potentially enable access to libraries of modified peptides, facilitating tailoring of their solubility, potency, toxicity, and uptake pathway. Apparently minor structural changes can significantly impact the binding, folding, and pharmacokinetics of the peptide. This review summarizes developments in chemical methods for C-terminal modification of peptides published since the last review on this topic in 2003.
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Affiliation(s)
- Christine A Arbour
- Wayne State University, Department of Chemistry, Detroit, Michigan, USA.
| | - Lawrence G Mendoza
- Wayne State University, Department of Chemistry, Detroit, Michigan, USA.
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Acosta GA, Murray L, Royo M, de la Torre BG, Albericio F. Solid-Phase Synthesis of Head to Side-Chain Tyr-Cyclodepsipeptides Through a Cyclative Cleavage From Fmoc-MeDbz/MeNbz-resins. Front Chem 2020; 8:298. [PMID: 32391324 PMCID: PMC7189019 DOI: 10.3389/fchem.2020.00298] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Accepted: 03/25/2020] [Indexed: 12/16/2022] Open
Abstract
Cyclic depsipeptides constitute a fascinating class of natural products. Most of them are characterized by an ester formed between the β-hydroxy function of Ser/Thr -and related amino acids- and the carboxylic group of the C-terminal amino acid. Less frequent are those where the thiol of Cys is involved rendering a thioester (cyclo thiodepsipeptides) and even less common are the cyclo depsipeptides with a phenyl ester coming from the side-chain of Tyr. Herein, the preparation of the later through a cyclative cleavage using the Fmoc-MeDbz/MeNbz-resin is described. This resin has previously reported for the synthesis of cyclo thiodepsipeptides and homodetic peptides. The use of that resin for the preparation of all these peptides is also summarized.
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Affiliation(s)
- Gerardo A Acosta
- CIBER-BBN, Networking Centre on Bioengineering, Biomaterials and Nanomedicine, University of Barcelona (UB), Barcelona, Spain.,Department of Organic Chemistry, University of Barcelona, Barcelona, Spain.,Institute of Advanced Chemistry of Catalonia (IQAC-CSIC), Spanish National Research Council (CSIC), Barcelona, Spain.,Associated Unit, Spanish National Research Council-University of Barcelona (CSIC-UB), Barcelona, Spain
| | - Laura Murray
- CIBER-BBN, Networking Centre on Bioengineering, Biomaterials and Nanomedicine, University of Barcelona (UB), Barcelona, Spain.,Department of Organic Chemistry, University of Barcelona, Barcelona, Spain
| | - Miriam Royo
- Institute of Advanced Chemistry of Catalonia (IQAC-CSIC), Spanish National Research Council (CSIC), Barcelona, Spain.,Associated Unit, Spanish National Research Council-University of Barcelona (CSIC-UB), Barcelona, Spain
| | - Beatriz G de la Torre
- KwaZulu-Natal Research Innovation and Sequencing Platform (KRISP), School of Laboratory Medicine and Medical Sciences, College of Health Sciences, University of KwaZulu-Natal, Durban, South Africa.,Peptide Science Laboratory, School of Chemistry and Physics, University of KwaZulu-Natal, Durban, South Africa
| | - Fernando Albericio
- CIBER-BBN, Networking Centre on Bioengineering, Biomaterials and Nanomedicine, University of Barcelona (UB), Barcelona, Spain.,Department of Organic Chemistry, University of Barcelona, Barcelona, Spain.,Institute of Advanced Chemistry of Catalonia (IQAC-CSIC), Spanish National Research Council (CSIC), Barcelona, Spain.,Associated Unit, Spanish National Research Council-University of Barcelona (CSIC-UB), Barcelona, Spain.,Peptide Science Laboratory, School of Chemistry and Physics, University of KwaZulu-Natal, Durban, South Africa
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8
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Tsuda S, Masuda S, Yoshiya T. Epimerization-Free Preparation of C-Terminal Cys Peptide Acid by Fmoc SPPS Using Pseudoproline-Type Protecting Group. J Org Chem 2019; 85:1674-1679. [DOI: 10.1021/acs.joc.9b02344] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Shugo Tsuda
- Peptide Institute, Inc., 7-2-9 Saito-asagi, Ibaraki-shi, Osaka 567-0085, Japan
| | - Shun Masuda
- Peptide Institute, Inc., 7-2-9 Saito-asagi, Ibaraki-shi, Osaka 567-0085, Japan
| | - Taku Yoshiya
- Peptide Institute, Inc., 7-2-9 Saito-asagi, Ibaraki-shi, Osaka 567-0085, Japan
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9
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Wang S, Thopate YA, Zhou Q, Wang P. Chemical Protein Synthesis by Native Chemical Ligation and Variations Thereof. CHINESE J CHEM 2019. [DOI: 10.1002/cjoc.201900246] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Siyao Wang
- Shanghai Key Laboratory for Molecular Engineering of Chiral Drugs, School of Chemistry and Chemical EngineeringShanghai Jiao Tong University 800 Dongchuan Road, Shanghai 200240 China
| | - Yogesh Abaso Thopate
- Shanghai Key Laboratory for Molecular Engineering of Chiral Drugs, School of Chemistry and Chemical EngineeringShanghai Jiao Tong University 800 Dongchuan Road, Shanghai 200240 China
| | - Qingqing Zhou
- Shanghai Key Laboratory for Molecular Engineering of Chiral Drugs, School of Chemistry and Chemical EngineeringShanghai Jiao Tong University 800 Dongchuan Road, Shanghai 200240 China
| | - Ping Wang
- Shanghai Key Laboratory for Molecular Engineering of Chiral Drugs, School of Chemistry and Chemical EngineeringShanghai Jiao Tong University 800 Dongchuan Road, Shanghai 200240 China
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10
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Nicke L, Horx P, Harms K, Geyer A. Directed C(sp 3)-H arylation of tryptophan: transformation of the directing group into an activated amide. Chem Sci 2019; 10:8634-8641. [PMID: 31803437 PMCID: PMC6844298 DOI: 10.1039/c9sc03440d] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2019] [Accepted: 08/03/2019] [Indexed: 12/18/2022] Open
Abstract
The aminoquinoline-directed C–H activation was used to synthezise unnatural tryptophans for solid phase peptide synthesis for the first time.
The 8-aminoquinoline (8AQ) directed C(sp3)–H functionalization was applied in the synthesis of β-arylated tryptophan derivatives. The laborious protecting group reorganization towards α-amino acids compatible for solid phase peptide synthesis (SPPS) was cut short by the transformation of the directing group into an activated amide, which was either used directly in peptide coupling or in the gram scale synthesis of storable Fmoc-protected amino acids for SPPS. In this work, directed C–H activation and nonplanar amide chemistry complement each other for the synthesis of hybrids between phenylalanine and tryptophan with restricted side chain mobility.
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Affiliation(s)
- Lennart Nicke
- Philipps-Universität Marburg , Fachbereich Chemie , Hans Meerwein Straße , 35032 Marburg , Germany .
| | - Philip Horx
- Philipps-Universität Marburg , Fachbereich Chemie , Hans Meerwein Straße , 35032 Marburg , Germany .
| | - Klaus Harms
- Philipps-Universität Marburg , Fachbereich Chemie , Hans Meerwein Straße , 35032 Marburg , Germany .
| | - Armin Geyer
- Philipps-Universität Marburg , Fachbereich Chemie , Hans Meerwein Straße , 35032 Marburg , Germany .
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11
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Arbour CA, Belavek KJ, Tariq R, Mukherjee S, Tom JK, Isidro-Llobet A, Kopach ME, Stockdill JL. Bringing Macrolactamization Full Circle: Self-Cleaving Head-to-Tail Macrocyclization of Unprotected Peptides via Mild N-Acyl Urea Activation. J Org Chem 2018; 84:1035-1041. [DOI: 10.1021/acs.joc.8b02418] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Christine A. Arbour
- Department of Chemistry, Wayne State University, Detroit, Michigan 48202, United States
| | - Kayla J. Belavek
- Department of Chemistry, Wayne State University, Detroit, Michigan 48202, United States
| | - Rooha Tariq
- Department of Chemistry, Wayne State University, Detroit, Michigan 48202, United States
| | - Subha Mukherjee
- Bristol-Myers Squibb, Chemical and Synthetic Development, New Brunswick, New Jersey 08903, United States
| | - Janine K. Tom
- Amgen, Inc., Pivotal Drug Substance Process Development, Thousand Oaks, California 91320, United States
| | | | | | - Jennifer L. Stockdill
- Department of Chemistry, Wayne State University, Detroit, Michigan 48202, United States
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12
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Arbour CA, Stockdill JL. A mild capping method for SPPS on the N-methyl diaminobenzoyl linker: Synthesis of an N-acyl urea appended C. elegans neuropeptide. Tetrahedron Lett 2018. [DOI: 10.1016/j.tetlet.2018.08.061] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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13
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Gless BH, Olsen CA. Direct Peptide Cyclization and One-Pot Modification Using the MeDbz Linker. J Org Chem 2018; 83:10525-10534. [DOI: 10.1021/acs.joc.8b01237] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Bengt H. Gless
- Center for Biopharmaceuticals and Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - Christian A. Olsen
- Center for Biopharmaceuticals and Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
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15
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Arbour CA, Stamatin RE, Stockdill JL. Sequence Diversification by Divergent C-Terminal Elongation of Peptides. J Org Chem 2018; 83:1797-1803. [PMID: 29293336 DOI: 10.1021/acs.joc.7b02655] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Sequence diversification at the C terminus is traditionally limited by significant epimerization of the C-terminal residue during its activation toward nucleophilic attack, thus mandating repetition of the peptide synthesis for each targeted variation. Here, we accomplish divergent C-terminal elongation of a single peptide substrate with concomitant resin cleavage via displacement of an N-acyl urea moiety. Sterically hindered amino acids such as Ile and Pro are well-tolerated in this approach, which proceeds reasonable conversion and no detectable epimerization of the starting peptide's C-terminal amino acid.
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Affiliation(s)
- Christine A Arbour
- Department of Chemistry, Wayne State University , Detroit, Michigan 48202, United States
| | - Ramona E Stamatin
- Department of Chemistry, Wayne State University , Detroit, Michigan 48202, United States
| | - Jennifer L Stockdill
- Department of Chemistry, Wayne State University , Detroit, Michigan 48202, United States
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