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Li Y, Shi H, Yin G. Synthetic techniques for thermodynamically disfavoured substituted six-membered rings. Nat Rev Chem 2024:10.1038/s41570-024-00612-3. [PMID: 38822206 DOI: 10.1038/s41570-024-00612-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/26/2024] [Indexed: 06/02/2024]
Abstract
Six-membered rings are ubiquitous structural motifs in bioactive compounds and multifunctional materials. Notably, their thermodynamically disfavoured isomers, like disubstituted cyclohexanes featuring one substituent in an equatorial position and the other in an axial position, often exhibit enhanced physical and biological activities in comparison with their opposite isomers. However, the synthesis of thermodynamically disfavoured isomers is, by its nature, challenging, with only a limited number of possible approaches. In this Review, we summarize and compare synthetic methodologies that produce substituted six-membered rings with thermodynamically disfavoured substitution patterns. We place particular emphasis on elucidating the crucial stereoinduction factors within each transformation. Our aim is to stimulate interest in the synthesis of these unique structures, while simultaneously providing synthetic chemists with a guide to approaching this synthetic challenge.
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Affiliation(s)
- Yangyang Li
- The Institute for Advanced Studies, Wuhan University, Wuhan, Hubei Province, China
| | - Hongjin Shi
- The Institute for Advanced Studies, Wuhan University, Wuhan, Hubei Province, China
| | - Guoyin Yin
- The Institute for Advanced Studies, Wuhan University, Wuhan, Hubei Province, China.
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2
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Du S, Wey M, Armstrong DW. d-Amino acids in biological systems. Chirality 2023; 35:508-534. [PMID: 37074214 DOI: 10.1002/chir.23562] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2022] [Revised: 03/06/2023] [Accepted: 03/07/2023] [Indexed: 04/20/2023]
Abstract
Investigations on the occurrence and biochemical roles of free D-amino acids and D-amino acid-containing peptides and proteins in living systems have increased in frequency and significance. Their occurrence and roles may vary substantially with progression from microbiotic to evermore advanced macrobiotic systems. We now understand many of the biosynthetic and regulatory pathways, which are outlined herein. Important uses for D-amino acids in plants, invertebrates, and vertebrates are reviewed. Given its importance, a separate section on the occurrence and role of D-amino acids in human disease is presented.
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Affiliation(s)
- Siqi Du
- Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, Texas, USA
| | - Michael Wey
- Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, Texas, USA
| | - Daniel W Armstrong
- Department of Chemistry and Biochemistry, University of Texas at Arlington, Arlington, Texas, USA
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3
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Woodman TJ, Lloyd MD. Analysis of enzyme reactions using NMR techniques: A case study with α-methylacyl-CoA racemase (AMACR). Methods Enzymol 2023; 690:159-209. [PMID: 37858529 DOI: 10.1016/bs.mie.2023.07.005] [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: 10/21/2023]
Abstract
α-Methylacyl-CoA racemase (AMACR; P504S) catalyzes the conversion of R-2-methylacyl-CoA esters into their corresponding S-2-methylacyl-CoA epimers enabling their degradation by β-oxidation. The enzyme also catalyzes the key epimerization reaction in the pharmacological activation pathway of ibuprofen and related drugs. AMACR protein levels and enzymatic activity are increased in prostate cancer, and the enzyme is a recognized drug target. Key to the development of novel treatments based on AMACR inhibition is the development of functional assays. Synthesis of substrates and purification of recombinant human AMACR are described. Incubation of R- or S-2-methylacyl-CoA esters with AMACR in vitro resulted in formation of epimers (at a near 1-1 ratio at equilibrium) via removal of their α-protons to form an enolate intermediate followed by reprotonation. Conversion can be conveniently followed by incubation in buffer containing 2H2O followed by 1H NMR analysis to monitor conversion of the α-methyl doublet to a single peak upon deuterium incorporation. Incubation of 2-methylacyl-CoA esters containing leaving groups results in an elimination reaction, which was also characterized by 1H NMR. The synthesis of substrates, including a double labeled substrate for mechanistic studies, and subsequent analysis is also described.
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Affiliation(s)
- Timothy J Woodman
- Department of Life Sciences, University of Bath, Claverton Down, Bath, United Kingdom.
| | - Matthew D Lloyd
- Department of Life Sciences, University of Bath, Claverton Down, Bath, United Kingdom.
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Mojanaga OO, Acharya KR, Lloyd MD. Recombinant protein production for structural and kinetic studies: A case study using M. tuberculosis α-methylacyl-CoA racemase (MCR). Methods Enzymol 2023; 690:1-37. [PMID: 37858526 DOI: 10.1016/bs.mie.2023.07.001] [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] [Indexed: 10/21/2023]
Abstract
Modern drug discovery is a target-driven approach in which a particular protein such as an enzyme is implicated in the disease process. Commonly, small-molecule drugs are identified using screening, rational design, and structural biology approaches. Drug screening, testing and optimization is typically conducted in vitro, and copious amounts of protein are required. The advent of recombinant DNA technologies has resulted in a rise in proteins purified by affinity techniques, typically by incorporating an "affinity tag" at the N- or C-terminus. Use of these tagged proteins and affinity techniques comes with a host of issues. This chapter describes the production of an untagged enzyme, α-methylacyl-CoA racemase (MCR) from Mycobacterium tuberculosis, using a recombinant E. coli system. Purification of the enzyme on a 100 mg scale using tandem anion-exchange chromatographies (DEAE-sepharose and RESOURCE-Q columns), and size-exclusion chromatographies is described. A modified protocol allowing the purification of cationic proteins is also described, based on tandem cation-exchange chromatographies (using CM-sepharose and RESOURCE-S columns) and size-exclusion chromatographies. The resulting MCR protein is suitable for biochemical and structural biology applications. The described protocols have wide applicability to the purification of other recombinant proteins and enzymes without using affinity chromatography.
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Affiliation(s)
- Otsile O Mojanaga
- Department of Life Sciences, University of Bath, Claverton Down, Bath, United Kingdom
| | - K Ravi Acharya
- Department of Life Sciences, University of Bath, Claverton Down, Bath, United Kingdom.
| | - Matthew D Lloyd
- Department of Life Sciences, University of Bath, Claverton Down, Bath, United Kingdom.
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5
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Bearne SL. Design and evaluation of substrate-product analog inhibitors for racemases and epimerases utilizing a 1,1-proton transfer mechanism. Methods Enzymol 2023; 690:397-444. [PMID: 37858537 DOI: 10.1016/bs.mie.2023.06.014] [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] [Indexed: 10/21/2023]
Abstract
Racemases and epimerases catalyze the inversion of stereochemistry at asymmetric carbon atoms to generate stereoisomers that often play important roles in normal and pathological physiology. Consequently, there is interest in developing inhibitors of these enzymes for drug discovery. A strategy for the rational design of substrate-product analog (SPA) inhibitors of racemases and epimerases utilizing a direct 1,1-proton transfer mechanism is elaborated. This strategy assumes that two groups on the asymmetric carbon atom remain fixed at active-site binding determinants, while the hydrogen and third, motile group move during catalysis, with the latter potentially traveling between an R- and S-pocket at the active site. SPAs incorporate structural features of the substrate and product, often with geminal disubstitution on the asymmetric carbon atom to simultaneously present the motile group to both the R- and S-pockets. For racemases operating on substrates bearing three polar groups (glutamate, aspartate, and serine racemases) or with compact, hydrophobic binding pockets (proline racemase), substituent motion is limited and the design strategy furnishes inhibitors with poor or modest binding affinities. The approach is most successful when substrates have a large, motile hydrophobic group that binds at a plastic and/or capacious hydrophobic site. Potent inhibitors were developed for mandelate racemase, isoleucine epimerase, and α-methylacyl-CoA racemase using the SPA inhibitor design strategy, exhibiting binding affinities ranging from substrate-like to exceeding that of the substrate by 100-fold. This rational approach for designing inhibitors of racemases and epimerases having the appropriate active-site architectures is a useful strategy for furnishing compounds for drug development.
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Affiliation(s)
- Stephen L Bearne
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS, Canada; Department of Chemistry, Dalhousie University, Halifax, NS, Canada.
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Brooke H, Ghoshray M, Ibrahim A, Lloyd MD. Steady-state kinetic analysis of reversible enzyme inhibitors: A case study on calf intestine alkaline phosphatase. Methods Enzymol 2023; 690:39-84. [PMID: 37858536 DOI: 10.1016/bs.mie.2023.06.015] [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] [Indexed: 10/21/2023]
Abstract
Enzymes are important drug targets and inhibition of enzymatic activity is an important therapeutic strategy. Enzyme assays measuring catalytic activity are utilized in both the discovery and development of new drugs. Colorimetric assays based on the release of 4-nitrophenol from substrates are commonly used. 4-Nitrophenol is only partly ionized to 4-nitrophenolate under typical assay conditions (pH 7-9) leading to under-estimation of product formation rates due to the much lower extinction coefficient of 4-nitrophenol compared to 4-nitrophenolate. Determination of 4-nitrophenol pKa values based on absorbance at 405 nm as a function of experimental pH values is reported, allowing for calculation of a corrected extinction coefficient at the assay pH. Characterization of inhibitor properties using steady-state enzyme kinetics is demonstrated using calf intestine alkaline phosphatase and 4-nitrophenyl phosphate as substrate at pH ∼8.2. The following kinetic parameters were determined: Km= 40±3 µM; Vmax= 72.8±1.2 µmolmin-1mg protein-1; kcat= 9.70±0.16 s-1; kcat/Km= 2.44±0.16 × 105 M-1s-1 (mean± SEM, N = 4). Sodium orthovanadate and EDTA were used as model inhibitors and the following pIC50 values were measured using dose-response curves: 6.61±0.08 and 3.07±0.03 (mean±SEM, N = 4). Rapid dilution experiments determined that inhibition was reversible for sodium orthovanadate and irreversible for EDTA. A Ki value for orthovanadate of 51±8 nM (mean±SEM, N = 3) was determined. Finally, data analysis and statistical design of experiments are discussed.
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Affiliation(s)
- Henry Brooke
- Department of Life Sciences, University of Bath, Claverton Down, Bath, United Kingdom
| | - Meghna Ghoshray
- Department of Life Sciences, University of Bath, Claverton Down, Bath, United Kingdom
| | - Archad Ibrahim
- Department of Life Sciences, University of Bath, Claverton Down, Bath, United Kingdom
| | - Matthew D Lloyd
- Department of Life Sciences, University of Bath, Claverton Down, Bath, United Kingdom.
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7
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Bearne SL, Hayden JA. Application of circular dichroism-based assays to racemases and epimerases: Recognition and catalysis of reactions of chiral substrates by mandelate racemase. Methods Enzymol 2023; 685:127-169. [PMID: 37245900 DOI: 10.1016/bs.mie.2023.03.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Racemases and epimerases have attracted much interest because of their astonishing ability to catalyze the rapid α-deprotonation of carbon acid substrates with high pKa values (∼13-30) leading to the formation of d-amino acids or various carbohydrate diastereomers that serve important roles in both normal physiology and pathology. Enzymatic assays to measure the initial rates of reactions catalyzed by these enzymes are discussed using mandelate racemase (MR) as an example. For MR, a convenient, rapid, and versatile circular dichroism (CD)-based assay has been used to determine the kinetic parameters accompanying the MR-catalyzed racemization of mandelate and alternative substrates. This direct, continuous assay permits real time monitoring of reaction progress, the rapid determination of initial velocities, and immediate recognition of anomalous behaviors. MR recognizes chiral substrates primarily through interactions of the phenyl ring of (R)- or (S)-mandelate with the hydrophobic R- or S-pocket at the active site, respectively. During catalysis, the carboxylate and α-hydroxyl groups of the substrate remain fixed in place through interactions with the Mg2+ ion and multiple H-bonding interactions, while the phenyl ring moves between the R- and S-pockets. The minimal requirements for the substrate appear to be the presence of a glycolate or glycolamide moiety, and a hydrophobic group of limited size that can stabilize the carbanionic intermediate through resonance or strong inductive effects. Similar CD-based assays may be applied to determine the activity of other racemases or epimerases with proper consideration of the molar ellipticity, wavelength, overall absorbance of the sample, and the light pathlength.
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Affiliation(s)
- Stephen L Bearne
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS, Canada; Department of Chemistry, Dalhousie University, Halifax, NS, Canada.
| | - Joshua A Hayden
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS, Canada
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Chernykh AV, Chernykh AV, Radchenko DS, Chheda PR, Rusanov EB, Grygorenko OO, Spies MA, Volochnyuk DM, Komarov IV. A stereochemical journey around spirocyclic glutamic acid analogs. Org Biomol Chem 2022; 20:3183-3200. [PMID: 35348173 PMCID: PMC10170626 DOI: 10.1039/d2ob00146b] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A practical divergent synthetic approach is reported for the library of regio- and stereoisomers of glutamic acid analogs built on the spiro[3.3]heptane scaffold. Formation of the spirocyclic scaffold was achieved starting from a common precursor - an O-silylated 2-(hydroxymethyl)cyclobutanone derivative. Its olefination required using the titanium-based Tebbe protocol since the standard Wittig reaction did not work with this particular substrate. The construction of the second cyclobutane ring of the spirocyclic system was achieved through either subsequent dichloroketene addition or Meinwald oxirane rearrangement as the key synthetic steps, depending on the substitution patterns in the target compounds (1,6- or 1,5-, respectively). Further modified Strecker reaction of the resulting racemic spirocyclic ketones with the Ellman's sulfinamide as a chiral auxiliary had low to moderate diastereoselectivity; nevertheless, all stereoisomers were isolated in pure form via chromatographic separation, and their absolute configuration was confirmed by X-ray crystallography. Members of the library were tested for the inhibitory activity against H. pylori glutamate racemase.
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Affiliation(s)
- Anton V Chernykh
- Enamine Ltd, Chervonotkatska Street 78, Kyiv 02094, Ukraine.,Taras Shevchenko National University of Kyiv, Volodymyrska Street 60, Kyiv 01601, Ukraine.
| | | | - Dmytro S Radchenko
- Enamine Ltd, Chervonotkatska Street 78, Kyiv 02094, Ukraine.,Taras Shevchenko National University of Kyiv, Volodymyrska Street 60, Kyiv 01601, Ukraine.
| | - Pratik Rajesh Chheda
- Division of Medicinal and Natural Products Chemistry, Department of Pharmaceutics and Experimental Therapeutics, College of Pharmacy, University of Iowa, Iowa City 52246, Iowa, USA
| | - Eduard B Rusanov
- Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanska Street 5, Kyiv 02660, Ukraine
| | - Oleksandr O Grygorenko
- Enamine Ltd, Chervonotkatska Street 78, Kyiv 02094, Ukraine.,Taras Shevchenko National University of Kyiv, Volodymyrska Street 60, Kyiv 01601, Ukraine.
| | - M Ashley Spies
- Division of Medicinal and Natural Products Chemistry, Department of Pharmaceutics and Experimental Therapeutics, College of Pharmacy, University of Iowa, Iowa City 52246, Iowa, USA.,Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City 52246, Iowa, USA
| | - Dmitriy M Volochnyuk
- Enamine Ltd, Chervonotkatska Street 78, Kyiv 02094, Ukraine.,Taras Shevchenko National University of Kyiv, Volodymyrska Street 60, Kyiv 01601, Ukraine. .,Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanska Street 5, Kyiv 02660, Ukraine
| | - Igor V Komarov
- Enamine Ltd, Chervonotkatska Street 78, Kyiv 02094, Ukraine.,Taras Shevchenko National University of Kyiv, Volodymyrska Street 60, Kyiv 01601, Ukraine.
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9
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Reetz MT, Garcia-Borràs M. The Unexplored Importance of Fleeting Chiral Intermediates in Enzyme-Catalyzed Reactions. J Am Chem Soc 2021; 143:14939-14950. [PMID: 34491742 PMCID: PMC8461649 DOI: 10.1021/jacs.1c04551] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2021] [Indexed: 02/07/2023]
Abstract
Decades of extensive research efforts by biochemists, organic chemists, and protein engineers have led to an understanding of the basic mechanisms of essentially all known types of enzymes, but in a formidable number of cases an essential aspect has been overlooked. The occurrence of short-lived chiral intermediates formed by symmetry-breaking of prochiral precursors in enzyme catalyzed reactions has been systematically neglected. We designate these elusive species as fleeting chiral intermediates and analyze such crucial questions as "Do such intermediates occur in homochiral form?" If so, what is the absolute configuration, and why did Nature choose that particular stereoisomeric form, even when the isolable final product may be achiral? Does the absolute configuration of a chiral product depend in any way on the absolute configuration of the fleeting chiral precursor? How does this affect the catalytic proficiency of the enzyme? If these issues continue to be unexplored, then an understanding of the mechanisms of many enzyme types remains incomplete. We have systematized the occurrence of these chiral intermediates according to their structures and enzyme types. This is followed by critical analyses of selected case studies and by final conclusions and perspectives. We hope that the fascinating concept of fleeting chiral intermediates will attract the attention of scientists, thereby opening an exciting new research field.
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Affiliation(s)
- Manfred T. Reetz
- Max-Planck-Institut
für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Muelheim, Germany
- Tianjin
Institute of Industrial Biotechnology, Chinese Academy of Sciences, 32 West 7th Avenue, Tianjin Airport
Economic Area, Tianjin 300308, China
| | - Marc Garcia-Borràs
- Institute
of Computational Chemistry and Catalysis (IQCC) and Departament de
Química, Universitat de Girona, Carrer Maria Aurèlia Capmany
69, 17003 Girona, Spain
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