1
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Shu P, Yang Y, Zhang H, Li N, Liu G, Zhang J, Zhao Q, Wei X, Yi W, Sun N, Xiao F. Isolation and characterization of antioxidative monoterpenes from Cynanchum atratum roots. Biosci Biotechnol Biochem 2022; 86:585-589. [PMID: 35191487 DOI: 10.1093/bbb/zbac026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2022] [Accepted: 02/13/2022] [Indexed: 11/14/2022]
Abstract
One novel monoterpene rhamnoside (1) and 7 known monoterpenes (2-8) were isolated from the ethanol extract of Cynanchum atratum for the first time. Their structures were identified by comprehensive spectroscopic data analysis such as nuclear magnetic resonance, high-resolution electrospray ionization mass spectra, optical rotatory dispersion, and acid hydrolysis. In the subsequent antioxidant assay, compound 8 exhibited obvious 2,2-diphenyl-2-picrylhydrazyl hydrate radical scavenging activity.
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Affiliation(s)
- Penghua Shu
- Food and Pharmacy College, Xuchang University, Xuchang, Henan, China
| | - Yuan Yang
- Food and Pharmacy College, Xuchang University, Xuchang, Henan, China
| | - Hui Zhang
- Food and Pharmacy College, Xuchang University, Xuchang, Henan, China
| | - Nianci Li
- Food and Pharmacy College, Xuchang University, Xuchang, Henan, China
| | - Guangwei Liu
- Food and Pharmacy College, Xuchang University, Xuchang, Henan, China
| | - Jialong Zhang
- Food and Pharmacy College, Xuchang University, Xuchang, Henan, China
| | - Qiuyue Zhao
- Food and Pharmacy College, Xuchang University, Xuchang, Henan, China
| | - Xialan Wei
- School of Information Engineering, Xuchang University, Xuchang, Henan, China
| | - Wenhan Yi
- Communist Youth League Committee, Xuchang University, Xuchang, Henan, China
| | - Na Sun
- Food and Pharmacy College, Xuchang University, Xuchang, Henan, China
| | - Fugang Xiao
- Food and Pharmacy College, Xuchang University, Xuchang, Henan, China
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2
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Shao N, Monnier V, Charles L, Rodriguez J, Bressy C, Quintard A. Multi‐catalytic Enantioselective Synthesis of 1,3‐Diols Containing a Tetrasubstituted Fluorinated Stereocenter. European J Org Chem 2022. [DOI: 10.1002/ejoc.202200031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Na Shao
- Aix Marseille Univ, CNRS, Centrale Marseille iSm2 Marseille France
| | - Valérie Monnier
- Aix Marseille Univ, CNRS, Centrale Marseille FSCM Marseille France
| | | | - Jean Rodriguez
- Aix Marseille Univ, CNRS, Centrale Marseille iSm2 Marseille France
| | - Cyril Bressy
- Aix Marseille Univ, CNRS, Centrale Marseille iSm2 Marseille France
| | - Adrien Quintard
- Aix Marseille Univ, CNRS, Centrale Marseille iSm2 Marseille France
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3
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Ge R, Zhu Y, Wang H, Gu S. Methods and Application of Absolute Configuration Assignment for Chiral Compounds. CHINESE J ORG CHEM 2022. [DOI: 10.6023/cjoc202108047] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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4
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Shao N, Liu X, Monnier V, Charles L, Rodriguez J, Bressy C, Quintard A. Enantioselective Synthesis of Acyclic Stereotriads Featuring Fluorinated Tetrasubstituted Stereocenters. Chemistry 2021; 28:e202103874. [PMID: 34821417 DOI: 10.1002/chem.202103874] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Indexed: 11/07/2022]
Abstract
Elaboration of enantioenriched complex acyclic stereotriads represents a challenge for modern synthesis even more when fluorinated tetrasubstituted stereocenters are targeted. We have been able to develop a simple strategy in a sequence of two unprecedented steps combining a diastereoselective aldol-Tishchenko reaction and an enantioselective organocatalyzed kinetic resolution. The aldol-Tishchenko reaction directly generates a large panel of acyclic 1,3-diols possessing a fluorinated tetrasubstituted stereocenter by condensation of fluorinated ketones with aldehydes under very mild basic conditions. The anti 1,3-diols featuring three contiguous stereogenic centers are generated with excellent diastereocontrol (typically >99 : 1 dr). Depending upon the precursors both diastereomers of stereotriads are accessible through this flexible reaction. Furthermore, from the obtained racemic scaffolds, development of an organocatalyzed kinetic resolution enabled to generate the desired enantioenriched stereotriads with excellent selectivity (typically er >95 : 5).
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Affiliation(s)
- Na Shao
- Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
| | - Xueyang Liu
- Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
| | - Valérie Monnier
- Aix Marseille Univ, CNRS, Centrale Marseille, FSCM, Marseille, France
| | | | - Jean Rodriguez
- Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
| | - Cyril Bressy
- Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
| | - Adrien Quintard
- Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
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5
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Desrues T, Merad J, Andrei D, Pons J, Parrain J, Médebielle M, Quintard A, Bressy C. Impact of the Difluoromethylene Group in the Organocatalyzed Acylative Kinetic Resolution of α,α‐Difluorohydrins. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202107041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Titouan Desrues
- Aix-Marseille Univ CNRS Centrale Marseille, iSm2 Marseille France
| | - Jérémy Merad
- Univ Lyon Université Lyon 1 CNRS INSA CPE-Lyon ICBMS UMR 5246 Bât. Lederer 1 rue Victor Grignard 69622 Villeurbanne France
| | - Daniela Andrei
- Univ Lyon Université Lyon 1 CNRS INSA CPE-Lyon ICBMS UMR 5246 Bât. Lederer 1 rue Victor Grignard 69622 Villeurbanne France
- Dominican University 7900 West Division Street River Forest IL 60305 USA
| | - Jean‐Marc Pons
- Aix-Marseille Univ CNRS Centrale Marseille, iSm2 Marseille France
| | - Jean‐Luc Parrain
- Aix-Marseille Univ CNRS Centrale Marseille, iSm2 Marseille France
| | - Maurice Médebielle
- Univ Lyon Université Lyon 1 CNRS INSA CPE-Lyon ICBMS UMR 5246 Bât. Lederer 1 rue Victor Grignard 69622 Villeurbanne France
| | - Adrien Quintard
- Aix-Marseille Univ CNRS Centrale Marseille, iSm2 Marseille France
| | - Cyril Bressy
- Aix-Marseille Univ CNRS Centrale Marseille, iSm2 Marseille France
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6
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Desrues T, Merad J, Andrei D, Pons JM, Parrain JL, Médebielle M, Quintard A, Bressy C. Impact of the Difluoromethylene Group in the Organocatalyzed Acylative Kinetic Resolution of α,α-Difluorohydrins. Angew Chem Int Ed Engl 2021; 60:24924-24929. [PMID: 34473886 DOI: 10.1002/anie.202107041] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2021] [Indexed: 12/15/2022]
Abstract
Due to the omnipresence of chiral organofluorine compounds in pharmaceutical, agrochemical, and material chemistry, the development of enantioselective methods for their preparation is highly desirable. In the present study, the enantioselective organocatalyzed acylation of α,α-difluorohydrins using a commercially available chiral isothiourea is reported through a kinetic resolution (KR) process. It reveals that the difluoromethylene moiety (C(sp3 )F2 ) can serve as a directing group through electrostatic fluorine-cation interactions, greatly improving the enantioselectivity of the KR. In this context, a broad range of fluorinated alcohols such as valuable 4,4-difluoro-1,3-diols could be synthesized with exquisite enantiocontrol (typically >99:1 er). Turning to 2,2-difluoro-1,3-diols, we also demonstrated that aromatic and fluorinated groups were mutually compatible to provide the expected enantioenriched adducts with >99:1 er.
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Affiliation(s)
- Titouan Desrues
- Aix-Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
| | - Jérémy Merad
- Univ Lyon, Université Lyon 1, CNRS, INSA, CPE-Lyon, ICBMS, UMR 5246, Bât. Lederer, 1 rue Victor Grignard, 69622, Villeurbanne, France
| | - Daniela Andrei
- Univ Lyon, Université Lyon 1, CNRS, INSA, CPE-Lyon, ICBMS, UMR 5246, Bât. Lederer, 1 rue Victor Grignard, 69622, Villeurbanne, France.,Dominican University, 7900 West Division Street, River Forest, IL, 60305, USA
| | - Jean-Marc Pons
- Aix-Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
| | - Jean-Luc Parrain
- Aix-Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
| | - Maurice Médebielle
- Univ Lyon, Université Lyon 1, CNRS, INSA, CPE-Lyon, ICBMS, UMR 5246, Bât. Lederer, 1 rue Victor Grignard, 69622, Villeurbanne, France
| | - Adrien Quintard
- Aix-Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
| | - Cyril Bressy
- Aix-Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
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7
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Hubler Z, Friedrich RM, Sax JL, Allimuthu D, Gao F, Rivera-León AM, Pleshinger MJ, Bederman I, Adams DJ. Modulation of lanosterol synthase drives 24,25-epoxysterol synthesis and oligodendrocyte formation. Cell Chem Biol 2021; 28:866-875.e5. [PMID: 33636107 PMCID: PMC8217109 DOI: 10.1016/j.chembiol.2021.01.025] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2020] [Revised: 12/23/2020] [Accepted: 01/28/2021] [Indexed: 02/07/2023]
Abstract
Small molecules that promote the formation of new myelinating oligodendrocytes from oligodendrocyte progenitor cells (OPCs) are potential therapeutics for demyelinating diseases. We recently established inhibition of specific cholesterol biosynthesis enzymes and resulting accumulation of 8,9-unsaturated sterols as a unifying mechanism through which many such molecules act. To identify more potent sterol enhancers of oligodendrocyte formation, we synthesized a collection of 8,9-unsaturated sterol derivatives and found that 24,25-epoxylanosterol potently promoted oligodendrocyte formation. In OPCs, 24,25-epoxylanosterol was metabolized to 24,25-epoxycholesterol via the epoxycholesterol shunt pathway. Increasing flux through the epoxycholesterol shunt using genetic manipulation or small-molecule inhibition of lanosterol synthase (LSS) increased endogenous 24,25-epoxycholesterol levels and OPC differentiation. Notably, exogenously supplied 24,25-epoxycholesterol promoted oligodendrocyte formation despite lacking an 8,9-unsaturation. This work highlights epoxycholesterol shunt usage, controlled by inhibitors of LSS, as a target to promote oligodendrocyte formation. Additionally, sterols beyond the 8,9-unsaturated sterols, including 24,25-epoxycholesterol, drive oligodendrocyte formation.
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Affiliation(s)
- Zita Hubler
- Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Ryan M Friedrich
- Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Joel L Sax
- Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Dharmaraja Allimuthu
- Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Farrah Gao
- Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Adrianna M Rivera-León
- Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Matthew J Pleshinger
- Department of Pharmacology, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Ilya Bederman
- Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Drew J Adams
- Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
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8
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Dooley CJ, Burtea A, Mitilian C, Dao WT, Qu B, Salzameda NT, Rychnovsky SD. Using the Competing Enantioselective Conversion Method to Assign the Absolute Configuration of Cyclic Amines with Bode's Acylation Reagents. J Org Chem 2020; 85:10750-10759. [PMID: 32806106 DOI: 10.1021/acs.joc.0c01275] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The competing enantioselective conversion (CEC) method is a quick and reliable means to determine absolute configuration. Previously, Bode's chiral acylated hydroxamic acids were used to determine the stereochemistry of primary amines, as well as cyclic and acyclic secondary amines. The enantioselective acylation has been evaluated for 4-, 5-, and 6-membered cyclic secondary amines, including medicinally relevant compounds. The limitations of the method were studied through computational analysis and experimental results. Piperidines with substituents at the 2-position did not behave well unless the axial conformer was energetically accessible, which is consistent with the transition state geometries proposed by Bode and Kozlowski. Control experiments were performed to investigate the cause of degrading selectivity under the CEC reaction conditions. The present study expands the scope of the CEC method for secondary amines and provides a better understanding of the reaction profile.
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Affiliation(s)
- Charles J Dooley
- Department of Chemistry, 1102 Natural Sciences II, University of California at Irvine, Irvine, California 92697, United States
| | - Alexander Burtea
- Department of Chemistry, 1102 Natural Sciences II, University of California at Irvine, Irvine, California 92697, United States
| | - Christina Mitilian
- Department of Chemistry, 1102 Natural Sciences II, University of California at Irvine, Irvine, California 92697, United States
| | - Wendy T Dao
- Department of Chemistry and Biochemistry, California State University Fullerton, Fullerton, California 92834, United States
| | - Bo Qu
- Chemical Development, Boehringer Ingelheim Pharmaceuticals, Inc., 900 Ridgebury Road, Ridgefield, Connecticut 06877, United States
| | - Nicholas T Salzameda
- Department of Chemistry and Biochemistry, California State University Fullerton, Fullerton, California 92834, United States
| | - Scott D Rychnovsky
- Department of Chemistry, 1102 Natural Sciences II, University of California at Irvine, Irvine, California 92697, United States
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9
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Zhang JL, Zhou FF, Li YZ, Feng T, Jiang LL, Jiang RW, Zhang XX, Li XD. New sesquiterpenoids with COX-2 inhibitory activity from the medical plant Physalis. alkekengi L. var. franchetii. Fitoterapia 2020; 141:104470. [DOI: 10.1016/j.fitote.2020.104470] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Revised: 12/30/2019] [Accepted: 01/05/2020] [Indexed: 02/08/2023]
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10
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Burns AS, Dooley C, Carlson PR, Ziller JW, Rychnovsky SD. Relative and Absolute Structure Assignments of Alkenes Using Crystalline Osmate Derivatives for X-ray Analysis. Org Lett 2019; 21:10125-10129. [DOI: 10.1021/acs.orglett.9b04133] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Alexander S. Burns
- Department of Chemistry, University of California at Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - Charles Dooley
- Department of Chemistry, University of California at Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - Paul R. Carlson
- Department of Chemistry, University of California at Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - Joseph W. Ziller
- Department of Chemistry, University of California at Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
| | - Scott D. Rychnovsky
- Department of Chemistry, University of California at Irvine, 1102 Natural Sciences II, Irvine, California 92697, United States
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11
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Brummel BR, Lee KG, McMillen CD, Kolis JW, Whitehead DC. One-Pot Absolute Stereochemical Identification of Alcohols via Guanidinium Sulfate Crystallization. Org Lett 2019; 21:9622-9627. [DOI: 10.1021/acs.orglett.9b03792] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Beau R. Brummel
- Department of Chemistry, Clemson University, Clemson, South Carolina 29634, United States
| | - Kinsey G. Lee
- Department of Chemistry, Clemson University, Clemson, South Carolina 29634, United States
| | - Colin D. McMillen
- Department of Chemistry, Clemson University, Clemson, South Carolina 29634, United States
| | - Joseph W. Kolis
- Department of Chemistry, Clemson University, Clemson, South Carolina 29634, United States
| | - Daniel C. Whitehead
- Department of Chemistry, Clemson University, Clemson, South Carolina 29634, United States
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12
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Yang S, Bian G, Sa R, Song L. Assigning the Absolute Configurations of Chiral Primary Amines Based on Experimental and DFT-Calculated 19F Nuclear Magnetic Resonance. Front Chem 2019; 7:318. [PMID: 31165055 PMCID: PMC6536038 DOI: 10.3389/fchem.2019.00318] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Accepted: 04/23/2019] [Indexed: 12/26/2022] Open
Abstract
In this work, a novel method for assigning the absolute configuration of a chiral primary amine has been developed based on the experimental and DFT-calculated 19F NMR chemical shift differences of its derived two fluorinated amides by reacting with two enantiomers of a chiral derivatizing agent FPP (α-fluorinated phenylacetic phenylselenoester) separately. Comparing the experimental chemical shift difference Δ δ α - F R , S of (R)-FPA-amide/(S)-FPA-amide with the calculated Δδα-F R,S of (R)-FPA-(R)-amide/(S)-FPA-(R)-amide, if the experimental Δδα-F R,S has the same symbol (positive or negative) as one of the theoretical Δδα-F R,S , the assigned configuration of the amine is considered to be consistent with the theoretical one. Our method could be applied to a broad substrate scope avoiding wrong conclusion due to empirical judgment.
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Affiliation(s)
- Shiwei Yang
- The Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Guangling Bian
- The Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Rongjian Sa
- Institute of Oceanography, Ocean College, Fujian Provincial Key Laboratory of Information Processing and Intelligent Control, Minjiang University, Fuzhou, China
| | - Ling Song
- The Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, China
- University of Chinese Academy of Sciences, Beijing, China
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13
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Lee SR, Park HB, Kim KH. Highly Sensitive, Simple, and Cost- and Time-Effective Method to Determine the Absolute Configuration of a Secondary Alcohol Using Competing Enantioselective Acylation Coupled with LC/MS. Anal Chem 2018; 90:13212-13216. [DOI: 10.1021/acs.analchem.8b03385] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Affiliation(s)
- Seoung Rak Lee
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Hyun Bong Park
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
- Chemical Biology Institute, Yale University, West Haven, Connecticut 06516, United States
| | - Ki Hyun Kim
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Republic of Korea
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14
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Brito GA, Della-Felice F, Luo G, Burns AS, Pilli RA, Rychnovsky SD, Krische MJ. Catalytic Enantioselective Allylations of Acetylenic Aldehydes via 2-Propanol-Mediated Reductive Coupling. Org Lett 2018; 20:4144-4147. [PMID: 29938513 PMCID: PMC6205292 DOI: 10.1021/acs.orglett.8b01776] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cyclometalated π-allyliridium C,O-benzoates modified by ( S)-SEGPHOS or ( S)-Cl,OMe-BIPHEP catalyze enantioselective 2-propanol-mediated reductive couplings of diverse nonmetallic allyl pronucleophiles with the acetylenic aldehyde TIPSC≡CCHO. Absolute stereochemistries of the resulting secondary homoallylic-propargylic alcohols were assigned using Rychnovsky's competing enantioselective conversion method.
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Affiliation(s)
- Gilmar A Brito
- Department of Chemistry , University of Texas at Austin , Austin , Texas 78712 , United States
- Institute of Chemistry, University of Campinas (UNICAMP) , P.O. Box 6154, CEP, 13083-970 Campinas , São Paulo , Brazil
| | - Franco Della-Felice
- Department of Chemistry , University of Texas at Austin , Austin , Texas 78712 , United States
- Institute of Chemistry, University of Campinas (UNICAMP) , P.O. Box 6154, CEP, 13083-970 Campinas , São Paulo , Brazil
| | - Guoshun Luo
- Department of Chemistry , University of Texas at Austin , Austin , Texas 78712 , United States
| | - Alexander S Burns
- Department of Chemistry , University of California at Irvine , 1102 Natural Sciences II , Irvine , California 92697 , United States
| | - Ronaldo A Pilli
- Institute of Chemistry, University of Campinas (UNICAMP) , P.O. Box 6154, CEP, 13083-970 Campinas , São Paulo , Brazil
| | - Scott D Rychnovsky
- Department of Chemistry , University of California at Irvine , 1102 Natural Sciences II , Irvine , California 92697 , United States
| | - Michael J Krische
- Department of Chemistry , University of Texas at Austin , Austin , Texas 78712 , United States
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