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Harada N. Chiral organic stereochemistry: Chiral HPLC, chiral auxiliaries, CD spectroscopy, X-ray crystallography, and light-powered chiral molecular motors. Chirality 2021; 34:253-294. [PMID: 34783096 DOI: 10.1002/chir.23372] [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: 07/30/2021] [Revised: 09/15/2021] [Accepted: 09/23/2021] [Indexed: 11/11/2022]
Abstract
In the studies of chiral organic stereochemistry, it is important to use enantiopure compounds. For this purpose, the chiral HPLC (High-Pressure Liquid Chromatography) columns containing chiral stationary phases were invented by Y. Okamoto and coworkers for enantio-separating various racemic compounds. In addition, the use of chiral auxiliaries is also useful for preparing enantiopure compounds and also for determining their absolute configurations, where covalent-bonded diastereomers are separated by HPLC on silica gel. In this review article, these HPLC methods will be discussed together with the applications to some interesting organic compounds including light-powered chiral molecular motors.
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Affiliation(s)
- Nobuyuki Harada
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan
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Application of deuterated THENA for assigning the absolute configuration of chiral secondary alcohols. Tetrahedron Lett 2019. [DOI: 10.1016/j.tetlet.2019.01.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Harada N. Chiral Molecular Science: How were the absolute configurations of chiral molecules determined? "Experimental results and theories". Chirality 2017; 29:774-797. [PMID: 28981959 DOI: 10.1002/chir.22748] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Revised: 07/27/2017] [Accepted: 07/31/2017] [Indexed: 11/08/2022]
Abstract
Molecular chirality is a key concept in chemistry, bioscience, and molecular technology, like the invention of a light-powered chiral molecular motor explained in this review. Thus, the primary research subject is how to determine the absolute configuration (AC) of chiral compounds. This review article focuses on the principle, theory, and practice of the nonempirical methods for determining ACs of chiral compounds, i.e., the Bijvoet method in X-ray crystallography and the circular dichroism (CD) exciton chirality method, together with the historical aspects of AC determination. The theoretical equations of X-ray crystallography and exciton CD spectroscopy are explained in detail, and these equations are useful for readers to understand the principle and mechanism of these methods. This review also focuses on the relative methods, where the internal reference with known AC is used and the relative configuration is determined by X-ray crystallography and/or 1 H nuclear magnetic resonance (NMR) diamagnetic anisotropy method. In these cases, CSDP acid and MαNP acid are useful for the chiral resolution of racemic alcohols, where their diastereomeric esters are easily separable by high-performance liquid chromatography (HPLC) on silica gel. Thus, these methods are useful for the preparation of enantiopure compounds and simultaneous determination of their ACs. In this review article, the above methods are explained mainly based on the author's own research results.
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Affiliation(s)
- Nobuyuki Harada
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University Sendai, Japan
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Harada N. HPLC Separation of Diastereomers: Chiral Molecular Tools Useful for the Preparation of Enantiopure Compounds and Simultaneous Determination of Their Absolute Configurations. Molecules 2016; 21:molecules21101328. [PMID: 27782036 PMCID: PMC6273210 DOI: 10.3390/molecules21101328] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2016] [Accepted: 09/26/2016] [Indexed: 11/16/2022] Open
Abstract
To obtain enantiopure compounds, the so-called chiral high performance liquid chromatography (HPLC) method, i.e., HPLC using a chiral stationary phase, is very useful, as reviewed in the present Special Issue. On the other hand, normal HPLC (on silica gel) separation of diastereomers is also useful for the preparation of enantiopure compounds and also for the simultaneous determination of their absolute configurations (ACs). The author and coworkers have developed some chiral molecular tools, e.g., camphorsultam dichlorophthalic acid (CSDP acid), 2-methoxy-2-(1-naphthyl)propionic acid (MαNP acid), and others suitable for this purpose. For example, a racemic alcohol is esterified with (S)-(+)-MαNP acid, yielding diastereomeric esters, which are easily separable by HPLC on silica gel. The ACs of the obtained enantiopure MαNP esters can be determined by the ¹H-NMR diamagnetic anisotropy method. In addition, MαNP or CSDP esters have a high probability of giving single crystals suitable for X-ray crystallography. From the X-ray Oak Ridge thermal ellipsoid plot (ORTEP) drawing, the AC of the alcohol part can be unambiguously determined because the AC of the acid part is already known. The hydrolysis of MαNP or CSDP esters yields enantiopure alcohols with the established ACs. The mechanism and application examples of these methods are explained.
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Affiliation(s)
- Nobuyuki Harada
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan.
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Characteristic conformation of Mosher's amide elucidated using the cambridge structural database. Molecules 2015; 20:12880-900. [PMID: 26193245 PMCID: PMC6332137 DOI: 10.3390/molecules200712880] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Revised: 07/09/2015] [Accepted: 07/10/2015] [Indexed: 11/16/2022] Open
Abstract
Conformations of the crystalline 3,3,3-trifluoro-2-methoxy-2-phenylpropanamide derivatives (MTPA amides) deposited in the Cambridge Structural Database (CSD) were examined statistically as Racid-enantiomers. The majority of dihedral angles (48/58, ca. 83%) of the amide carbonyl groups and the trifluoromethyl groups ranged from –30° to 0° with an average angle θ1 of −13°. The other conformational properties were also clarified: (1) one of the fluorine atoms was antiperiplanar (ap) to the amide carbonyl group, forming a staggered conformation; (2) the MTPA amides prepared from primary amines showed a Z form in amide moieties; (3) in the case of the MTPA amide prepared from a primary amine possessing secondary alkyl groups (i.e., Mosher-type MTPA amide), the dihedral angles between the methine groups and the carbonyl groups were syn and indicative of a moderate conformational flexibility; (4) the phenyl plane was inclined from the O–Cchiral bond of the methoxy moiety with an average dihedral angle θ2 of +21°; (5) the methyl group of the methoxy moiety was ap to the ipso-carbon atom of the phenyl group.
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Ichikawa A, Ono H, Mikata Y. Crystal structures of Mosher's salt and ester elucidated by X-ray crystallography. CrystEngComm 2013. [DOI: 10.1039/c3ce41160e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Chiral Derivatizing Agents, Macrocycles, Metal Complexes, and Liquid Crystals for Enantiomer Differentiation in NMR Spectroscopy. Top Curr Chem (Cham) 2013; 341:1-68. [DOI: 10.1007/128_2013_433] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Ichikawa A, Ono H, Mikata Y. Naphthyl groups in chiral recognition: structures of salts and esters of 2-methoxy-2-naphthylpropanoic acids. Chem Asian J 2012; 7:2294-304. [PMID: 22829564 DOI: 10.1002/asia.201200345] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Revised: 05/11/2012] [Indexed: 11/11/2022]
Abstract
The crystal structures of salt 8, which was prepared from (R)-2-methoxy-2-(2-naphthyl)propanoic acid ((R)-MβNP acid, (R)-2) and (R)-1-phenylethylamine ((R)-PEA, (R)-6), and salt 9, which was prepared from (R)-2-methoxy-2-(1-naphthyl)propanoic acid ((R)-MαNP acid, (R)-1) and (R)-1-(p-tolyl)ethylamine ((R)-TEA, (R)-7), were determined by X-ray crystallography. The MβNP and MαNP anions formed ion-pairs with the PEA and TEA cations, respectively, through a methoxy-group-assisted salt bridge and aromatic CH⋅⋅⋅π interactions. The networks of salt bridges formed 2(1) columns in both salts. Finally, (S)-(2E,6E)-(1-(2) H(1) )farnesol ((S)-13) was prepared from the reaction of (2E,6E)-farnesal (11) with deuterated (R)-BINAL-H (i.e., (R)-BINAL-D). The enantiomeric excess of compound (S)-13 was determined by NMR analysis of (S)-MαNP ester 14. The solution-state structures of MαNP esters that were prepared from primary alcohols were also elucidated.
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Affiliation(s)
- Akio Ichikawa
- Division of Insect Sciences, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8634, Japan.
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Ichikawa A, Ono H, Echigo T, Mikata Y. Crystal structures and chiral recognition of the diastereomeric salts prepared from 2-methoxy-2-(1-naphthyl)propanoic acid. CrystEngComm 2011. [DOI: 10.1039/c1ce05155e] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Fujita T, Obata K, Kuwahara S, Nakahashi A, Monde K, Decatur J, Harada N. (R)-(+)-[VCD(-)984]-4-Ethyl-4-methyloctane: A Cryptochiral Hydrocarbon with a Quaternary Chiral Center. (1) Synthesis of the Enantiopure Compound and Unambiguous Determination of Absolute Configuration. European J Org Chem 2010. [DOI: 10.1002/ejoc.201000777] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Tetrahydro-1,4-epoxynaphthalene-1-carboxylic acid: a chiral derivatizing agent for the determination of the absolute configuration of secondary alcohols. Tetrahedron Lett 2010. [DOI: 10.1016/j.tetlet.2010.07.062] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Inoue Y, Matsumoto T, Watanabe M, Katagiri H, Kumagai T. ( R)-2-Benzyl-4-methylpentyl ( R)-2-methoxy-2-(1-naphthyl)propionate. Acta Crystallogr Sect E Struct Rep Online 2010; 66:o1665. [PMID: 21587891 PMCID: PMC3007046 DOI: 10.1107/s160053681002101x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2010] [Accepted: 06/02/2010] [Indexed: 11/11/2022]
Abstract
The relative configuration of the alcohol component in the title ester, C27H32O3, has been assigned as (R) from the known configuration of (R)-(−)-2-methoxy-2-(1-naphthyl)propionic acid [(R)-MαNP acid]. In the crystal structure, the C atom of the methyl group of the MαNP acid lies in the extended plane of the naphthyl ring system [methyl C atom deviates from plane by 0.211 (2) Å; r.m.s. deviation of fitted atoms = 0.0187 Å] and a weak intramolecular C—H⋯O hydrogen bond links the naphthyl ring system and the methoxy group. These structural properties are similar to those of most MαNP acid esters.
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Murakami S, Kato A, Katagiri H, Matsumoto T, Kijima T. Conformation and absolute configuration of (1 S,2 S)-2-(phenylselanyl)cyclohexyl ( R)-2-methoxy-2-(1-naphthyl)propionate. Acta Crystallogr Sect E Struct Rep Online 2010; 66:o1677. [PMID: 21587902 PMCID: PMC3006699 DOI: 10.1107/s1600536810022233] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2010] [Accepted: 06/10/2010] [Indexed: 11/10/2022]
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Ichikawa A, Ono H, Takenaka M, Mikata Y. Crystal conformations and molecular packing of (S)-2-methoxy-2-(9-phenanthryl)propanoic acid and a diastereomeric amide prepared from (R)-2-methoxy-2-(1-naphthyl)propanoic acid. CrystEngComm 2010. [DOI: 10.1039/b926356j] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Ichikawa A, Ono H, Mikata Y. Characteristic conformations and molecular packings in crystal structures of diastereomeric esters prepared from (S)-2-methoxy-2-(1-naphthyl)propanoic acid. ACTA ACUST UNITED AC 2008. [DOI: 10.1016/j.tetasy.2008.11.016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Preparation of single-enantiomer biofunctional molecules with (S)-2-methoxy-2-(1-naphthyl)propanoic acid. Biosci Biotechnol Biochem 2008; 72:2418-22. [PMID: 18776678 DOI: 10.1271/bbb.80100] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
(RS)-beta-Ionol and (RS)-2-methyl-4-octanol were resolved by using (S)-2-methoxy-2-(1-naphthyl)propanoic acid [(S)-MalphaNP acid]. The specific stereochemistry of each MalphaNP ester was elucidated by 2D NMR analyses, and shielding by the 1-naphthyl group was observed in both the 1H- and 13C-NMR spectra. Solvolysis of the individual (S)-MalphaNP esters gave four single-enantiomer alcohols. The normal-phase HPLC elution order of each MalphaNP ester is also discussed.
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Stereoselective synthesis of 2,3,7-trimethylcyclooctanone and related compounds and determination of their relative and absolute configurations by the MαNP acid method. Chirality 2008; 20:1053-65. [DOI: 10.1002/chir.20637] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Sekiguchi S, Akagi M, Naito J, Yamamoto Y, Taji H, Kuwahara S, Watanabe M, Ozawa Y, Toriumi K, Harada N. Synthesis of Enantiopure Aliphatic Acetylene Alcohols and Determination of Their Absolute Configurations by1H NMR Anisotropy and/or X-ray Crystallography. European J Org Chem 2008. [DOI: 10.1002/ejoc.200800012] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Sekiguchi S, Naito J, Taji H, Kasai Y, Sugio A, Kuwahara S, Watanabe M, Harada N. Synthesis of enantiopure 2-aryl-2-methoxypropionic acids and determination of their absolute configurations by X-ray crystallography. Chirality 2008; 20:251-64. [PMID: 17559106 DOI: 10.1002/chir.20416] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Racemic 2-aryl-2-methoxypropionic acids were enantioresolved by the use of (S)-(-)-phenylalaninol 4. For instance, racemic 2-methoxy-2-phenylpropionic acid (+/-)-7 was condensed with phenylalaninol (S)-(-)-4 yielding a diastereomeric mixture of amides, which was easily separated by HPLC on silica gel affording the first-eluted amide (-)-13a and the second-eluted amide (+)-13b: alpha = 3.19, Rs = 3.49. The absolute configuration of amide (-)-13a was determined to be (R;S) by X-ray crystallography by reference to the S configuration of the phenylalaninol moiety. Amide (R;S)-(-)-13a was converted to oxazoline (R;S)-(-)-14a, from which enantiopure 2-methoxy-2-phenylpropionic acid (R)-(-)-7 was recovered. Other 2-aryl-2-methoxypropionic acids, (R)-(-)-8, (R)-(-)-9, (R)-(+)-10, (R)-(-)-11, and (R)-(-)-12, were similarly prepared in enantiopure forms with the use of phenylalaninol (S)-(-)-4, and their absolute configurations were clearly determined by X-ray crystallography or by chemical correlation.
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Affiliation(s)
- Satoshi Sekiguchi
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan
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Harada N. Determination of absolute configurations by X-ray crystallography and1H NMR anisotropy. Chirality 2008; 20:691-723. [DOI: 10.1002/chir.20478] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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(R)-(+)-[VCD(+)945]-4-Ethyl-4-methyloctane, the simplest chiral saturated hydrocarbon with a quaternary stereogenic center. Tetrahedron Lett 2007. [DOI: 10.1016/j.tetlet.2007.04.079] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Kasai Y, Sugio A, Sekiguchi S, Kuwahara S, Matsumoto T, Watanabe M, Ichikawa A, Harada N. Conformational Analysis of MαNP Esters, Powerful Chiral Resolution and1H NMR Anisotropy Tools – Aromatic Geometry and Solvent Effects on Δδ Values. European J Org Chem 2007. [DOI: 10.1002/ejoc.200600856] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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