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Mo MY, Wang XJ, Shen RZ, Hu CY, Li XC, Li GW, Liu LT. Enantiospecific Analysis of Carboxylic Acids Using Cinchona Alkaloid Dimers as Chiral Solvating Agents. Anal Chem 2024; 96:7487-7496. [PMID: 38695134 DOI: 10.1021/acs.analchem.4c00053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/15/2024]
Abstract
Cinchona alkaloid derivatives as Brønsted base catalysts have attracted considerable attention in the field of asymmetric catalysis. However, their potential application as chiral solvating agents has not been described. In this research, we investigated the use of the Cinchona alkaloid dimer, namely, (DHQ)2PHAL, as a chiral solvating agent for discerning various mandelic acid derivatives through 1H NMR spectroscopy. The addition of catalytic amounts of DMAP facilitated this process. Our experimental results demonstrate that dimeric (DHQ)2PHAL exhibits remarkable chiral discrimination properties regarding the diagnostic split protons of 1H NMR signals (including 24 examples, up to 0.321 ppm). Furthermore, it serves as an excellent chiral discriminating agent and provides good resolution for racemic chiral phosphoric acid as determined by 31P NMR spectroscopy. The quality of enantiodifferentiation has also been evaluated by means of the parameter "resolution (Rs)". Significantly, this class of CSAs based on (alkaloid)2linker systems with an azaaromatic linker can be directly employed, which is commercially available in an enantiopure form at very low cost and exhibits promising potential in determining the enantiopurity of α-hydroxy acids by chemoselective and biocatalytic reactions.
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Affiliation(s)
- Ming-Yang Mo
- School of Chemistry, Zhengzhou University, Zhengzhou, 450001, China
- College of Chemistry and Chemical Engineering, Henan Engineering Research Center for Green Synthesis of Pharmaceuticals, Shangqiu Normal University, Shangqiu 476000, China
| | - Xiao-Juan Wang
- College of Chemistry and Chemical Engineering, Henan Engineering Research Center for Green Synthesis of Pharmaceuticals, Shangqiu Normal University, Shangqiu 476000, China
| | - Ren-Zeng Shen
- College of Chemistry and Chemical Engineering, Henan Engineering Research Center for Green Synthesis of Pharmaceuticals, Shangqiu Normal University, Shangqiu 476000, China
| | - Chang-Yan Hu
- College of Chemistry and Chemical Engineering, Henan Engineering Research Center for Green Synthesis of Pharmaceuticals, Shangqiu Normal University, Shangqiu 476000, China
| | - Xue-Chun Li
- College of Chemistry and Chemical Engineering, Henan Engineering Research Center for Green Synthesis of Pharmaceuticals, Shangqiu Normal University, Shangqiu 476000, China
| | - Gao-Wei Li
- School of Chemistry, Zhengzhou University, Zhengzhou, 450001, China
- College of Chemistry and Chemical Engineering, Henan Engineering Research Center for Green Synthesis of Pharmaceuticals, Shangqiu Normal University, Shangqiu 476000, China
| | - Lan-Tao Liu
- School of Chemistry, Zhengzhou University, Zhengzhou, 450001, China
- College of Chemistry and Chemical Engineering, Henan Engineering Research Center for Green Synthesis of Pharmaceuticals, Shangqiu Normal University, Shangqiu 476000, China
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Lv JX, Ding YQ, Huang CM, Guo LL, Fang JL, Jia X, Zhang WH, You S, Qin B. Enzyme- and Chemo-enzyme-Catalyzed Stereodivergent Synthesis. PHARMACEUTICAL FRONTS 2022. [DOI: 10.1055/s-0042-1755556] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022] Open
Abstract
Multiple stereoisomers can be found when a substance contains chiral carbons in its chemical structure. To obtain the desired stereoisomers, asymmetric synthesis was proposed in the 1970s and developed rapidly at the beginning of this century. Stereodivergent synthesis, an extension of asymmetric synthesis in organic synthesis with the hope to produce all stereoisomers of chiral substances in high conversion and selectivity, enriches the variety of available products and serves as a reference suggestion for the synthesis of their derivatives and other compounds. Since biocatalysis has outstanding advantages of economy, environmental friendliness, high efficiency, and reaction at mild conditions, the biocatalytic reaction is regarded as an efficient strategy to perform stereodivergent synthesis. Thus, in this review, we summarize the stereodivergent synthesis catalyzed by enzymes or chemo-enzymes in cases where a compound contains two or three chiral carbons, i.e., at most four or eight stereoisomers are present. The types of reactions, including reduction of substituent ketones, cyclization reactions, olefin addition, and nonredox transesterification reactions, are also discussed for the understanding of the progress and application of biocatalysis in stereodivergent synthesis.
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Affiliation(s)
- Jia-Xiang Lv
- Wuya College of Innovation, Shenyang Pharmaceutical University, Shenyang, People's Republic of China
| | - Ya-Qi Ding
- Wuya College of Innovation, Shenyang Pharmaceutical University, Shenyang, People's Republic of China
| | - Chen-Ming Huang
- Wuya College of Innovation, Shenyang Pharmaceutical University, Shenyang, People's Republic of China
| | - Ling-Ling Guo
- Microbial Research Institute of Liaoning Province, Liaoyang, People's Republic of China
| | - Jia-Li Fang
- Wuya College of Innovation, Shenyang Pharmaceutical University, Shenyang, People's Republic of China
| | - Xian Jia
- School of Pharmaceutical Engineering, Shenyang Pharmaceutical University, Shenyang, People's Republic of China
| | - Wen-He Zhang
- School of Life Sciences and Biopharmaceutical Sciences, Shenyang Pharmaceutical University, Shenyang, People's Republic of China
| | - Song You
- School of Life Sciences and Biopharmaceutical Sciences, Shenyang Pharmaceutical University, Shenyang, People's Republic of China
| | - Bin Qin
- Wuya College of Innovation, Shenyang Pharmaceutical University, Shenyang, People's Republic of China
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3
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Tyson B, Pask CM, George N, Simone E. Crystallization Behavior and Crystallographic Properties of dl-Arabinose and dl-Xylose Diastereomer Sugars. CRYSTAL GROWTH & DESIGN 2022; 22:1371-1383. [PMID: 35140548 PMCID: PMC8815043 DOI: 10.1021/acs.cgd.1c01329] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Revised: 01/07/2022] [Indexed: 05/12/2023]
Abstract
Natural sugar molecules such as xylose and arabinose exhibit sweetness profiles similar to sucrose, which makes them a valuable alternative in low-calorie foods as well as excipients or cocrystallization agents in pharmaceutical formulations. Xylose and arabinose are also chiral diastereomers that can exhibit specific crystallization behavior. In this work, the solid-state landscapes of the chiral pairs of both xylose and arabinose have been investigated to determine whether racemic compounds or conglomerates are formed. Furthermore, single crystals of xylose and arabinose have been grown and characterized by X-ray diffraction and optical microscopy to study their crystallographic properties and relate them to the crystallization behavior. Differential scanning calorimetry (DSC) measurements were used to determine the phase diagrams of the two analyzed chiral systems. The solubilities of the different solid forms of xylose and arabinose were measured in different solvent mixtures by a thermogravimetric method. An analysis was conducted to assess the main thermodynamic parameters and the activity coefficients of the compounds in solution. Finally, slurry experiments in a 50:50 w/w ethanol/water solvent have also been performed to determine the relative stability of each solid form and the kinetics of transformation in this solvent mixture. It was found that dl-arabinose crystallizes as a stable racemic compound, which transforms quickly from its constituent enantiomers when in solution; whereas d- and l-xylose molecules crystallize separately as a conglomerate.
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Affiliation(s)
- Bradley Tyson
- School
of Chemical and Process Engineering, University
of Leeds, Leeds LS2 9JT, United Kingdom
| | | | - Neil George
- School
of Chemical and Process Engineering, University
of Leeds, Leeds LS2 9JT, United Kingdom
- Syngenta
Jealotts Hill Int. Research Centre, Bracknell, Berkshire RG42
6EY, United Kingdom
| | - Elena Simone
- School
of Food Science and Nutrition, Food Colloids and Bioprocessing Group, University of Leeds, Leeds LS2 9JT, United Kingdom
- Department
of Applied Science and Technology (DISAT), Politecnico di Torino, 10129 Torino, Italy
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4
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Purification of N-acetylgalactosamine-modified-oligonucleotides using orthogonal anion-exchange and mixed-mode chromatography approaches. J Chromatogr A 2021; 1661:462679. [PMID: 34871941 DOI: 10.1016/j.chroma.2021.462679] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Accepted: 11/08/2021] [Indexed: 11/23/2022]
Abstract
N-acetylgalactosamine (GalNAc)-modified small interfering ribonucleic acids (siRNA) have shown promising outcomes for targeted siRNA delivery resulting in gene silencing in vivo; however, their structural complexity requires development of new purification methods to address high purity and recovery requirements. The current study evaluates complementary purification approaches using a mixed-mode Scherzo SS-C18 and anion-exchange (AEX) TSK-gel SuperQ-5PW for a range of single-stranded triantennary GalNAc-oligonucleotides. Initially, the semi-preparative mixed-mode support (10 × 250 mm, 3 µm) was compared against the preparative AEX analogue (21.5 × 300 mm, 13 µm), with the former affording double the recovery and higher purity of 95% over its AEX counterpart displaying 91% for a selected siRNA conjugate. An assortment of GalNAc-modified oligonucleotides was later purified using the mixed-mode resin revealing good recoveries (∼30-60%) and high purities of 90-94% ranging from straightforward to more challenging purifications. High sample loading in the 20 mg range was achieved, which was comparable with the larger preparative TSKgel SuperQ-5PW support. The Scherzo-SS-C18 resin also afforded some degree of resolution between diastereomers containing phosphorothioate functionalities. The TSKgel SuperQ-5PW support was later investigated to provide orthogonal separation selectivity to the Scherzo-SS-C18 column enabling purification of a selected, GalNAc-siRNA conjugate. The developed pH (8.5-11) and salt (0.3-0.7 M) gradients method provided enhanced separation selectivity between the free and conjugated siRNA, while minimizing formation of secondary structures and highlighting a complementary approach to deal with challenging purifications of oligonucleotide-GalNAc conjugates. Together, the use of AEX and mixed-mode columns provide much needed orthogonality to deal with complex GalNAc-modified oligonucleotides and potentially other upcoming modalities.
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Takino J, Kotani A, Ozaki T, Peng W, Yu J, Guo Y, Mochizuki S, Akimitsu K, Hashimoto M, Ye T, Minami A, Oikawa H. Biochemistry-Guided Prediction of the Absolute Configuration of Fungal Reduced Polyketides. Angew Chem Int Ed Engl 2021; 60:23403-23411. [PMID: 34448341 DOI: 10.1002/anie.202110658] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2021] [Indexed: 11/08/2022]
Abstract
Highly reducing polyketide synthases (HR-PKSs) produce structurally diverse polyketides (PKs). The PK diversity is constructed by a variety of factors, including the β-keto processing, chain length, methylation pattern, and relative and absolute configurations of the substituents. We examined the stereochemical course of the PK processing for the synthesis of polyhydroxy PKs such as phialotides, phomenoic acid, and ACR-toxin. Heterologous expression of a HR-PKS gene, a trans-acting enoylreductase gene, and a truncated non-ribosomal peptide synthetase gene resulted in the formation of a linear PK with multiple stereogenic centers. The absolute configurations of the stereogenic centers were determined by chemical degradation followed by comparison of the degradation products with synthetic standards. A stereochemical rule was proposed to explain the absolute configurations of other reduced PKs and highlights an error in the absolute configurations of a reported structure. The present work demonstrates that focused functional analysis of functionally related HR-PKSs leads to a better understanding of the stereochemical course.
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Affiliation(s)
- Junya Takino
- Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, 060-0810, Japan
| | - Akari Kotani
- Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, 060-0810, Japan
| | - Taro Ozaki
- Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, 060-0810, Japan
| | - Wenquan Peng
- State Key Laboratory of Chemical Oncogenomics, Peking University Shenzhen Graduate School, Xili, Nanshan District, Shenzhen, 518055, China
| | - Jie Yu
- State Key Laboratory of Chemical Oncogenomics, Peking University Shenzhen Graduate School, Xili, Nanshan District, Shenzhen, 518055, China.,School of Biotechnology and Health Sciences, Wuyi University, Jiangmen, 529020, China
| | - Yian Guo
- State Key Laboratory of Chemical Oncogenomics, Peking University Shenzhen Graduate School, Xili, Nanshan District, Shenzhen, 518055, China.,School of Biotechnology and Health Sciences, Wuyi University, Jiangmen, 529020, China
| | - Susumu Mochizuki
- International Institute of Rare Sugar Research and Education & Faculty of Agriculture, Kagawa University, Kagawa, 761-0795, Japan
| | - Kazuya Akimitsu
- International Institute of Rare Sugar Research and Education & Faculty of Agriculture, Kagawa University, Kagawa, 761-0795, Japan
| | - Masaru Hashimoto
- Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, 036-8561, Japan
| | - Tao Ye
- State Key Laboratory of Chemical Oncogenomics, Peking University Shenzhen Graduate School, Xili, Nanshan District, Shenzhen, 518055, China
| | - Atsushi Minami
- Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, 060-0810, Japan
| | - Hideaki Oikawa
- Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, 060-0810, Japan
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6
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Takino J, Kotani A, Ozaki T, Peng W, Yu J, Guo Y, Mochizuki S, Akimitsu K, Hashimoto M, Ye T, Minami A, Oikawa H. Biochemistry‐Guided Prediction of the Absolute Configuration of Fungal Reduced Polyketides. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202110658] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Junya Takino
- Department of Chemistry Faculty of Science Hokkaido University Sapporo 060-0810 Japan
| | - Akari Kotani
- Department of Chemistry Faculty of Science Hokkaido University Sapporo 060-0810 Japan
| | - Taro Ozaki
- Department of Chemistry Faculty of Science Hokkaido University Sapporo 060-0810 Japan
| | - Wenquan Peng
- State Key Laboratory of Chemical Oncogenomics Peking University Shenzhen Graduate School Xili, Nanshan District Shenzhen 518055 China
| | - Jie Yu
- State Key Laboratory of Chemical Oncogenomics Peking University Shenzhen Graduate School Xili, Nanshan District Shenzhen 518055 China
- School of Biotechnology and Health Sciences Wuyi University Jiangmen 529020 China
| | - Yian Guo
- State Key Laboratory of Chemical Oncogenomics Peking University Shenzhen Graduate School Xili, Nanshan District Shenzhen 518055 China
- School of Biotechnology and Health Sciences Wuyi University Jiangmen 529020 China
| | - Susumu Mochizuki
- International Institute of Rare Sugar Research and Education & Faculty of Agriculture Kagawa University Kagawa 761-0795 Japan
| | - Kazuya Akimitsu
- International Institute of Rare Sugar Research and Education & Faculty of Agriculture Kagawa University Kagawa 761-0795 Japan
| | - Masaru Hashimoto
- Faculty of Agriculture and Life Science Hirosaki University Hirosaki 036-8561 Japan
| | - Tao Ye
- State Key Laboratory of Chemical Oncogenomics Peking University Shenzhen Graduate School Xili, Nanshan District Shenzhen 518055 China
| | - Atsushi Minami
- Department of Chemistry Faculty of Science Hokkaido University Sapporo 060-0810 Japan
| | - Hideaki Oikawa
- Department of Chemistry Faculty of Science Hokkaido University Sapporo 060-0810 Japan
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7
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Khalfaoui M, Chebrouk F, Ziani BE, Bennamane N, Cherfaoui B, Frites W, Valega M, Mendes RF, Paz FAA, Chebout R, Bachari K, Talhi O, Silva AM. Hemi-synthesis, in-vitro and in-silico bioactivities of new chiral-Schiff bases and benzodiazepine derivatives from Ammodaucus leucotrichus(S)-perillaldehyde. J Mol Struct 2021. [DOI: 10.1016/j.molstruc.2021.130690] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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8
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Gamidi RK, Dandawate M, Tothadi S, Choudhury R, Nangia AK, Reddy DS. Separation of a diastereomeric diol pair using the mechanical properties of crystals. CrystEngComm 2021. [DOI: 10.1039/d1ce01055g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The visually indistinguishable acicular crystals of a (2S,3R/S)-3-ethyl-1-phenylhex-5-ene-2,3-diol (ephd) diastereomeric pair are separated via the mechanical response based on elastic (2S,3R, right) and brittle (2S,3S, left) crystals.
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Affiliation(s)
- Rama Krishna Gamidi
- Organic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India
| | - Monica Dandawate
- Organic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India
| | - Srinu Tothadi
- Organic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India
| | - Rahul Choudhury
- Organic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
| | - Ashwini K. Nangia
- Organic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India
- School of Chemistry, University of Hyderabad, Hyderabad 500046, India
| | - D. Srinivasa Reddy
- Organic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
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9
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How and How Much Molecular Conformation Affects Electronic Circular Dichroism: The Case of 1,1-Diarylcarbinols. Molecules 2018; 23:molecules23010128. [PMID: 29315220 PMCID: PMC6017593 DOI: 10.3390/molecules23010128] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2017] [Revised: 12/29/2017] [Accepted: 01/08/2018] [Indexed: 11/25/2022] Open
Abstract
Chiroptical spectra such as electronic circular dichroism (ECD) are said to be much more sensitive to conformation than their non-chiroptical counterparts, however, it is difficult to demonstrate such a common notion in a clear-cut way. We run DFT and TDDFT calculations on two closely related 1,1-diarylmethanols which show mirror-image ECD spectra for the same absolute configuration. We demonstrate that the main reason for the different chiroptical response of the two compounds lies in different conformational ensembles, caused by a single hydrogen-to-methyl substitution. We conclude that two compounds, having the same configuration but different conformation, may exhibit mirror-image ECD signals, stressing the importance and impact of conformational factors on ECD spectra.
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10
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Calcaterra A, D’Acquarica I. The market of chiral drugs: Chiral switches versus de novo enantiomerically pure compounds. J Pharm Biomed Anal 2018; 147:323-340. [DOI: 10.1016/j.jpba.2017.07.008] [Citation(s) in RCA: 195] [Impact Index Per Article: 32.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2017] [Revised: 07/06/2017] [Accepted: 07/08/2017] [Indexed: 10/19/2022]
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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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12
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Recent Advances in Multinuclear NMR Spectroscopy for Chiral Recognition of Organic Compounds. Molecules 2017; 22:molecules22020247. [PMID: 28178223 PMCID: PMC6155827 DOI: 10.3390/molecules22020247] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Revised: 01/26/2017] [Accepted: 01/30/2017] [Indexed: 12/17/2022] Open
Abstract
Nuclear magnetic resonance (NMR) is a powerful tool for the elucidation of chemical structure and chiral recognition. In the last decade, the number of probes, media, and experiments to analyze chiral environments has rapidly increased. The evaluation of chiral molecules and systems has become a routine task in almost all NMR laboratories, allowing for the determination of molecular connectivities and the construction of spatial relationships. Among the features that improve the chiral recognition abilities by NMR is the application of different nuclei. The simplicity of the multinuclear NMR spectra relative to 1H, the minimal influence of the experimental conditions, and the larger shift dispersion make these nuclei especially suitable for NMR analysis. Herein, the recent advances in multinuclear (19F, 31P, 13C, and 77Se) NMR spectroscopy for chiral recognition of organic compounds are presented. The review describes new chiral derivatizing agents and chiral solvating agents used for stereodiscrimination and the assignment of the absolute configuration of small organic compounds.
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