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(±)-3-Deoxyradicinin Induces Stomata Opening and Chloroplast Oxidative Stress in Tomato ( Solanum lycopersicum L.). Int J Mol Sci 2023; 24:ijms24108467. [PMID: 37239812 DOI: 10.3390/ijms24108467] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Revised: 05/03/2023] [Accepted: 05/05/2023] [Indexed: 05/28/2023] Open
Abstract
Radicinin is a phytotoxic dihydropyranopyran-4,5-dione isolated from the culture filtrates of Cochliobolus australiensis, a phytopathogenic fungus of the invasive weed buffelgrass (Cenchrus ciliaris). Radicinin proved to have interesting potential as a natural herbicide. Being interested in elucidating the mechanism of action and considering radicinin is produced in small quantities by C. australiensis, we opted to use (±)-3-deoxyradicinin, a synthetic analogue of radicinin that is available in larger quantities and shows radicinin-like phytotoxic activities. To obtain information about subcellular targets and mechanism(s) of action of the toxin, the study was carried out by using tomato (Solanum lycopersicum L.), which, apart from its economic relevance, has become a model plant species for physiological and molecular studies. Results of biochemical assays showed that (±)-3-deoxyradicinin administration to leaves induced chlorosis, ion leakage, hydrogen peroxide production, and membrane lipid peroxidation. Remarkably, the compound determined the uncontrolled opening of stomata, which, in turn, resulted in plant wilting. Confocal microscopy analysis of protoplasts treated with (±)-3-deoxyradicinin ascertained that the toxin targeted chloroplasts, eliciting an overproduction of reactive singlet oxygen species. This oxidative stress status was related by qRT-PCR experiments to the activation of transcription of genes of a chloroplast-specific pathway of programmed cell death.
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Mitochondrial Role in Intrinsic Apoptosis Induced by a New Synthesized Chalcone in Hepatocellular Carcinoma Cells. Biomedicines 2022; 10:biomedicines10123120. [PMID: 36551876 PMCID: PMC9775964 DOI: 10.3390/biomedicines10123120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2022] [Revised: 11/26/2022] [Accepted: 12/01/2022] [Indexed: 12/12/2022] Open
Abstract
Hepatocellular carcinoma (HCC) is the most common type of liver cancer and the fourth cause of cancer-related deaths worldwide. Presently, a few drugs are available for HCC treatment and prevention, including both natural and synthetic compounds. In this study, a new chalcone, (E)-1-(2,4,6-triethoxyphenyl)-3-(3,4,5-trimethoxyphenyl)prop-2-en-1-one (ETTC), was synthesized and its effects and mechanisms of action over human hepatoma cells were investigated. Cytotoxic activity was revealed in HCC cells, while no effects were observed in normal hepatocytes. In HCC cells, ETTC caused subG1 cell cycle arrest and apoptosis, characterized by nuclear fragmentation. The activation of caspases 3/7 and 9, the increase in pro-apoptotic BAX, and the decrease in anti-apoptotic BCL-2 suggest the activation of the intrinsic pathway of apoptosis. ETTC mitochondrial targeting is confirmed by the reduction in mitochondrial membrane potential and Complex I activity together with levels of superoxide anion increasing. Our outcomes prove the potential mitochondria-mediated antitumor effect of newly synthesized chalcone ETTC in HCC.
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Synthesis and Stereochemical Characterization of a Novel Chiral α-Tetrazole Binaphthylazepine Organocatalyst. Molecules 2022; 27:molecules27165113. [PMID: 36014353 PMCID: PMC9413694 DOI: 10.3390/molecules27165113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Revised: 08/02/2022] [Accepted: 08/08/2022] [Indexed: 12/03/2022] Open
Abstract
A novel α-tetrazole-substituted 1,1′-binaphthylazepine chiral catalyst has been synthesized and its absolute configuration has been determined by DFT computational analysis of the vibrational circular dichroism (VCD) spectrum of its precursor. The VCD analysis, carried out through the model averaging method, allowed to assign the absolute configuration of a benzylic stereocenter in the presence of a chiral binaphthyl moiety. The 1,1′-binaphthylazepine tetrazole and the nitrile its immediate synthetic precursor, have been preliminarily tested as chiral organocatalysts in the asymmetric intramolecular oxa-Michael cyclization of 2-hydroxy chalcones for the synthesis of chiral flavanones obtaining low enantioselectivity.
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In Vitro Effects of Fungal Phytotoxins on Cancer Cell Viability: First Insight into Structure Activity Relationship of a Potent Metabolite of Cochliobolus australiensis Radicinin. Toxins (Basel) 2022; 14:toxins14080517. [PMID: 36006179 PMCID: PMC9415302 DOI: 10.3390/toxins14080517] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Revised: 07/15/2022] [Accepted: 07/23/2022] [Indexed: 01/18/2023] Open
Abstract
Natural compounds have always represented an important source for new drugs. Although fungi represent one such viable source, to date, no fungal metabolite has been marketed as an anticancer drug. Based on our work with phytotoxins as potential chemical scaffolds and our recent findings involving three phytopathogenic fungi, i.e., Cochliobolus australiensis, Kalmusia variispora and Hymenoscyphus fraxineus, herein, we evaluate the in vitro anti-cancer activity of the metabolites of these fungi by MTT assays on three cancer cell models harboring various resistance levels to chemotherapeutic drugs. Radicinin, a phytotoxic dihydropyranopyran-4,5-dione produced by Cochliobolus australiensis, with great potential for the biocontrol of the invasive weed buffelgrass (Cenchrus ciliaris), showed significant anticancer activity in the micromolar range. Furthermore, a SAR study was carried out using radicinin, some natural analogues and hemisynthetic derivatives prepared by synthetic methods developed as part of work aimed at the potential application of these molecules as bioherbicides. This investigation opens new avenues for the design and synthesis of novel radicinin analogues as potential anticancer agents.
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Computational Approaches and Use of Chiroptical Probes in the Absolute Configuration Assignment to Natural Products by ECD Spectroscopy: A 1,2,3-Trihydroxy-p-menthane as a Case Study. Biomolecules 2022; 12:biom12030421. [PMID: 35327613 PMCID: PMC8945943 DOI: 10.3390/biom12030421] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Revised: 03/02/2022] [Accepted: 03/06/2022] [Indexed: 12/13/2022] Open
Abstract
In this study, the computational analysis of electronic circular dichroism (ECD) spectra and the employment of biphenyl chiroptical probes were compared in the absolute configuration assignment of (-)-1α,2α,3β-trihydroxy-p-menthane (1), taken as a representative example of a UV-transparent chiral natural product. The usefulness of chiroptical probes in the configurational assignments of natural products and their complementarity to the computational protocols is herein highlighted. The biphenyl probe approach proves to be straightforward, reliable, and suitable for conformationally mobile and ECD silent compounds, not treatable by computational analysis of chiroptical data.
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Further secondary metabolites produced by the fungus
Pyricularia grisea
isolated from buffelgrass (
Cenchrus ciliaris
). Chirality 2020; 32:1234-1242. [DOI: 10.1002/chir.23270] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Revised: 07/05/2020] [Accepted: 07/06/2020] [Indexed: 02/06/2023]
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Absolute Configuration Assignment to Chiral Natural Products by Biphenyl Chiroptical Probes: The Case of the Phytotoxins Colletochlorin A and Agropyrenol. JOURNAL OF NATURAL PRODUCTS 2020; 83:1061-1068. [PMID: 32091903 PMCID: PMC7997626 DOI: 10.1021/acs.jnatprod.9b01068] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
The application of flexible biphenyls as chiroptical probes for the absolute configuration assignment to chiral natural products is described. The method is straightforward and reliable and can be applied to conformationally mobile and ECD silent compounds, not treatable by computational analysis of chiroptical data. By this approach, the (6'R) absolute configuration of the phytotoxin colletochlorin A (1) was confirmed, while the absolute configuration of the phytotoxin agropyrenol (2), previously assigned by the NMR Mosher method, was revised and assigned as (3'S,4'S). Moreover, with the biphenyl method the configurational assignment can be obtained simply by the sign of a diagnostic Cotton effect at 250 nm in the ECD spectrum, thus allowing application without the need of advanced knowledge of chiroptical spectroscopy and computational protocols.
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Amplification of the chiroptical response of UV-transparent amines and alcohols by N-phthalimide derivatization enabling absolute configuration determination through ECD computational analysis. Org Biomol Chem 2020; 18:2094-2102. [PMID: 32107518 DOI: 10.1039/d0ob00052c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The stereoselective transformation of chiral UV-transparent amines and alcohols to phthalimides has proved to be a simple and efficient method to enhance the chiroptical response of these substrates allowing their reliable absolute configuration determination by computational analysis of ECD spectra. Such a transformation also leads to a significant reduction in the molecular conformational flexibility thus simplifying the conformational analysis required by the computational treatment. The method described herein thus allows the absolute configuration assignment to these challenging substrates to be much easier and reliable.
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Regio- and stereoselective intermolecular carbolithiation reactions. RSC Adv 2020; 10:32581-32601. [PMID: 35516521 PMCID: PMC9056694 DOI: 10.1039/d0ra06101h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Accepted: 08/22/2020] [Indexed: 01/02/2023] Open
Abstract
Carbolithiation of alkenes provides a powerful tool for the construction of up to two novel carbon–carbon or carbon–heteroatoms bonds in a regio- and stereo-controlled manner. The synthetic potentiality of this reaction is highlighted.
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Synthesis and Herbicidal Activity Against Buffelgrass ( Cenchrus ciliaris) of (±)-3-deoxyradicinin. Molecules 2019; 24:molecules24173193. [PMID: 31484319 PMCID: PMC6749313 DOI: 10.3390/molecules24173193] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Revised: 08/17/2019] [Accepted: 08/28/2019] [Indexed: 02/06/2023] Open
Abstract
A novel synthetic strategy for obtainment of (±)-3-deoxyradicinin (2) is reported. This synthetic methodology is more efficient than those previously reported in the literature and also shows higher versatility towards the introduction of different side-chains at both C-7 and C-2. The obtained compound (±)-2 shows phytotoxicity against the grass-weed buffelgrass comparable to that of the natural phytotoxin radicinin (1). Therefore, (±)-2 can constitute a more practical synthetic alternative to 1 as bioherbicide for buffelgrass control.
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Cover Feature: Absolute Configuration Assignment from Optical Rotation Data by Means of Biphenyl Chiroptical Probes (Chem. Eur. J. 22/2019). Chemistry 2019. [DOI: 10.1002/chem.201901165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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12
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Absolute Configuration Assignment from Optical Rotation Data by Means of Biphenyl Chiroptical Probes. Chemistry 2019; 25:5682-5690. [PMID: 30730078 DOI: 10.1002/chem.201806435] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2018] [Revised: 02/06/2019] [Indexed: 11/10/2022]
Abstract
A non-empirical approach for the assignment of the absolute configuration of chiral 2-alkyl-substituted carboxylic acids and primary amines by [α]D measurements has been developed. The method requires the conversion of the chiral acids or amines into the corresponding 4,4'-disubstituted biphenylamides or biphenylazepines, respectively. In these derivatives a central-to-axial chirality transfer induces a preferred torsion in the biphenyl moiety revealed by the sign of the biphenyl A band in the ECD spectrum. By 4,4'-substitution on the biphenyl moiety a redshift of the A band is obtained, leading to an increase of its relative contribution to optical rotation. This allows to reliably establish a direct correlation between the [α]D sign, the biphenyl twist and, then, the substrate absolute configuration. This approach thus constitutes a really practical and reliable method to assign the absolute configuration of chiral carboxylic acids and primary amines by simple and straightforward [α]D measurement, readily obtainable by a routine instrumentation like the polarimeter.
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Central-to-axial chirality induction in biphenyl chiroptical probes for the stereochemical characterization of chiral primary amines. Org Biomol Chem 2019; 16:555-565. [PMID: 29292442 DOI: 10.1039/c7ob02730c] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Flexible biphenyls have been applied as efficient and practical chiroptical probes for absolute configuration assignment to chiral primary amines. The mechanism of the central-to-axial chirality transfer from the amine moiety to the conformationally flexible biphenyl system has been determined by NMR and computational studies. This allowed proposing a general non-empirical rule in order to establish, simply by looking at the sign of the 250 nm A band in the ECD spectrum of the biphenyl derivative, the torsion of the biphenyl and thus the absolute configuration of the amine. The method proved to be very reliable and sensitive, allowing treatment of samples on the μmol scale and permitting the simultaneous determination of the amine sample's absolute configuration and enantiopurity.
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Asymmetric synthesis and structure-activity studies of the fungal metabolites colletorin A, colletochlorin A and their halogenates analogues. Tetrahedron 2018. [DOI: 10.1016/j.tet.2018.05.077] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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15
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Absolute Configuration Determination by Quantum Mechanical Calculation of Chiroptical Spectra: Basics and Applications to Fungal Metabolites. Curr Med Chem 2018; 25:287-320. [DOI: 10.2174/0929867324666170310112009] [Citation(s) in RCA: 97] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Revised: 10/11/2016] [Accepted: 10/19/2016] [Indexed: 11/22/2022]
Abstract
Background:
Quantum mechanical simulations of chiroptical properties, such as
electronic circular dichroism (ECD), optical rotation (OR), and vibrational circular dichroism
(VCD), have rapidly become very popular to assign the absolute configuration of novel natural
products.
Objective:
We review the application of the ECD/OR/VCD computational methodology to
chiral metabolites of fungal origin. First, we summarize the fundamentals of the three spectroscopies;
then, we focus on the specific experimental and computational issues allied to the
application of their calculations.
Methods:
We surveyed the entire literature describing the use of ECD/OR/VCD computations
for fungal metabolites, and catalogued all papers according to the method employed and to
the structural family of compounds. Then, we chose several examples to illustrate the use of
the techniques and highlight the practical application of the computational approach.
Results:
Our literature survey demonstrates that the simulation of ECD/OR/VCD spectra is
nowadays widespread and accessible also to non-experts, although a good computational
practice is necessary to avoid wrong assignments. ECD is still the most common technique
used in the context of fungal metabolites. OR and VCD may be profitably employed when the
compound of interest lacks chromophoric groups. Our examples illustrate that the combination
of two or more chiroptical methods is strongly advisable in some cases, especially in the
presence of high conformational flexibility, where a single technique does not lead to a safe
conclusion.
Conclusion:
The ECD/OR/VCD computational approach is a reliable and versatile method to
assign the absolute configuration of fungal metabolites and related natural products.
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Abstract
This paper describes the enantioselective synthesis of analogues of sapinofuranones A and B, namely 5-substitutes dihydro- and 5 H-furan-ones, and their in vitro growth inhibitory activity against six cancer cell lines in comparison with fungal furanones such as diplofuranone A, diplobifuranylones A and B, as well as ( S,S)-enantiomer of sapinofuranone B. The compounds under study displayed weak if any in vitro growth inhibitory activity against the analysed cancer cell lines. However, it seems that among dihydro- and 5 H-furan-ones bearing a 1-hydroxypentyl side chain, the stereochemistry of the furanone ring and that of hydroxylated methine could modify the in vitro growth activity of these compounds. The natural furanones that showed a different unsaturated chain at C-4 or rearranged into a dihydrofuran ring appeared to be inactive in terms of growth inhibitory activity, e.g. displaying growth inhibitory concentration at 50% (GI50) > 100 μM in all six cancer cell lines analysed.
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17
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Natural and Synthetic Furanones with Anticancer Activity. Nat Prod Commun 2016; 11:1471-1474. [PMID: 30549601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023] Open
Abstract
This paper describes the enantioselective synthesis of analogues of sapinofuranones A and B, namely 5-substitutes dihydro- and 5H-furan-ones, and their in vitro growth inhibitory activity against six cancer cell lines in comparison with fungal furanones such as diplofuranone A, diplobifuranylones A and B, as well as (S,S)-enantiomer of sapinofuranone B. The compounds under study displayed weak if any in vitro growth inhibitory activity against the analysed cancer cell lines. -However, it seems that among dihydro- and 5H-furan-ones bearing a 1-hydroxypentyl side chain, the stereochemistry of the furanone ring and that of hydroxylated methine could modify the in vitro growth activity of these compounds. The natural furanones that showed a different unsaturated chain at C-4 or rearranged into a dihydrofuran ring appeared to be inactive in terms of growth inhibitory activity, e.g. displaying growth inhibitory concentration at 50% (GIs) > 100 ptM in all six cancer cell lines analysed.
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18
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TroposAmino Alcohol Mediated Enantioselective Aryl Transfer Reactions to Aromatic Aldehydes. European J Org Chem 2014. [DOI: 10.1002/ejoc.201402702] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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19
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Combined use of three forms of chiroptical spectroscopies in the study of the absolute configuration and conformational properties of 3-phenylcyclopentanone, 3-phenylcyclohexanone, and 3-phenylcycloheptanone. Tetrahedron 2013. [DOI: 10.1016/j.tet.2013.10.016] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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20
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In memory of Prof. Alessandro Degl'Innocenti. J Sulphur Chem 2013. [DOI: 10.1080/17415993.2013.785549] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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21
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Asymmetric addition of dimethylzinc to alkylidenmalonates mediated by phosphorous ligands: A new synthetic route to floral fragrances. Chirality 2011; 23:761-7. [DOI: 10.1002/chir.20987] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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22
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Asymmetric addition of phenylboronic acid to cycloalkanones mediated by a Rh/phosphoramidite complex: a comparison between tropos versus nontropos behavior. ACTA ACUST UNITED AC 2011. [DOI: 10.1016/j.tetasy.2011.02.030] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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23
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Biphenyl dioxolanes as circular dichroism probes for the assignment of absolute configuration to aliphatic diols: Extending the scope to anti 1,n-diols and cyclic syn 1,2-diols. Chirality 2010; 22 Suppl 1:E3-10. [DOI: 10.1002/chir.20877] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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24
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A vibrational circular dichroism approach to the determination of the absolute configuration of flexible and transparent molecules: fluorenone ketals of 1,n-diols. Phys Chem Chem Phys 2010; 12:4725-32. [DOI: 10.1039/b913213a] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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25
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The absolute configuration of simple aliphatic alcohols through a chemical/computational approach: triarylether derivatives of (+)-endo-2-norborneol as a case study. ACTA ACUST UNITED AC 2009. [DOI: 10.1016/j.tetasy.2009.10.028] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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26
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Conformation and absolute configuration of 2-naphthylalkylsulfoxides by combined use of dynamic NMR, ECD spectroscopy, DFT computations, and X-ray diffraction. Chirality 2009; 21:16-23. [DOI: 10.1002/chir.20587] [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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A new efficient enantioselective synthesis of (+)-cis-2-methyl- 4-propyl-1,3-oxathiane, a valuable ingredient for the aroma of passion fruit. Chirality 2009; 21:176-82. [DOI: 10.1002/chir.20632] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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A New Case of Induced Helical Chirality in a Bichromophoric System: Absolute Configuration of Transparent and Flexible Diols from the Analysis of the Electronic Circular Dichroism Spectra of the Corresponding Di(1-naphthyl)ketals. Org Lett 2008; 10:3421-4. [DOI: 10.1021/ol8012149] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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A Chemical/Computational Approach to the Determination of Absolute Configuration of Flexible and Transparent Molecules: Aliphatic Diols As a Case Study. J Org Chem 2008; 73:4865-73. [DOI: 10.1021/jo800516f] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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31
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Asymmetric conjugate additions of dialkylzinc reagents to enones promoted by new purely atropisomeric phosphoramidite ligands. ARKIVOC 2008. [DOI: 10.3998/ark.5550190.0009.811] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
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32
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Enantioselective oxidation of sulfides catalyzed by titanium complexes of 1,2-diarylethane-1,2-diols: Effect of the aryl substitution. Chirality 2008; 20:592-6. [DOI: 10.1002/chir.20456] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Origin of enantioselectivity in palladium-catalyzed asymmetric allylic alkylation reactions using chiral N,N-ligands with different rigidity and flexibility. Dalton Trans 2007:1509-19. [PMID: 17404652 DOI: 10.1039/b618347f] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The chiral bidentate-N,N ligands, (S(a))-1, (S(a))-2, (S,S)-3 and (S,S)-4, were synthesized. They were shown to contain rigid 2-pyridinyl or 8-quinolinyl building blocks and the C(2)-symmetric chiral frameworks trans-2,5-dimethylpyrrolidinyl or (S)-(+)-2,2'-(2-azapropane-1,3-diyl)-1,1'-binaphthalene. In the (S(a))-2, and (S,S)-4 ligands pair, the 8-quinolinyl skeleton is directly bonded to the C(2)-symmetric chiral frameworks (S)-(+)-2,2'-(2-azapropane-1,3-diyl)-1,1'-binaphthalene or trans-2,5-dimethylpyrrolidinyl. This feature induces rigidity in this pair of ligands upon the N,N-framework. However, this does not occur for the (S(a))-1 and (S,S)-3 ligands, in which the presence of the -CH(2)- spacer between the frameworks bearing the nitrogen atom donors gives greater flexibility to the ligand. A further difference between the pairs of ligands is significant from the electronic properties of the chiral framework N-donor atom. The coordinating properties and the specific steric structural features of the (S(a))-1, (S(a))-2, (S,S)-3, and (S,S)-4 ligands are explained by their reactions with the [Pd(PhCN)(2)Cl(2)] and [Pd(eta(3)-PhCHCHCHPh)(mu-Cl)](2) substrates, in which the reported ligands form chelate complexes, with the exception of (S(a))-2, which failed to react with [Pd(eta(3)-PhCHCHCHPh)(mu-Cl)](2). The ligands were used in the palladium-allyl catalyzed substitution reaction of 1,3-diphenylallyl acetate with dimethylmalonate, with the best result being obtained using the (S(a))-1 ligand, giving the substitution product 2-(1,3-diphenylallyl)dimethylmalonate with an enantiomeric excess of 82% in the S form and a yield of 96%. The work demonstrates that in the presence of a steric ligand control, the electronic properties of the ligand donor atoms play a role though not significant in determining the enantioselectivity of palladium(II) catalyzed allylic substitution reactions. The results of the catalytic reaction do not provide a convincing explanation considering the coordinated chiral ligand features, as rigidity or flexibility and electronic properties of the N-donor atoms. A rationalization of the results is proposed on the basis of NMR studies and DFT calculation on the cationic complexes [Pd(eta(3)-PhCHCHCHPh)(N-N*)]CF(3)SO(3), (N-N* = (S(a))-1, 9; (S,S)-3, 10; (S,S)-4, 11).
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An alternative stereoselective synthesis of the macrocyclic fragrances (R)-12-methyltridecanolide and (S)-muscolide by means of an asymmetric catalytic conjugate addition/Baeyer–Villiger oxidation. ACTA ACUST UNITED AC 2006. [DOI: 10.1016/j.tetasy.2006.09.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Asymmetric activation of tropos catalysts in the stereoselective catalytic conjugate additions of R2Zn to α,β-enones: an efficient synthesis of (−)-muscone. Tetrahedron 2004. [DOI: 10.1016/j.tet.2004.07.034] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Catalytic enantioselective conjugate addition of dialkyl zinc reagents to α,β-unsaturated ketones mediated by new phosphite ligands containing binaphthalene/1,2-diphenylethane moieties: a practical synthesis of (R)-(−)-muscone. ACTA ACUST UNITED AC 2003. [DOI: 10.1016/j.tetasy.2003.09.017] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Application of deoxycholic acid-based copper–phosphite complexes as ligands in the enantioselective conjugate addition of diethylzinc to acyclic enones. ACTA ACUST UNITED AC 2003. [DOI: 10.1016/s0957-4166(03)00044-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Conformational Analysis Using Infrared and Vibrational Circular Dichroism Spectroscopies: The Chiral Cyclic Sulfoxides 1-Thiochroman-4-one S-Oxide, 1-Thiaindan S-Oxide and 1-Thiochroman S-Oxide. J Phys Chem A 2002. [DOI: 10.1021/jp021225u] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Rational design of chiral 1,1′-binaphthylazepine-based ligands for the enantioselective addition of ZnEt2 to aromatic aldehydes. ACTA ACUST UNITED AC 2002. [DOI: 10.1016/s0957-4166(02)00323-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Determination of absolute configuration using vibrational circular dichroism spectroscopy: the chiral sulfoxide 1-thiochromanone S-oxide. Chirality 2002; 14:400-6. [PMID: 11984755 DOI: 10.1002/chir.10103] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
We reexamined the absolute configuration (AC) of the chiral sulfoxide 1-thiochromanone S-oxide (1) using vibrational circular dichroism (VCD) spectroscopy. The VCD spectrum of 1 was analyzed using density functional theory (DFT). DFT predicts two stable conformations of 1, separated by <1 kcal/mole. Their VCD spectra were calculated using the DFT/GIAO methodology. The VCD spectrum predicted for the equilibrium mixture of the two conformations of (S)-1 is in excellent agreement with the experimental spectrum of (+)-1. The AC of 1 is therefore definitively R(-)/S(+).
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Hexamethyldisilathiane: Its Use in the Conversion of Aromatic and Heteroaromatic Azides to Amines. J Org Chem 2002. [DOI: 10.1021/jo00112a054] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Monobenzylethers of (R,R)-1,2-diphenylethane-1,2-diol as a possible alternative to cyclohexyl-based chiral auxiliaries in the stereoselective reduction of α-ketoesters. Tetrahedron 2002. [DOI: 10.1016/s0040-4020(01)01117-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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43
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Determination of absolute configuration using vibrational circular dichroism spectroscopy: the chiral sulfoxide 1-thiochroman S-oxide. ACTA ACUST UNITED AC 2001. [DOI: 10.1016/s0957-4166(01)00235-x] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Synthesis and stereochemical characterization of optically active 1,2-diarylethane-1,2-diols: useful chiral controllers in the Ti-mediated enantioselective sulfoxidation. Chirality 2001; 13:258-65. [PMID: 11317347 DOI: 10.1002/chir.1028] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The series of phenylsubstituted 1,2-diphenylethane-1,2-diols 2a-h was prepared in high chemical (70--80%) and optical yields (approximately 90%) by Sharpless syn-dihydroxylation of the corresponding (E)-1,2-diarylethenes, in turn obtained by McMurry or Wittig reactions. The enantiomeric excesses of the samples were determined by HPLC analysis using Chiralcel OD chiral stationary phase (CSP). This CSP was able to resolve all the diols, except for 2g, with alpha values ranging between 1.10--1.64. In all cases the (R,R) antipode was eluted first. (R,R) absolute configuration was assigned to the dextrorotatory (CHCl(3)) diols 2a--h by analyzing the CD spectra of their 2,2-dimethyl-1,3-dioxolanes 3a--h. In fact, the CD spectra of all these dioxolanes present a positive couplet (210--180 nm range) which can be nonempirically related to an (R,R) absolute configuration of the two stereocenters.
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The reactivity of α- and β-iodo propenoylsilanes: an alternative access to polyunsaturated acylsilanes. ARKIVOC 2000. [DOI: 10.3998/ark.5550190.0001.402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
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A Facile Access to Polycyclic Homo- and Heteroaromatic Hydrocarbons Based on the Ceric Ammonium Nitrate-Promoted Oxidative Addition of 3-Aryl-1-[(trimethylsilyl)oxy]cyclohexenes to Ethyl Vinyl Ether. J Org Chem 1999; 64:3364-3368. [PMID: 11674447 DOI: 10.1021/jo982195n] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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A New Synthetic Approach to Substituted 1(2H)-Phenanthrenones Based on the Ceric Ammonium Nitrate-Promoted Oxidative Addition of 3-Aryl-1-[(trimethylsilyl)oxy]- cyclohexenes to Ethyl Vinyl Ether. J Org Chem 1998. [DOI: 10.1021/jo972233n] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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50
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Reactions of Hexamethyldisilathiane with Silyl Acetals: a General Access to Thioformylsilanes. Synlett 1997. [DOI: 10.1055/s-1997-791] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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