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Son J, Wu Z, Dou J, Fujita H, Cao PLD, Liu Q, Lindsey JS. Tethered Indoxyl-Glucuronides for Enzymatically Triggered Cross-Linking. Molecules 2023; 28:molecules28104143. [PMID: 37241884 DOI: 10.3390/molecules28104143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 05/14/2023] [Accepted: 05/16/2023] [Indexed: 05/28/2023] Open
Abstract
Indoxyl-glucuronides, upon treatment with β-glucuronidase under physiological conditions, are well known to afford the corresponding indigoid dye via oxidative dimerization. Here, seven indoxyl-glucuronide target compounds have been prepared along with 22 intermediates. Of the target compounds, four contain a conjugatable handle (azido-PEG, hydroxy-PEG, or BCN) attached to the indoxyl moiety, while three are isomers that include a PEG-ethynyl group at the 5-, 6-, or 7-position. All seven target compounds have been examined in indigoid-forming reactions upon treatment with β-glucuronidase from two different sources and rat liver tritosomes. Taken together, the results suggest the utility of tethered indoxyl-glucuronides for use in bioconjugation chemistry with a chromogenic readout under physiological conditions.
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Affiliation(s)
- Juno Son
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| | - Zhiyuan Wu
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| | - Jinghuai Dou
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| | - Hikaru Fujita
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| | - Phuong-Lien Doan Cao
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| | - Qihui Liu
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| | - Jonathan S Lindsey
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
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Mass spectrometric characterization of glucuronides formed by a new concept, combining Cunninghamella elegans with TEMPO. J Pharm Biomed Anal 2013; 84:278-84. [DOI: 10.1016/j.jpba.2013.06.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Revised: 06/05/2013] [Accepted: 06/06/2013] [Indexed: 01/21/2023]
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Stachulski AV, Meng X. Glucuronides from metabolites to medicines: a survey of the in vivo generation, chemical synthesis and properties of glucuronides. Nat Prod Rep 2013; 30:806-48. [DOI: 10.1039/c3np70003h] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Subhani MA, Beigi M, Eilbracht P. Polyurethane- and Polystyrene-Supported 2,2,6,6-Tetramethyl- piperidine-1-oxyl (TEMPO); Facile Preparation, Catalytic Oxidation and Application in a Membrane Reactor. Adv Synth Catal 2008. [DOI: 10.1002/adsc.200800369] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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5
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Wang X, Liu R, Jin Y, Liang X. TEMPO/HCl/NaNO2 catalyst: a transition-metal-free approach to efficient aerobic oxidation of alcohols to aldehydes and ketones under mild conditions. Chemistry 2008; 14:2679-85. [PMID: 18293352 DOI: 10.1002/chem.200701818] [Citation(s) in RCA: 146] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Hydrochloric acid, a very inexpensive and readily available inorganic acid, has been found to cooperate exquisitely with NaNO(2)/TEMPO in catalyzing the molecular-oxygen-driven oxidation of a broad range of alcohol substrates to the corresponding aldehydes and ketones. This transition-metal-free catalytic oxidative conversion is novel and represents an interesting alternative route to the corresponding carbonyl compounds to the metal-catalyzed aerobic oxidation of alcohols. The reaction is highly selective with respect to the desired product when carried out at room temperature in air at atmospheric pressure. Notably, the use of very inexpensive NaNO(2) and HCl in combination with TEMPO for this highly selective aerobic oxidation of alcohols in air at ambient temperature makes the reaction operationally and economically very attractive. The results of mechanistic studies, performed with the aid of electrospray ionization mass spectrometry (ESI-MS), are presented and discussed. TEMPO, TEMPOH, and TEMPO(+) were observed in the redox cycle by means of ESI-MS. On the basis of these observations, a mechanism is proposed that may provide an insight into the newly developed aerobic alcohol oxidation.
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Affiliation(s)
- Xinliang Wang
- Dalian Institute of Chemical Physics, Institution Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, PR China
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6
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Huang HH, Lin LH, Zhang P, Qi XL, Zhong DF. Formation of glucoside conjugate of acetaminophen by fungi separated from soil. Eur J Drug Metab Pharmacokinet 2007; 31:103-8. [PMID: 16898078 DOI: 10.1007/bf03191126] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
The phase II metabolite of acetaminophen in filamentous fungi and actinomycetes separated from soil was investigated. Fifty-four filamentous fungi and twenty-seven actinomycetes were screened to transform acetaminophen. The metabolites of acetaminophen were assayed using liquid chromatography-tandem mass spectrometry. The only metabolite was subject to enzymatic hydrolysis to confirm its structure. Acetaminophen was converted into glucoside conjugate, by filamentous fungi JX1-60, LN17-2, LN20-1 and the yield of the conjugate was 60.01%, 44.27%, 100%, respectively, and no phase I metabolites were detected. Glucoside conjugation of acetaminophen in filamentous fungi differs from the phase II metabolism of glucuronidation in humans. The fungus LN20-1 could be a suitable model to synthesize glucoside conjugate of acetaminophen.
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Affiliation(s)
- H H Huang
- Shanghai Drug-Metab Biotech Co., Ltd, People's Republic of China
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7
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Sancéau JY, Larouche D, Caron B, Bélanger P, Coquet A, Bélanger A, Labrie F, Gauthier S. Synthesis and deuterium labelling of the pure selective estrogen receptor modulator (SERM) acolbifene glucuronides. J Labelled Comp Radiopharm 2007. [DOI: 10.1002/jlcr.1260] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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8
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Aerobic photocatalytic oxidation of activated benzylic and allylic alcohols to carbonyl compounds catalyzed by molecular iodine. Tetrahedron Lett 2006. [DOI: 10.1016/j.tetlet.2006.10.036] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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9
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El Alaoui A, Schmidt F, Monneret C, Florent JC. Protecting Groups for Glucuronic Acid: Application to the Synthesis of New Paclitaxel (Taxol) Derivatives. J Org Chem 2006; 71:9628-36. [PMID: 17168579 DOI: 10.1021/jo0612675] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To prepare two new glucuronide conjugates, allyl ester and allyl carbonates were used as protecting groups of the glucuronic moiety. In this way, an aniline glycosyl carbamate spacer linked to the 2'-OH of paclitaxel was obtained. By using palladium chemistry, an efficient one-step removal of all the allyl groups at the end of the synthesis afforded the desired compounds in good yields.
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Affiliation(s)
- Abdessamad El Alaoui
- UMR 176 CNRS/Institut Curie, Centre de Recherche, 26 rue d'Ulm, 75248 Paris Cedex 05, France
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10
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Mild and selective oxidation of alcohols to aldehydes and ketones using NaIO4/TEMPO/NaBr system under acidic conditions. Tetrahedron 2006. [DOI: 10.1016/j.tet.2006.07.022] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Kloth K, Brünjes M, Kunst E, Jöge T, Gallier F, Adibekian A, Kirschning A. Practical TEMPO-Mediated Oxidation of Alcohols using Different Polymer-Bound Co-Oxidants. Adv Synth Catal 2005. [DOI: 10.1002/adsc.200505005] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Tanaka H, Chou J, Mine M, Kuroboshi M. The Oxidation of Alcohols inN-Oxyl-Immobilized Silica Gel/Aqueous NaOCl Disperse Systems. A Prominent Access to a Column-Flow System. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2004. [DOI: 10.1246/bcsj.77.1745] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Palmacci ER, Seeberger PH. Toward the modular synthesis of glycosaminoglycans: synthesis of hyaluronic acid disaccharide building blocks using a periodic acid oxidation. Tetrahedron 2004. [DOI: 10.1016/j.tet.2004.06.037] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Yu Y, Ko KS, Zea CJ, Pohl NL. Discovery of the Chemical Function of Glycosidases: Design, Synthesis, and Evaluation of Mass-Differentiated Carbohydrate Libraries. Org Lett 2004; 6:2031-3. [PMID: 15176811 DOI: 10.1021/ol049389b] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
[reaction: see text] Discovery of the catalytic chemical function of the many putative glycosidases coded in genomes currently relies on individual testing of possible substrates, usually as their p-nitrophenol conjugate. Herein, we present an alternative chemical proteomics approach using a synthetic mass-differentiated heat-stable substrate library with mass spectrometry readout. Library components do not serve as reaction inhibitors and both primary and secondary enzyme substrates can be delineated.
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Affiliation(s)
- Yang Yu
- Department of Chemistry and the Plant Sciences Institute, Gilman Hall, Iowa State University, Ames, Iowa 50011-3111, USA
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15
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Patching SG, Brough AR, Herbert RB, Rajakarier JA, Henderson PJF, Middleton DA. Substrate Affinities for Membrane Transport Proteins Determined by 13C Cross-Polarization Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopy. J Am Chem Soc 2004; 126:3072-80. [PMID: 15012136 DOI: 10.1021/ja037163i] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We have devised methods in which cross-polarization magic-angle spinning (CP-MAS) solid-state NMR is exploited to measure rigorous parameters for binding of (13)C-labeled substrates to membrane transport proteins. The methods were applied to two proteins from Escherichia coli: a nucleoside transporter, NupC, and a glucuronide transporter, GusB. A substantial signal for the binding of methyl [1-(13)C]-beta-d-glucuronide to GusB overexpressed in native membranes was achieved with a sample that contained as little as 20 nmol of GusB protein. The data were fitted to yield a K(D) value of 4.17 mM for the labeled ligand and 0.42 mM for an unlabeled ligand, p-nitrophenyl beta-d-glucuronide, which displaced the labeled compound. CP-MAS was also used to measure binding of [1'-(13)C]uridine to overexpressed NupC. The spectrum of NupC-enriched membranes containing [1'-(13)C]uridine exhibited a large peak from substrate bound to undefined sites other than the transport site, which obscured the signal from substrate bound to NupC. In a novel application of a cross-polarization/polarization-inversion (CPPI) NMR experiment, the signal from undefined binding was eliminated by use of appropriate inversion pulse lengths. By use of CPPI in a titration experiment, a K(D) value of 2.6 mM was determined for uridine bound to NupC. These approaches are broadly applicable to quantifying binding of substrates, inhibitors, drugs, and antibiotics to numerous membrane proteins.
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Affiliation(s)
- Simon G Patching
- Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology, Sackville Street, Post Office Box 88, Manchester M60 1QD, United Kingdom
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Merbouh N, Bobbitt JM, Brückner C. PREPARATION OF TETRAMETHYLPIPERDINE-1-OXOAMMONlUM SALTS AND THEIR USE AS OXIDANTS IN ORGANIC CHEMISTRY. A REVIEW. ORG PREP PROCED INT 2004. [DOI: 10.1080/00304940409355369] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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17
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Rye CS, Withers SG. Elucidation of the mechanism of polysaccharide cleavage by chondroitin AC lyase from Flavobacterium heparinum. J Am Chem Soc 2002; 124:9756-67. [PMID: 12175234 DOI: 10.1021/ja020627c] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Chondroitin AC lyase from Flavobacterium heparinum degrades chondroitin sulfate glycosaminoglycans via an elimination mechanism resulting in disaccharides or oligosaccharides with delta4,5-unsaturated uronic acid residues at their nonreducing end. Mechanistic details concerning the ordering of the bond-breaking and -forming steps of this enzymatic reaction are nonexistent, mainly due to the inhomogeneous nature of the polymeric substrates. The creation of a new class of synthetic substrates for this enzyme has allowed the measurement of defined and reproducible k(cat) and K(m) values and has expanded the range of mechanistic studies that can be performed. The primary deuterium kinetic isotope effect upon k(cat)/K(m) for the abstraction of the proton alpha to the carboxylic acid was measured to be 1.67 +/- 0.07, showing that deprotonation occurs in a rate-limiting step. Using substrates with leaving groups of differing reactivity, a flat linear free energy relationship was produced, indicating that the C4-O4 bond is not broken in a rate-determining step. Taken together, these results strongly suggest a stepwise mechanism. Consistent with this was the measurement of a secondary deuterium kinetic isotope effect upon k(cat)/K(m) of 1.01 +/- 0.03 on a 4-[(2)H]-substrate, indicating that no sp2 character is developed at C4 during the rate-limiting step, thereby ruling out a concerted syn-elimination.
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Affiliation(s)
- Carl S Rye
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada, V6T 1Z1
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18
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Regio- and stereoselective synthesis of the major metabolite of quercetin, quercetin-3-O-β-d-glucuronide. Tetrahedron Lett 2002. [DOI: 10.1016/s0040-4039(02)01264-9] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Fey T, Fischer H, Bachmann S, Albert K, Bolm C. Silica-supported TEMPO catalysts: synthesis and application in the Anelli oxidation of alcohols. J Org Chem 2001; 66:8154-9. [PMID: 11722219 DOI: 10.1021/jo010535q] [Citation(s) in RCA: 182] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The application of silica-supported TEMPO as a recyclable catalyst in the Anelli oxidation of alcohols is reported. The catalyst is easily obtained in a one-step reductive amination procedure starting from a commercially available aminopropyl-functionalized silica. Details of the synthesis of the supported catalyst and its analysis by MAS NMR are presented. Various alcohol oxidations according to the Anelli protocol have been carried out and the stability of the applied silica-supported TEMPO has been studied.
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Affiliation(s)
- T Fey
- Institut für Organische Chemie der RWTH Aachen, Professor-Pirlet Strasse 1, D-52056 Aachen, Germany
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Adam W, Saha-Möller CR, Ganeshpure PA. Synthetic applications of nonmetal catalysts for homogeneous oxidations. Chem Rev 2001; 101:3499-548. [PMID: 11840992 DOI: 10.1021/cr000019k] [Citation(s) in RCA: 326] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Nonmetal oxidation catalysts have gained much attention in recent years. The reason for this surge in activity is 2-fold: On one hand, a number of such catalysts has become readily accessible; on the other hand, such catalysts are quite resistant toward self-oxidation and compatible under aerobic and aqueous reaction conditions. In this review, we have focused on five nonmetal catalytic systems which have attained prominence in the oxidation field in view of their efficacy and their potential for future development; stoichiometric cases have been mentioned to provide overview and scope. Such nonmetal oxidation catalysts include the alpha-halo carbonyl compounds 1, ketones 2, imines 3, iminium salts 4, and nitroxyl radicals 5. In combination with a suitable oxygen source (H2O2, KHSO5, NaOCl), these catalysts serve as precursors to the corresponding oxidants, namely, the perhydrates I, dioxiranes II, oxaziridines III, oxaziridinium ions IV, and finally oxoammonium ions V. A few of the salient features about these nonmetal, catalytic systems shall be reiterated in this summary. The first class entails the alpha-halo ketones, which catalyze the oxidation of a variety of organic substrates [figure: see text] by hydrogen peroxide as the oxygen source. The perhydrates I, formed in situ by the addition of hydrogen peroxide to the alpha-halo ketones, are quite strong electrophilic oxidants and expectedly transfer an oxygen atom to diverse nucleophilic acceptors. Thus, alpha-halo ketones have been successfully employed for catalytic epoxidation, heteroatom (S, N) oxidation, and arene oxidation. Although high diastereoselectivities have been achieved by these nonmetal catalysts, no enantioselective epoxidation and sulfoxidation have so far been reported. Consequently, it is anticipated that catalytic oxidations by perhydrates hold promise for further development, especially, and should ways be found to transfer the oxygen atom enantioselectively. The second class, namely, the dioxiranes, has been extensively used during the last two decades as a convenient oxidant in organic synthesis. These powerful and versatile oxidizing agents are readily available from the appropriate ketones by their treatment [figure: see text] with potassium monoperoxysulfate. The oxidations may be performed either under stoichiometric or catalytic conditions; the latter mode of operation is featured in this review. In this case, a variety of structurally diverse ketones have been shown to catalyze the dioxirane-mediated epoxidation of alkenes by monoperoxysulfate as the oxygen source. By employing chiral ketones, highly enantioselective (up to 99% ee) epoxidations have been developed, of which the sugar-based ketones are so far the most effective. Reports on catalytic oxidations by dioxiranes other than epoxidations are scarce; nevertheless, fructose-derived ketones have been successfully employed as catalysts for the enantioselective CH oxidation in vic diols to afford the corresponding optically active alpha-hydroxy ketones. To date, no catalytic asymmetric sulfoxidations by dioxiranes appear to have been documented in the literature, an area of catalytic dioxirane chemistry that merits attention. A third class is the imines; their reaction with hydrogen peroxide or monoperoxysulfate affords oxaziridines. These relatively weak electrophilic oxidants only manage to oxidize electron-rich substrates such as enolates, silyl enol ethers, sulfides, selenides, and amines; however, the epoxidation of alkenes has been achieved with activated oxaziridines produced from perfluorinated imines. Most of the oxidations by in-situ-generated oxaziridines have been performed stoichiometrically, with the exception of sulfoxidations. When chiral imines are used as catalysts, optically active sulfoxides are obtained in good ee values, a catalytic asymmetric oxidation by oxaziridines that merits further exploration. The fourth class is made up by the iminium ions, which with monoperoxysulfate lead to the corresponding oxaziridinium ions, structurally similar to the above oxaziridine oxidants except they possess a much more strongly electrophilic oxygen atom due to the positively charged ammonium functionality. Thus, oxaziridinium ions effectively execute besides sulfoxidation and amine oxidation the epoxidation of alkenes under catalytic conditions. As expected, chiral iminium salts catalyze asymmetric epoxidations; however, only moderate enantioselectivities have been obtained so far. Although asymmetric sulfoxidation has been achieved by using stoichiometric amounts of isolated optically active oxaziridinium salts, iminium-ion-catalyzed asymmetric sulf-oxidations have not been reported to date, which offers attractive opportunities for further work. The fifth and final class of nonmetal catalysts concerns the stable nitroxyl-radical derivatives such as TEMPO, which react with the common oxidizing agents (sodium hypochlorite, monoperoxysulfate, peracids) to generate oxoammonium ions. The latter are strong oxidants that chemoselectively and efficiently perform the CH oxidation in alcohols to produce carbonyl compounds rather than engage in the transfer of their oxygen atom to the substrate. Consequently, oxoammonium ions behave quite distinctly compared to the previous four classes of oxidants in that their catalytic activity entails formally a dehydrogenation, one of the few effective nonmetal-based catalytic transformations of alcohols to carbonyl products. Since less than 1 mol% of nitroxyl radical is required to catalyze the alcohol oxidation by the inexpensive sodium hypochlorite as primary oxidant under mild reaction conditions, this catalytic process holds much promise for future practical applications.
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Affiliation(s)
- W Adam
- Institute of Organic Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
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Merino P, Franco S, Merchan FL, Tejero T. Stereodivergent approaches to the synthesis of isoxazolidine analogues of alpha-amino acid nucleosides. Total synthesis of isoxazolidinyl deoxypolyoxin C and uracil polyoxin C. J Org Chem 2000; 65:5575-89. [PMID: 10970296 DOI: 10.1021/jo0002689] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The synthesis of new nucleoside analogues is currently of high interest. We report here full details of a study leading to the synthesis of novel isoxazolidinyl analogues of alpha-amino acid nucleosides. Three different synthetic approaches starting from L-serine have been evaluated for the construction of the isoxazolidine ring. These approaches consisted of Michael addition of N-benzylhydroxylamine to alpha,beta-unsaturated esters, nucleophilic addition of silyl ketene acetals to nitrones and 1, 3-dipolar cycloaddition of nitrones with vinyl acetate. Both Michael addition and nucleophilic addition of enolates could be carried out with stereocontrol at the newly formed stereogenic carbon. The stereocontrol observed in these reactions arises from the protecting group arrangement in the L-serine-derived substrates. Thus, whereas compounds having a diprotected nitrogen led to syn adducts, compounds having a monoprotected nitrogen gave rise to anti adducts. On the other hand, substrates having either a diprotected or monoprotected nitrogen atom led to anti adducts through the cycloaddition route. So, by choosing the appropriate route, isoxazolidinyl analogues having either syn or anti configuration with respect to the glycine unit can be prepared in enantiomerically pure form. The stereoselective synthesis of isoxazolidinyl analogues of deoxypolyoxin C and uracil polyoxin C in both D and L enantiomeric forms using these techniques has been achieved in good yields.
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Affiliation(s)
- P Merino
- Departamento de Quimica Organica, ICMA, Facultad de Ciencias, Universidad de Zaragoza, E-50009 Zaragoza, Aragon, Spain.
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