- Glycosyl Vinylogous Carbonates as Glycosyl Donors by Metal-Free Activation
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Synthesis of glycoconjugates employs a glycosylation reaction wherein an electrophile and a nucleophile known as a glycosyl donor and an aglycon, respectively, are involved. Glycosyl donors often contain a leaving group at the anomeric carbon that upon reaction with activator(s) results in a highly reactive electrophilic species reported as an oxycarbenium ion contact pair that will then be attacked by the aglycon. Therefore, identification of the correct glycosyl donor and activation protocol is essential for the synthesis of all glycoconjugates. Recently identified [Au]/[Ag]-catalyzed activation of ethynylcyclohexyl glycosyl carbonates is one such versatile method for the synthesis of glycosides, oligosaccharides, and glycoconjugates. In this work, stable glycosyl vinylogous carbonates were identified to undergo glycosidation in the presence of a sub-stoichiometric quantity of TfOH. The reaction is fast and suitable for donors containing both C2-ethers and C2-esters. Donors positioned with C2-ethers resulted in anomeric mixtures with greater selectivity toward 1,2-cis glycosides, whereas those with C2-esters gave 1,2-trans selective glycosides. The versatility of the method is demonstrated by conducting the glycosylation with more than 25 substrates. Furthermore, the utility of the glycosyl vinylogous carbonate donors is demonstrated with the successful synthesis of the branched pentaarabinofuranoside moiety of the Mycobacterium tuberculosis cell wall.
- Kasdekar, Niteshlal,Walke, Gulab,Deshpande, Kshitij,Hotha, Srinivas
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p. 5472 - 5484
(2022/04/28)
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- Anti-tick-borne encephalitis virus activity of novel uridine glycoconjugates containing amide or/and 1,2,3-triazole moiety in the linker structure
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Tick-borne encephalitis virus (TBEV) transmitted by ticks is a pathogen of great medical importance. As still no effective antiviral treatment is available, in the present study, a series of uridine glycoconjugates containing amide or/and 1,2,3-triazole moiety in the linker structure was synthesized and evaluated for the antiviral activity against two strains of TBEV: a highly virulent Hypr strain and less virulent Neudoerfl strain, using standardized previously in vitro assays. Our data have shown that four compounds from the series (18–21) possess strong activity against both TBEV strains. The half maximal inhibitory concentration (IC50) values of compounds 18–21 were between 15.1 and 3.7 μM depending on the virus strain, which along with low cytotoxicity resulted in high values of the selectivity index (SI). The obtained results suggest that these compounds may be promising candidates for further development of new therapies against flaviviruses.
- Brzuska, Gabriela,Pastuch-Gawolek, Gabriela,Krawczyk, Monika,Szewczyk, Boguslaw,Krol, Ewelina
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- Chemo-selective Rh-catalysed hydrogenation of azides into amines
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Rh/Al2O3 can be used as an effective chemo-selective reductive catalyst that combines the mild conditions of catalytic hydrogenation with high selectivity for azide moieties in the presence of other hydrogenolysis labile groups such as benzyl and benzyloxycarbonyl functionalities. The practicality of this strategy is exemplified with a range of azide-containing carbohydrate and amino acid derivatives.
- Galan, M. Carmen,Ghirardello, Mattia,Ledru, Helene,Sau, Abhijit
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supporting information
(2020/02/18)
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- Gold(III)-Catalyzed Glycosylation using Phenylpropiolate Glycosides: Phenylpropiolic Acid, An Easily Separable and Reusable Leaving Group
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An efficient and operationally simple gold(III)-catalyzed glycosylation protocol was developed using newly synthesized benchtop stable phenylpropiolate glycosyl (PPG) donors. Gold(III)-catalyzed activation of PPGs proceeds well with various carbohydrate a
- Shaw, Mukta,Thakur, Rima,Kumar, Amit
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p. 589 - 605
(2019/01/14)
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- Nucleofuge Generating Glycosidations by the Remote Activation of Hydroxybenzotriazolyl Glycosides
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Hydroxybenzotriazole is routinely used in peptide chemistry for reducing racemization due to the increased reactivity. In this article, very stable hydroxybenzotriazolyl glucosides were identified to undergo glycosidation. The reaction was hypothesized to go through the remote activation by the Tf2O at the N3-site of HOBt followed by the extrusion of the oxocarbenium ion that was attacked by the glycosyl acceptor. Further, equilibration of the zwitterionic benzotriazolyl species makes the leaving group noncompetitive and generates the nucleofuge that has been reconverted to the glycosyl donor. The reaction is mild, high yielding, fast and suitable for donors containing both C2-ethers and C2-esters as well. The regenerative-donor glycosidation strategy is promising as it enables us to regenerate the glycosyl donor for further utilization. The utility of the methodology for the oligosaccharide synthesis was demonstrated by the successful synthesis of the branched pentamannan core of the HIV1-gp120 complex.
- Neralkar, Mahesh,Mishra, Bijoyananda,Hotha, Srinivas
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p. 11494 - 11504
(2017/11/10)
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- Traceless Staudinger ligation of glycosyl azides with triaryl phosphines: Stereoselective synthesis of glycosyl amides
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α-Glycosyl amides can be synthesized from the corresponding O-benzyl-α-glycosyl azides using a traceless Staudinger ligation with diphenylphosphanyl-phenyl esters 4. All the phosphines employed and their phenol precursors are stable to air at 4 °C for months. Fast intramolecular trapping of the reduction intermediates results in the direct formation of the amide link, which, in turn, prevents epimerisation and allows retention of configuration at the anomeric carbon. Yields and α-selectivity are high when the reaction is performed in polar aprotic solvents. Removal of the benzyl ether protecting groups is achieved by catalytic hydrogenation. α-Glycosyl amides represent a class of virtually unexplored nonhydrolyzable monosaccharide derivatives that may find a useful application as sugar mimics. Conformational studies by NMR spectroscopy confirm that deprotected α-glycosyl amides in the gluco, galacto, and fuco series retain the normal pyranose conformation of the monosaccharide. The reaction of phosphines 4 with tetra-O-acetyl-glycosyl azides is nonstereoconservative, and β-glycosyl amides are obtained in good yields and with complete stereoselectivity starting from both α and β azides.
- Bianchi, Aldo,Bernardi, Anna
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p. 4565 - 4577
(2007/10/03)
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- Azide and Cyanide Displacements via Hypervalent Silicate Intermediates
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Hypervalent azido- and cyanosilicate derivatives, prepared in situ by the reaction of trimethylsilyl azide or trimethylsilyl cyanide, respectively, with tetrabutylammonium fluoride, are effective sources of nucleophilic azide or cyanide. Primary and secondary alkyl halides and sulfonates undergo rapid and efficient azide or cyanide displacement in the absence of phase transfer catalysts with the silicate derivatives. Application of these reagents to the stereoselective synthesis of glycosyl azide derivatives is reported.
- Soli, Eric D.,Manoso, Amy S.,Patterson, Michael C.,DeShong, Philip,Favor, David A.,Hirschmann, Ralph,Smith III, Amos B.
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p. 3171 - 3177
(2007/10/03)
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- Process for the preparation of azide derivatives
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A process for the preparation of azide derivatives useful as drugs, perfumes or intermediates of dyes by reacting an alcohol derivative with di-p-nitrophenyl phosphorazidate in the presence of 1,8-diazabicyclo[5.4.0]-7-undecene.
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- Efficient method for the one-pot azidation of alcohols using bis(p-nitrophenyl) phosphorazidate
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The direct stereoselective conversion of various alcohols and hexopyranoses into the corresponding alkyl azides and glycosyl azides, respectively, is efficiently accomplished by using bis(p-nitrophenyl) phosphorazidate and DBU.
- Mizuno, Masanori,Shioiri, Takayuki
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p. 2165 - 2166
(2007/10/03)
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- Anionic Additions to Glycosyl Iodides: Highly Stereoselective Syntheses of β C-, N-, and O-Glycosides
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Classically, glycosyl halides are activated as glycosyl donors by metal chelation under KoenigsKnorr or Helferich conditions. These reactions often proceed through oxonium formation, and the stereochemical outcome is dictated by the anorneric effect and/or the nature of the protecting group on the C2 hydroxyl. Alternatively, glycosyl halides may undergo direct displacement of the halide by an incoming nucleophile in an SN2 mechanism. The latter reaction is far less common, and before this study it was primarily performed with glycosyl bromides. Having recently shown that both α and βglycosyl iodides could be efficiently generated, we embarked upon an investigation of nucleophilic additions to glycosyl iodides. The studies reported herein show that additions of stabilized anions to α-glycosyl iodides proceed with inversion of stereochemistry to give β-glycosides, even in the absence of a C2 participatory group. Glucosyl, galactosyl, and mannosyl iodides were studied, and the combined results indicate that the reactivity of 2,3,4,6-tetra-O-benzyl-α-D-galactosyl iodide > 2,3,4,6-tetra-O-benzyl-α-D-glucosyl iodide > 2,3,4,6-tetra-O-benzyl-α-D-mannosyl iodide. Both the glucosy] and galactosyl iodides are susceptible to E-2 elimination when treated with highly basic anions. In contrast, the mannosyl iodide undergoes substitution to give the 1,2 cis configuration. The overall sequence involves reaction of an anorneric acetate with trimethylsilyl iodide with in vacua removal of the resulting trimethylsilyl acetate. The iodide is then treated with a nucleophile without further characterization. A variety of nucleophiles were stereoselectively added to the glycosyl halides providing β-, C-, N-, and O-glycosides.
- Gervay, Jacquelyn,Hadd, Michael J.
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p. 6961 - 6967
(2007/10/03)
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- An efficient method for converting alcohols to azides with 2,4,4,6-tetrabromo-2,5-cyclohexadienone/PPh3/Zn(N3)2·Py
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Treatment of the salt generated from 2,4,4,6-tetrabromo-2,5-cyclohexadienone and PPh3 in a mixed solvent of CH3CN/toluene with primary and secondary alcohols in the presence of Zn(N3)2·Py led to azides in excellent yields with inversion of configuration. Addition of hexamethylphosphorictriamide considerably accelerated the reaction.
- Saito, Akiko,Saito, Kazumi,Tanaka, Akira,Oritani, Takayuki
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p. 3955 - 3958
(2007/10/03)
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- The Use of Tetramethylguanidinium Azide in Non-halogenated Solvents Avoids Potential Explosion Hazards
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Tetramethylguanidinium azide was used in the quantitative conversion of glycosyl halides 1 - 5 to the corresponding glycosyl azides 10 -14.The stereoselective reactions occurred with complete inversion at the anomeric centers.The titled reagent was also employed in the selective synthesis of pseudoglycosyl azide 16 and two steroidal azides 17 and 18.All reactions were carried out in nonhalogenated solvents to avoid potential explosion hazards.
- Li, C.,Shih, Tzenge-Lien,Jeong, Jae Uk,Arasappan, Ashok,Fuchs, P. L.
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p. 2645 - 2646
(2007/10/02)
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- Generation of α-D-Glucopyranosylacetonitrilium Ions. Concerning the Reverse Anomeric Effect
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Reaction of the α- and β-anomers of the pent-4-enyl D-glucopyranoside (10) with N-bromosuccinimide in dry acetonitrile generated stereospecifically the α-D-glucopyranosylacetonitrilium ion (5α), which reacts in situ with 2-chlorobenzoic acid to afford the α-imide (8α).The result is in contrast to that predicted by the reverse anomeric effect and previous work on trapping carbohydrate acetonitrilium ions with 2-chlorobenzoic acid.The unusually large J12 7.3 Hz for 1-H of (8α) is rationalised by a substantial flattening of the pyranose ring at C-1 and C-2.Molecular dynamic studies on the model α-imide (12) support a flattened 4C1 conformation.Treatment of imide (8α) with sodium methoxide leads to the α-2-chlorobenzamide (9α), which was substantiated by intependent synthesis of the β-2-chlorobenzamide (9β).
- Ratcliffe, Andrew J.,Fraser-Reid, Bert
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p. 747 - 750
(2007/10/02)
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