1
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Hoard DJ, Sutar Y, Demchenko AV. Direct Synthesis of Glycosyl Chlorides from Thioglycosides. J Org Chem 2024; 89:6865-6876. [PMID: 38669055 DOI: 10.1021/acs.joc.4c00244] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/18/2024]
Abstract
Reported herein is a new method for the direct synthesis of glycosyl chlorides from thioglycosides using sulfuryl chloride at rt. A variety of thioglycosides and thioimidates could be used as substrates. Both acid- and base-sensitive protecting groups were found compatible with these reaction conditions. Preliminary investigation of the reaction mechanism indicates chlorination of the leaving group at the anomeric sulfur as the key step of the reaction.
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Affiliation(s)
- Daniel J Hoard
- Department of Chemistry, Saint Louis University, 3501 Laclede Ave, St. Louis, Missouri 63103, United States
| | - Yogesh Sutar
- Department of Chemistry, Saint Louis University, 3501 Laclede Ave, St. Louis, Missouri 63103, United States
| | - Alexei V Demchenko
- Department of Chemistry, Saint Louis University, 3501 Laclede Ave, St. Louis, Missouri 63103, United States
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2
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Forsythe N, Liu L, Kashiwagi GA, Demchenko AV. Activation of thioglycosides under mild alkylation conditions. Carbohydr Res 2023; 531:108872. [PMID: 37348387 PMCID: PMC10528260 DOI: 10.1016/j.carres.2023.108872] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2023] [Revised: 06/08/2023] [Accepted: 06/09/2023] [Indexed: 06/24/2023]
Abstract
Reported herein is the development of a novel method for the activation of thioglycosides and thioimidates using benzyl trichloroacetimidate in the presence of catalytic triflic acid. Excellent yields have been achieved with reactive substrates, whereas efficiency of reactions with unreactive glycosyl donors and/or acceptors was modest.
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Affiliation(s)
- Nicholas Forsythe
- Department of Chemistry, Saint Louis University, 3501 Laclede Ave, St. Louis, Missouri, 63103, USA
| | - Leah Liu
- Department of Chemistry, Saint Louis University, 3501 Laclede Ave, St. Louis, Missouri, 63103, USA
| | - Gustavo A Kashiwagi
- Department of Chemistry, Saint Louis University, 3501 Laclede Ave, St. Louis, Missouri, 63103, USA
| | - Alexei V Demchenko
- Department of Chemistry, Saint Louis University, 3501 Laclede Ave, St. Louis, Missouri, 63103, USA.
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3
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Escopy S, Singh Y, Stine KJ, Demchenko AV. HPLC‐Based Automated Synthesis of Glycans in Solution. Chemistry 2022; 28:e202201180. [DOI: 10.1002/chem.202201180] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2022] [Indexed: 11/09/2022]
Affiliation(s)
- Samira Escopy
- Department of Chemistry and Biochemistry University of Missouri - St. Louis One University Boulevard St. Louis Missouri 63121 USA
- Department of Chemistry Saint Louis University 3501 Laclede Ave St. Louis Missouri 63103 USA
| | - Yashapal Singh
- Department of Chemistry and Biochemistry University of Missouri - St. Louis One University Boulevard St. Louis Missouri 63121 USA
| | - Keith J. Stine
- Department of Chemistry and Biochemistry University of Missouri - St. Louis One University Boulevard St. Louis Missouri 63121 USA
| | - Alexei V. Demchenko
- Department of Chemistry and Biochemistry University of Missouri - St. Louis One University Boulevard St. Louis Missouri 63121 USA
- Department of Chemistry Saint Louis University 3501 Laclede Ave St. Louis Missouri 63103 USA
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4
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Javed, Khanam A, Mandal PK. Glycosyl 3-Phenyl-4-pentenoates as Versatile Glycosyl Donors: Reactivity and Their Application in One-Pot Oligosaccharide Assemblies. J Org Chem 2022; 87:6710-6729. [PMID: 35522927 DOI: 10.1021/acs.joc.2c00404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Both glycoconjugates and oligosaccharides are important biomolecules having significant roles in several biological processes, and a new strategy for their synthesis is crucial. Here, we report a versatile N-iodosuccinimide/trimethylsilyl triflate (NIS/TMSOTf) promoted glycosidation approach with shelf-stable 3-phenyl-4-pentenoate glycosyl as a donor for the efficient synthesis of O/C-glycosides with free alcohols, silylated alcohols, and C-type nucleophile acceptors in good to excellent yields. The mild activation conditions and outstanding reactivity of phenyl substituted pentenoate donors analogous to 4-pentenoate glycosyl donors enhance their applicability to various one-pot strategies for the synthesis of oligosaccharides, such as single-catalyst one-pot and acceptor reactivity-controlled one-pot strategies.
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Affiliation(s)
- Javed
- Medicinal and Process Chemistry Division, CSIR─Central Drug Research Institute, BS-10/1, Sector 10, Jankipuram Extension, Sitapur Road, P.O. Box 173, Lucknow 226031, India
| | - Ariza Khanam
- Medicinal and Process Chemistry Division, CSIR─Central Drug Research Institute, BS-10/1, Sector 10, Jankipuram Extension, Sitapur Road, P.O. Box 173, Lucknow 226031, India
| | - Pintu Kumar Mandal
- Medicinal and Process Chemistry Division, CSIR─Central Drug Research Institute, BS-10/1, Sector 10, Jankipuram Extension, Sitapur Road, P.O. Box 173, Lucknow 226031, India.,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
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5
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Chhabra M, Wimmer N, He QQ, Ferro V. Development of Improved Synthetic Routes to Pixatimod (PG545), a Sulfated Oligosaccharide-Steroid Conjugate. Bioconjug Chem 2021; 32:2420-2431. [PMID: 34652896 DOI: 10.1021/acs.bioconjchem.1c00453] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The heparan sulfate (HS) mimetic pixatimod (PG545) is a highly potent inhibitor of angiogenesis, tumor growth, and metastasis currently in clinical trials for cancer. PG545 has also demonstrated potent antiviral activity against numerous HS-dependent viruses, including SARS-CoV-2, and shows promise as an antiviral drug for the treatment of COVID-19. Structurally, PG545 consists of a fully sulfated tetrasaccharide conjugated to the steroid 5α-cholestan-3β-ol. The reported synthesis of PG545 suffers from a low yield and poor selectivity in the critical glycosylation step. Given its clinical importance, new efficient routes for the synthesis of PG545 and analogues were developed. Particular attention was given to improving the key glycosylation step by using more stable protecting groups and optimized glycosyl donors.
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Affiliation(s)
- Mohit Chhabra
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.,Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Norbert Wimmer
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.,Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Qi Qi He
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.,Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Vito Ferro
- School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.,Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland 4072, Australia
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6
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Steber HB, Singh Y, Demchenko AV. Bismuth(iii) triflate as a novel and efficient activator for glycosyl halides. Org Biomol Chem 2021; 19:3220-3233. [PMID: 33885577 PMCID: PMC8112625 DOI: 10.1039/d1ob00093d] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Presented herein is the discovery that bismuth(iii) trifluoromethanesulfonate (Bi(OTf)3) is an effective catalyst for the activation of glycosyl bromides and glycosyl chlorides. The key objective for the development of this methodology is to employ only one promoter in the lowest possible amount and to avoid using any additive/co-catalyst/acid scavenger except molecular sieves. Bi(OTf)3 works well in promoting the glycosidation of differentially protected glucosyl, galactosyl, and mannosyl halides with many classes of glycosyl acceptors. Most reactions complete within 1 h in the presence of only 35% of green and light-stable Bi(OTf)3 catalyst.
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Affiliation(s)
- Hayley B Steber
- Department of Chemistry and Biochemistry, University of Missouri - St Louis, One University Boulevard, St Louis, Missouri 63121, USA.
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7
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See NW, Wimmer N, Krenske EH, Ferro V. A Substituent‐Directed Strategy for the Selective Synthesis of L‐Hexoses: An Expeditious Route to L‐Idose. European J Org Chem 2021. [DOI: 10.1002/ejoc.202100042] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Nicholas W. See
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane Queensland 4072 Australia
| | - Norbert Wimmer
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane Queensland 4072 Australia
| | - Elizabeth H. Krenske
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane Queensland 4072 Australia
| | - Vito Ferro
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane Queensland 4072 Australia
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8
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Escopy S, Singh Y, Demchenko AV. Palladium(II)-assisted activation of thioglycosides. Org Biomol Chem 2021; 19:2044-2054. [PMID: 33599667 DOI: 10.1039/d1ob00004g] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Described herein is the first example of glycosidation of thioglycosides in the presence of palladium(ii) bromide. While the activation with PdBr2 alone was proven feasible, higher yields and cleaner reactions were achieved when these glycosylations were performed in the presence of propargyl bromide as an additive. Preliminary mechanistic studies suggest that propargyl bromide assists the reaction by creating an ionizing complex, which accelerates the leaving group departure. A variety of thioglycoside donors in reactions with different glycosyl acceptors were investigated to determine the initial scope of this new reaction. Selective and chemoselective activation of thioglycosides over other leaving groups has also been explored.
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Affiliation(s)
- Samira Escopy
- Department of Chemistry and Biochemistry, University of Missouri - St. Louis, One University Boulevard, St. Louis, MO 63121, USA.
| | - Yashapal Singh
- Department of Chemistry and Biochemistry, University of Missouri - St. Louis, One University Boulevard, St. Louis, MO 63121, USA.
| | - Alexei V Demchenko
- Department of Chemistry and Biochemistry, University of Missouri - St. Louis, One University Boulevard, St. Louis, MO 63121, USA.
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9
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Rönnols J, Engström O, Schnupf U, Säwén E, Brady JW, Widmalm G. Inter-residual Hydrogen Bonding in Carbohydrates Unraveled by NMR Spectroscopy and Molecular Dynamics Simulations. Chembiochem 2019; 20:2519-2528. [PMID: 31066963 DOI: 10.1002/cbic.201900301] [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: 05/07/2019] [Indexed: 12/15/2022]
Abstract
Carbohydrates, also known as glycans in biological systems, are omnipresent in nature where they as glycoconjugates occur as oligo- and polysaccharides linked to lipids and proteins. Their three-dimensional structure is defined by two or three torsion angles at each glycosidic linkage. In addition, transglycosidic hydrogen bonding between sugar residues may be important. Herein we investigate the presence of these inter-residue interactions by NMR spectroscopy in D2 O/[D6 ]DMSO (70:30) or D2 O and by molecular dynamics (MD) simulations with explicit water as solvent for disaccharides with structural elements α-d-Manp-(1→2)-d-Manp, β-d-GlcpNAc-(1→2)-d-Manp, and α-d-Glcp-(1→4)-β-d-Glcp, all of which have been suggested to exhibit inter-residue hydrogen bonding. For the disaccharide β-d-GlcpNAc-(1→2)-β-d-Manp-OMe, the large extent of O5'⋅⋅⋅HO3 hydrogen bonding as seen from the MD simulation is implicitly supported by the 1 H NMR chemical shift and 3 JHO3,H3 value of the hydroxy proton. In the case of α-d-Glcp-(1→4)-β-d-Glcp-OMe, the existence of a transglycosidic hydrogen bond O2'⋅⋅⋅HO3 was proven by the presence of a cross-peak in 1 H,13 C HSQC-TOCSY experiments as a result of direct TOCSY transfer between HO3 of the reducing end residue and H2' (detected at C2') of the terminal residue. The occurrence of inter-residue hydrogen bonding, albeit transient, is judged important for the stabilization of three-dimensional structures, which may be essential in maintaining a conformational state for carbohydrate-protein interactions of glycans to take place in biologically important environments.
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Affiliation(s)
- Jerk Rönnols
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 106 91, Stockholm, Sweden
| | - Olof Engström
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 106 91, Stockholm, Sweden
| | - Udo Schnupf
- Department of Chemistry and Biochemistry, Bradley University, Peoria, IL, 61625, USA
| | - Elin Säwén
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 106 91, Stockholm, Sweden
| | - John W Brady
- Department of Food Science, Cornell University, Ithaca, NY, 14853, USA
| | - Göran Widmalm
- Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 106 91, Stockholm, Sweden
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10
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Pistorio SG, Geringer SA, Stine KJ, Demchenko AV. Manual and Automated Syntheses of the N-Linked Glycoprotein Core Glycans. J Org Chem 2019; 84:6576-6588. [PMID: 31066275 DOI: 10.1021/acs.joc.8b03056] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Presented herein are two complementary approaches to the synthesis of the core N-glycan pentasaccharide. The first, a traditional manual approach in solution, makes use of the H-bond-mediated aglycone delivery method for the highly diastereoselective introduction of the β-mannosidic linkage at room temperature. The synthesis of the core pentasaccharide was also accomplished using an high-performance liquid chromatography-assisted automated approach. The overall assembly was swift (8 h) and efficient (31%).
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Affiliation(s)
- Salvatore G Pistorio
- Department of Chemistry and Biochemistry , University of Missouri-St. Louis One University Boulevard , St. Louis , Missouri 63121 , United States
| | - Scott A Geringer
- Department of Chemistry and Biochemistry , University of Missouri-St. Louis One University Boulevard , St. Louis , Missouri 63121 , United States
| | - Keith J Stine
- Department of Chemistry and Biochemistry , University of Missouri-St. Louis One University Boulevard , St. Louis , Missouri 63121 , United States
| | - Alexei V Demchenko
- Department of Chemistry and Biochemistry , University of Missouri-St. Louis One University Boulevard , St. Louis , Missouri 63121 , United States
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11
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Brekalo J, Despras G, Lindhorst TK. Pseudoenantiomeric glycoclusters: synthesis and testing of heterobivalency in carbohydrate–protein interactions. Org Biomol Chem 2019; 17:5929-5942. [DOI: 10.1039/c9ob00124g] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Multivalent carbohydrate–protein interactions are key events in cell recognition processes and have been extensively studied by means of synthetic glycomimetics.
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Affiliation(s)
- Jasna Brekalo
- Christiana Albertina University of Kiel
- Otto Diels Institute of Organic Chemistry
- Kiel
- Germany
| | - Guillaume Despras
- Christiana Albertina University of Kiel
- Otto Diels Institute of Organic Chemistry
- Kiel
- Germany
| | - Thisbe K. Lindhorst
- Christiana Albertina University of Kiel
- Otto Diels Institute of Organic Chemistry
- Kiel
- Germany
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12
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Wen L, Edmunds G, Gibbons C, Zhang J, Gadi MR, Zhu H, Fang J, Liu X, Kong Y, Wang PG. Toward Automated Enzymatic Synthesis of Oligosaccharides. Chem Rev 2018; 118:8151-8187. [DOI: 10.1021/acs.chemrev.8b00066] [Citation(s) in RCA: 112] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Liuqing Wen
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30303, United States
| | - Garrett Edmunds
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30303, United States
| | - Christopher Gibbons
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30303, United States
| | - Jiabin Zhang
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30303, United States
| | - Madhusudhan Reddy Gadi
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30303, United States
| | - Hailiang Zhu
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30303, United States
| | - Junqiang Fang
- National Glycoengineering Research Center and State Key Laboratory of Microbial Technology, Shandong University, Jinan 250100, China
| | - Xianwei Liu
- National Glycoengineering Research Center and State Key Laboratory of Microbial Technology, Shandong University, Jinan 250100, China
| | - Yun Kong
- National Glycoengineering Research Center and State Key Laboratory of Microbial Technology, Shandong University, Jinan 250100, China
| | - Peng George Wang
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30303, United States
- National Glycoengineering Research Center and State Key Laboratory of Microbial Technology, Shandong University, Jinan 250100, China
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Abstract
Previously, we communicated 3,3-difluoroxindole (HOFox)-mediated glycosylations wherein 3,3-difluoro-3H-indol-2-yl (OFox) imidates were found to be key intermediates. Both the in situ synthesis from the corresponding glycosyl bromides and activation of the OFox imidates could be conducted in a regenerative fashion. Herein, we extend this study to the synthesis of various glycosidic linkages using different sugar series. The main outcome of this study relates to enhanced yields and/or reduced reaction times of glycosylations. The effect of HOFox-mediated reactions is particularly pronounced in case of unreactive glycosyl donors and/or glycosyl acceptors. A multistep regenerative synthesis of oligosaccharides is also reported.
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Affiliation(s)
- Yashapal Singh
- Department of Chemistry and Biochemistry, University of Missouri—St. Louis, One University Boulevard, St. Louis, Missouri 63121, United States
| | - Tinghua Wang
- Department of Chemistry and Biochemistry, University of Missouri—St. Louis, One University Boulevard, St. Louis, Missouri 63121, United States
| | - Scott A. Geringer
- Department of Chemistry and Biochemistry, University of Missouri—St. Louis, One University Boulevard, St. Louis, Missouri 63121, United States
| | - Keith J. Stine
- Department of Chemistry and Biochemistry, University of Missouri—St. Louis, One University Boulevard, St. Louis, Missouri 63121, United States
| | - Alexei V. Demchenko
- Department of Chemistry and Biochemistry, University of Missouri—St. Louis, One University Boulevard, St. Louis, Missouri 63121, United States
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14
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Daikoku S, Pendrill R, Kanie Y, Ito Y, Widmalm G, Kanie O. Synthesis and structural investigation of a series of mannose-containing oligosaccharides using mass spectrometry. Org Biomol Chem 2018; 16:228-238. [PMID: 29234770 DOI: 10.1039/c7ob02723k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A series of compounds associated with naturally occurring and biologically relevant glycans consisting of α-mannosides were prepared and analyzed using collision-induced dissociation (CID), energy-resolved mass spectrometry (ERMS), and 1H nuclear magnetic resonance spectroscopy. The CID experiments of sodiated species of disaccharides and ERMS experiments revealed that the order of stability of mannosyl linkages was as follows: 6-linked > 4-linked ≧ 2-linked > 3-linked mannosyl residues. Analysis of linear trisaccharides revealed that the order observed in disaccharides could be applied to higher glycans. A branched trisaccharide showed a distinct dissociation pattern with two constituting disaccharide ions. The estimation of the content of this ion mixture was possible using the disaccharide spectra. The hydrolysis of mannose linkages at 3- and 6-positions in the branched trisaccharide revealed that the 3-linkage was cleaved twice as fast as the 6-linkage. It was observed that the solution-phase hydrolysis and gas-phase dissociation have similar energetics.
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Affiliation(s)
- S Daikoku
- Department of Applied Biochemistry, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan.
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15
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Practical synthesis of latent disarmed S -2-(2-propylthio)benzyl glycosides for interrupted Pummerer reaction mediated glycosylation. Tetrahedron Lett 2017. [DOI: 10.1016/j.tetlet.2017.05.014] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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16
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Lian G, Zhang X, Yu B. Thioglycosides in Carbohydrate Research. Carbohydr Res 2015; 403:13-22. [DOI: 10.1016/j.carres.2014.06.009] [Citation(s) in RCA: 143] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2014] [Revised: 05/29/2014] [Accepted: 06/10/2014] [Indexed: 11/30/2022]
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17
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Kumar V, Taxak N, Jangir R, Bharatam PV, Kartha KPR. In(III) triflate-mediated solvent-free synthesis and activation of thioglycosides by ball milling and structural analysis of long chain alkyl thioglycosides by TEM and quantum chemical methods. J Org Chem 2014; 79:3427-39. [PMID: 24669760 DOI: 10.1021/jo5001753] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Conventional solution-phase synthesis of thioglycosides from glycosyl acetates and thiols in the presence of In(III) triflate as reported for benzyl thioglucoside failed when applied to the synthesis of phenolic and alkyl thioglycosides. But, it was achieved in high efficiency and diastereospecificity with ease by solvent-free grinding in a ball mill. The acetates in turn were also obtained by the homogenization of free sugars with stoichiometric amounts of acetic anhydride and catalytic In(OTf)3 in the mill as neat products. Per-O-benzylated thioglycosides on grinding with an acceptor sugar in the presence of In(OTf)3 yield the corresponding O-glycosides efficiently. The latter in the case of a difficult secondary alcohol was nearly exclusive (>98%) in 1,2-cis-selectivity. In contrast, the conventional methods for this purpose require use of a coreagent such as NIS along with the Lewis acid to help generate the electrophilic species that actually is responsible for the activation of the thioglycoside donor in situ. The distinctly different self-assembling features of the peracetylated octadecyl 1-thio-α- and β-D-galactopyranosides observed by TEM could be rationalized by molecular modeling.
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Affiliation(s)
- Vajinder Kumar
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research , S.A.S. Nagar, Punjab 160062, India
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