- Photooxidation of thiosaccharides mediated by sensitizers in aerobic and environmentally friendly conditions
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A series of β-d-glucopyranosyl derivates have been synthesized and evaluated in photooxidation reactions promoted by visible light and mediated by organic dyes under aerobic conditions. Among the different photocatalysts employed, tetra-O-acetyl riboflavin afforded chemoselectively the respective sulfoxides, without over-oxidation to sulfones, in good to excellent yields and short reaction times. This new methodology for the preparation of synthetically useful glycosyl sulfoxides constitutes a catalytic, efficient, economical, and environmentally friendly oxidation process not reported so far for carbohydrates.
- Traverssi, Miqueas G.,Pe?é?ory, Alicia B.,Varela, Oscar,Colomer, Juan P.
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p. 9262 - 9273
(2021/03/16)
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- Direct, stereoselective thioglycosylation enabled by an organophotoredox radical strategy
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While strategies involving a 2e- transfer pathway have dictated glycosylation development, the direct glycosylation of readily accessible glycosyl donors as radical precursors is particularly appealing because of high radical anomeric selectivity and atom- and step-economy. However, the development of the radical process has been challenging owing to notorious competing reduction, elimination and/or SN side reactions of commonly used, labile glycosyl donors. Here we introduce an organophotocatalytic strategy through which glycosyl bromides can be efficiently converted into corresponding anomeric radicals by photoredox mediated HAT catalysis without a transition metal or a directing group and achieve highly anomeric selectivity. The power of this platform has been demonstrated by the mild reaction conditions enabling the synthesis of challenging α-1,2-cis-thioglycosides, the tolerance of various functional groups and the broad substrate scope for both common pentoses and hexoses. Furthermore, this general approach is compatible with both sp2 and sp3 sulfur electrophiles and late-stage glycodiversification for a total of 50 substrates probed.
- Bi, Fangchao,Gao, Feng,Ji, Peng,Wang, Wei,Zhang, Yueteng
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p. 13079 - 13084
(2021/01/09)
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- Photochemical Functionalization of Heterocycles with EBX Reagents: C?H Alkynylation versus Deconstructive Ring Cleavage**
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The development of novel methodologies for the functionalization of saturated heterocycles is highly desirable. Herein, we report a cheap and efficient photochemical method for the C?H functionalization of saturated O-heterocycles, as well as the deconstructive ring-cleavage of S-heterocycles, employing hypervalent iodine alkynylation reagents (ethynylbenziodoxolones, EBX). This photochemical alkynylation is performed utilizing phenylglyoxylic acid as the photoinitiator, leading to the corresponding products in good to high yields, under household fluorescent light bulb irradiation. When O-heterocycles were employed, the expected α-C?H alkynylation took place. In contrast, oxidative ring-opening to form a thioalkyne and an aldehyde was observed with S-heterocycles. Preliminary mechanistic experiments are presented to give first insights into this puzzling divergent reactivity.
- Voutyritsa, Errika,Garreau, Marion,Kokotou, Maroula G.,Triandafillidi, Ierasia,Waser, Jér?me,Kokotos, Christoforos G.
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supporting information
p. 14453 - 14460
(2020/10/12)
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- Dehydrative Thioglycosylation of 1-Hydroxyl Glycosides Catalyzed by In Situ-Generated AlI3
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Thioglycosylation of 1-hydroxyl glycosides catalyzed by in situ-generated AlI3 from elemental aluminium and molecular iodine has been developed. This method provides an alternative route to access anomeric thioglycosides without the use of hazard Lewis acidic activators or per-modified activated thiol sources. The major advantages of this dehydrative procedure are environmental friendly, ease of operation, high anomeric diastereoselectivity, and mild reaction conditions.
- Weng, Shiue-Shien,Hsieh, Kun-Yi,Zeng, Zih-Jian
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p. 464 - 473
(2017/05/19)
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- Urea–hydrogen peroxide prompted the selective and controlled oxidation of thioglycosides into sulfoxides and sulfones
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A practical method for the selective and controlled oxidation of thioglycosides to corresponding glycosyl sulfoxides and sulfones is reported using urea–hydrogen peroxide (UHP). A wide range of glycosyl sulfoxides are selectively achieved using 1.5 equiv of UHP at 60 °C while corresponding sulfones are achieved using 2.5 equiv of UHP at 80 °C in acetic acid. Remarkably, oxidation susceptible olefin functional groups were found to be stable during the oxidation of sulfide.
- Singh, Adesh Kumar,Tiwari, Varsha,Mishra, Kunj Bihari,Gupta, Surabhi,Kandasamy, Jeyakumar
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supporting information
p. 1139 - 1144
(2017/06/20)
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- Remote Activation of Disarmed Thioglycosides in Latent-Active Glycosylation via Interrupted Pummerer Reaction
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S-glycosides, S-2-(2-propylthio)benzyl (SPTB) glycosides, were converted to the corresponding oxidized glycosyl donors, S-2-(2-propylsulfinyl)benzyl (SPSB) glycosides, by simple and selective oxidation. Treatment of disarmed SPSB donor and various acceptors with triflic anhydride provided the desired glycosides in good to excellent yields. Meanwhile, observation of thiosulfinate, thiosulfonate, and disulfide suggested that the leaving group was activated via an interrupted Pummerer reaction. The disarmed SPSB thioglycosyl donors could be selectively activated in the presence of various thioglycosides with remote activation mode. Finally, two natural hepatoprotective glycosides, Leonoside E and Leonuriside B, were efficiently synthesized in a convergent manner with this newly developed method.
- Xiao, Xiong,Zhao, Yueqi,Shu, Penghua,Zhao, Xiang,Liu, Yan,Sun, Jiuchang,Zhang, Qian,Zeng, Jing,Wan, Qian
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p. 13402 - 13407
(2016/10/22)
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- Solid phase synthesis of glycopeptides using Shoda's activation of unprotected carbohydrates
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An expedient and simple protocol to access S-linked glycopeptides by Fmoc SPPS using unprotected carbohydrates is reported. The utility of the method was demonstrated with the solid phase synthesis of a MUC1 fragment (20 mer) containing two glycosylation sites that were substituted with S-linked glycans. The Royal Society of Chemistry.
- Novoa, Alexandre,Barluenga, Sofia,Serba, Christelle,Winssinger, Nicolas
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supporting information
p. 7608 - 7610
(2013/09/02)
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- Towards dynamic drug design: Identification and optimization of β-galactosidase inhibitors from a dynamic hemithioacetal system
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A discovery strategy relying on the identification of fragments through resolution of a constitutional dynamic system, coupled to subsequent static ligand design and optimization, is demonstrated. The strategic design and synthesis of the best molecular fragments identified from a dynamic hemithioacetal system into static ligand structures yielded a range of β-galactosidase inhibitors. Two series of structures mimicking the hemithioacetal motif were envisaged: thioglycosides and C-glycosides. Inhibition studies provided important structural information for the two groups, and 1-thiobenzyl-b-d-galactopyranoside demonstrated the best inhibitory effects.
- Caraballo, Remi,Sakulsombat, Morakot,Ramstroem, Olof
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experimental part
p. 1600 - 1606
(2011/05/06)
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- Diastereoselective thioglycosylation of peracetylated glycosides catalyzed by in situ generated iron(III) iodide from elemental iodine and iron
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A facile in situ preparation of Fe(III) iodide from cheap, abundant elemental iodine and iron metal served as an efficient catalyst for the thioglycosylation of peracetylated glycosides with various alkyl and aryl mercaptans. Due to neighboring participation, the anomerically pure β-thioglycosides were obtained in good to high yields with exclusive diastereocontrol.
- Weng, Shiue-Shien
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supporting information; experimental part
p. 6414 - 6417
(2010/02/28)
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- Involvement of the S-aglycon in the conformational preferences of thioglucosides
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The conformational preferences of two series of alkyl β-d-thioglucopyranosides in solution were investigated by NMR and CD. The rotamer populations of the hydroxymethyl group were found to depend on the structural nature of the S-aglycon. The population of the gt rotamer increased and that of the gg rotamer decreased as the alkyl group attached to the S atom increased in size. These rotamer populations have a linear correlation with the Taft' steric parameters, the nS s(-) σC s(-) O* exo-anomeric interaction may express these rotational preferences. Comparative analysis of the hydroxymethyl populations between alkyl O- and S-glucosides revealed identical or slightly higher gt and smaller gg populations for the latter compounds.
- Sanhueza, Carlos A.,Dorta, Rosa L.,Vazquez, Jesus T.
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p. 258 - 264
(2008/09/19)
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- Microwave irradiation for accelerating the synthesis of thioglycosides
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A simple and efficient procedure for the synthesis of thioglycosides has been achieved from the reaction of glycosylisothiouronium salts with alkyl or heteroaryl halides under microwave irradiation, in much shorter times and in yields comparable with conventional methods. Copyright Taylor & Francis Group, LLC.
- El Ashry,Awad,Hamid, H. M. Abdel,Atta
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p. 2769 - 2785
(2007/10/03)
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- Highly diastereoselective thioglycosylation of functionalized peracetylated glycosides catalyzed by MoO2Cl2
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Among 18 oxometallic species, MoO2Cl2 was found to be the most reactive in catalytic thioglycosylation of O-acetylated glycosides with functionalized thiols in CH2Cl2, leading cleanly to 1,2-trans-thioglycosides with exclusive diastereocontrol. The new catalytic protocol is applicable to a monoglycoside building block and β-(1→6)-S-linked-thiodisaccharide synthesis.
- Weng, Shiue-Shien,Lin, Yow-Dzer,Chen, Chien-Tien
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p. 5633 - 5636
(2007/10/03)
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- Modified one-pot protocol for the preparation of thioglycosides from unprotected aldoses via S-glycosyl isothiouronium salts
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An efficient one-pot protocol for the direct preparation of thioglycosides starting from unprotected reducing sugars via S-glycosyl isothiouronium salts is reported. In this one-pot methodology, BF3·OEt2 has been used as a general catalyst for both per-O-acetylation of sugars and conversion of sugar per-O-acetates into S-glycosyl isothiouronium salts, which was allowed to react with alkylating agents in the presence of a base to furnish thioglycosides in excellent yield. Copyright Taylor & Francis, Inc.
- Tiwari, Pallavi,Agnihotri, Geetanjali,Misra, Anup Kumar
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p. 723 - 732
(2007/10/03)
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- Reaction of 1,2-trans-glycosyl acetates with thiourea: A new entry to 1-thiosugars
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The reaction of 1,2-trans-glycosyl acetates with thiourea under boron trifluoride etherate catalysis affording acetylated S-glycosyl isothiourea derivatives is described. The isothiourea derivatives obtained can be readily transformed into the desired 1-thiosugar derivative by reaction with triethylamine and subsequent alkylation or acylation of the in situ formed 1-thioaldose.
- Ibatullin, Farid M.,Shabalin, Konstantin A.,J?nis, Janne V.,Shavva, Alexander G.
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p. 7961 - 7964
(2007/10/03)
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- Synthesis of both possible isomers of the northwest quadrant of Altromycin B
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The synthesis of the northwest quadrant of Altromycin B is described. The preparation of the two epimers at the quaternary carbon of the 6-deoxy-C-altrose moiety in the northwest quadrant is accomplished starting from D-glucose. A key step of our synthetic sequence is the formation of the C-glycoside linkage via the Ramberg-Baecklund reaction. Two different routes are explored, which differ mainly on the timing of the conversion of glucose to altrose, either before or after the preparation of the C-glycoside. The conformation behavior of variously substituted C-altropyranoside rings is also discussed.
- Pasetto, Paolo,Franck, Richard W.
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p. 8042 - 8060
(2007/10/03)
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- A new route to exo-glycals using the Ramberg-Baecklund rearrangement
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A new route to exo-glycals 4 is described in which glycosyl sulfones 3 are subjected to the Meyers variant of the Ramberg-Baecklund rearrangement. The conversion of sulfones derived from glucose, galactose, mannose, cellobiose, and ribose into di-, tri-, and tetra-substituted alkenes is reported. Preliminary mechanistic studies of this process are also described. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
- Griffin, Frank K.,Paterson, Duncan E.,Murphy, Paul V.,Taylor, Richard J. K.
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p. 1305 - 1322
(2007/10/03)
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- Synthetic applications of Ramberg-Backlund derived exo-glycals
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Synthetic applications of the title glycals, prepared from S-glycoside dioxides using the Meyers' variant of the Ramberg-Backlund rearrangement are described. These include a formal total synthesis of a novel β-glycosidase inhibitor, and an efficient route to spirocyclic glucose derivatives. In addition, silyl methodology has been developed which allows unprotected exo- glycals to be synthesised.
- Alcaraz, Marie-Lyne,Griffin, Frank K.,Paterson, Duncan E.,Taylor, Richard J. K.
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p. 8183 - 8186
(2007/10/03)
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- Silver fluoroborate promoted sulfur alkylation of β-silyl ethyl sulfides. Selective synthesis of β-thioglycosides
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Silver (I) activation of α-glucosyl bromide in the presence of 2-trimethylsilylethyl sulfides as sulfur nucleophiles selectively provides β-thioglycosides.
- Mahadevan,Li,Fuchs
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p. 3099 - 3107
(2007/10/02)
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- Reaction of sugar thiocyanates with Grignard reagents. New synthesis of thioglycosides
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Glycosyl thiocyanates having hydroxyl groups protected with acetyl or benzoyl groups react readily at -40°C with Grignard reagents to afford the corresponding alkyl or aryl thioglycosides in good yields. Monosaccharide derivatives having the SCN grouping at other positions form under similar conditions thioethers. Axial thiocyanates do not react. Elevated temperatures induce side reactions leading to mercaptans.
- Pakulski, Zbigniew,Pierozynski, Donat,Zamojski, Aleksander
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p. 2975 - 2992
(2007/10/02)
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- SYNTHESIS OF 1-THIOGLYCOSIDES IN A CATALYTIC TWO-PHASE SYSTEM
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An improved preparation of thioglycosides involves a reaction of 1,2-cis-gluco- and galactopyranosyl bromides with thiols in a catalytic two-phase system.The reaction is considered to proceed according to SN2 mechanism.Formation of orthothioesters is favored for tetra-O-acetyl-β-D-glucopyranosyl chloride and thiophenol.
- Bogusiak, Jadwiga,Szeja, Wieslaw
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p. 293 - 298
(2007/10/02)
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