- Iodine and its interhalogen compounds: Versatile reagents in carbohydrate chemistry v. synthesis of 1,2-trans-linked 1-thioglycosides from the per-o-acetylated glycoses
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Treatment of per-O-acetylated mono- and di-saccharides with (alkyl/arylthio)trimethylsilane and iodine at ambient temperature results in the formation of the corresponding 1,2-trans-1-thioglycosides in very high yield. In the case of higher boiling thiols such as ethanethiol, the reaction can be effectively carried out in the presence of the thiol itself instead of the silylated derivative, but the reaction is not stereospecific. Moreover, in the latter reactions a portion of the starting material remains unchanged even on prolonged reaction. With β-D-glucose pentaacetate (11) as the starting material, its epimerisation occurred during the reaction and therefore the recovered starting material was of α-D-configuration. In addition, the methyl disulphide-hexamethyldisilane system has been found to serve as an effective and cheaper alternative to the expensive (methylthio)-trimethylsilane.
- Kartha, K. P. Ravindranathan,Field, Robert A.
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p. 693 - 702
(2007/10/03)
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- Synthesis of a di-, tri-, and tetra-saccharide unit of the group B streptococcal common antigen.
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Condensation of methyl 2,3-O-isopropylidene-alpha-L-rhamnopyranoside with methyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside activated by nitrosyl tetrafluoroborate gave an excellent yield of the protected disaccharide 9, which was transformed into glycosyl acceptor 11. Methyl 2,3,4,6-tetra-O-acetyl-1-thio-beta-D-galactopyranoside, obtained from D-galactose penta-acetate and methyl trimethylsilyl sulfide, under catalysis by boron trifluoride etherate, was converted into glycosyl donor 25, which was condensed with 11 under halide-ion catalysis to give the trisaccharide derivative 26. Rhamnosylation with 28 of 27, obtained by selective deprotection of 26, gave the protected tetrasaccharide 29. Deprotection of 10, 26, and 29 gave di- (2), tri- (3) and tetra-saccharide (4) methyl glycosides which form part of the group-specific polysaccharide antigen of Group B Streptococci.
- Pozsgay,Jennings
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- A NEW, STEREOSELECTIVE SYNTHESIS OF METHYL 1,2-TRANS-1-THIOGLYCOSIDES
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Per-O-acetylated glycopyranoses were converted by methylthiotrimethylsilane in the presence of boron trifluoride or trimethylsilyl trifluoromethanesulfonate to the corresponding methyl 1,2-trans-1-thioglycopyranosides in a highly stereoselective process.
- Pozsgay, Vince,Jennings, Harold J.
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p. 1375 - 1376
(2007/10/02)
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