One-pot synthesis of per-O-acetylated thioglycosides from unprotected reducing sugars (original) (raw)
Related papers
The Journal of Organic Chemistry, 2004
Solvent-free per-O-acetylation of sugars with stoichiometric acetic anhydride and catalytic iodine proceeds in high yield (90-99%) to give exclusively pyranose products as anomeric mixtures. Without workup, subsequent anomeric substitution employing iodine in the presence of hexamethyldisilane (i.e., TMS-I generated in situ) gives the corresponding glycosyl iodides in 75-95% isolated yield. Alternatively, and without workup, further treatment with dimethyl disulfide or thiol (ethanethiol or thiocresol) gives anomerically pure thioglycosides in more than 75% overall yield.
Benzoylated ethyl 1-thioglycosides: direct preparation from per-O-benzoylated sugars
Carbohydrate Research, 2012
D-Glucose, lactose, maltose, and melibiose were benzoylated with Bz 2 O-Et 3 N reagent to give fully benzoylated β products. Under the same conditions, D-mannose produced a mixture where the β-benzoate predominated. Treatment of the foregoing compounds with EtSH at slightly elevated temperature (50-60 °C) in the presence of BF 3 •Et 2 O as a promoter gave the corresponding ethyl 1-thio glycosides in high yields. The α-products predominated in all cases in the anomeric mixtures formed. Individual products of all reactions were isolated by chromatography, they were obtained in analytically pure state, and were fully characterized by 1 H and 13 C NMR data and physical constants.
Synthesis of Thioglycosides by Tetrathiomolybdate-Mediated Michael Additions of Masked Thiolates
European Journal of Organic Chemistry, 2004
An efficient one-pot methodology for the synthesis of thioglycosides in excellent yields under neutral conditions through the use of benzyltriethylammonium tetrathiomolybdate [(BnNEt 3 ) 2 MoS 4 ; 1] as a sulfur-transfer reagent has been developed. The reagent 1 reacts with sugar halides to give sugar disulfides, which then undergo reductive cleavage in situ to provide the corresponding thiolates, followed by Michael addition to give the corresponding thioglycosides. most commonly used methods include the use of isothiourea derivatives of sugars (in turn derived from the glycosyl halides and thiourea) as precursors, treatment of glycosyl halides with thiolate anions, or the reaction between a 1thioglycopyranose and an alkyl halide. Other methods are based on Lewis acid catalyzed glycosylation of thiols. By this approach, thioglycosides have been prepared by starting from 1,2-trans-glycosyl esters, trichloroacetimid- [a] Further, the utility of this one-pot reaction in aqueous medium has been exemplified through the use of ammonium tetrathiomolybdate [(NH 4 ) 2 MoS 4 ; 2]. The application of this methodology has been extended to the synthesis of a variety of thiosugar analogues with excellent diastereoselectivity through inter-and intramolecular reactions.
Efficient synthesis of thioglycosides via a Mitsunobu condensation
Tetrahedron Letters, 1999
Thioglycosides were synthesised from 1-thiosugars and a series of alcohols under Mitsunobu conditions using 1, l'-(azodicarbonyl)dipiperidine and trimethylphosphine. The conditions were found to be compatible with a wide range of functionalities and protecting groups.
Tetrahedron: Asymmetry, 1994
Mild and stereoselective arylthio glycoside syntheses were accomplished by inversion of configuration of glycosyl halides under phase transfer catalyzed conditions. Under such conditions, aryl a-thiosialosides having electron donating and withdrawing substituents were evaluated as active and latent thioglycosyl donors. A sialyl-cc-(2+6)-galactoside was prepared in good yield using the above strategy. Sialic acids constitute a family of about 30 derivatives of neursminic acid, the most ubiquitous member of which being a nine carbon amino sugar called N-acetylneuraminic acid.' In most cases, sialic acids occupy the penultimate non-reducing end of glycolipids and glycoproteins. Their involvement in a wide number of biological phenomena and their receptor binding properties toward human influenza virus hemagglutinin (HA) have been well docurnented.2 Recent interests for the synthesis of multivalent influenza virus HA inhibitors, 3.4 together with the rationale design of suitable cc-stereoselective sialosyl donors in blcckwise oligosaccharide synthesis prompted widespread resertrch activities toward this family of carbohydrate derivatives5 Hasegawa and his co-workers have previously demonstrated the usefulness of anomeric mixtures of peracetylated methyl and phenyl 2-thio-a@-sialosides as stereoselective thioglycosyl donors in complex sialyloligosacchtide syntheses.6 These observations and the fact that human influenza A and B viruses also possess, beside their HA properties, a-sialidase (neuraminidase) activities,2 prompted us to prepare a number of other a-thiosialoside derivatives. These compounds were initially synthesized to serve as powerful glycosylating reagents and as potential sialidase inhbitors. Moreover, by a careful choice of the thiolated aglycon moieties, it became possible to design a new glycosylation strategy in which the thioglycosides could be used as "active and latent" thioglycosyl donors.7 This paper describes fnrtber applications of stereoselective phase transfer catalyzed (PTC) syntheses of glycosyl derivatives as applied to aryl thio-sialosides and galactosides. It will also illustrate an example of the "active and latent" principle in which an active Cmethoxyphenylthio sialoside was used as an efficient glycosyl donor while a latent (temporary inactive) 4-nitrophenylthio galactoside having a primary hydroxyl group was used as glycosyl acceptor.
Carbohydrate Research, 2000
Disaccharides of 1-thioglycosides, an important class of glycomimics, can be synthesized by direct S-alkylation in exceptionally high yields when iminophosphorane bases are employed. The reaction conditions employed appear to be general and stereospecific. Axial and equatorial 4-triflates and primary tosylates of alkyl pyranosides provided excellent yields of thio-disaccharides without substantial elimination products. The iminophosphorane bases also proved to be useful in solid support-bound couplings of thioglycosides though with lower efficiency.