Synthesis of S- and C-galactofuranosides via a galactofuranosyl iodide. Isolable 1-galactofuranosylthiol derivative as a new glycosyl donor

New syntheses of thiosaccharides utilizing substitution reactions

Novel synthetic methods published since 2005 affording carbohydrates containing sulfur atom(s) are reviewed. The review is divided to subchapters based on the position of sulfur atom(s) in the sugar molecule. Only those methods that take advantage of substitution are discussed.

Nucleophilic substitution at the anomeric position of furanose carbohydrates. The case of the C-allylations

Taking advantage of the locked conformation of cyclic furanose form, carbohydrate derivatives have been transformed into relevant tetrahydrofuran moieties through a chemical operation commonly known as C-glycosylation reaction. Consequently, a large number of total synthesis of naturally occurring products containing this heterocycle have been accomplished by applying this reaction. In this regard, the C-allylation reaction of furanose carbohydrates provides flexible routes for stereoselective anomeric functionalization by incorporating an allyl group, which is eventually re-functionalized into advanced natural product intermediates. Therefore, this mini review deals with the description of the origin of the stereoselectivity and synthetic applications of this type of glycosylation reaction, which can be also called as: "Nucleophilic Substitution at the Anomeric Position", conducted by various research groups including our own group.

Switching between X-Pyrano-, X-Furano-, and Anhydro-X-pyranoside Synthesis (X = C, N) under Lewis acid Catalyzed Conditions

A variety of C-glycosides can be obtained from the fluoroarylborane (B(C6F5)3) or silylium (R3Si+) catalyzed functionalization of 1-MeO- and per-TMS-sugars with TMS-X reagents. A one-step functionalization with a change as simple as the addition order and/or Lewis acid and TMS-X enables one to afford chiral synthons that are common (C-pyranosides), have few viable synthetic methods (C-furanosides), or are virtually unknown (anhydro-C-pyranosides), which mechanistically arise from whether a direct substitution, isomerization/substitution, or substitution/isomerization occurs, respectively.

Improvement of the versatility of an arabinofuranosidase against galactofuranose for the synthesis of galactofuranoconjugates

A new performant biocatalyst was developed for the synthesis ofO-,S- and acyl-galactofuranoconjugates.

Expedient synthesis of 1,6-anhydro-α-D-galactofuranose, a useful intermediate for glycobiological tools

A new and efficient three-step procedure for the synthesis of 1,6-anhydro-α-D-galactofuranose is described. The key step involves the formation of the galactofuranosyl iodide by treatment of per-O-TBS-D-Galf with TMSI, the selective 6-O-desilylation by an excess of TMSI, and the simultaneous nucleophilic attack of the 6-hydroxy group on the anomeric carbon, with the iodide as a good leaving group. This compound is a good precursor for building blocks for the construction of 1→6 linkages.

Synthetic tools for the characterization of galactofuranosyl transferases: glycosylations via acylated glycosyl iodides

With the aim of developing synthetic tools for the characterization of galactofuranosyltransferases, the synthesis of 9-decenyl glycosides of D-Manp, D-Galf, and β-D-Galf-(1→3)-D-Manp was targeted. The interest in the alkenyl aglycone arises via potential conjugation reactions, once the terminal double bond has been conveniently functionalized. The glycosylation of β-D-Galf-(1→3)-D-Manp was attempted by two different approaches: the trichloroacetimidate method and the glycosylation via the glycosyl iodide. The conditions for the latter were established on the basis of glycosylation assays of per-O-acetylmannose. On the other hand, the study of glycosylation reactions via per-O-benzoylated galactofuranosyl iodide confirms the versatility of glycosyl iodides as donors.