Pyranoside‐into‐Furanoside Rearrangement: New Reaction in Carbohydrate Chemistry and Its Application in Oligosaccharide Synthesis

Abstract

Great interest in natural furanoside-containing compounds has challenged the development of preparative methods for their synthesis. Herein a novel reaction in carbohydrate chemistry, namely a pyranoside-into-furanoside (PIF) rearrangement permitting the transformation of selectively O-substituted pyranosides into the corresponding furanosides is reported. The discovered process includes acid-promoted sulfation accompanied by rearrangement of the pyranoside ring into a furanoside ring followed by solvolytic O-desulfation. This process, which has no analogy in organic chemistry, was shown to be a very useful tool for the synthesis of furanoside-containing complex oligosaccharides, which was demonstrated by synthesizing disaccharide derivatives α-D-Galp-(1→3)-β-D-Galf-OPr, 3-O-s-lactyl-β-D-Galf-(1→3)-β-D-Glcp-OPr, and α-L-Fucf-(1→4)-β-D-GlcpA-OPr related to polysaccharides from the bacteria Klebsiella pneumoniae and Enterococcus faecalis and the brown seaweed Chordaria flagelliformis.

Orthogonal protection of saccharide polyols through solvent-free one-pot sequences based on regioselective silylations

“…The only disappointing result observed in attempted TPDPS protections was the poor yield recorded with glucal 7 (Table 2, entry 13), a surprising outcome which is somehow consistent with the very slow rate observed for the same reaction under standard conditions [39–40]. As already observed for the synthesis of 2 , the herein described conditions for regioselective TBDMS and TBDPS protections entail shorter reaction times than most of the reported protocols in the literature on monosaccharide polyols [14–18 20,41–53]; comparable silylation rates were indeed be found in a few examples, often involving relatively less polar thioaryl glycosides as the substrates and DMF as the solvent [19,54–59]. Having established the scope of TBAB-catalyzed mono silylations with a minimal excess of pyridine, some effort was devoted to ascertain the feasible exploitation of a similar strategy to either regioselective di- O -silylations or the protection of secondary alcohols in absence of primary ones (Table 3).…”

Convergent synthesis of isomeric heterosaccharides related to the fragments of galactomannan from Aspergillus fumigatus

“…8,9 The herein reported first syntheses of heterosaccharides related to the galactomannan from A. fumigatus were performed with the use of PIF-rearrangement as a key step.…”

“…8 In order to obtain an appropriately substituted furanoside for the simplification of the final orthogonal protective group placement, galactopyranoside 8 was chosen as a substrate for the PIF-rearrangement ((Scheme 1). This compound was prepared by regioselective benzylation of allyl galactoside 7 10 via the organotin intermediate.…”

Lysozyme's lectin-like characteristics facilitates its immune defense function

“…The synthesis of disaccharide 1 was performed using the recently discovered pyranoside-into-furanoside rearrangement (Krylov et al 2014(Krylov et al , 2016. The synthesis of tetrasaccharide 2 (Verkhnyatskaya et al 2017) was based on similar approaches and is described in the online supplementary information (Scheme S1).…”

“…S1 in Supplementary Information). To assess whether the O-chains of these LPSs were involved in the observed interactions, we combined nuclear magnetic resonance (NMR), molecular modeling, data mining and X-ray crystallography techniques to investigate HL binding to synthetic disaccharide 1 (Krylov et al 2014) and tetrasaccharide 2 (Fig. 1d), which represented one and two repeating units of the O-chain of K. pneumoniae O1, respectively, at the sub-molecular level.…”