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

Abstract

Aspergillus fumigatus is a very common fungus with high pathogenic potential for immunosuppressed hospital patients. A. fumigatus galactomannan, being the part of its cell wall, is considered as a promising candidate for vaccine and diagnostic test-systems. In this article we report the convergent synthesis of pentasaccharide fragments of the galactomannan containing the β-(1→5)-linked galactofuranoside chain attached to O-3 or O-6 of a spacer-armed mannopyranoside residue. The synthesis of selectively protected galactofuranoside precursors has been performed using recently developed pyranoside-into-furanoside (PIF) rearrangement. For assembling the target galactomannan structures the [1 + 2 + 2]-scheme was applied. This strategy was shown to be highly efficient and can easily be extended to the synthesis of longer fragments of thegalactomannan.

Pyranoside‐into‐Furanoside Rearrangement of 4‐Pentenyl Glycosides in the Synthesis of a Tetrasaccharide‐Related to Galactan I of Klebsiella pneumoniae

“…Previously, a preparative protocol for the PIF rearrangement of different glycosides bearing an allyl group as a temporary protecting group at anomeric position was developed . In this communication, we expand the scope of this process by using an aglycon that can act as a leaving group during glycosylation.…”

“…This was then subjected to the PIF rearrangement (Scheme ). The standard protocol for this rearrangement, which was successfully applied in the synthesis of oligosaccharides related to polysaccharides from Aspergillus fumigatus ,, Enterococcus feacalis , Chordaria flagelliformis , involves treatment with a Py · SO 3 /HSO 3 Cl mixture, followed by neutralization with NaHCO 3 , and solvolytic desulfation in the presence of acidic resin IR‐120 (H + ). Unfortunately, under these conditions substrate 9 gave only 27 % of target disaccharide 16 (Scheme , Table , entry 1).…”

“…tecting group at anomeric position was developed. [12][13][14][15][16][17] In this communication, we expand the scope of this process by using an aglycon that can act as a leaving group during glycosylation. Previous studies revealed that the PIF rearrangement proceeds efficiently for substrates bearing an electron-donating aglycon in an equatorial orientation.…”

Synthesis of oligosaccharides related to galactomannans fromAspergillus fumigatusand their NMR spectral data

“…Previously, 21 we reported the synthesis of two galactomannan related pentasaccharides 7 and 10 and oligosaccharides 9, 11 and 12. 22 In the present work, additionally required models such as homo-galactofuranosides 1-4 containing both β-(1→5)-and β-(1→6)-linked galactofuranosyl units and hetero- Table 1 Assigned signals in the 13 C NMR spectra for the previously described oligosaccharides a Not described.…”

“…The synthesis of compounds 1-6, 8 and 13 is also reported, while the preparation of oligosaccharides 7 and 9-12 was previously published. 21,22 Results and discussion…”