758
3
Chemical Glycosylation Reactions
⊡ Figure 2
Naturally occurring compounds containing the C-glycosidic linkage
One-step synthesis of β-glycosyl ketone from unprotected carbohydrate in aqueous media was
reported by Rubineau and co-workers ( > Scheme 1) [4]. Unprotected D-glucose, mannose,
and galactose were treated with pentane-2,4-dione at 90 °C in aqueous sodium bicarbonate to
afford β-glycosyl ketones in high yields. The reaction began with Knoevenagel condensation
to give the unsaturated ketone, which underwent an intramolecular conjugate addition of the
alkoxide. The reaction conducted at room temperature gave a mixture of the four possible furanosides and pyranosides. It is worth noting that epimerization at the C-2 position did not occur
in the reaction with glucose and mannose, while the same reactions with N-acetyl-gluco-,
manno-, and galactosamine afforded a mixture of the C-2 epimeric products. The β-glycosyl
ketone was transformed into β-1-formyl sugar, a versatile synthetic intermediate for a variety
of C-glycosidic compounds.
3
Chemical Glycosylation Reactions
⊡ Figure 2
Naturally occurring compounds containing the C-glycosidic linkage
One-step synthesis of β-glycosyl ketone from unprotected carbohydrate in aqueous media was
reported by Rubineau and co-workers ( > Scheme 1) [4]. Unprotected D-glucose, mannose,
and galactose were treated with pentane-2,4-dione at 90 °C in aqueous sodium bicarbonate to
afford β-glycosyl ketones in high yields. The reaction began with Knoevenagel condensation
to give the unsaturated ketone, which underwent an intramolecular conjugate addition of the
alkoxide. The reaction conducted at room temperature gave a mixture of the four possible furanosides and pyranosides. It is worth noting that epimerization at the C-2 position did not occur
in the reaction with glucose and mannose, while the same reactions with N-acetyl-gluco-,
manno-, and galactosamine afforded a mixture of the C-2 epimeric products. The β-glycosyl
ketone was transformed into β-1-formyl sugar, a versatile synthetic intermediate for a variety
of C-glycosidic compounds.