Regio and Stereoselective Synthesis of Derivatives of L-Idopyranuronic Acid and D-Glucopyranuronic Acid from D4-Uronates

Abstract

The stereoselective synthesis of β-d-glucopyranosiduronic, α-l-idopyranosiduronic, and α-l-altropyranosiduronic acids has been performed from different Δ4-uronate monosaccharides. Bromination of the C-4,5 double bond provided the trans-diaxial bromohydrin derivatives, which were converted to the corresponding epoxides in high yields. Direct reduction of the epoxides using borane−tetrahydrofuran complex led to the corresponding glucuronic acids in low to good yields. Glucuronic acids were also obtained in satisfactory yields through a two-steps procedure involving bromination of the epoxide with titanium(IV) bromide followed by reduction using tributyltin hydride. Lewis acid-catalyzed rearrangement of these epoxides led to the corresponding α-l C-4 ketopyranosides adopting the 1C4 chair conformation. Hydride reduction afforded the α-l-idopyranosiduronic or the α-l-altropyranosiduronic acids, the stereoselectivity of the reduction being controlled by the appropriate substitution pattern.