Regio and stereoselective conversion of Δ4-uronic acids to L-ido- and D-glucopyranosiduronic acids

Abstract

Synthesis of L-ido- and D-glucopyranosiduronic acids was performed starting from protected Δ4-uronic acids 3a-f. Bromination of the C-4,5 double bond provided the trans-diaxial bromohydrin derivatives 6a-d, which were converted to the corresponding epoxides 7a-d in high yields. Direct reduction of these epoxides using borane-tetrahydrofuran complex afforded the D-glucopyranosiduronic acids 9b-d, while Lewis acid rearrangement through the C-4 keto intermediate 10b-d afforded the L-idopyranosiduronic acids 11b-d.