Regio- and Stereoselective Synthesis of beta-D-Gluco-, alpha-L-Ido-, and alpha-L-Altropyranosiduronic Acids from Delta(4)-Uronates.

The stereoselective synthesis of beta-D-glucopyranosiduronic, alpha-L-idopyranosiduronic, and alpha-L-altropyranosiduronic acids has been performed from different Delta(4)-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 alpha-L C-4 ketopyranosides adopting the (1)C(4) chair conformation. Hydride reduction afforded the alpha-L-idopyranosiduronic or the alpha-L-altropyranosiduronic acids, the stereoselectivity of the reduction being controlled by the appropriate substitution pattern.