Total Synthesis of 6-Deoxy-6-aminoheptopyranuronic Acid Derivatives

Two enantio couples of terminal C-glycopyranosyl alfa-amino acids, namely the aminopyranuronic acids L-9, D-9 and L-10, D-10, have been synthesized from the serine-derived pair L-2, D-2 by exploiting enantiomerically pure butenolide intermediates 3 and 4. The key synthetic steps involved the sequential antiselective cis dihydroxylation of the butenolide double bond and the clean furanose-to-pyranose ring expansion to construct the sugar skeleton with the proper stereochemistry. In our best performance, homogeneous L-9 was prepared from L-2 in four steps and 10 reactions in 20% overall yield.