Diastereoselective hydroboration of substituted exo-glucals revisited. A convenient route for the preparation of L-iduronic acid derivatives

Article abstract of DOI:10.1016/S0008-6215(97)00149-3

Suitably protected derivatives of methyl 3-O-benzyl-6-deoxy-α-D-xylo- hex-5-enopyranoside, readily prepared from 3-O-benzyl-D-glucopyranose, were reacted with various boranes to prepare the corresponding L-idose components. Reaction of methyl 2-O-benzoyl-3-O-benzyl-6-deoxy-4-O-tert- butyldimethylsilyl-α-D-xylo-hex-5-enopyranoside with 9- borabicyclo[3.3.1]nonane (9-BBN) afforded an easily separable 9:1 L-ido:D- gluco mixture. The L-ido isomer was then transformed in a straightforward manner into suitably protected L-iduronic acid glycosyl donors (chloride, bromide, trichloroacetimidate) which could serve as highly elaborated building blocks in syntheses of L-iduronic acid containing glycosaminoglycan fragments. An unexpected side-reaction occurring in the preparation of 1-O- trichloroacetimidoyl derivatives is also reported.