Rapid Synthesis of L-Idosyl Glycosyl Donors from α- Thioglucosides for the Preparation of Heparin Disaccharides

A new methodology for the synthesis of the most challenging heparin building block has been developed. Orthogonally protected L-idosyl glycosyl donors were prepared by C5 epimerization of the corresponding thioglucosides using the hydroboration/oxidation method followed by a 4,6-acetal formation. The -anomeric configuration was crucial and the bulky C4 substituent was advantageous for the high L-ido diastereoselectivity. The 4,6-arylmethylene group proved to be a directing element in glycosylation thereby stereoselective -idosylation could be achieved by using idosyl donors without a C-2 participating group