Laminaribiose as the Starting Material: Facile Synthesis of β-(1↠3)-Linked Gal-Gal Disaccharide Derivatives and Related Compounds

The synthesis of β-(1→3)-linked galactobiose octaacetate (14) was achieved in a 6-step reaction sequence in more than 30% overall yield, starting from the readily available laminaribiose octaacetate (2). The key steps in this synthesis involved the efficient transformation of 4,6:4′,6′-di-O-benzylidene derivative (5) into the diol (6) through regioselective reductive ring opening of the two benzylidene acetals, the preparation of the corresponding ditriflate (12) and dimesylate (8), and their subsequent SN2 displacement by benzoate and/or thiolacetate anion to give the β-(1→3)-linked Gal-Gal disacharide derivative (10) and related thio compounds 11 and 13. The big difference of the reactivities between the two mesyloxyl groups of 8 enabled their replacement with different nucleophiles.