β-Disaccharides for Mithramycin Analog Synthesis. Triflate Rearrangement in Disaccharide Preparation.

Three disaccharides (13, 16, and 20), compounds to be utilized in the preparation of analogs of the anticancer agent mithramycin (1), have been synthesized from appropriately protected 2,6-dideoxy sugars. In these syntheses triflate rearrangement was used to invert configuration at specific chiral centers. Silver-silicate controlled reaction generated the desired β-linkages between saccharide units. Silver-silicate also catalyzed β-glycoside formation when the glycosyl bromides derived from 13 and 20 each were coupled with o-methylphenol (a model aglycon).