Attempted synthesis of type-A inositolphosphoglycan mediators - Synthesis of a pseudohexasaccharide precursor

A block synthesis approach to the inositol-containing pseudohexasaccharide 1 is presented. The myo-inositol building block 6 has been prepared using a key regioselective acylation through a boron-tin exchange reaction and the 2-azido-2-deoxy glycosyl donors 15 and 17 have been synthesized from D-glu cosamine using a diazo transfer reaction. The anomeric position of the mono - and disaccharide building blocks has been temporarily protected as phenyl thioglycoside and this function was then converted into the different leav ing groups to perform the glycosylation reactions. Both trichloroacetimidat es and fluorides have been used as glycosyl donors for the construction of the different glycosidic linkages. The protected pseudohexasaccharides 44, 48-50, which are precursors of pseudohexasaccharide 1, have been efficientl y prepared and fully characterized. Pseudohexasaccharide 1 contains the fun damental structural features which have been proposed for type A inositolph osphoglycans, which may be involved in the insulin-signaling process.