STUDIES RELATED TO SYNTHESIS OF GLYCOPHOSPHATIDYLINOSITOL MEMBRANE-BOUND PROTEIN ANCHORS .6. CONVERGENT ASSEMBLY OF SUBUNITS

Glycophosphatidylinositol anchors of membrane-bound proteins are thought to comprise a common pentasaccharide core containing mannan, glucosamine, and inositol residues. A synthetic route to this core is described. In addition, the complete heptasaccharide moiety of the rat brain Thy-1 membrane anchor, the first mammalian membrane anchor to be characterized, has been synthesized. In the case of the Thy-1 anchor, the synthetic plan is based on three building blocks comprising glucosamine-inositol, galactosamine-mannose, and trimannan residues. Although glycosyl donors other than n-pentenyl glycosides (NPGs) have been used in preparing each of these building blocks, the final assembly of the heptasaccharide utilizes NPGs as the only glycosyl donors. The mildness of the conditions for these coupling reactions has allowed us to make provisions for subsequent installation of the three phosphodiester units.