SYNTHESIS OF NOVEL OLIGOSACCHARIDES

The synthesis of the Le(x) family of glycosphingolipids (monomeric, dimeric, and trimeric Le(x) is outlined. The strategy involves enantioselective construction of a sphingosine equivalent which is then coupled to oligosaccharide fragments to build the skeletons of the targeted molecules utilizing the two-stage activation procedure. The careful definition of protecting groups allowed easy differentiation of functional groups and stereospecific construction of the glycoside bonds in these complex targets culminating in highly efficient entries into these structures. Model studies in the area of the antibiotic calicheamicin gamma-lI oligosaccharide are also described. A key [3,3]-sigmatropic rearrangement was utilized as a central operation to set the stage for the successful construction of a model for the ABC ring system of this oligosaccharide. Thus solutions for the construction of the most crucial bonds of this novel oligosaccharide have been demonstrated.