| Abstract
| - Retrosynthesis of the fully phosphorylated glycosylphosphatidyl inositol (GPI) anchor pseudohexasaccharide 1a led to building blocks 2−6, of which 5 and 6 are known. The formation ofpseudodisaccharide building block 2 is based on readily available building block 7, which gave, viaderivative 11 and its glycosylation with known donor 12, the desired compound 2. Building block3, with the required access to all hydroxy groups being permitted, was prepared from mannose infive steps. From a readily available precursor, building block 4 was obtained, which on reactionwith 3 gave disaccharide 23. The synthesis of the decisive pseudohexasaccharide intermediate 32was based on the reaction of 23 with 5, then with 6, and finally with 2. To obtain highstereoselectivity and good yields in the glycosylation reactions, anchimeric assistance was employed.To enable regioselective attachment of the two different phosphorus esters, the 6f-O-silyl group of32 was first removed and the aminoethyl phosphate residue was attached. Then the MPM groupwas oxidatively removed, and the second phosphate residue was introduced. Unprotected 1a wasthen liberated in two steps: treatment with sodium methanolate removed the acetyl protectinggroups, and finally, catalytic hydrogenation afforded the desired target molecule, which could befully structurally assigned.
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