APPLICATION OF THE GLYCAL ASSEMBLY METHOD TO THE CONCISE SYNTHESIS OFNEOGLYCOCONJUGATES OF LE(Y) AND LE(B) BLOOD-GROUP DETERMINANTS AND OFH-TYPE-I AND H-TYPE-II OLIGOSACCHARIDES

The power of the glycal assembly strategy for reaching Lewis and H-typ e blood group determinants is demonstrated herein. Three key elements form the basis of the method. Thus, alpha-epoxides derived from galact al cyclic carbonate 13 are produced stereospecifically and are highly effective beta-galactosyl donors. Also, 6-monoprotected glucals can be regiospecifically glycosylated at the C-3 hydroxyl (see 23 + 13 --> 2 4). Moreover, glycosylation via a glycal epoxide produces a unique C-2 hydroxyl in the product which can be exploited as the acceptor site f or branching (see formation of 26).