Fucosyl transferase III (FucT III) has previously been characterized as the most general enzyme of the FucT family, as judged from its ability to catalyze the transfer of fucose to both Galβ(1-3)GlcNAc and Galβ(1-4)GlcNAc. In order to explore the synthetic potential of FucT III for the enzymatic synthesis of sialyl Lewisxand sialyl Lewisaderivatives, its substrate specificity has been probed using a number of natural substrate mimetics. A remarkable range of acceptor substrates was found when N-acetyl glucosamine was replaced by D-glucal, (R,R)-1,2-cyclohexanediol and (R,R)-butan-2,3-diol. Although the reaction rates were low compared to the reaction with the natural substrates, they proved to be sufficient for the synthesis of preparative amounts.Key words: fucosyl transferase III, sialyl Lewisa, sialyl Lewisx, carbohydrate mimetics.
Research over the past two decades has uncovered numerous biological roles for carbohydrates, e.g. in cell adhesion processes, signal transduction, malignant transformation, or viral and bacterial cell-surface recognition. Carbohydrates and structural analogues thereof are therefore considered as potential new leads. Although the chemical synthesis of carbohydrates is well established, the preparation of particular oligosaccharides still remains a costly and cumbersome challenge. A complementary approach to the chemical synthesis is the use of enzymatic methods. The transfer of monosaccharide moieties to natural substrates, catalyzed by glycosyltransferases, exhibits excellent chemo-, regio- and stereoselectivity. In addition, enzymatic glycosylations permit the synthesis of carbohydrate derivatives and even carbohydrate mimetics. Our results reveal a remarkable synthetic potential of fucosyltransferases VI (EC 2.4.1.65) and III (EC 2.4.1.65), and ? (2?3)-sialyltransferase ST3Gal III (EC 2.4.99.6). Their use for the preparative synthesis of oligosaccharides and derivatives as well as mimetics thereof is demonstrated.