Chemo-enzymatic synthesis of trimeric sialyl Lewisx pentadecasaccharide

The enzymatic synthesis of trimeric sialyl Lewisx pentadecasaccharide (6), a 15-mer, from a trimannoside precursor required six different glycosyltransferase enzymes and four nucleotide donor sugars. Three N-acetylglucosaminyl residues were transferred from UDP-N-acetylglucosamine to a trimannoside by N-acetylglucosaminyltransferases I, II, and V, respectively. Galactosylation using β(14) galactosyltransferase and UDP-galactose gave three N-acetyl lactosamine units in nonasaccharide 4. Sialylation of 4 with α(23) sialyltransferase and CMP-N-acetylneuraminic acid was followed by fucosylation with α(13) fucosyltransferase and GDP-fucose giving the 15-mer 6 in mg quantities. Compound 4 was also converted to a trimeric Lewisx dodecasaccharide 12-mer with α(13) fucosyltransferase and GDP-fucose and to a trimeric α-2,6-sialyl N-acetyllactosamine dodecasaccharide 12-mer with α(26) sialyltransferase and CMP-N-acetylneuraminic acid. Key words: glycosyltransferases, pentadecasaccharide, sialyl Lewisx.