RECOGNITION OF SYNTHETIC ANALOGS OF THE ACCEPTOR, BETA-D-GALP-OR, BY THE BLOOD-GROUP-H GENE-SPECIFIED GLYCOSYLTRANSFERASE

The acceptor-substrate specificity of a cloned alpha-(1 --> 2) fucosyltransferase has been explored using structural analogues of octyl beta-D-galactopyranoside (4). This monosaccharide is the minimum acceptor-substrate for the H-transferase, one of two enzymes responsible for the biosynthesis of the O blood-group antigen, which terminates in the sequence alpha-L-Fuc p-(1 --> 2)-beta-D-Gal p. Galactoside 4 has a K-m of 6 mM with this enzyme. Eighteen analogues of 4 have been prepared, including those where the hydroxyl groups at C-3, C-4, and C-6 have been replaced, independently, with deoxy, fluoro, O-methyl, amino, and acetamido functionalities. The C-3 and C-4 epimers have been prepared as has the C-5 de(hydroxymethyl)ated derivative. These compounds were screened as potential accepters and inhibitors of the fucosyltransferase. The C-6 analogues that do not possess a charge show substrate activity with relative rates in the range of 27-316% that of 4. The C-3 modified analogues are inhibitors with estimated K-i values of 0.9-43 mM. Those analogues with modifications at C-4 were both poor inhibitors and acceptors.