UDP-6-deoxy-6-fluoro-alpha-D-galactose binds to two different galactosyltransferases, but neither can effectively catalyze transfer of the modified galactose to the appropriate acceptor.

The effect of substitution of the HO-6 of D-galactose with fluorine on the ability of alpha-(1-->3)-galactosyltransferase (EC 2.4.1.151) and beta-(1-->4)-galactosyltransferase (EC 2.4.1.22) to catalyze its transfer from UDP to an appropriate acceptor was determined. HPLC analyses indicated that each transferase properly catalyzed formation of the expected product beta-D-Gal-(1-->4)-D-GlcNAc] for the beta-(1-->4)-galactosyltransferase and alpha-D-Gal-(1-->3)-beta-D-Gal-(1-->4)-D-GlcNAc for the alpha-(1-->3)-D-galactosyltransferase] when UDP-alpha-D-Gal was the substrate. When UDP-6-deoxy-6-fluoro-alpha-D-galactose (6) was used in conjunction with each transferase, no product indicative of transfer of 6-deoxy-6-fluoro-D-galactose to its respective acceptor sugar was identified. 6-Deoxy-6-fluoro-D-galactose (3) was obtained by hydrolysis of methyl 6-deoxy-6-fluoro-alpha-D-galactopyranoside, synthesized by the selective fluorination of methyl alpha-D-galactopyranoside with diethylaminosulfur trifluoride (DAST), with aqueous trifluoroacetic acid. Acetylation of 3 gave crystalline 1,2,3,4-tetra-O-acetyl-6-deoxy-6-fluoro-beta-D-galactopyranose, which was converted to the corresponding 1-alpha-phosphate and used for the synthesis of 6.