Chemical synthesis of GDP-fucose analogs and their utilization by the Lewis *A(1 → 4) fucosyltransferase

Chemical syntheses are reported for GDP-fucose (5), GDP-3-deoxy-fucose (6), and GDP-arabinose (7), the demethyl analog of 5. All three sugar nucleotides were found to act as donor substrates for an α(1 → 4) fucosyltransferase isolated from human milk when *BDGal(1 → 3)*BDGlcNAc-O(CH 2 ) 8 COOMe (1) was used as the acceptor. The rate of transfer of sugar residues to 1 was measured using a coupled spectrophotometric assay and was found to be 100% (5), 2.3% (6), and 5.9% (7). The product Le a -active oligosaccharide analogs were identified by both an enzyme-linked immunosorbent assay (ELISA) and by 1 H NMR spectroscopy.