Combined chemical-enzymic synthesis of deoxygenated oligosaccharide analogs: transfer of deoxygenated D-GlcpNAc residues from their UDP-GlcpNAc derivatives using N-acetylglucosaminyltransferase I.

The 3''-, 4''-, and 6''-deoxy analogs of UDP-GlcpNAc have been synthesized chemically and found to act as donor-substrates for N-acetylglucosaminyltransferase-I (GnT-I) from human milk. Incubation of UDP-GlcpNAc and these deoxy analogs with GnT-I in the presence of alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Manp -O(CH2)8COOMe gave beta-D-GlcpNAc-(1----2)-alpha-D-Manp-(1----3)-[alpha-D-Manp- (1----6)]- beta-D-Manp-O(CH2)8COOMe (6), and the deoxy analogs 12-14 where HO-3, HO-4, and HO-6, respectively, of the beta-D-GlcNAc residue were replaced by hydrogen. The tetrasaccharide glycosides 6 and 12-14 were characterized by 1H-n.m.r. spectroscopy and evaluated as acceptors for GnT-II, the next enzyme in the pathway of biosynthesis of Asn-linked oligosaccharides. Deoxygenation of the 3-position of the beta-D-GlcNAc residue of 6 completely abolished its acceptor activity, whereas removal of HO-4 or HO-6 caused only modest decreases in activity.