Enzymatic synthesis and carbon-13 nuclear magnetic resonance conformational studies of disaccharides containing beta-D-galactopyranosyl and beta-D-[1-13C]galactopyranosyl residues.

Partially purified UDPgalactosyltransferase (EC 2.4.1.22) from bovine milk has been used to synthesize millimolar amounts of compounds such as Gal beta (1 leads to 4)Glc, Gal beta (1 leads to 4)GlcNAc-beta-hexanolamine, and Gal beta (1 leads to 4)GlcNAc beta (1 leads to 4)GlcNAc. The same method has been used to prepare similar compounds containing 13C-enriched galactopyranosyl moieties. Gal beta (1 leads to 4)GlcNAc-beta-hexanolamine was also synthesized in a solid-phase system in which the GlcNAc-beta-hexanolamine glycoside was covalently linked to agarose beads. At pH 7.0 and at 1--5 mM Mn2+ the yields of the galactosyl saccharides are greater than 90% by using 10% excess of UDPGal donor. The use of a 90% enriched [1-13C]galactosyl residue allowed the determination of the most abundant conformer about the galactopyranosyl--glycoside linkage by analysis of the carbon--carbon coupling constants from C1 of Gal to the C3', C4, and C5' of GlcNAc or Glc.