Identification and synthesis of a trisaccharide produced from lactose by transgalactosylation

Enzymatic transgalactosylation of lactose by means of Streptococcus thermophilus, subspecies DN-001065, led to a mixture of D-galactose (similar to 4%), D-glucose ( similar to 15%), lactose (similar to 51%), minor disaccharides (6%), trisaccharides ( similar to 20%) and tetrasaccharides (3%). The major trisaccharide ( similar to 16%) was identified by NMR spectroscopy and chemical synthesis as bring the known beta-D-galactopyranosyl-(1-->3)-beta-D-galactopyranosyl-(1-->4)-D-glucose (3'-beta-D-galactopyranosyl-lactose). It was purified from a mixture of peracetylated oligosaccharides by column chromatography followed by deacetylation. For the first time, 3'-beta-D-galactopyranosyl-lactose has been obtained on the 1 g scale, by resorting to simple techniques and equipment. NMR spectra have been unambiguously assigned. (C) 3000 Elsevier Science Ltd. All rights reserved.