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 (∼4%), d-glucose (∼15%), lactose (∼51%), minor disaccharides (6%), trisaccharides (∼20%) and tetrasaccharides (3%). The major trisaccharide (∼16%) was identified by NMR spectroscopy and chemical synthesis as being the known β-d-galactopyranosyl-(1→3)-β-d-galactopyranosyl-(1→4)-d-glucose (3′-β-d-galactopyranosyl-lactose). It was purified from a mixture of peracetylated oligosaccharides by column chromatography followed by deacetylation. For the first time, 3′-β-d-galactopyranosyl-lactose has been obtained on the 1 g scale, by resorting to simple techniques and equipment. NMR spectra have been unambiguously assigned.