SCOPE OF INTERANOMERIC GLYCOSYL TRANSFER REACTIONS - HETERO-DIALDOSIDE SYNTHESIS BY ENZYMIC GLUCOSYLATION OF D-GALACTOSE AND D-MANNOSE

Hitherto, all de novo syntheses of nonreducing di- and trisaccharides from sucrose and its analogs by soluble enzymes have involved either aldopyranosyl (i.e., α-d-glucopyranosyl) transfers to the anomeric-OH of ketofuranoses, or ketofuranosyl (e.g., β-d-fructofuranosyl) transfers to the anomeric-OH of aldopyranoses. It is now clear that soluble as well as cellular dextransucrase preparations from L. mesenteroides can transfer the α-d-glucopyranosyl moiety from sucrose to the anomeric-OH of certain aldoses, yielding unique hetero-dialdosides. Bourne et al. (1961) first recovered a small quantity of an α-d-glucopyranosyl d-galactofuranoside among saccharides produced by a culture of strain Birmingham grown with sucrose and d-galactose. By use of acetone-killed B-742 cells as enzyme source we have isolated 1.5 g of this disaccharide, and have established its full structure as α-d-glucopyranosyl β-d-galactofuranoside. In a parallel synthesis, similar cells acting on sucrose and d-mannose have provided the first known example of a nonreducing disaccharide of d-glucose and d-mannose, α-d-glycopyranosyl β-d-mannopyranoside. Both dialdosides also were synthesized by soluble dextransucrase preparations from three different L. mesenteroides strains. As the enzymes were not highly purified, these results may not provide conclusive proof of identity of the catalyst. But the syntheses by the soluble enzymes do demonstrate the occurrence of α-d-glucopyranosyl transfer reactions beyond the limits set for interanomeric glycosyl transfers by previous collective experience with various enzymes. © 1969.