Synthetic study and structural analysis of the antifreeze agent xylomannan from Upis ceramboides.

ABSTRACT

The novel antifreeze factor, xylomannan, first isolated from the freeze-tolerant Alaskan beetle Upis ceramboides , demonstrates a high degree of thermal hysteresis, comparable to that of the most active insect antifreeze proteins. Although the presence of a lipid component in this factor has not yet been verified, it has been proposed that the glycan backbone consists of a ß-D-mannopyranosyl-(1→4)-ß-D-xylopyranose-disaccharide-repeating structure according to MS and NMR analyses. In this contribution, we report the stereoselective synthesis of the tetrasaccharide ß-D-mannopyranosyl-(1→4)-ß-D-xylopyranosyl-(1→4)-ß-D-mannopyranosyl-(1→4)-D-xylopyranoside, a structural component of xylomannan. Our synthesis features the use of 2-naphthylmethyl (NAP)-ether-mediated intramolecular aglycon delivery (IAD) as the key reaction in obtaining ß-mannopyranoside stereoselectively. Various donors for NAP-IAD were tested to determine the most suitable for the purposes of this synthesis. Fragment coupling between a disaccharyl fluoride and a disaccharide acceptor obtained from a common ß-D-mannopyranosyl-(1→4)-ß-D-xylopyranoside derivative was successfully carried out to afford the desired tetrasaccharide in the presence of Cp(2)HfCl(2)-AgClO(4). Structural analysis of the resulting synthetic tetrasaccharide using NMR techniques and molecular modeling was performed in order to demonstrate the presence of the proposed xylomannan linkages in this molecule.