Synthesis and structural verification of the xylomannan antifreeze substance from the freeze-tolerant Alaskan beetle Upis ceramboides

Abstract

Tetra-, hexa-, and octasaccharide subunits of the [→4)-β-D-Manp-(1→4)-β-D-Xylp-(1→](n) xylomannan motif proposed as the structure of a novel nonprotein, thermal hysteresis-producing antifreeze substance from the freeze-tolerant Alaskan beetle Upis ceramboides have been accessed by total chemical synthesis. Comparison of their NMR spectral data with data of the isolate lends strong support to the proposed structure. Synthetic tetrasaccharides representing various linkage isomers considered (α- rather than β-manno, and linkage through mannose O3 rather than O4) show more significant chemical shift differences with the isolate and are therefore excluded from further consideration.

Figure 1

¹³C Δδ values for the chemical shifts of 15-17, 23, 31, and 37 with the isolated glycan. m = mannopyranoside, x = xylopyranoside.

Fig. 2

¹H Δδ values for the chemical shifts of 15-17, 23, 31, and 37 with the isolated glycan. m = mannopyranoside, x = xylopyranoside

Scheme 1

Synthesis of the four disaccharyl units 6-9.

Scheme 2

Convergent assembly of the tetra-, hexa- and octasaccharides 10-14.

Scheme 3

Completion of the tetra-, hexa- and octasaccharides 15-17.

Scheme 4

Synthesis of linkage isomer 23

Scheme 5

Synthesis of linkage isomer 31

Scheme 6

Synthesis of linkage isomer 37