Recent studies by Duman and coworkers have revealed the presence of a novel glycolipid in the Alaskan beetle, Upis ceramboides, that possesses potent thermal hysteresis properties (Walters et al., Proc. Natl. Acad. Sci. 2009, 106, 20210-20215). This antifreeze glycolipid (AFGL) is comprised of alternating βXylp and βManp residues connected by (1→4) O-glycosidic linkages 1, although branching and covalent modification of this core structure may also occur. To study the preferred conformations about the φ and ψ torsion angles in the two different O-glycosidic linkages in 1, four singly 13C-labeled disaccharides (21’, 22’, 31’ and 32’) and a triply 13C-labeled tetrasaccharide 4 were prepared chemically. Multiple JCH and JCC values across the “isolated” linkages in 2 and 3, and across the “in-context” linkages in 4 were measured by 1H and 13C NMR spectroscopy, respectively. The trans-O-glycoside J-couplings (Bose-Basu et al., J. Am. Chem. Soc. 1998, 120, 11158-11173) were fit by a new software program, MA’AT©, to deconvolute the redundant J-couplings into conformatinal models for the φ and ψ torsion angles comprising each glycosidic linkage. The results show that (a) context plays a minimal role in determining linkage conformation in 4, and (b) the two types of β-(1→4) linkages in 4 are conformationally distinct.

Chemical synthesis and O-glycosidic linkage conformation in a 13C-labeled βMan(1→4)βXyl(1→4)βMan(1→4)βXylOCH3 tetrasaccharide: Effects of linkage structure and context

249th National Meeting (2015)

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