SOLUTION-PHASE C-13 AND H-1 CHEMICAL-SHIFT ANISOTROPY OF SIALIC-ACID AND ITS HOMOPOLYMER (COLOMINIC ACID) FROM CROSS-CORRELATED

Sensitive pulse sequences were developed in order to determine geometr y dependent H-1 and C-13 chemical shift anisotropy terms (CSAg) of sim ple carbohydrates and carbohydrate polymers in solution. The methods a re capable of monitoring CSA/DD cross-correlated relaxation for ca. 1 M solutions at natural abundance. Measured spectral densities were qua ntitatively interpreted for sialic acid and its alpha-(2-->8) linked h omopolymer, colominic acid. Although the geometric factors could not b e separated from anisotropy terms, this is the first report of CSA dat a on a carbohydrate polymer, and its values differ substantially from those of monomeric sialic acid. The most pronounced differences were o bserved at C5, C6, and C7 for both H-1- and C-13-shift anisotropies. T he differences may be attributed to conformational changes around the C6/C7 and C7/C8 bonds, and possible changes in hydrogen bonding intera ctions, and in OH rotamer populations. Application of these combined N MR methods provide a new parameter which may be sensitive to structura l changes not detected with conventional NMR techniques.