A quantitative mathematical algorithm (MA'AT) has been developed to derive conformational models based solely on redundant NMR J-couplings in saccharides (JHH, JCH and JCC).  MA'AT uses J-coupling ensembles as input, such as those across the O-glycosidic linkages of oligosaccharides (Scheme 1), although the approach can be applied to other ensembles sensitive to a particular conformational element (e.g., flexible furanose and pyranose rings). The treatment relies on DFT-derived parameterized equations for the J-couplings of interest, and the population is modeled as the sum of 1-3 gaussian functions, whose relative heights, widths, and positions are optimized.  Since no initial assumptions are made about the positions and relative magnitudes of the peaks, the method is more rigorous than prior simpler treatments (e.g., J. Am. Chem. Soc. 1998 , 120, 11158-11173; J. Phys. Chem. B 2008 , 112, 4447-4453).  The program output yields quantitative values for the positions and abundances of stable conformations, and the degree of libration about each maximum.  This method provides a means to test theoretical (e.g., MD) predictions of saccharide conformation, which are typically resistant to validation by experiment.  The treatment has been applied to conformational domains that qualitatively exhibit specific J-coupling trends (e.g., J-couplings across the O-glycosidic linkages (J. Am. Chem. Soc. 1999 , 121, 9843-9851) of several 13C-labeled b-(1�4)-linked disaccharides, or have conformational behaviors reported previously (e.g., exocyclic CH2OH conformation in aldohexopyranosyl rings; J. Am. Chem. Soc. 2004 , 126, 15668-15685).  The biologically relevant linkage, a-Man-(1�2)-a-Man, has also ben re-examined to test conclusions drawn previously (Computational Chemistry of Carbohydrates Symposium, Division of Carbohydrate Chemistry, 227th ACS National Meeting, 2004, Anaheim, CA, CARB 8) about the relative flexibilities of f and y.

Experimental validation of saccharide molecular dynamics simulations: Quantitative treatment of NMR J-coupling ensembles

245th National Meeting (2013)

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