Comparison between DFT- and NMR-based conformational analysis of methyl galactofuranosides

• DFT solution energies determined for methyl α- and β-galactofuranosides (1 and 2).
• New Karplus-type equations for galactofuranosides.
• Measured 3JH–H for 1 and 2 to calculate solution conformation in PSEUROT.
• Major solution conformations—2E for 1, varied for 2.
• Low-energy DFT and NMR conformations are the same for 1, differ for 2.

Galactofuranose (Galf) residues are found in a number of microbial polysaccharides, and knowledge of their conformation is key for developing a molecular-level understanding of their biological roles. To this end, we studied 180 conformations of methyl α- and β-Galf in aqueous solution (COSMO solvation model) using density functional theory (DFT). We compare the calculated low energy conformations to those determined from the program PSEUROT using 1H NMR data. The lowest energy ring conformation for methyl α-Galf is 2E, and this conformer is also the major solution conformation obtained by NMR spectroscopy. For methyl β-Galf, 4E is the lowest energy ring conformation; however, DFT results do not agree with the solution NMR spectroscopic results. Additionally, we developed Galf-specific Karplus-like equations from these conformations.

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