Restricted Conformational Flexibility of Furanose Derivatives:  Ab Initio Interpretation of Their Nuclear Spin−Spin Coupling Constants

Abstract

Indirect spin-spin NMR 1 H-1 H coupling constants of newly synthesized furanose monosaccharide derivatives were interpreted on the basis of ab initio modeling. Epoxy, epithio, and epimino groups were inserted into the sugars and significantly limited their conformational flexibility, which was confirmed by a systematic conformer analysis. Because of the restriction, the performance of the computations and the dependence of the coupling constants on the geometry could be estimated more easily. Conventional Karplus equations are not optimized for this class of compounds and cannot be used for reliable interpretation of the NMR spectra. Fully analytical B3LYP/IGLOII computations of the coupling constants were performed including all the four important magnetic terms (SD, DSO, PSO, FC) in the Hamiltonian. Good agreement of the calculated and the experimental coupling constants was achieved, and computed structural parameters are consistent with available X-ray data. The influence of the different functional groups on the spin-spin coupling constants was discussed.

Relative importance of first and second derivatives of nuclear magnetic resonance chemical shifts and spin-spin coupling constants for vibrational averaging

“…Unlike for the shielding, DFT established as a reliable method for estimation of the indirect spin-spin coupling constants. 24,26,31,45 Indeed, the calculated equilibrium J͑C-H͒ and J͑H-H͒ coupling constants in the methane derivatives ͑J 0 in Table V͒ faithfully mimic the experimental values. However, couplings involving the fluorine atom are notoriously difficult for DFT.…”

“…Unfortunately, the precision of the DFT computations is limited, and from the comparison of the B3LYP and BPW91 values in Table VIII we can estimate that the overall error is similar as the vibrational part itself. As discussed before 31 the error might also be caused by incomplete basis set; even a presence of another conformer in the sample cannot be completely excluded. As for the methanes, it is pleasant to see that the J-coupling vibrational corrections obtained at the two levels ͑BPW91, B3LYP, c.f.…”

“…In order to verify the tendencies on more applied systems and having in mind the tremendous power of NMR for biomolecular studies 1,29 we also vibrationally average J-coupling constants for three variously charged alanine forms and two sugar derivatives, experimental results for which are reported in previous works. 30,31 Indeed, the averaging led to a considerable increase in precision of the alanine spin-spin coupling constants. For the sugars, it may enhance the overall precision, but the vibrational effects are comparable to the error of the DFT computations and experimental inaccuracy.…”

Conformational behavior of simple furanosides studied by optical rotation

“…In the past, we discussed the structural information that could be obtained from the NMR data. 13 In this work, we concentrate on the optical rotation that can be measured more easily. As shown below, also the analysis of the OR data can be significantly enhanced by an ab initio conformational search coupled to state-of-the-art calculations of optical rotations.…”

Dependencies of J-Couplings upon Dihedral Angles on Proteins

“…In this sense, exploring the dependence of a given J-coupling over the entire range of values of the corresponding dihedral angle can be better achieved using ab initio calculations [24,80,[87][88][89][90][91][92][93][94][95][96][97][98][99][100][101][102][103][104]107,[111][112][113][114][115][116][117][118][119][120][121][122][123]. Whether or not the associated Karplus fit will improve over the empirical ones for structure determination critically depends on the ability of the computational model (i.e.…”