Section 8
Chapter 7,034

Apramycin complete proton and carbon 13 nmr assignments and study of the solution conformation by roesy measurements

Szilagyi, L.; Pusztahelyi, Z.S.

Magnetic Resonance in Chemistry 30(2): 107-117


ISSN/ISBN: 0749-1581
DOI: 10.1002/mrc.1260300204
Accession: 007033217

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Complete and self-consistent assignments have been achieved, through the concerted use of various 2D techniques, for the 1H and 13C NMR spectra of the free base and protonated forms, respectively, of apramycin (1) in D2O solution. It is shown that J-relayed dipolar (or J/R) and coherent transfer (HOHAHA) processes in ROESY experiments can hardly be eliminated with spin systems such as that studied here. True ROE cross-peaks can, nevertheless, be identified by varying the experimental conditions. The solution conformation of 1 has been characterized based on the ROESY data, proton-proton coupling constants and 13C T1 measurements. The 4-aminoglucose unit appears to be locked together with the octodiose fragment in a conformation satisfying the requirements of the exo-anomeric effects around the C-1''.sbd.O.sbd.C-8' bond; the 2-deoxystreptamine unit, on the other hand, enjoys more rotational freedom around the respective glycosidic bond. The undistorted chair conformations of all six-membered rings in 1, and the overall conformation of the molecule, are totally independent of the pH, i.e. the protonation state of the molecule.

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