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Apramycin: Complete 1 H and 13 C NMR assignments and study of the solution conformation by ROESY measurements
Author(s) -
Szilágyi László,
Puzstahelyi Zita Sz.
Publication year - 1992
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260300204
Subject(s) - chemistry , protonation , anomer , glycosidic bond , crystallography , molecule , stereochemistry , proton , j coupling , coupling constant , nuclear magnetic resonance spectroscopy , physics , ion , organic chemistry , quantum mechanics , enzyme , biochemistry , particle physics
Complete and self‐consistent assignments have been achieved, through the concerted use of various 2D techniques, for the 1 H and 13 C NMR spectra of the free base and protonated forms, respectively, of apramycin (1) in D 2 O 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 13 C T 1 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"OC‐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.