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1H and 13C Nuclear magnetic resonance studies of leucine-enkephalin glucoconjugates

Synthetic leucine-enkephalin glucoconjugates (1-3) were studied by several one- and two-dimensional 'H and 13C nuclear magnetic resonance (NMR) methods. Although all the values of the temperature coefficients of amide protons were larger than expected for protons involved in hydrogen bonds, using ROESY spectra, it was possible to detect several inter- and intraresidual nuclear Overhauser effects. The results do not support the existence of a single folded conformation, indicating that the structures of glucoconjugates 1-3 in DMSO-đe solution are not completely random. The interresidual ROESY cross-peaks 1 point to the existence of at least one con- former with two turns in 1, involving the Tyr1 and Gly2, and the Leu5 and glucose residues, while, in the glucoconjugates 2 and 3, inter-residual ROESY cross-peaks indicate the presence of a conformer with a different compact structure.

opioid ; enkephalin ; NMR

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