Glycoconjugates of opioid peptides

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Abstract
Three N‐glycoconjugates of the general formula H‐Tyr‐Gly‐Gly‐Phe‐Leu‐NH‐R (R = carbohydrate residue) were synthesized in order to determine the influence of some carbohydrate molecules (6‐amino‐6‐deoxy‐d‐glucopyranose, 2‐amino‐2‐deoxy‐d‐glucopyranose, β‐d‐glucopyranosylamine) on the biological activity, conformation, and stability of the opioid pentapeptide [Leu5]enkephalin. For the preparation of this compound different methods of peptide synthesis (active ester and mixed anhydride) were investigated. In comparison with [Leu5]enkephalin, all three N‐glycoconjugates showed higher potency in the guinea pig ileum assay and lower potency in the mouse vas deferens assay, indicating a decrease in b opioid receptor selectivity.