Acetylated glucopyranosyl esters of enkephalins

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Abstract
Acetylated D-glucopyranosyl esters of enkephalins were prepared by two different fragment condensation procedures involving direct participation of imidazole in the ester linkage formation. By both methods anomeric mixtures of D-glucosyl esters were obtained and resolved by column chromatography. Depending on coupling conditions, racemization of either the C-terminal or the penultimate amino acid residue of the enkephalin molecule occurred. The glucoconjugates with inverted stereochemistry were quantitated and separated from the main product by reversed-phase high-performance liquid chromatography. The opioid agonist potencies of the synthesized glucopyranosyl esters of enkephalins on electrically stimulated guinea pig ileum and mouse vas deferens preparations were determined in comparison with [Leu5]enkephalin.