Synthesis and characterization of mannose-related imidazolidinones formed by the intramolecular rearrangement of the mannopyranose ester of leucine-enkephalin
Abstract
Detailed scrutiny of the intramolecular reactivity of mannopyranose ester 1, a neoglycopeptide in which D-mannose is linked to leucine-enkephalin through an ester bond involving the carboxylic function of the C-terminal leucine residue and the hydroxylic function at C-6 in the D-mannopyranose moiety, demonstrates for the first time that, in addition to intramolecular Amadori rearrangement (in Py–HOAc), an alternative pathway is possible. Thus, incubation of 1 in methanol or water as solvent gives the previously unknown bicyclic mannose-related imidazolidinone 2. Its formation is studied as a function of solvent and temperature. Hydrolysis of the ester linkage in bicyclic compound 2 gives the novel mannose-related imidazolidinone 3, in almost quantitative yield.
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