title: N-terminal 4-imidazolidinone prodrugs of Leu-enkephalin: synthesis, chemical and enzymatic stability studies.
abstract: Four N-terminal 4-imidazolidinone prodrugs of Leu-enkephalin are prepared and characterized. Their enzymatic and chemical stability are assessed using high-performance liquid chromatography. The prodrug derivatives are shown to degrade stoichiometrically to Leu-enkephalin in phosphate buffer [t1/2 (0.05 M phosphate buffer without KCl): acetone prodrug (II) 930 min; cyclopentanone prodrug (III): 216 min; cyclohexanone prodrug (IV): 432 min; 4-methylcyclohexanone prodrug (V): 792 min]. Furthermore, the prodrugs are shown to afford global stabilization of the Leu-enkephalin molecule towards the enzymes, aminopeptidase N and angiotensin converting enzyme, primarily responsible for degradation of Leu-enkephalin at the blood-brain barrier and in plasma. Therefore, the 4-imidazolidinones, being metabolic stable and bioreversible, may be suitable prodrug candidates for delivery of Leu-enkephalin to important target areas such as the brain, if given intravenously.
authors.affiliation: Department of Analytical and Pharmaceutical Chemistry, The Royal Danish School of Pharmacy, Universitetsparken 2, Copenhagen DK-2100, Denmark.
authors.forename: A
authors.initials: A
authors.lastname: Bak
authors.forename: M
authors.initials: M
authors.lastname: Fich
authors.forename: B D
authors.initials: BD
authors.lastname: Larsen
authors.forename: S
authors.initials: S
authors.lastname: Frokjaer
authors.forename: G J
authors.initials: GJ
authors.lastname: Friis
mesh_terms: D001812:Blood-Brain Barrier; D002021:Buffers; D018826:CD13 Antigens / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives* / Q000097:blood / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007093:Imidazoles / Q000138:chemical synthesis* / Q000737:chemistry; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism; D011355:Prodrugs / Q000138:chemical synthesis* / Q000737:chemistry; D012996:Solutions