title: Morphiceptin and beta-casomorphin-5 analogues containing a reduced peptide bond: selective mu-receptor agonists and a novel mu antagonist, H-Tyr-Pro psi (CH2-NH)Phe-Pro-Gly-OH.
abstract: In order to prevent enzymatic degradation of beta-casomorphin-5 (1) and morphiceptin, reduced peptide bonds were incorporated at the 2-3 and 3-4 bonds, respectively. The analogues were synthesized by a combination of solid phase methodology and reductive alkylation of resin-bound peptide amines with Boc-amino acid aldehydes (Boc: tert-butyloxycarbonyl) in the presence of NaBH3CN. During reversed phase high pressure liquid chromatography purification, peak shape distortions could be observed. Epimerization was excluded, based on gas chromatography/mass spectroscopy analysis, which indicated acceptable levels of racemization (less than 3%) in the crude product. Instead, the phenomena could be attributed to slow cis/trans isomerizations originating from the Xxx-Pro bonds in the sequence. The presence of different conformational isomers was also established by 1H-nmr spectroscopy in DMSO-d6. All analogues showed high stability in blood plasma, enhanced binding affinity for the mu receptor, and very low binding to the delta receptor. While the Phe 3 psi(CH2-N)Pro4 analogues (3) and (5) displayed agonist activity, the Pro 2 psi(CH2-NH)Phe3 modified analogue (2) showed antagonist activity comparable to D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2.
authors.affiliation: Eenheid Organische Chemie, Vrije Universiteit Brussel, Belgium.
authors.forename: N G
authors.initials: NG
authors.lastname: Delaet
authors.forename: P M
authors.initials: PM
authors.lastname: Verheyden
authors.forename: D
authors.initials: D
authors.lastname: Tourwe
authors.forename: G
authors.initials: G
authors.lastname: Van Binst
authors.forename: P
authors.initials: P
authors.lastname: Davis
authors.forename: T F
authors.initials: TF
authors.lastname: Burks
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002364:Caseins / Q000037:antagonists & inhibitors / Q000737:chemistry*; D004558:Electric Stimulation; D004723:Endorphins / Q000737:chemistry* / Q000378:metabolism; D006168:Guinea Pigs; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009842:Oligopeptides / Q000737:chemistry* / Q000494:pharmacology; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D002364:Caseins; D004723:Endorphins; D009842:Oligopeptides; D010446:Peptide Fragments; D010455:Peptides; D017450:Receptors, Opioid, mu; C072948:CM 2-3; C034812:beta-casomorphin 5; C028889:morphiceptin