title: Synthesis and opioid activity of [D-Pro10]dynorphin A-(1-11) analogues with N-terminal alkyl substitution.
abstract: Several N-terminal di- and monoalkylated derivatives of [D-Pro10]dynorphin A-(1-11) were synthesized in order to explore the structure-activity relationships for antagonist vs agonist activity at kappa-opioid receptors. N,N-Dialkylated and N-monoalkylated (alkyl = allyl, benzyl, and cyclopropylmethyl (CPM) tyrosine derivatives were prepared from tyrosine tert-butyl ester and the corresponding alkyl halides. [D-Pro10]Dyn A-(2-11) was prepared by solid phase synthesis using Fmoc-protected amino acids, and the tyrosine derivatives were coupled to the peptide with BOP ((benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate). Both the degree of substitution and the identity of the alkyl group affected kappa-receptor affinity, selectivity, and efficacy. All of the N-monoalkylated derivatives exhibited much higher affinity (Ki < 0.05 nM) for kappa receptors in the guinea pig cerebellum and greatly enhanced kappa-receptor selectivity (Ki ratio (kappa/mu) > 200) compared to the N,N-dialkyl [D-Pro10]Dyn A-(1-11) analogues, although one disubstituted analogue, N,N-diCPM[D-Pro10]Dyn A-(1-11), retained high affinity (Ki = 0.19 nM) for kappa receptors. Thus the introduction of the second alkyl group at the N-terminus lowered kappa-receptor affinity and selectivity. The N-allyl and N-CPM analogues were moderately potent agonists in the guinea pig ileum (GPI) assay, while the N-benzyl derivative was a weak agonist in this assay. In vivo in the phenylquinone abdominal stretching assay the N-CPM analogue exhibited potent antinociceptive activity (ED50 = 1.1 micrograms/mouse), while N-allyl[D-Pro10]Dyn A-(1-11) exhibited weak antinociceptive activity (ED50 = 27 micrograms/mouse). For the N,N-dialkyl derivatives the identity of the N-terminal alkyl group affected the efficacy observed in the smooth muscle assays. The N,N-diCPM analogue exhibited negligible agonist activity, and N,N-diallyl[D-Pro10]Dyn A-(1-11) showed weak antagonist activity against Dyn A-(1-13)NH2 in the GPI. In contrast, the N,N-dibenzyl compound showed appreciable opioid agonist activity in this assay. In vivo the N,N-diallyl analogue exhibited weak antinociceptive activity (ED50 = 26 micrograms/mouse in the phenylquinone abdominal stretching assay). The N-monoalkylated peptides are among the most kappa-selective opioid peptides reported to date, showing comparable or greater selectivity and higher affinity than the kappa-selective non-peptide agonists U-50,488 and U-69,593. The N,N-diCPM and N,N-diallyl peptides are lead compounds in the development of peptide-based kappa-receptor antagonists.
authors.affiliation: College of Pharmacy, Oregon State University, Corvallis 97331, USA.
authors.forename: H
authors.initials: H
authors.lastname: Choi
authors.forename: T F
authors.initials: TF
authors.lastname: Murray
authors.forename: G E
authors.initials: GE
authors.lastname: DeLander
authors.forename: W K
authors.initials: WK
authors.lastname: Schmidt
authors.forename: J V
authors.initials: JV
authors.lastname: Aldrich
mesh_terms: D000478:Alkylation; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004399:Dynorphins / Q000737:chemistry* / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D051379:Mice; D008956:Models, Chemical; D009292:Narcotic Antagonists; D011957:Receptors, Opioid / Q000819:agonists*; D013329:Structure-Activity Relationship
chemical_list: D000596:Amino Acids; D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D004399:Dynorphins