Cyclic morphiceptin analogs: cyclization studies and opioid activities in vitro.
Attempts were undertaken to develop cyclic beta-casomorphin-5 analogs with improved opioid activity profiles by deletion of the glycine residue in position 5, leading to analogs structurally related to the opioid peptide morphiceptin (H-Tyr-Pro-Phe-Pro-NH2). The tetrapeptide sequence Boc-Tyr(tBu)-D-Xaa-Phe-Yaa-OH (Xaa = Lys, Orn, A2bu; Yaa = Pro in L- or D-configuration) was used to study the influence of ring size and chirality on the yield of cyclization between the omega-amino group of Xaa and the C-terminal carboxyl group. In all cases the cyclization reaction was performed under identical experimental conditions to allow a direct comparison with regard to yield and homogeneity. The reaction products were purified by crystallization and liquid chromatography, and were characterized by HPLC, TLC, electrospray mass spectrometry and 1H-NMR spectroscopy. In none of the reactions performed with the cyclization precursors containing proline in the L-configuration could a cyclic monomer be detected, and the cyclodimer (7-9) was the exclusive product in each case. Cyclodimerization was also the favored reaction in the attempted formation of the 11-membered ring of the cyclic [D-A2bu2, D-Pro4]-morphiceptin analog 12, since only traces of the monomer were found. In the case of both the [D-Lys2, D-Pro4]-analog 10 and the [D-Orn2, D-Pro4]-analog 11, the cyclomonomer/cyclodimer ratio was about 80:20. The cyclic monomers 10 and 11 showed high opioid activity in the mu-receptor-representative guinea pig ileum assay (IC50 = 2-5 nM) and in the delta-receptor representative mouse vas deferens assay (IC50 = 50-60 nM), whereas the potency of the cyclodimers was 2-3 orders of magnitude lower in both in vitro bioassays.
Vogel
D
D
Department of Drug Biochemistry, Hans-Knoell-Institute of Natural Product Research Jena, Halle, Saale, Germany.
Schmidt
R
R
Hartung
K
K
Demuth
H U
HU
Chung
N N
NN
Schiller
P W
PW
D000700:Analgesics / Q000138:chemical synthesis / Q000302:isolation & purification / Q000494:pharmacology; D000818:Animals; D004723:Endorphins / Q000494:pharmacology*; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D013058:Mass Spectrometry; D051379:Mice; D009119:Muscle Contraction / Q000187:drug effects; D018847:Opioid Peptides / Q000138:chemical synthesis* / Q000302:isolation & purification / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000302:isolation & purification / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D014649:Vas Deferens / Q000187:drug effects / Q000378:metabolism
D000700:Analgesics; D004723:Endorphins; D018847:Opioid Peptides; D010446:Peptide Fragments; D010456:Peptides, Cyclic; C034812:beta-casomorphin 5; C028889:morphiceptin