Structure‐activity relationships of dermorphin analogues containing N‐substituted amino acids in the 2‐position of the peptide sequence

Abstract

A series of dermorphin analogues containing an N-alkylated amino-acid residue Xaa in the 2-position of the peptide sequence was synthesized (Xaa = N-methylalanine, proline, pipecolic acid, N-methylphenylalanine, 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid [Tic]). These peptides have the potential of assuming a cis Tyrl-Xaa2 peptide bond. Their in vitro opioid activity profiles were determined in p-and b-receptorrepresentative binding assays and bioassays. Aside from [ ~-Pro~]dermorphin, all analogues showed high affinity for p-and/or 6-opioid receptors. Whereas most compounds were found to be full p-agonists in the guinea pig ileum (GPI) assay, [Tic2]dermorphin (compound 7) was a partial p-agonist. Replacement of Gly4 in 7 with Phe resulted in an analogue (8) with weak p-antagonist activity. Furthermore, analogues 7 and 8 both were potent &antagonists ( K , = 3-40 nM) against the 6-agonists Leu-enkephalin, DPDPE and deltorphin I in the mouse vas deferens (MVD) assay. Compound 3, containing L-Pro in the 2-position, turned out to be one of the most preceptor-selective linear dermorphin analogues reported to date. Low-temperature HPLC experiments using micropellicular octadecyl silica as stationary phase revealed conformational heterogeneity of the dermorphin analogues which was ascribed to cis-trans isomerization around the Tyrl-Xaa2and Tyr5-Pro6 peptide bonds. In the case of analogue 7 four separate peaks corresponding to the four possible isomers were apparent at -5°C. Since opioid peptide analogues with a non-N-akylated L-amino acid residue in the 2-position are nearly inactive and cannot assume a cis peptide bond at the 1-2 position, these results support the hypothesis that the bioactive conformation of opioid peptides containing an N-alkylated L-amino acid residue in position 2 is characterized by a cis Tyrl-Xaa2 peptide bond. 0 Munksgaard 1995. Since the discovery of the enkephalins, other opioid peptides originating from distinct mammalian precur-

Design, Synthesis and Pharmacological Characterization of Endomorphin Analogues with Non‐Cyclic Amino Acid Residues in Position 2

“…The best substituents for position 2 turned out to be d ‐Ala and N‐methylated Ala or Gly residues. Much earlier, structure–activity relationship studies of dermorphins, atypical μ‐selective opioids from frog skin extracts, revealed the crucial role of the d ‐amino acid residue in the 2‐position for opioid activity [25]. Interestingly, analogues with L‐configuration in this position were completely inactive [26], but the activity was restored when the position 2 residue was N‐methylated [25].…”

“…Much earlier, structure–activity relationship studies of dermorphins, atypical μ‐selective opioids from frog skin extracts, revealed the crucial role of the d ‐amino acid residue in the 2‐position for opioid activity [25]. Interestingly, analogues with L‐configuration in this position were completely inactive [26], but the activity was restored when the position 2 residue was N‐methylated [25]. Due to isomerization around Tyr‐Pro peptide bond, EMs exist as a mixture of cis and trans rotamers and despite the extensive research, it is still unknown whether they adopt the cis or trans configuration around this bond when bound to the receptor [27].…”

Structure‐activity relationship and metabolic stability studies of backbone cyclization and N‐methylation of melanocortin peptides

“…They have also shown enhanced potency19–22 and new receptor subtype selectivity 23–25. For example, N‐methylated cyclic RGD peptides22 and dermorphin analogs26 have been shown to be more potent following mono N‐methylation. Multiple N‐Methylation (MNM) is an approach where a library of all possible N‐methylated peptide analogs, based on the sequence of a linear or cyclic bioactive peptide, is synthesized and screened to select an active N‐methylated analog 17.…”

Reaction Parameters for the Synthesis of N,N-Dimethyl Fatty Hydrazides from Oil

“…The FTIR spectrum of fatty hydrazides shows absorption bands for the primary amine N-H stretching at 3318. 8 The disappearance of absorption bands of the primary amine N-H stretching and N-H bending indicated that the reaction occurred at the NH 2 group. However, a weak absorption band of primary amine N-H stretching was observed with 0.003 mol KOH at frequencies 3343.…”

“…Many N-alkylation methods have been reported by Salvatore and co-workers, 2001 7 . N-methylated amines hold critical importance in amine chemistry 8 . Recently, Badr and co-workers 2010 reported direct N-methylation of primary amines using dimethyl sulfate with 80 yield.…”