Antinociceptive effects in rodents of the dipeptide Lys-Trp (Nps) and related compounds

Solid-phase synthesis of new Trp(Nps)-containing dipeptide derivatives as TRPV1 channel blockers

Trp(Nps)-Lys-NH₂ derivatives, bearing alkyl or guanidine groups either at the N–terminus or on the Lys side-chain or at both positions were conveniently prepared on solid-phase and evaluated as TRPV1 channel antagonists.

Old Molecules for New Receptors: Trp(Nps) Dipeptide Derivatives as Vanilloid TRPV1 Channel Blockers

The transient receptor potential vanilloid member 1 (TRPV1), an integrator of multiple pain-producing stimuli, is regarded nowadays as an important biological target for the discovery of novel analgesics. Here, we describe the first experimental evidence for the behavior of an old family of analgesic dipeptides, namely Xaa-Trp(Nps) and Trp(Nps)-Xaa (Xaa=Lys, Arg) derivatives, as potent TRPV1 channel blockers. We also report the synthesis and biological investigation of a series of new conformationally restricted Trp(Nps)-dipeptide derivatives with improved TRPV1/NMDA selectivity. Compound 15 b, which incorporates an N-terminal 2S-azetidine-derived Arg residue, was the most selective compound in this series. Collectively, a new family of TRPV1 channel blockers emerged from our results, although further modifications are required to fine-tune the potency/selectivity/toxicity balance.

Effects of peptides on animal and human behavior: a review of studies published in the first twenty years of the journal Peptides

This review catalogs effects of peptides on various aspects of animal and human behavior as published in the journal Peptides in its first twenty years. Topics covered include: activity levels, addiction behavior, ingestive behaviors, learning and memory-based behaviors, nociceptive behaviors, social and sexual behavior, and stereotyped and other behaviors. There are separate tables for these behaviors and a short introduction for each section.

CNS effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides, 1986-1993

The centrally mediated effects of peptides as published in the journal Peptides from 1986 to 1993 are tabulated in two ways. In one table, the peptides are listed alphabetically. In another table, the effects are arranged alphabetically. Most of the effects observed after administration of peptides are grouped, wherever possible, into categories such as cardiovascular and gastrointestinal. The species used in most cases has been rats; where other animals were used, the species is noted. The route of administration of peptides and source of information also are included in the tables, with a complete listing provided at the end. Many peptides have been shown to exert a large number of centrally mediated effects.

Hypoalgesic action of bestatin analogues that inhibit central aminopeptidases, but not neutral endopeptidase

Two analogues of the aminopeptidase inhibitor bestatin, Z 4212 (N-[(2S, 3R)-3-Amino-2-hydroxy-4-(4-methylsulphonyl-phenyl)-1-oxobutyl]-1- aminocyclopentanecarboxylic) and Z 1796 ((2S)-N-[(2S,3R)-3-Amino-2-hydroxy-4-(4-methylsulphonyl-phenyl)-1- oxobutyl]-L-leucine) were found to behave as hypoalgesics when intracerebroventricularly (i.c.v.) administered to mice in the hot-plate test. At high doses, Z 4212 was also found to reduce the pain threshold after intraventricular (i.v.) administration. Hypoalgesia induced by bestatin analogues was prevented by prior treatment with the opiate receptor blocker naloxone. Thiorphan, a potent inhibitor of NEP, was found to enhance the hypoalgesic effect of low doses of either Z 4212 or Z 1796. These results indicate that both the major opioid-degrading peptidases, i.e. aminopeptidases and neutral endopeptidase (NEP), are individually implicated in the hypoalgesia induced by peptidase inhibitors. In vitro studies showed that these new bestatin analogues readily inhibit aminopeptidases in membranes from mouse c. striatum whereas more than 1000 times the concentration was required for NEP to be blocked. Ex vivo experiments showed that, at variance with bestatin, the hypoalgesic action of Z 4212 or Z 1796 appeared to implicate central aminopeptidases but not NEP, so partially sparing the metabolism of other NEP substrates that might produce additional alterations (substance P and ANP). On the basis of the antitumour and immunomodulatory actions of bestatin, these new analogues might be potentially useful as mixed antitumour and hypoalgesic agents in malignancy.

Synthesis and inhibitory activities against enkephalin degrading aminopeptidase of H-Trp(Nps)-Lys-OMe analogues bearing chelating groups

With the aim of increasing the inhibitory potency of the analgesic dipeptide H-Trp(Nps)-Lys-OMe against enkephalin-degrading aminopeptidases, the following derivatives bearing chelating groups at the N-terminus have been synthesized: Ac-Trp(Nps)-Lys-OMe (3), HS(CH2)nCO-Trp(Nps)-Lys-OMe [n = 1 (4), n = 2 (5)], MeOCO(CH2)n-Trp(Nps)-Lys-OMe [n = 1 (6), n = 2 (7)] and analogues in which the N alpha-amino group has been replaced by a methoxycarbonyl group (8) and a bidentate hydroxamate function (9), respectively. The inhibitory activities of all these compounds and the S-protected derivatives EtNHCOS(CH2)nCO-Trp(Nps)-Lys-OMe [n = 1 (16), n = (17)] against the mentioned enzyme, isolated from rat striatum, are compared with those of the parent dipeptide 2 and bestatin. All the new derivatives showed, in general, inhibitory potencies of the same order of magnitude as compound 2.

Prolonged antinociceptive activity of pseudodipeptide analogues of Lys-Trp(Nps) and Trp(Nps)-Lys

Peptide bond substitution in the molecules of Lys-Trp(Nps) (LTN) and Trp(Nps)-Lys (TNL) by an aminomethylene and ketomethylene bond, respectively, afforded pseudodipeptides with analgesic activity. The new compounds Lys psi(CH2NH)-Trp(Nps)-OMe (LTNAM) and Trp(Nps)psi(COCH2)(R,S)-Lys (TNLKM) induced a dose-dependent and naloxone-reversible analgesia following intracerebroventricular (ICV) administration to mice. The antinociceptive effects were longer lasting compared to those induced by the parent compounds. The pseudodipeptides protected Met-enkephalin degradation by rat striatal slices and, combined with an ineffective dose of the opioid peptide, induced analgesia. LTNAM and TNLKM were as potent as LTN to inhibit brain aminopeptidase in vitro and ex vivo. An increased resistance to proteolysis of the pseudodipeptides may explain their prolonged analgesic activity.

Analgesic dipeptides. VI.: Synthesis and structure-activity relationships of N-terminal modified analogues of the analgesic compounds H-Xaa-Trp(Nps)-OMe (Xaa=Lys, Orn, Arg)

In order to determine the influence of the N-terminal amino group of the dipeptide derivatives H-Xaa-Trp(Nps)-OMe[Xaa = Lys (2a), Orn (2b), Arg (2c)] on their antinociceptive effects, the syntheses of their corresponding deaminated, acetylated and dimethylated analogues have been achieved. Deamino and dimethyl analogues of 2a,b,6a,b, and 18a,b were prepared by coupling the corresponding N omega-Z- and N omega-Z-N alpha-Me2 amino acids with H-Trp-OMe, using the DCC/HOSu method, followed by sulfenylation of the resulting compounds and removal of the Z groups. Guanidylation of 6b and 18b provided the arginine analogues 6c and 18c, respectively. Ac-Xaa-Trp(Nps)-OMe [Xaa = Lys (11a), Orn (11b) were synthesized by acetylation of H-Xaa(Z)-Trp(Nps)-OMe with acetic anhydride, in the presence of 4-dimethylaminopyridine, and subsequent removal of the Z groups. Coupling of Ac-Arg-OH.HC1 with H-Trp-OMe, using the DCC/HOSu procedure, followed by sulfenylation of the resulting 8:3 diastereomeric mixture of L,L and L,D dipeptides afforded Ac-ambo-Arg-Trp(Nps)-OMe 11c+11d. The antinociceptive effects of 6a-c, 11a-d, and 18 a-c were evaluated after i.c.v. administration in mice. The N alpha-acetyl dipeptides 11 were found to exhibit a naloxone-reversible antinociceptive effects comparable with those of 2, while N-deaminated and N,N-dimethylated analogues were inactive.