Conversion of Enkephalin and Dermorphin into δ‐Selective Opioid Antagonists by Single‐Residue Substitution

Abstract

The properties of di-and tri-peptides containing 1,2,3,6tetrahydroisoquinoline-3-carboxylic acid (Tic) in second position suggest that the message domain of opioid peptides can be composed of only two residues [Temussi, P. A., Salvadori, S., Amodeo, P., Guerrini, R., Tomatis, R., Lazarus, L. H., Picone, D. & Tancredi, T. (1994) Biochem. Biophys. Res. Commun. 198,. As a crucial test of the possibility that the Tyr-Tic segment be a message domain in longer peptide sequences, we have inserted it in the sequences of two typical opioid peptides: [Leulenkephalin, a non-selective agonist, and dermorphin, a selective p agonist. Here we report the synthesis and biological activity of [~-Tic'] Abhreviations. (C2H3)2S0, fatty deuterated dimethylsulfoxide; DQF-COSY, double quantum filtered correlation spectroscopy; Fmoc, fluoren-9-ylmethoxycarbonyl; NOESY, nuclear Overhauser effect spectroscopy ; Pen, p,p-dimethylcysteine (penicillamine) ; ROESY, rotating frame Overhauser effect spectroscopy; Tic, 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid ; TOCSY, total correlation spectroscopy. MATERIALS AND METHODS Synthesis of peptidesPeptide amides were synthesized by solid-phase methods using fluoren-9-ylmethoxycarbonyl (Fmoc) in the peptide amide linker [5-(4'-Fmoc-aminomethyl-3',5'-dimethoxyphenoxy)-valeric acid] on the poly(ethy1ene glycol)/polystyrene suport (0.18 mmol/g, 0.09 mmol; Millipore. Nu-Fmoc derivatives of amino acids were used in the coupling reactions. The reactive side chains of Tyr and Ser were protected

Conformational analysis of potent and very selective δ opioid dipeptide antagonists

“…In spite of the different configuration of the peptide bond, both conformers (i.e. c/T/T and t/T/T) have a similar compact shape reminiscent of that of the conformer of Tyr-Tic-NH 2 (Clb + f) that we proposed as the bioactive conformation of that antagonist [2,4].…”

“…Notwithstanding, to make a homogeneous comparison with the solution study of Tyr-Tic-NH> we ran all quantitative experiments in a 90110 (v:v) DMSOa6/H20 cryoprotective mixture [2] at 278 K. In fact, we have shown that the use of biocompatible media with viscosities of the order of 7 10 cp, not only leads to a quantitative increase of all NOEs observed at lower viscosity, as expected by the theory of microviscosity, but also to selective growth of (conformationally diagnostic) effects involving backbone protons with respect to intrachain ones [22].…”

“…For instance, enkephalin (a non-selective agonist) and dermorphin (a # selective agonist) are both converted into 6 selective antagonists [2] when their second residue is substituted with Tic. The surprising change of selectivity induced by the change of chirality in peptides containing the tetrahydro-3-isoquinoline carboxylic acid {Tic) in second position, originally interpreted [1] as a conformational preference induced on the Tyr-Xaa-Phe domain, can be *Corresponding author.…”

Design and Solution Structure of a Partially Rigid Opioid Antagonist Lacking the Basic Center — Models of Antagonism

“…However, before drawing any conclusion it is (essential to investigate the conformational preferences of this molecule, also in view of the observation that the corresponding linear compound [Ac-Tyr(Me),-Tic-NH,] shows a higher antagonism but a lower binding affinity. The increase of antagonistic potency of cycle[-Tyr(Me),-Tic-] with respect to cyclo(-Tyr-Tic-) can be attributed to different conformational preferences and/or greater affinity of the Tyr(Me), side chain for the receptor, Since the apparent cause of the low activity of cyclo( -Tyr-Tic-) is the unfavorable 'sandwiched' arrangement of its aromatic rings [20], it is crucial to know whether cycle[-Tyr(Me),-Tic-] can exist in conformations characterized by a 90" arrangement of those rings, consistent with the bioactive conformations of Tyr-Tic-NH,, Tyr(Me),-Tic-NH, and naltrindole [9,10,13,221.…”

“…An opioid antagonist lacking the basic nitrogen (Boc-Tyr-Pro-Gly-PheLeu-Thr-OH) has been reported [19], but the extreme difficulty of finding the bioactive conformation in a flexible linear peptide makes this compound of modest usefulness and prompted us to design a rigid antagonist. The N-terminal Tyr-Tic sequence offers a very versatile basis for the synthesis of such a molecule since the conformational preferences of this dipeptide are limited and very well studied [9][10][11]. As a first approximation we thought that a simple way to get a molecule with the right conformation of the two aromatic moieties and lacking the basic nitrogen might be to prepare the diketopiperazine of Tyr-Tic.…”