Synthesis and biological activity of analogs of dynorphin-A(1–13) substituted in positions 2 and 4: Design of [Ala²,Trp⁴]-Dyn-A(1–13) as a putative selective opioid antagonist

Abstract

Mono- and di-substituted analogs of dynorphin-A(1-13) (Dyn-A(1-13)) were synthesized by the solid-phase procedure. The products were purified and analyzed for their ability to inhibit the electrically evoked contractions of the guinea pig ileum (GPI) and mouse vas deferens (MVD) and to compete with the binding of [3H]etorphine ([3H]ET) and [3H]ethylketocyclazocine ([3H]EKC) to homogenates of rat brain (mu-, delta-, kappa 2-receptors) and guinea pig cerebellum (kappa-receptor), respectively. Introduction of Ala in position 2 caused a drastic decrease in the activity of the peptide on the smooth muscle preparations (IC50 of 104 and 2.250 nM in the GPI and the MVD as compared with 0.7 and 21 nM for the parent peptide, respectively). Conversely, this analog retained much of the opioid binding activity of Dyn-A(1-13) (relative binding potencies of 15 and 72% for the displacement of [3H]ET and [3H]EKC, respectively). The replacement of Phe4 by Trp also caused drastic decreases in the activity of the peptide in the smooth muscle preparations (relative potencies of 0.8 and 8.8% on the GPI and MVD) while much of the binding potency to the opioid receptors was retained (31 and 67% for the displacement of [3H]ET and [3H]EKC, respectively). [Ala2,Trp4]-Dyn-A(1-13) was the least potent peptide tested in the smooth muscle assays (relative potencies: 0.1 and 0.6%). However, this latter analog still retained some opioid binding activity in the displacement of [3H]ET to rat brain homogenates (3%).(ABSTRACT TRUNCATED AT 250 WORDS)

N,N‐diallyl‐tyrosyl substitution confers antagonist properties on the κ‐selective opioid peptide [D‐Pro10]dynorphin A(1–11)

“…This idea recently emerged from the fact that, in the case of many biological peptide (hormone)-receptor systems, antagonists are generally analogues derived from the endogenous ligand itself (for reviews, see Manning & Sawyer, 1984;Regoli, 1985). In the case of the opioid receptors, [Ala2, Trp4]dyn A (1-13) has been claimed to be a K-selective opioid antagonist (Lemaire & Turcotte, 1986) and we have shown that D-Trp substitution at positions 2, 4, 5 and 8 in the sequence of [D-Pro'l]-dyn A (1-1 1XDPDYN), a K-selective analogue of dyn A (Gairin et al, 1984), led to analogues with opioid antagonist properties (Gairin et al, 1986). An alternative approach in the search for opioid antagonist peptides may be to design peptides in which the Nterminal tyrosyl residue possesses an N-allyl substituent, by analogy with that of the nitrogen atom of the piperidine ring of the most powerful alkaloid opiate antagonists.…”

Opioid Receptors and their Ligands

“…The development of Dyn A analogs with κ antagonist properties has met with only limited success so far. Several Dyn A-derived κ antagonists have been described [169][170][171][172], but none of them showed both, high κ antagonist potency and high κ receptor selectivity. Among various non-peptide κ antagonists reported to date, norbinaltorphimine (norBNI) and GNTI display high activity and κ selectivity.…”

Rational Approach to the Design of Bioactive Peptidomimetics: Recent Developments in Opioid Agonist Peptides

“…Peptides obtained through the application of this technique, possess decreased GPI potencies as reported by GPI bioassay, with exception of peptide containing Ala 8 in Dyn A(1-13) sequence, which is well tolerated; these studies revealed that Arg 6 , Arg 7 , Arg 9 , Lys 11 , N-terminal Tyr and Phe 4 residues are essential for the bioactivity and their suppression causes a drastic loss of potency at k-opioid receptor, whereas Ile 8 and Pro 10 can be substituted by different amino acids to improve potency [141,142].…”