Cyclic Enkephalin Analogues with Exceptional Potency and Selectivity for δ-Opioid Receptors

Abstract

Superpotent and highly delta-opioid receptor selective cyclic peptides of the general formula H-Tyr-c[D-Pen-Gly-Phe(p-X)-Pen]-Phe-OH (where X = hydrogen or halogen) have been synthesized. In the binding assays the most selective and most potent compound is the p-bromophenyl-alanine-4 analogue (IC50 value = 0.19 nM, selectivity ratio = 21,000 for delta vs mu). In the GPI and MVD bioassays the most selective and most potent analogue is the p-fluoro-substituted analogue Tyr-[D-Pen-Gly-Phe(p-F)-Pen]-Phe-OH. In the MVD assay it has an exceptionally low IC50 value of 0.016 nM and a delta vs mu selectivity ratio of 45,000.

Structure–activity relationships of bifunctional cyclic disulfide peptides based on overlapping pharmacophores at opioid and cholecystokinin receptors

“…In fact, analogue 1 is six time more potent than DPDPE. This increased potency at the MVD is consistent with the observations when bulkier analogues, such as Nal [26] and para-substituted Phe [7,19] are substituted in position 4 of enkephalin analogues.…”

Efficient introduction of aryl bromide functionality into proteins in vivo

“…Incorporation of p ‐Br‐phe into short peptides by solid state peptide synthesis has been reported previously [36–38]. The results reported here constitute the first demonstration of an efficient strategy for incorporation of p ‐Br‐phe into protein in vivo.…”

Synthesis and Opioid Activity of Tyr1‐ψ[(Z)CF=CH]‐Gly2 and Tyr1‐ψ[(S)/(R)‐CF3CH‐NH]‐Gly2 Leu‐enkephalin Fluorinated Peptidomimetics

“…However, clinical administration of Leu‐enkephalin is limited by a poor pharmacokinetic (PK) profile, including rapid proteolysis of Tyr 1 ‐Gly 2 by aminopeptidase N in human plasma ( t 1/2 =0.69 min; 0.50 U mL −1 purified enzyme) and of Gly 3 ‐Phe 4 by angiotensin‐converting enzyme at the blood–brain barrier ( t 1/2 =130 min; 0.12 U mL −1 purified enzyme), both of which inhibit penetration into the central nervous system . To improve potency and selectivity, many cyclic and linear analogues of enkephalin have been developed that possess excellent affinities and selectivities for the DOPR, and in some cases, the replacement of hydrolyzable amide bonds at various positions with peptidomimetics (e.g., trans ‐alkene, thioamide, ester or N ‐methyl amide dipeptide isostere) have modulated stability and PK properties of enkephalins, without major loss of agonist activity at the DOPR. However, many of these analogues still lack appropriate physicochemical and biophysical properties for in vivo use.…”

“…[24,25] However, clinicala dministration of Leu-enkephalin is limited by ap oor pharmacokinetic (PK) profile, including rapid proteolysis of Tyr 1 -Gly 2 by aminopeptidaseN in human plasma (t 1/2 = 0.69 min;0 .50 UmL À1 purified enzyme) [26,27] and of Gly 3 -Phe 4 by angiotensin-converting enzyme at the blood-brain barrier (t 1/2 = 130 min;0 .12 UmL À1 purified enzyme), [28] both of which inhibit penetration into the central nervouss ystem. [29] To improve potencyand selectivity,many cyclic and linear analogues of enkephalin have been developed that possess excellent affinities and selectivities for the DOPR, [24,[30][31][32] and in some cases,t he replacement of hydrolyzablea mide bonds at various positions with peptidomimetics (e.g., trans-alkene, [24] thioamide, [33] ester [34] or N-methyl amide dipeptide isostere) [34] have modulated stability andP Kp roperties of enkephalins, without major loss of agonista ctivity at the DOPR.H owever,m any of these analogues still lacka ppropriate physicochemicaland biophysicalp roperties for in vivo use. To generate analogues of enkephalin with improved drug like properties, we herein present new fluorinated Tyr 1 -Gly 2 peptidomimetic analogues.The strategic incorporation of fluorine onto at arget molecule alters several biophysical properties including solubility, lipophilicity,c onformation, and metabolic stability, which in turn affect transporta cross biological membranes, binding efficiencyt ob iological targets and clearance from the host (Figure 1).…”