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Conformationally Restricted Peptides as Tools in Opioid Receptor Studies

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The discovery of endogenous opioid peptides with their limited receptor selectivity more than two decades ago implicated their involvement in analgesia and initiated efforts to understand the molecular mechanisms underlying their action. Opioid peptides mediate their physiological and pharmacological effects through three major opioid receptor types (μ, δ, κ), but the role of each of these receptors is not easy to distinguish. There has therefore, been an increasing need for potent and selective agonists and antagonists in this area.

The incorporation of conformational constraints into analogs of biologically active peptides is a well-known approach for enhancing receptor selectivity and modulating efficacy. Conformational restriction has proven a valuable means for assessing disparities between the peptide binding characteristics at each of the opioid receptor types, since peptide analogs designed with appropriate conformational constraints possess the ability to adopt the conformation required for interaction at one receptor type but not another.

In efforts to obtain better conformational integrity various conformationally restricted analogs of endogenous opioid peptides have been developed. In this paper we review the development of opioid analogs whose conformation was restricted either globally through different types of cyclization (such as amide bond formation, disulfide and monosulfide bridges, carbonyl and amine bridges) or locally, through incorporation of side-chain conformational constraints at a specific amino acid residue by synthesizing cyclic amino acids or constraining torsion angles by suitable substitutions. These two approaches have led to the development of potent and very selective agonists and antagonists at all three opioid receptor types.

Keywords: agonists and antagonists; opioid peptides; receptor binding; receptor selectivity; structure-activity relationships

Document Type: Review Article


Affiliations: Department of Medicinal Chemistry, Medical University of Lodz, Mazowiecka 6 / 8, 92-215 Lodz, Poland.

Publication date: February 1, 2005

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  • Current Medicinal Chemistry covers all the latest and outstanding developments in medicinal chemistry and rational drug design. Each issue contains a series of timely in-depth reviews written by leaders in the field covering a range of the current topics in medicinal chemistry. Current Medicinal Chemistry is an essential journal for every medicinal chemist who wishes to be kept informed and up-to-date with the latest and most important developments.

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