title: Extended TIP(P) analogues as precursors for labeled delta-opioid receptor ligands.
abstract: Tyr-Tic-Phe-Phe-OH (TIPP) and the shorter Tyr-Tic-Phe-OH (TIP) peptides are potent and highly selective antagonists at the delta-opioid receptor and, therefore, are ideal candidates for the attachment of labels to assist in the study of delta-opioid receptors. Peptides extended at the C-terminus with residues which can be used as handles for further modification and/or labeling (i.e. Asx, Glx, and Lys) were synthesized. The TIPP-D/L-Asx/Glx derivatives exhibited similar delta-receptor affinity to TIPP (K(i) = 5-10 nM vs K(i) = 6 nM), and neither the location of the carboxylic acid moiety nor the stereochemistry of the C-terminal residue significantly affected the delta-receptor affinity of these derivatives. Extension of TIPP with an additional residue did not increase mu-receptor affinity, even though the position of the acidic group, which imparts delta-receptor selectivity to TIPP, was shifted relative to the carboxylic acid moiety of TIPP. The delta-receptor affinities of the TIP-D/L-Asx/Glx derivatives were found to be influenced mainly by the position of the carboxylic acid function rather than the stereochemistry of the C-terminal residue. TIP(P)-D/L-Lys(Ac)-OH derivatives exhibited moderate delta-receptor affinity (K(i)(delta) = 16-28 nM). The most potent compounds found in the extended TIP(P) series were TIPP-D-Gln-OH and TIP-D-Gln-OH (K(i)(delta) = 5 nM) which had similar affinities to TIPP.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, Maryland 21201, USA.
authors.forename: V
authors.initials: V
authors.lastname: Kumar
authors.forename: T F
authors.initials: TF
authors.lastname: Murray
authors.forename: J V
authors.initials: JV
authors.lastname: Aldrich
mesh_terms: D000345:Affinity Labels / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D011869:Radioligand Assay; D017465:Receptors, Opioid, delta / Q000037:antagonists & inhibitors* / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013329:Structure-Activity Relationship; D044005:Tetrahydroisoquinolines
chemical_list: D000345:Affinity Labels; D009842:Oligopeptides; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D044005:Tetrahydroisoquinolines; C082263:tyrosyl-1,2,3,4-tetrahydro-3-isoquinolinecarbonyl-phenylalanyl-phenylalanine