| Oligomeric peptide analogues represent interesting biological probes to investigate molecular recognition and receptor aggregation. This dissertation describes the design and the synthesis of a series of branched peptides emanating from an oligolysine core. Such species resemble dendritic types of molecules, some of which have been used to elicit antibody production more readily (the latter have been termed multiple antigenic peptides or MAPs).; Opioid peptides, potential analgesic agents, bind to various subtypes {dollar}(mu, delta,{dollar} and {dollar}kappa){dollar} of G protein-coupled receptors. The linear bioactive pharmacophore, Tyr-D-Ala-Phe, a common element in highly potent and selective deltorphins and dermorphin sequences, was selected for attachment to a branched lysine core. The specific goal of this dissertation is the design of dimeric and tetrameric opioid analogues that have spacer groups (Gly, aminocaproic acid (Aca), {dollar}alpha{dollar}-aminoisobutyric acid (Aib), and 4-trans-aminomethylcyclohexane carboxylic acid (Amcca)) incorporated into the modified lysine core.; Several analogues (H-Tyr-D-Ala-Phe-Xxx-Gly{dollar}rmsb{lcub}n{rcub}{dollar}-) {dollar}sb2{dollar}-Lys-Aca-Ala-OH, where Xxx = Asp or Glu and n = 0, 1, and 2, were found to be biologically inactive in an in vitro bioassay using isolated smooth muscle preparations of guinea pig ileum ({dollar}mu){dollar} and mouse vas deferens ({dollar}delta).{dollar} It was hypothesized that the inactivity was due to aggregation ("hydrophobic collapse") between the pharmacophores. Accordingly, incorporation of more rigid spacer groups (Aib and Amcca), between the opioid ligands, Tyr-D-Ala-Phe, generally resulted in improved activity in both GPI and MVD bioassays with the most potent analogue, (H-Tyr-D-Ala-Phe-Aib-Amcca{dollar}sb2{dollar}-) {dollar}sb2{dollar}-Lys-Aca-Ala-OH, resulting in an IC{dollar}sb{lcub}50{rcub}{dollar} of 236 nM in the GPI assay and 723 nM in the MVD assay.; A total number of 19 dimeric and 4 tetrameric analogues were synthesized by solid phase techniques on Merrifield resin using orthogonal (Boc and Fmoc) amine-protecting groups. The peptides were purified using reverse phase high performance liquid chromatography and were characterized by amino acid analysis and electrospray-mass spectrometry.; A representative series of dimeric analogues were selected for 1D and 2D NMR studies. In spite of their decreased bioactivities, no evidence of intramolecular ligand aggregation could be shown; a diagnostic upfield shift ({dollar}delta{dollar} 0.67-0.75 ppm) of the D-Ala{dollar}sp2{dollar} methyl protons, observable in both dermorphin and deltorphins, and usually attributable to adjacent aromatic ring current effects, was also evident in this series. |
