-Methyl Substitution of Cyclohexylalanine in Dmt-Tic-Cha-Phe Peptides Results in Highly Potent g src="http://pubs.
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The opioid peptide TIPP (H-Tyr-Tic-Phe-Phe-OH, Tic:1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) wassubstituted with Dmt (2',6'-dimethyltyrosine) and a new unnatural amino acid, G SRC="/images/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-MeCha (ges/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-methyl-cyclohexylalanine). This double substitution led to a new series of opioid peptides displaying subnanomolarges/gifchars/delta.gif" BORDER=0 > antagonist activity and ges/entities/mgr.gif"> agonist or antagonist properties depending on the configuration of the ges/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-MeCharesidue. The most promising analog, H-Dmt-Tic-(2S,3S)-ges/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-MeCha-Phe-OH was a very selective ges/gifchars/delta.gif" BORDER=0 > antagonistboth in the mouse vas deferens (MVD) assay (Ke = 0.241 ± 0.05 nM) and in radioligand binding assay (Kiges/gifchars/delta.gif" BORDER=0 >= 0.48 ± 0.05 nM, Kiges/entities/mgr.gif">/Kiges/gifchars/delta.gif" BORDER=0 > = 2800). The epimeric peptide H-Dmt-Tic-(2S,3R)-ges/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-MeCha-Phe-OH and thecorresponding peptide amide turned out to be mixed partial ges/entities/mgr.gif"> agonist/ges/gifchars/delta.gif" BORDER=0 > antagonists in the guinea pig ileumand MVD assays. Our results constitute further examples of the influence of Dmt and ges/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-methyl substitutionas well as C-terminal amidation on the potency, selectivity, and signal transduction properties of TIPPrelated peptides. Some of these compounds represent valuable pharmacological tools for opioid research.

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