Novel TIPP (H-Tyr-Tic-Phe-Phe-OH) analogues displaying a wide range of efficacies at the δ opioid receptor. Discovery of two highly potent and selective δ opioid agonists.

Analogues of the δ opioid antagonist peptide TIPP (H-Tyr-Tic-Phe-Phe-OH; Tic=1,2,3,4-tetrahydroisoquinoline3-carboxylic acid) containing various 4'-[N-(alkyl or aralkyl)carboxamido]phenylalanine analogues in place of Tyr(1) were synthesized. The compounds showed subnanomolar or low nanomolar δ opioid receptor binding affinity and various efficacy at the δ receptor (antagonism, partial agonism, full agonism) in the [(35)S]GTPγS binding assay. Two analogues, [1-Ncp(1)]TIPP (1-Ncp=4'-[N-(2-(naphthalene-1-yl)ethyl)carboxamido]phenylalanine) and [2-Ncp(1)]TIPP (2-Ncp=4'-[N-(2-(naphthalene-2-yl)ethyl)carboxamido]phenylalanine), were identified as potent and selective δ opioid agonists.

Oxytocin-Gly-Lys-Arg: a novel cardiomyogenic peptide.

Background: Oxytocin (OT), synthesized in the heart, has the ability to heal injured hearts and to promote cardiomyogenesis from stem cells. Recently, we reported that the OT-GKR molecule, a processing intermediate of OT, potently increased the spontaneous formation of cardiomyocytes (CM) in embryonic stem D3 cells and augmented glucose uptake in newborn rat CM above the level stimulated by OT. In the present experiments, we investigated whether OT-GKR exists in fetal and newborn rodent hearts, interacts with the OT receptors (OTR) and primes the generation of contracting cells expressing CM markers in P19 cells, a model for the study of early heart differentiation.

N-methylated cyclic enkephalin analogues retain high opioid receptor binding affinity.

In an effort to improve the bioavailability of the non-selective, cyclic enkephalin analogues H-Dmt-c[d-Cys-Gly-Phe-d(or L)-Cys]NH(2) (Dmt = 2',6'-dimethyltyrosine), analogues N-methylated at the Phe(4) and/or Cys(5) residue were synthesized. In comparison with the non-methylated parent peptides, all mono- and N-di-methylated analogues in general retained high binding affinities at all three opioid receptors and high opioid agonist potencies in functional opioid activity assays. The results indicate that the progressive conformational restriction in these compounds upon mono- and di-N-methylation did not significantly affect the in vitro opioid activity profile.

Agonist vs antagonist behavior of delta opioid peptides containing novel phenylalanine analogues in place of Tyr(1).

The novel phenylalanine analogues 4'-[N-((4'-phenyl)phenethyl)carboxamido]phenylalanine (Bcp) and 2',6'-dimethyl-4'-[N-((4'-phenyl)phenethyl)carboxamido]phenylalanine (Dbcp) were substituted for Tyr(1) in the delta opioid antagonist TIPP (H-Tyr-Tic-Phe-Phe-OH; Tic = tetrahydroisoquinoline-3-carboxylic acid). Unexpectedly, [Bcp(1)]TIPP was a potent, selective delta opioid agonist, whereas [Dbcp(1)]TIPP retained high delta antagonist activity. Receptor docking studies indicated similar binding modes for the two peptides except for the biphenylethyl moiety which occupied distinct receptor subsites.

Cyclic opioid peptide agonists and antagonists obtained via ring-closing metathesis.

The opioid peptide H-Tyr-c[D-Cys-Phe-Phe-Cys]NH(2) cyclized via a methylene dithiother is a potent and selective mu opioid agonist (Przydial M.J. et al.