Analogues of β-LPH61–64 posessing selective agonist activity at μ-opiate receptors

Peptides based on the stabilised tetrapeptide HTyr-D-Ala-Gly-MePheOH have been synthesised and shown to have substantial opioid activity both in vitro and in vitro. The selectivity of these compounds for different receptor populations has been investigated using both isolated tissue assays and binding studies. Results suggest that the compounds are potent agonists at μ-receptors with little or no affinity for the δ-receptor population. One of the compounds, RX783006 (HTyr-D-Ala-Gly-MePhe-NH(CH₂)₂OH), has been tritiated to high specific radioactivity and may prove to be a useful probe in the elucidation of the function of the heterogenous opiate receptor population.