TRITIATED DELTORPHIN ANALOGS WITH HIGH SPECIFIC RADIOACTIVITY AND HIGH-AFFINITY AND SELECTIVITY FOR DELTA-OPIOID RECEPTORS

New conformationally constrained deltorphin I and II analogues were de signed and synthesized, using a more lipophilic amino acid (Ile) inste ad of Val at positions 5 and 6, and 2-aminotetralin-2-carboxylic acid (Ate) at position 3. Two analogues (Tyr-D-Ala-(S)-Atc-Asp-Ile-lle-Gly- NH2 and Tyr-D-Ala-(R)-Atc-Glu-Ile-IIe-Gly-NH2) with high potency and s electivity for 6 opioid receptors were chosen for tritiation, with 3,5 -I-2-Tyr(1)-deltorphin analogues as precursors. Catalytic dehalotritia tion of these precursors resulted in tritiated peptides with high spec ific radioactivity (1.28 TBq/mmol (34.5 Ci/mmol) and 1.33 TBq/mmol(36. 0 Ci/mmol), respectively).