Solid Phase Synthesis and Opioid Receptor Binding Activities of[D-Ala², D-Leu⁵]Enkephalin Analogs Containing a Fluorinated Aromatic Amino Acid

Abstract

Five [D-Ala², D-Leu⁵⁵]enkephalin (DADLE) analogs containing fluorinated Tyr¹ or Phe⁴ residue, that is, [Phe(2F)⁴] (I), [Phe(3F)⁴] (II), [Phe(4F)⁴] (III), [Tyr(3F)¹] (IV) and [Try(2F)¹] (V), were synthesized by the solid phase method and their opioid receptor affinities were examined. Affinity profiles of five derivatives for the μ- and δ-receptor were similar to those of DADLE, and the affinity for κ-receptor was zero or negligible.