Enkephalin analogues with 2′,6′-dimethylphenylalanine replacing phenylalanine in position 4

Four Leu-enkephalin (Enk) analogues containing 2′,6′-dimethyphenylalanine (Dmp) in position 4 were prepared and tested for their receptor binding and biological activities. Among the analogues prepared, [2′, 6′-dimethyltyrosine1, -Dmp4]Enk was found to be an antagonist toward μ and δ opioid receptors with pA2 values of 6.90 and 5.57, respectively.