Novel analogs of enkephalin: identification of functional groups required for biological activity

Abstract
Novel tri and tetrapeptide analogs of enkephalin, in conjunction with earlier structure-activity data, confirm that chemical substituents present in the 1st and 4th residues of enkephalin are required for in vitro biological activity. A class of arylamino and alkylamino derivatized tripeptides had significant in vitro opioid-like activity [in guinea pig ileum] indistinguishable from [D-Ala2,D-Leu5]enkephalin and morphine.