Novel analogues of enkephalin: indentification of functional groups required for biological activity

Novel tri- and tetrapeptide analogues of enkephalin, in conjunction with earlier structure-activity data, confirm that chemical substitutents present in the first and fourth residues of enkephalin are required for in vitro biological activity. A class of arylamino and alkylamino derivatized tripeptides also were found to have significant in vitro opioid-like activity indistinguishable from [D-Ala2,D-Leu5]enkephalin and morphine.