Design, synthesis, and evaluation of opioid analogues with non-peptidic beta-turn scaffold: enkephalin and endomorphin mimetics.

We have identified a mu-selective opioid receptor agonist without a cationic amino group in the molecule from libraries of bicyclic beta-turn peptidomimetics. The biologically active conformation of the lead is proposed to mimic an endomorphin type III 4 --> 1 beta-turn conformation.