beta-endorphin: synthesis and morphine-like activity of analogs with D-amino acid residues in positions 1, 2, 4, and 5.

The solid-phase syntheses of [D-Tyr1]-, [D-Ala2]-, [D-Phe4]- and [D-Met5]-beta c-endorphins are described. A comparison of certain methods of purification and criteria of homogeneity is made with the use of these compounds. Bioassay of these synthetic analogs both in vitro and in vivo show that [D-Ala2]-beta c-endorphin possesses significant opiate activity whereas the other analogs have minimal activity.