Human beta-endorphin: synthesis and biological activity of analogs with substitutions in positions 2, 9, 18, 27 and 31

Four analogs of the opioid peptide human beta-endorphin (Bh-EP) have been synthesized: D-Lys9, Phe27, Gly31]-beta h-EP, D-PHe18,Phe27,Gly31]-beta h-EP, D-Thr2,D-Lys9,Phe27,Gly31]-beta h-EP, and D-Thr2,D-Phe18,Phe27,Gly31]-beta h-EP. All are practically indistinguishable from beta h-EP in the guinea pig ileum assay. All show diminished analgesic potency in the mouse tail-flick assay.