Modifications of the 4,4′-residues and sar studies of biphalin, a highly potent opioid receptor active peptide

Modifications of 4,4′ residues of Biphalin have resulted in greater binding selectivity and biological potency for the μ opioid receptor. A higher partition coefficient across the phospholipid bilayer membrane has been achieved by using a β-branched unusual amino acids. Biphalin, a highly potent antinociceptive peptide, has been modified on 4, 4′ positions by using β-branched and aromatic substituted unusual amino acids. For example: (Tyr-D-Ala-Gly-Phe-NH) 2 ---> (Tyr-D-Ala-Gly-(2S,3R)β-Me-Phe-NH) 2