β-Casomorphins: substitution of phenylalanine with β-homo phenylalanine increases the μ-type opioid receptor affinity

Two analogues of bovine β-casomorphin-7 and β-casomorphin-5 containing a β-homo phenylalanine in substitution of the phenylalanine in position 3 were synthesised and tested for their μ-opioid receptor affinity. The modification enhanced the μ receptor affinity 5-fold in the case of modified β-CM-7 and 2-fold for modified β-CM-5 when compared to the natural peptides.