Synthesis and binding properties of deltorphin I analogues containing [R] and [S]-alpha-hydroxymethylnaphtylalanine

New analogues of deltorphin I (DT I), in which the phenylalanine residue in position 3 is substituted with amphiphilic a,a-disubstituted amino acid enantiomers, (R) and (S)-a-hydroxymethylnaphtylalanine, were synthesized and tested for u and δ opioid re­ceptor affinity and selectivity. Although both analogues have lower affinity to δ recep­tors than DT I, they both expressed specificity to δ receptors.