The biological consequences of replacing hydrophobic amino acids in deltorphin I with amphiphilic α-hydroxymethylamino acids

: New analogues of deltorphin I (DT I), in which the Phe residue in position 3, and the Val residue in position 5 or 6 are replaced with respective amphiphilic α‐hydroxymethylamino acid residues (HmAA), were synthesized and tested for receptor affinity and selectivity to μ and δ opioid receptors. The analogue with (R)‐HmPhe at position 3 lost receptor selectivity, as a result of a partial decrease of affinity to δ and a significant increase of affinity to μ receptors. In contrast, an analogue with (S)‐HmPhe in the same position, was very potent and more specific to δ receptors than parent DT I. The analogue with (R)‐HmVal at position 5 expressed higher δ affinity and selectivity than parent DT I. The analogue with other possible isomer (S)‐HmVal was less selective for δ opioid receptors, as a result of decreasing affinity to δ and increasing affinity to μ receptors. The analogues with (R)‐ or (S)‐HmVal in position 6 expressed equally low receptor affinity and selectivity. The data obtained support a previously proposed model of active conformation of deltorphins.