[D-Ala2]-Deltorphin II (cas# 122752-16-3) is a useful research chemical.Deltorphin II is one of the naturally occurring peptides with high affinity and selectivity for δ-??opioid binding sites. Deltorphin II showed even higher affinity for δ-??opioid receptors than previously characterized deltorphins. Also, Deltorphin II were identified as new transport substrates of OATP-??A