6-Hydroxy-1,2,3,4-tetrahydro-isoquinoline-3-carboxylic acid mimics active conformation of tyrosine in opioid peptides

6-Hydroxy-1,2,3,4-tetrahydro-isoquinoline-3-carboxylic acid (6Htc) has been proposed as a rigid mimic of tyrosine conformation in opioid ligand–receptor complex. The significant receptor binding to mu and delta opioid receptors of respective analogues of deltorphin, dermorphin, and endomorphin with d,l -6Htc prove initial prediction.