5'-Guanidinonaltrindole (TFA)

5'-Guanidinonaltrindole TFA is a selective kappa-opioid receptor antagonist with significant opioid antagonist activity. 5'-Guanidinonaltrindole TFA exhibits 5 times the antagonistic potency of the prototypical kappa-opioid receptor antagonist norbinatorphimine in smooth muscle preparations, with a selectivity ratio exceeding 500 times. Binding and functional studies of 5'-Guanidinonaltrindole TFA showed pA(2) values comparable to smooth muscle data. 5'-Guanidinonaltrindole TFA is regarded as a potentially valuable pharmacological tool for studying opioids due to its high selectivity and potency.