SYNTHESIS OF [H-3] DIPPA - A POTENT IRREVERSIBLE ANTAGONIST SELECTIVE FOR THE KAPPA-OPIOID RECEPTOR

2-(3,4-Dichlorophenyl)-N-methyl-N-[(1S)-1-(3-isothiocyanatophenyl)-2-(1-pyrrolidinyl)ethyl]acetamide (1, DIPPA) has been previously reported to be an opioid receptor affinity label that produces selective and long-lasting kappa opioid receptor antagonism in mice. High specific activity [H-3]DIPPA (39.7 Ci/mmol) was prepared by bromination and catalytic tritiation of the amino precursor of DIPPA followed by conversion to the isothiocyanate with thiophosgene.