SYNTHESIS OF THE TRITIUM LABELED BETA-CASOMORPHINE ANALOGS H-3-PHE-PRO-GLY-OH AND H-3(2)-TYR-PRO-H-3-PHE-PYRROLIDIDE

The precursor peptides H-Phe(I)-Pro-Gly-OH (III) and H-Tyr(I2)-Pro-Phe(I)-pyrrolidide (VIII) were synthesized by stepwise elongation from the C-terminal end and by coupling of Boc-Tyr(I2)-Pro-OH with H-Phe(I)-pyrrolidide and following deprotection of the Boc-residue respectively. Catalytic dehalotritiation yielded tritated peptides with specific radioactivities of 450 and 1500 GBq/mmol respectively. Cleavage of H-3(2)-Tyr-Pro-H-3-Phe-pyrrolidide by dipeptidylpeptidase IV resulted in fragments with specific radioactivities of 950 (H-3(2)-Tyr-Pro) and 590 GBq/mmol (H-3-Phe-pyrrolidide).