Tritiated photoactivatable analogs of the native human thrombin receptor (PAR‐1) agonist peptide,SFLLRN‐NH2

Abstract: Six photoactivatable analogs of the human thrombin receptor activating peptide (TRAP), SFLLRN‐NH₂, were synthesized by substituting the photoactive amino acid, p‐benzoylphenylalanine (Bpa), into each position of the peptide sequence. Platelet aggregation assays indicated that the peptides with Bpa substitutions at positions 3 to 6 retained agonist activity. These peptides were prepared in tritiated form as potential thrombin receptor photoaffinity labels. The [³H]Bpa‐containing analogs were constructed by resynthesizing the peptides with the amino acid, 4‐benzoyl‐2′,5′‐dibromophenylalanine (Br₂Bpa), and subjecting the purified peptides to Pd‐catalyzed tritiodebromination. The radiochemical yields for the reductive tritiation were < 2% for peptides with [³H]Bpa in the third and fourth positions, and between 7 and 16% for the peptides with substitutions at the fifth and sixth positions. The low yields were due to over‐reduction of the Bpa carbonyl group and nonspecific degradation during reductive tritiation. This report describes the first use of Br₂Bpa for the preparation of tritiated photoactivatable peptides.