Chloramine‐t for “no‐carrier‐added” labelling of aromatic biomolecules with bromine‐75,77

Abstract

Abstract The applicability of chloramine‐T (CAT) was examined for “no‐carrier‐added” labelling of aromatic compounds with the short‐lived isotopes bromine‐77 (T 1/2 = 56 h) and bromine‐75 (T 1/2 = 98 min). In aqueous solution the optimum reaction conditions with respect to pH, concentration of CAT, reaction time and added brominecarrier were determined using tyrosine as a model substrate. Highest radiochemical yields (>85%) were obtained at pH 1 within a few seconds at a CAT concentration of 10 −3 M. At pH 7 a maximum radiochemical yield of 65% was achieved with 10 −2 M after 2.5 minutes. Studies with some model peptides showed that only the tyrosyl residues were brominated and similar yields were obtained as in free tyrosine. Some aromatic molecules such as α‐methyl‐tyrosine, phenylalanine, uracil, cytosine, and phenol were radiobrominated by the CAT method with yields up to 90%. Separation and identification of the labelled products were achieved by means of radio high performance liquid chromatography.