Synthesis and characterization of N-bromoacetyl-3,3',5-triiodo-L-thyronine

N-Bromoacetyl-3,3',5-triiodo-L-thyronine and carrier-free [3'-125I]-N-bromoacetyl-3,3',5-triiodo-L-thyronine, to be used for affinity labeling of thyroid hormone receptors, were synthesized using a one-step procedure: a solution of the thyroid hormone 3,3',5-triiodo-L-thyronine and bromoacetyl bromide in ethyl acetate was refluxed for an optimal period of time which depends on the amount of hormone processed. The bromoacetylated hormone thus obtained was then fractionated by high-speed counter-current chromatography which yielded N-bromoacetyl-3,3',5-triiodo-L-thyronine that was pure by the criteria of high-performance liquid chromatography and thin-layer chromatography with different solvent systems. The pure product was well separated from all contaminants including one which in high-performance liquid chromatography was not easily separated from N-bromoacetyl-3,3',5-triiodo-L-thyronine. The latter was characterized by 1H nuclear magnetic resonance, plasma desorption mass spectrometry, thin-layer chromatography, high-performance liquid chromatography, UV spectrophotometry, and melting point. Amounts of 3,3',5-triiodo-L-thyronine ranging from picograms, including carrier-free 125I-labeled triiodothyronine, to 200 to 300 mg can be processed with the equipment used in the present investigation.