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Radioiodinated Biotin Derivatives for In Vitro Radioassays

N.R.C. Demokritos, Athens, and University of Patras, Patras, Greece

Correspondence: For reprints contact: Professor D.S. Ithakissios, Laboratory of Pharmaceutical Technology, Dept. of Pharmacy, University of Patras, Patras 261 10, Greece.

ABSTRACT

The synthesis of two radioiodinated biotin derivatives with the biotin-ureido group intact is described. This synthesis was performed by coupling (pH 8.5, 20–22°C, 90 min) N-hydroxysuccinimidobiotin to tyramine, which was radioiodinated prior to this using a modified chloramine-T method. Two derivatives were produced, the N-[ß-(4-OH-3-¹²⁵I-phenyl) ethyl] and the N-[ß-(4-OH-3,5-di¹²⁵I-phenyl)ethyl] biotin amides, depending on the amount of tyramine used in the radioiodination reaction. The final products were separated by thin layer chromatography (n-butanol: 2N NH₄OH: ethanol,3:1:1, v/v/v). The radioiodinated derivatives that were synthesized or their resulting mixture were found to compete with biotin for the avidin-binding sites; thus, they were capable of being used as tracers in biotin radioassays. The specific activity of their mixture was high—>350 Ci/mmol—and they were stable for 2 mo at 4°C.