Radiolabeled biotin amides from triazenyl precursors: Synthesis, binding, and in‐vivo properties

The synthesis of N‐(4‐[^127/125/123l]iodobenzyl)biotin amides 4a — 4c performed by the direct decomposition of N‐[4‐(3′,3′‐dimethyltriazenyl)benzyl)biotin amide with sodium iodide in the presence of CF₃COOH is described. Iodinated in this way biotin formed a stable complex with avidin (K_d = 2.84 ± 0.45 × 10⁻¹⁵ M, n = 3.9 ± 0.6) which dissociated in the presence of excess native biotin with a rate constant of 0.034 ± 0.006 hr¹. Blood clearance studies and the lack of thyroid uptake indicated that this compound was not deiodinated in vivo and behaved in circulation much like native biotin. This aryltriazene precursor method is suitable for labeling with short‐lived radiohalides. It can be used to produce no‐carrier‐added derivatives of biotin for use in biologic studies and assays involving avidin or streptavidin.