Synthesis of 7′-[123I]iodo-d-luciferin for in vivo studies of firefly luciferase gene expression

d-(−)-2-(6′-Hydroxy-7′-[123I]iodobenzothiazolyl)-Δ2-thiazoline-4-caroxylic acid (7′-[123I]iodo-d-luciferin) was synthesized as a novel reporter probe for in vivo studies of firefly luciferase gene expression. 7′-Iodo-d-luciferin, a nonradioactive standard, was synthesized and showed the binding property (KM=4.28 μM) similar to that of d-luciferin (2.53 μM) for firefly luciferase in luminescence assay.