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Sammelson RE, Casida JE: Synthesis of a tritium-labeled, fipronil-based, highly potent, photoaffinity probe for the GABA receptor. J Org Chem. 2003 Oct 17;68(21):8075-9.
3-[4-[1-(2,6-dichloro-4-trifluoromethylphenyl) pyrazolo]]-3-(trifluoromethy l) diazirine is a fipronil-based (i.e. fiprole), high-affinity probe for the GABA receptor. For synthesis of the tritium-labeled version of this trifluoromethyldiazirinylfiprole ([(3) H] TDF) the required intermediate, 3-[4-[1-(2,6-dichloro-3-iodo-4-trifluoromethylphenyl)-5-iodopyrazolo]]-3-( trifluoromethyl) diazirine, was prepared in 10 steps from pyrazole and 3,5-dichloro-4-fluorobenzotrifluoride. One of the key transformations was lithiation and subsequent iodination of the 4-(2,2,2-trifluoro-1-hydroxyethyl) pyrazole intermediate. The last step involved reduction of the diiodofiprole with tritium, Pd/C, and triethylamine in ethyl acetate and afforded [(3) H] TDF with a specific activity of 15 Ci/mmol and 99% radiopurity. |
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