Method for labeling with tritium

#The present invention is related to a method for preparing a tritium-labeled compound characterized by reacting an organic compound with a tritium-labeled hydride reagent in the presence of a solvent and a catalyst, the tritium-labeling method, a tritium-labeled compound obtained according to said production method, a method for establishing pharmacokinetics by using the tritium-labeled compound, a screening method to identify a new useful compound in which the tritium-labeled compound is used as a labeling ligand for a known receptor and a compound obtained by said method, a screening method to identify an unknown protein in which a tritium-labeled compound is used as a labeling agent for a bioactive compound and a protein obtained by said method.

#A radiolabeled compound is essential to a development of a pharmaceutical agent at various stages as a tracer because it has an excellent sensitivity and is easily detectable. For the purpose of the radiolabeling, a radioisotope such as 14C (Maximum specific radioactivity about 60 mCi/mmol) and 3H(tritium)(Maximum specific radioactivity about 30 Ci/mmol) are mainly used. Since a tritium-labeled compound has high specific radioactivity and is an excellent tracer, it is especially useful for various experiments in which a labeled compound having high specific radioactivity is required, such as a protein-binding receptor assay.

#At present, a tritium-labeled compound is prepared by using a catalytic reduction with a large amount of tritium gas or a conversion with tritium water. The catalytic reduction is usually used rather than the conversion process because in the latter it is difficult to obtain a tritium-labeled compound having high specific radioactivity. However, in the catalytic reduction, when a compound has a functional group such as nitro, a double-bond and benzyl ether the functional group is reduced prior to or simultaneously with tritium-labeling. Accordingly, if interesting tritium-labeled compound has a variety of functional groups, then tritiation must be conducted at a relatively early stage of a synthesis of compound in multi-steps. Such labeling at an early stage requires extensive labor in its practice, because it requires a special synthetic route for synthesis of a labeled compound; a reaction and purification at an ultra-micro scale via difficult several steps; and disposal of a large amount of radwaste from each steps of reaction, frequent radiological monitoring, and complicated removal of by-products. In addition, degradation of the labeled compound may be occurred via several reaction steps, which causes a reduction of the yield. J. Chem. Research (S), 1996, 150-151 discloses a method for obtaining 2,3- or 2,4-dibromotiophene by treating 2,3,5-tribromotiophene with NaBH4 in the presence of for example palladium catalyst, but a tritium-labeling. In general, in the tritium-labeling, tritium is considered to show a different nature from 1H due to influence of ultra-micro scale procedure and autolysis by radiation etc.

#A variety of transition metal complexes and metal salts were used as a catalyst for a tritiation of 4-bromobiphenyl as shown in the following Schema I to select a catalyst. 4 1 TABLE 1 Tritiation of 4-bromobiphenyl using a transition metal complex Total Radio Specific Test activity Radioactivity No. Catalyst (μCi) (μCi/mmol) 1 Pd(PPh3)4 26.4 465 2 Pd(OAc)2 36.9 588 3 Pd(PhCN)2Cl2 34.0 547 4 Pd2(dba)3 27.0 622 5 Ru(PPh3)3Cl2 1.69 264 6 Rh(PPh3)3Cl 15.6 427

#2 TABLE 2 Tritiation of 4-bromobipheny with a metal salt Total Radio Specific Test activity Radioactivity No. Catalyst (μCi) (μCi/mmol) 7 NiCl2 7.08 534 8 CoCl2 47.6 655 9 RhCl3 13.3 222

#According to the results shown in Tables 1 and 2, Pd(PPh3)4, which provided a stable yield with the highest reproducibility and utility in the study for a variety of compounds, was used for the subsequent tritiation.