Synthesis and in vivo evaluation of 7-chloro-5-[123I]iodo-4-oxo-1,4-dihydroquinoline-2-carboxylic acid

As a possible radioligand for SPECT visualization of the NMDA receptors in the central nervous system, 7-chloro-5-[123I]iodokynurenic acid was prepared. This paper presents the synthesis of both the radioactive and the non-radioactive product, starting from 5-bromo-7-chlorokynurenic accid and using a non-isotopic nucleophilic halogen exchange reaction in the presence of iodide (Na123I or KI). Under the best labelling conditions, the radiochemical yield was 85%. The specific activity based on UV detection was found to be higher than 1 Ci/μmol (= 37 GBq/μmol) and the chemical and radiochemical (>95%) purity of the tracer was checked by RP-HPLC.