Stereo Selective Synthesis, Characterization, and Application of d-Ritalinic Acid as Renal Imaging Agent in Nuclear Medicine

Renal imaging is a well-established technique in nuclear medicine. The renal imaging agents used in the current methods have some drawbacks as they take lot of time so as to produce good quality images. Hence, newer renal imaging agents were explored that can reduce the time taken to produce quality images. dl-Ritalinic acid (dlRA) was synthesized and d- and l- isomers were separated by resolution using resolving agent, (+)-dibenzoyl-D-tartaric acid. The purity of d-ritalinic acid (dRA) was determined by HPLC analysis and the structure was characterized by spectroscopic techniques (IR, mass, NMR). The complex, 99mTc-dRA, was prepared by the addition of 99mTc sodiumpertechnetate using stannous chloride dihydrate as reducing agent. The various factors which affect the radiolabeling efficiency such as reaction time, amount of ligand (dRA), reducing agent, anti-oxidant, and pH of reaction medium were studied. Radiochemical purity and in vitro stability of the labeled complex, 99mTc-dRA, were studied using ascending paper chromatography in saline and acetone media. Biodistribution studies of the complex (99mTc-dRA) and commercially available renal imaging agents (99mTc-DTPA and 99mTc-EC) in Wistar rats were studied by drawing region of interest over the organs without sacrificing the animal and the results were compared. Radiochemical purity of 99mTc-dRA was found to be 95.65 ± 3.36% at a pH range of 5.5–6.5 and was stable up to 6 h at room temperature. The optimum labeling was found to be in the ratio of 1:4:0.5 of ligand (dRA), ascorbic acid, and stannous chloride dihydrate. Compared to commercial renal imaging agents (99mTc-DTPA and 99mTc-EC), the synthesized complex, 99mTc-dRA, showed high target to non-target (T/NT) counts, clear images in early stages and is harmless as it is a metabolite of drug already taken up by body organs.