Synthesis Labelled And Evaluation Of High Selective Ligands For Benzodiazepine Receptors

PBR and CBR are good molecular drug targets correlative to many more diseases such as neuropathy,psychopaths or even tumors. To the best of my knowledge, the availability of a radio labeled ligand for the study of the CBR and PBR, however, is restricted to institutions, and is not used in the clinic. This dissertation has detaily studied on the synthesis, labeled and evaluation of high selective ligands for PBR and CBR. Some significant original results were obtained.Firstly, a novel fluorine-substitute Zolpidem analogue was prepared. The synthetic program was initiated base on Zolpidem as leading compound. In receptor binding studies F-Zolpidem displays a high affinity (Ki = 9.83+1.3 nmol.L-1, IC50 = 10.77 +2.1 nmol.L-1) and excellent selectivity for BZ1 over other receptor (KiBZ2 /KiBZ1 > 31; KiBZ2 /KiPBR > 482), F-Zolpidem is a potent and selective BZ1 receptor ligand.Secondly, nucleophilic substitution of fluorine replacement reaction was proceeded by oil bath heating using no carrier added [18F] fluorine and Zolpidem triflate in CH3CN. The radiochemical yield of [18F] F-Zolidem was 40.6% (non-decay corrected) with a specific activity of 44.4GBq.μmol-1 at the end of synthesis. The average time of synthesis including HPLC purifity was 56 min with a radiochemical purity >98%. [18F]F-Zolpidem is provided with some good fundamental characteristic for imaging such as stability in vivo, lipophilic, low toxicity and safety.Thirdly, study on pharmacodynamics of [18F] F-Zolpidem showed that the radio- activity was mainly retained in liver, kidney, lung and heart. The radioactivity in the bone did not increase with time, suggesting that in vivo defluorination might not be the major route of metabolism. Fourthly, in the tissue distribution studies of [18F] F-Zopidem in rats, a higher uptake was observed in the cerebral cortex and cerebellum, a region high in BZ1 receptor density compared to the brain stem. A higher target to nontarget ratio in the cerebellum was observed and reached a maximum of 3.26 at 45 min. Pre- administration of the specific BZ1 drugs Zolpidem significantly reduced the uptake of [18F]F-Zolpidem by 80.7%.Fifthly, the autoradiography of [18F] F-Zolpidem showed that the accumulation of a higher uptake in cerebellum at 45 min after iv. The ratio of cerebellum to brain stem was 3.98+0.02. The uptake in cerebellum was significantly reduced (3.98+0.02 vs. 0.36+0.01) by pretreatment with Zolpidem. A higher uptake in cerebellum implied [18F]-F-Zolpidem was able to pass through the blood brain barrier, suggesting specific bind to BZ1 receptor and a promising PET tracer.Sixthly, a novel imidazol[1,2-a]pyridine analogue ITFZOL as peripheral benzo- diazepine receptor ligand was synthesized based on the lead compound N,N-diethyl- 6-chloro-(4-choro-phenyl)imidazol[1,2-a]pyridine-3-acetamide (CLINDE). The high affinity (Ki = 0.52±0.01 nmol. L-1, IC50 = 0.82±0.01nmol. L-1) and excellent selectivity for PBR over other receptor (KiBZ1 /KiPBR > 980; KiBZ2 /KiPBR > 1200) were observed. ITFZOL is a potent and selective PBR receptor ligand.Seventhly, [125I]-ITFZOL was radio-iodinated from the corresponding tributyltin deriveative using Na125I, and oxidized in situ with hydrogen peroxide. The radiochemical yield of [125I]-ITFZOL was 80.0%, with a radiochemical or chemical purity better than 98% and a specific activity greater than 76GBq.μmol-1. Eighthly, in biodistribution studies in normal or bearing tumor mice, the highest uptake of [125I]-ITFZOL was found 30 min post injection in adrenals, followed by lung, liver, kidney, heart and brain, consistent with the distribution of PBR binding sites.Ninthly, in the tissue distribution studies of [125I]-ITFZOL in mice, a higher uptake was observed in the olfactory bulb and cerebellum, a region high in PBR density compared to the Thalamus. A higher target to nontarget ratio in the cerebellum was observed and reached a maximum of 2.32 at 30 min. Pre-administration of the specific PBR drug PK11195 significantly reduced the uptake of [125I] ITFZOL by 61.9% as well as the autoradiography and SPECT. All these results revealed that [125I] ITFZOL is a specific binding and potent SPECT tracer for PBR.Based on the development of high performance radioligands for PBR and CBR, the process of synthesis, radiolabeling and evaluation were discussed. The effects of structure modification to imidazol[1,2-a]pyridine analogues on selective and specific properties of PBR and CBR were systematically investigated. Developing the new receptor imaging technology of [18F] F-Zolpidem and ITFZOL is very important for improving and perfecting PET or SPECT applied to neuroreceptor and tumor imaging.