@misc{oai:repo.qst.go.jp:00068555,
 author = {Fukumura, Toshimitsu and Akaike, Shihoko and Yoshida, Yuichirou and Suzuki, Kazutoshi and 福村 利光 and 吉田 勇一郎 and 鈴木 和年},
 month = {May},
 note = {AIMS: Recent development of PET radiopharmaceutical production technique has made it possible to prepare C-11 labelled compounds with extremely high specific activity (more than 10 Ci/_mol). C-11-Ro 15-4513 has been used for benzodiazepine receptor imaging and recently is needed to be labelled with such an extremely high specific activity to image high affinity binding site. However, large amount of radioactivity and extremely high specific activity might cause the possibility of radiolysis. Therefore we investigated the mechanism of radiolysis of C-11-Ro 15-4513 to suppress the decomposition of C-11-Ro 15-4513 in aqueous solution.
METHODS: C-11-Ro 15 4513 was prepared by C-11 methylation of desmethy precursor with C-11-CH3I. After purification with HPLC system (column: C-18, mobile phase: 40% CH3CN), C-11-Ro 15-4513 fraction was evaporated to dryness and C-11-Ro 15-4513 was dissolved in pure H2O. C-11-Ro 15-4513 solution was allowed to stand to give degradation product. And the degradation products were estimeted with decomposed samples of authentic Ro 15-4513 solution by Co-60 or UV photolysis by comparing with those retention time. Chemical structure of degrdation products was estimeted with LC/MS. Effect of additives (MeOH, EtOH, HCOONH4, NaNO3, etc) on radiolysis of Ro 15-4513 was also examined. 
RESULTS: C-11-Ro 15-4513 solution underwent radiolysis to give one major and another minor radioactive degradation product. The major degradation product had same retention time with that of degradation product with Co-60. And minor degradation product was corresponded to degradation product by UV photolysis. The structure of degradation product by radiolysis and photolysis was estimated that azido group in Ro 15-4513 was displaced by amine and hydroxylamine group respectively from mass spectra. From the examination of radiolysis with Co-60 and radiolysis of C-11-Ro 15-4513 in the presence of additives, addition of selective hydroxyradical scavenger such as MeOH and EtOH accelerated the radiolysis of Ro 15-4513. In contrast the radiolysis was effectively suppressed by addition of selective hydrated electron scavenger (e.g. NaNO3), suggesting a possibility that hydrated electron would play important role to the radiolysis of C-11-Ro 15-4513.
CONCLUSION: From this investigation addition of selective hydroxyl radical scavenger accelerated the radiolysis of C-11-Ro 15-4513, in contrast the radiolysis was suppressed perfectly by addition of selective hydrated electron scavenger. These results would suggest the participation of hydrated electron to the radiolysis of Ro-15-4513., Ninth International Worksshop on Targetry and TargetChemistry},
 title = {RADIOLYSIS OF C-11-Ro 15-4513 IN AN AQUEOUS SOLUTION},
 year = {2002}
}