[11C]Carbon Monoxide and Aryl Triflates in Palladium-Mediated Carbonylation Reactions Synthetic approaches to [11C]Carbonyl Compounds and [11C]Amines

Sammanfattning: The usefulness of low concentrations (typically 10 to 100 µM) of [11C]carbon monoxide and aryl triflates as substrates in 11C-carbonylation using different nucleophiles in the presence of lithium bromide was investigated. The reactions were performed in a micro autoclave of 200 µL volume and catalysed (mediated) by palladium(0). A peripheral type benzodiazepine receptor (PBR) ligand, 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)isoquinoline-3-carboxamide (PK11195) and its structural analogues including an irreversible ligand for PBR, some other amides, ketones and carboxylic acids, were all labelled with 11C using this approach. The [carbonyl-11C]PK11195, analogues and other amides were prepared from aryl triflates and amines, and the [carbonyl-11C]ketones were prepared from aryl triflates and organoboranes. In the synthesis of [carboxyl-11C]carboxylic acids, water was utilised as nucleophile. The decay-corrected radiochemical yields were 10 to 55% for [11C]PK11195 and analogues, 2 to 63% for other [11C]amides, 10 to 75% for [11C]ketones and 25 to 65% for [11C]carboxylic acids. The specific radioactivity of the labelled compounds was in the range of 150 to 900 GBq/µmol. Some [11C]amines were prepared by a reductive amination of the corresponding [carbonyl-11C]ketones. These reactions were performed using different amines in the presence of TiCl4 and NaBH3CN. The radiochemical yields of the [11C]amines varied from 2 to 78% (determined by analytical HPLC). In order to confirm the labelling position, synthesis of selected 13C-substituted compounds were performed. For each substance group/ synthesis method, a selected compound was synthesised using (13C)carbon monoxide and the 13C-substituted compound was then analysed by 13C NMR.A synthetic route was developed for the preparation of 1-(2-chloro-phenyl)-isoquinolin-3-yl trifluoromethanesulfonate used as the precursor in the synthesis of [carbonyl-11C]PK11195 and analogues.