A facile method for the preparation of [11C]cyanide from [11C]methyl iodide

Objectives. [11C]Cyanide is a useful intermediate for labelling functional groups such as CN, COOH, CONH2 and CH2NH2 in organic compounds. Conventional method for the preparation of [11C]cyanide, however, requires dedicated infrastructure. [11C]Cyanide is generally prepared by heating [11C]CH4 under NH3 gas flow at more than 900°C over a platinum filled column. Furthermore, the starting material, [11C]CH4, is produced by the irradiation of N2/H2 gas or by heating [11C]CO2 under H2 gas flow over nickel. In the previous meeting (ISRS2017), we reported that [11C]cyanide was prepared by the dehydration of [11C]formaldoxime, though the radiochemical yield was insufficient (around 20% from [11C]CO2). Thus, we explored more efficient method to prepare [11C]cyanide without any special equipment and reagents. In this study, we investigated the applicability of hydroxylamine-O-sulfonic acid (HOSA) to [11C]cyanide preparation from [11C]CH3I which is widely used for 11C-labelling. HOSA has been used as a reagent for the conversion of aldehydes into nitriles.Methods. [11C]CH3I (300–400 MBq) was trapped in a 1 mL of trimethylammonium oxide (TMAO, 15 mg) solution in DMF or DMSO and heated for 2 min to prepare [11C]HCHO (at 70°C for DMF solution, at 100°C for DMSO solution). The [11C]HCHO solution (200 μL) was subsequently added to the HOSA solution in the corresponding solvents (200 μL). The reaction conditions are summarized in Table 1. Radiochemical yields from [11C]CH3I were determined by radio-HPLC analysis of the reaction solution. More than 87% of radioactivity in the injected solution was eluted during the HPLC analysis.Results. The results are summarized in Table 1. Higher reaction temperature enhanced the formation of [11C]cyanide. The use of DMSO showed better yield of [11C]cyanide compared with DMF. The use of more than 1 equivalent of HOSA based on the amount of TMAO was required to obtain good yields of [11C]cyanide. Consequently, [11C]cyanide was produced in 87% radiochemical yield after 3 min reaction time.Conclusions. [11C]Cyanide was efficiently prepared from [11C]CH3I in one-pot using conventional reagents and lab-ware. Further optimization of reaction conditions for the production of [11C]cyanide with an automated system is in progress.ISRS2019 (The 23rd International Symposium on Radiopharmaceutical Sciences