MESYMO (MEthionine SYnthesis MOdule) is a dedicated module suitable for the synthesis of the radiopharmaceutical [11C]-methionine. The computer controlled, fully automated and GMP compliant module has two functional units, integrated into one device:
The process which delivers the highest yield in the shortest time and is very robust (requires little maintenance of the synthesis unit) is the gas phase 11CH3I synthesis process. The process is based on passing of 11CH4 through a high-temperature quartz reactor filled with iodine vapors. The produced 11CH3I is trapped in a column at low temperature after the quartz reactor, in order to concentrate the product. During the recirculation the 11CH4 through the reactor this adsorbing column prevents successive passage of 11CH3I through the reactor, which would lead to the synthesis of unwanted 11CH2I2 and 11CHI3. At the end of the process 11CH3I is desorbed from the column by increasing its temperature and transferred into the reaction vessel by a stream of helium. The whole process is accomplished in 3-4 min. and the typical yields are about 40-50%.
11C-methionine is produced in a solid phase supported regioselective synthesis. Using Al2O3/KF as a solid support in a mixture with L-homocysteine in ethanol, one can perform the synthesis by simply purging helium carrying 11CH3I through the slurry and achieve yields above 90% in only 2 min. Another excellent feature of this approach is that one need no HPLC purification of the product: it is sufficient to pass the physiological solution containing the reaction product through SepPak C18plus and AluminaN extraction cartridges and to obtain a product fulfilling the requirements of the EU and US Pharmacopoeia.