Enzyme catalysed synthesis of L‐[4‐ 11 C]aspartate and L‐[5‐ 11 C]glutamate

The nitriles β‐[ 11 C]cyano‐L‐alanine 1 and γ‐[ 11 C]cyano‐α‐amino‐L‐butyric acid 2 were obtained by enzymatic catalysis from O ‐acetyl‐L‐serine and O ‐acetyl‐L‐homoserine with carrier added hydrogen [ 11 C]cyanide (0.1 µmol), using O ‐acetyl‐L‐serine sulfhydrylase [EC.4.2.99.8] and O ‐acetyl‐L‐homoserine sulfhydrylase [EC.4.2.99.10], respectively. L‐[4‐ 11 C]Aspartate 3 and L‐[5‐ 11 C]glutamate 4 were then obtained by alkaline hydrolysis of 1 and 2 , respectively. Purification by semi‐preparative HPLC yielded 3 and 4 with radiochemical purities higher than 95% and with decay corrected radiochemical yields of 60–70% and 50–60%, respectively based on the total amount of collected hydrogen [ 11 C]cyanide. The enantiomeric purities were determined, after derivatisation with N ‐α‐(2,4‐dinitrophenyl‐5‐fluoro‐)‐L‐alaninamide, by HPLC to be higher than 97.5%. The total reaction times for 3 and 4 , counted from end of bombardment, were 50–55 min. The specific radioactivity of 3 and 4 were approximately 30 GBq/µmol at end of synthesis starting from 20 GBq hydrogen [ 11 C]cyanide. Copyright © 2001 John Wiley & Sons, Ltd.