Low temperature synthesis of no-carrier-added [11C]formaldehyde with metal hydrides and preparation of [1-11C]1,2,3,4-Tetrahydro-β-Carboline Derivatives

A comparative study has been performed on the selective reduction of cyclotron-produced [11C]carbon dioxide to [11C]formaldehyde with solutions of various complex metal hydrides at temperatures between −52 and +25°C. Under optimal reaction conditions, lithium tetrahydridoaluminate gave the highest yield of [11C]formaldehyde (58%, decay-corrected), followed by lithium triethylhydridoborate (34%) and sodium tetrahydridoborate (22%). Radiochemically pure [11C]formaldehyde could be obtained with lithium tetrahydridoaluminate and sodium tetrahydridoborate, but not with lithium triethyl hydridoborate. The produced [11C]formaldehyde was used for the synthesis of [1-11C]1,2,3,4-tetrahydro-β-carboline derivatives by the Pictet–Spengler reaction.