Synthesis of [211C]5,5dimethyl2,4oxazolidinedione with and without added dimethyl carbonate as a carrier for studies with positron tomography

Two methods were developed for the synthesis of [2-¹¹C]5,5-dimethyl-2,4-oxazolidinedione ([2-¹¹C]DMO) for use with positron emission tomography to measure regional cerebral tissue pH in vivo in man. In both methods, A and B, [2-¹¹C]dimethyl carbonate (DMC) was prepared from [¹¹C]phosgene and excess of sodium methoxide in methanol containing 2-hydroxyisobutyramide (HIBA). In method A, an excess of DMC was used as a carrier, while in method B none was used. In both methods, the [2-¹¹C]DMC solution was then heated for 10 min at 150°±2°C causing the reaction of [2-¹¹C]DMC with HIBA to yield [2-¹¹C]DMO with a radiochemical purity of greater than 99%. Method A gave significantly higher radioactive yields, a pure organic product, but lower specific activities. Flash chromatography was used for the separation and purification of [2-¹¹C]DMO prepared by method B.