Synthesis of [3-N-(11) C-methyl]temozolomide via in situ activation of 3-N-hydroxymethyl temozolomide and alkylation with [(11) C]methyl iodide.

Temozolomide is a chemotherapeutic drug that is mainly used in the treatment of primary glioblastoma multiforme and recurrent high-grade glioma. Here, we report an efficient good manufacturing practice compliant method for the synthesis of [3-N-(11) C-methyl]temozolomide from 3-N-hydroxymethyl temozolomide that cleaves off formaldehyde in situ and becomes activated towards alkylation with [(11) C]methyl iodide. The labelling method was developed for an on-going patient study in which the predictive value of [3-N-(11) C-methyl]temozolomide and positron emission tomography on the outcome of temozolomide treatment is being investigated. The precursor was reacted with [(11) C]methyl iodide in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene in acetonitrile, heated at stepwise increasing temperature. Purification by semipreparative HPLC with pharmaceutical grade eluent and filtration gave approximately 10 mL sterile product solution ready for injection containing 1.55 ± 0.38 GBq (n = 5), the specific activity was 88 ± 25 GBq/µmol and the radiochemical purity was 98.5 ± 1.9%. (13) C-NMR spectroscopy confirmed the labelled position after colabelling with (11) C and (13) C.