SYNTHESIS OF NCA C-11 LABELED CLOZAPINE AND ITS MAJOR METABOLITE CLOZAPINE-N-OXIDE AND COMPARISON OF THEIR BIODISTRIBUTION IN MICE

N.c.a. [C-11]clozapine, [8-chloro-11-(4-[methyl-C-11]methyl-1-piperazinyl)-5H-dibenzo[b,e]-1,4-diazepine], 1, an atypical neuroleptic was synthesized by N-methylation of the desmethyl compound norclozapine, 3, using [C-11]methyl iodide or [C-11]methyl triflate for comparison. Subsequent oxidation of 1 with m-chloroperoxybenzoic acid yielded clozapine-N-oxide, 2, the major metabolite of 1. Purification of both radiolabelled products was carried out using a combined semi-preparative HPLC/solid phase extraction procedure. In preparative scale runs overall radiochemical yields for 1 and 2 were 70 and 65%, respectively. The radiochemical purities of both compounds exceeded 98% and the specific activities were in the range of 92-130 GBq/mu mol (2.5-3.5 Ci/mu mol). Biodistribution of 1 and 2 has been studied in NMRI mice. 10 min p.i. clozapine shows a 24-fold higher brain uptake than its major metabolite. At 60 min p.i., however, the cerebral uptake of both compounds is almost identical.