A captive solvent method for rapid N-[ 11C]methylation of secondary amides: Application to the benzodiazepine, 4′-chlorodiazepam (RO5-4864)

[ 11C]4′-Chlorodiazepam (RO5-4864), for PET studies of peripheral benzodiazepine receptors, was synthesized by alkylation of 1-desmethyl-4′-chlorodiazepam, in a small volume of acetone adsorbed on acrylic yarn, with [ 11C]methyl iodide in the injection loop of a liquid chromatograph. The reaction mixture was introduced directly onto a small, disposable alumina chromatographic column. Elution with pentane:ethanol gave a product of high chemical and radiochemical purity. A simple heating and cooling device for the injection loop is described.