title: Reinvestigation of the synthesis and evaluation of [N-methyl-(11)C]vorozole, a radiotracer targeting cytochrome P450 aromatase.
abstract: BACKGROUND
  We reinvestigated the synthesis of [N-methyl-(11)C]vorozole, a radiotracer for aromatase, and discovered the presence of an N-methyl isomer which was not removed in the original purification method. Herein we report the preparation and positron emission tomography (PET) studies of pure [N-methyl-(11)C]vorozole.
  
  
  METHODS
  Norvorozole was alkylated with [(11)C]methyl iodide as previously described and also with unlabeled methyl iodide. A high-performance liquid chromatography (HPLC) method was developed to separate the regioisomers. Nuclear magnetic resonance (NMR) spectroscopy ((13)C and 2D-nuclear Overhauser effect spectroscopy NMR) was used to identify and assign structures to the N-methylated products. Pure [N-methyl-(11)C]vorozole and the contaminating isomer were compared by PET imaging in the baboon.
  
  
  RESULTS
  Methylation of norvorozole resulted in a mixture of isomers (1:1:1 ratio) based on new HPLC analysis using a pentafluorophenylpropyl bonded silica column, in which vorozole coeluted one of its isomers under the original HPLC conditions. Baseline separation of the three labeled isomers was achieved. The N-3 isomer was the contaminant of vorozole, thus correcting the original assignment of isomers. PET studies of pure [N-methyl-(11)C]vorozole with and without the contaminating N-3 isomer revealed that only [N-methyl-(11)C]vorozole binds to aromatase. [N-methyl-(11)C]Vorozole accumulated in all brain regions with highest accumulation in the aromatase-rich amygdala and preoptic area. Accumulation was blocked with vorozole and letrozole consistent with reports of some level of aromatase in many brain regions.
  
  
  CONCLUSIONS
  The discovery of a contaminating labeled isomer and the development of a method for isolating pure [N-methyl-(11)C]vorozole combine to provide a new scientific tool for PET studies of the biology of aromatase and for drug research and development.
authors.affiliation: Medical Department, Brookhaven National Laboratory, Upton, NY 11973, USA. swkim@bnl.gov
authors.forename: Sung Won
authors.initials: SW
authors.lastname: Kim
authors.forename: Anat
authors.initials: A
authors.lastname: Biegon
authors.forename: Zachary E
authors.initials: ZE
authors.lastname: Katsamanis
authors.forename: Carolin W
authors.initials: CW
authors.lastname: Ehrlich
authors.forename: Jacob M
authors.initials: JM
authors.lastname: Hooker
authors.forename: Colleen
authors.initials: C
authors.lastname: Shea
authors.forename: Lisa
authors.initials: L
authors.lastname: Muench
authors.forename: Youwen
authors.initials: Y
authors.lastname: Xu
authors.forename: Payton
authors.initials: P
authors.lastname: King
authors.forename: Pauline
authors.initials: P
authors.lastname: Carter
authors.forename: David L
authors.initials: DL
authors.lastname: Alexoff
authors.forename: Joanna S
authors.initials: JS
authors.lastname: Fowler