Synthesis of the dopamine D2/D3 receptor agonist (+)-PHNO via supercritical fluid chromatography: preliminary PET imaging study with [3-11C]-(+)PHNO

- Improved synthesis of the dopamine agonist pharmaceutical (+)-PHNO.
- First reported synthesis of key precursors for radiolabeling with [11C]CH3I.
- Application of supercritical fluid chromatography to separate HNO enantiomers.
- Modifications for consistent preparation of [3-11C]-(+)-PHNO.

Carbon-11 labeled (+)-4-[1-11C]propyl-3,4,4a,5,6,10b-hexahydro-2H-naphtho[1,2-b][1,4]oxazin-9-ol ([1-11C]-(+)-PHNO) is a dopamine D3-preferring agonist radiopharmaceutical used for medical imaging by positron emission tomography (PET). We report the synthesis of (+)-PHNO using supercritical fluid chromatography for enantiomeric resolution of its norpropyl derivative, HNO, followed by propylation. (+)-HNO was used to prepare the radiolabeling precursor, (+)-trans-4-acetyl-9-triisopropylsilyloxy-2,3,4a,5,6,10b-hexahydro-4H-naphth[1,2b][1,4]oxazine, in 12 steps. Modifications to the labeling procedure were made to ensure consistent preparation of [3-11C]-(+)-PHNO via [11C]CH3I. A preliminary PET imaging study was carried out with this tracer in an attempt to image dopamine receptors in brown adipose tissue (brown fat) in vivo.