Synthesis and Purification of PET Radioligands

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Synthesis and Purification of PET Radioligands

• PET Chemistry Lab
• NIH/NIMH Molecular Imaging Branch
• Dr. Leshing Cai
• Brenna Houlihan
• John Ernst

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Our work at the MIB
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Background

• Alzheimers disease affects 5 million
  Americans. Alzheimer's destroys brain cells,
  causing problems with memory, thinking and
  behavior severe enough to affect work, lifelong
  hobbies or social life.  It is a degenerative and
  terminal disease.
• Bipolar disorder affects over 5 million
  Americans.
• Both associated with ß - amyloid plaques and tau
  neurofibril tangles in the brain.
• Marking and imaging these plaques in situ plays a
  critical role in diagnosis of these two
  debilitating diseases.

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Background

• Plaques composed of the polypeptide amyloid ßeta
  form on the cell bodies of neurons.
• Ligands are molecules that bind to proteins.
• Radio ligands have a radioactive component (in
  this case a radioisotope
• C-11 or F-18 t1/2 110 minutes)
• that emits positrons which can
• be detected in PET scan
• imaging (Positron Emission
• Tomography).

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The Method

• The synthesis of a radioligand must be as
  efficient as possible to cut expenses.
• The product must be very pure so that the ligand
  can bind efficiently to the neuronal plaques and
  have no unwanted side effects/reactions in vivo.
• IT IS THIS PURITY TO WHICH I ASPIRE!

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The Molecule(FMHPC)
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Procedure

• Microwave Synthesis reaction
• Purify with HPLC Prep machine
• Product reads 360nm
• Collect in test tubes
• Analyze eluate with HPLC Analyzer
• Evaporative concentration with Rotovap
• Desiccate with vacuum jar/pump
• Calculate percent yield
• Make a new hypothesis adjust concentration,
  time, temperature, etc.

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The Reaction

• microwave reactor

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Purificationold column chromatography
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New HPLC !
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Results

• We were able to synthesize 170mg FMHPC product.
  After purification and testing, we calculated a
  percent yield of 86.
• Identification of impurity compounds was revealed
  using NMR analysis.

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• Monkey brain

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Human Brain Pet Scan
120 minutes
2 6 minutes
20 -30 minutes
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PET scan image
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Conclusions

• Synthesis in microwave reduces reaction time from
  hours to seconds
• Purification can be achieved efficiently by
  Beckman HPLC
• Analysis for purity is achieved with Beckman HPLC
  Analyzer
• Purified and desiccated sample product shows 86
  percent yield by weight.
• NMR analysis shows sample had various minor
  impurities.

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Possible sources experimental error

• partial loss of sample in HPLC collection process
• contamination from communal Rootovap machine
• Side reactions at low pressure and elevated temps
  in Rotovap
• unclean glassware
• broken glassware in sample accuracy of electronic
  lab scales

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Fun Facts

• CEM Discover Microwave reactor 10K
• Beckman Coulter HPLC machine 13K
• Bruker 400 NMR machine 400K
• You break it you bought it!

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Acknowledgements

• Lesheng Cai, Ph.D. - Prefect
• Victor W. Pike, Ph.D. Principle Investigator,
  NIMH, MIB
• Brenna Houlihan - Researcher
• Omar Buccari