Synthesis and evaluation of methylated arylazepine compounds for PET imaging of 5-HT(2c) receptors

ACS Chem Neurosci. 2013 Feb 20;4(2):261-5. doi: 10.1021/cn300223d. Epub 2012 Dec 7.

Abstract

The serotonin 5-HT(2c) receptor is implicated in a number of diseases including obesity, depression, anxiety, and schizophrenia. In order to ascribe the role of 5-HT(2c) in these diseases, a method for measuring 5-HT(2c )density and function in vivo, such as with positron emission tomography (PET), must be developed. Many high-affinity and relatively selective ligands exist for 5-HT(2c) but cannot be accessed with current radiosynthetic methods for use as PET radiotracers. We propose that N-methylation of an arylazepine moiety, a frequent structural feature in 5-HT(2c) ligands, may be a suitable method for producing new radiotracers for 5-HT(2c). The impact of N-methylation has not been previously reported. For the agonists that we selected herein, N-methylation was found to increase affinity up to 8-fold without impairing selectivity. Compound 5, an N-methylated azetidine-derived arylazepine, was found to be brain penetrant and reached a brain/blood ratio of 2.05:1. However, our initial test compound was rapidly metabolized within 20 min of administration and exhibited high nonspecific binding. N-Methylation, with 16 ± 3% isolated radiochemical yield (decay corrected), is robust and may facilitate screening other 5-HT(2c) ligands as radiotracers for PET.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Azepines / chemical synthesis*
  • Azepines / metabolism
  • Brain / diagnostic imaging*
  • Carbon Radioisotopes* / metabolism
  • Methylation
  • Papio anubis
  • Positron-Emission Tomography
  • Radiopharmaceuticals / chemical synthesis*
  • Radiopharmaceuticals / metabolism
  • Receptor, Serotonin, 5-HT2C / metabolism*
  • Serotonin 5-HT2 Receptor Agonists / chemical synthesis*
  • Serotonin 5-HT2 Receptor Agonists / metabolism

Substances

  • Azepines
  • Carbon Radioisotopes
  • Radiopharmaceuticals
  • Receptor, Serotonin, 5-HT2C
  • Serotonin 5-HT2 Receptor Agonists