title: Synthesis and in vivo evaluation of [O-methyl-11C](2R,4R)-4-hydroxy-2-[2-[2-[2-(3-methoxy)phenyl]ethyl]phenoxy]ethyl-1-methylpyrrolidine as a 5-HT2A receptor PET ligand.
abstract: The serotonin2A (5-HT2A) receptor is implicated in the pathophysiology of schizophrenia and mood disorders, and in vivo studies of this receptor would be of value in studying the pathophysiology of these disorders and in measuring the relationship of clinical response to receptor occupancy for 5-HT2A antagonists such as atypical antipsychotics. Therefore, (2R,4R)-4-hydroxy-2-[2-[2-[2-(3-methoxy)-phenyl]ethyl]phenoxy]ethyl-1-methylpyrrolidine (MPM) (13), a selective and high-affinity (K(i)=0.79 nM) 5HT2A antagonist, has been radiolabeled with carbon-11 by O-methylation of the corresponding desmethyl analogue (2R,4R)-4-hydroxy-2-[2-[2-[2-(3-hydroxy)phenyl]ethyl]phenoxy]ethyl-1-methylpyrrolidine (12) with [11C]methyltriflate in order to determine the suitability of [11C]MPM to quantify 5-HT2A in living brain using PET. Desmethyl-MPM 12 and standard MPM were prepared, starting from 3-hydroxymethylphenol (2), in excellent yield. The yield obtained for radiolabeling was 40+/-5% (EOB), and the total synthesis time was 30 min at EOS. PET studies with [11C]MPM in baboon showed a distribution in the brain consistent with the known distribution of 5-HT2A receptors. The time-activity curves for the high-binding regions peaked at approximately 45 min after injection. Blocking studies with M100907 demonstrated not only 38-57% blocking of tracer binding in brain regions known to have 5-HT2A receptors but also 38% blocking in cerebellum, which has a low 5-HT2A receptor concentration. Although [11C]MPM exhibits appropriate kinetics in baboon for imaging 5-HT2A receptors, its specific binding in cerebellum and higher proportion of nonspecific binding limit its usefulness for the in vivo quantification of 5-HT2A receptors with PET.
authors.affiliation: Department of Psychiatry, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA. dk2038@columbia.edu
authors.forename: J S Dileep
authors.initials: JS
authors.lastname: Kumar
authors.forename: Jaya
authors.initials: J
authors.lastname: Prabhakaran
authors.forename: Kjell
authors.initials: K
authors.lastname: Erlandsson
authors.forename: Vattoly J
authors.initials: VJ
authors.lastname: Majo
authors.forename: Norman R
authors.initials: NR
authors.lastname: Simpson
authors.forename: Mali
authors.initials: M
authors.lastname: Pratap
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Van Heertum
authors.forename: J John
authors.initials: JJ
authors.lastname: Mann
authors.forename: Ramin V
authors.initials: RV
authors.lastname: Parsey
mesh_terms: D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism*; D007553:Isotope Labeling / Q000379:methods; D008024:Ligands; D008657:Metabolic Clearance Rate; D048530:Papio anubis; D049268:Positron-Emission Tomography / Q000379:methods*; D011759:Pyrrolidines / Q000737:chemistry / Q000493:pharmacokinetics*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D044402:Receptor, Serotonin, 5-HT2A / Q000378:metabolism*; D014018:Tissue Distribution
chemical_list: C476157:(2R,4R)-4-hydroxy-2-(2-(2-(2-(3-methoxy)phenyl)ethyl)phenoxy)ethyl-1-methylpyrrolidine hydrochloride; D008024:Ligands; D011759:Pyrrolidines; D019275:Radiopharmaceuticals; D044402:Receptor, Serotonin, 5-HT2A