Takuya Arai

Synthesis, in vitro and in vivo pharmacology of a C-11 labeled analog of CP-101,606, (±)threo-1-(4-hydroxyphenyl)-2-[4-hydroxy-4-(p-[11C]methoxyphenyl)piperidino]-1-propanol, as a PET tracer for NR2B subunit-containing NMDA receptors

A carbon-11 labeled methoxyl analog of CP-101,606, (+/-)threo-1-(4-hydroxyphenyl)-2-[4-hydroxy-4-(p-[11C]methoxyphenyl)piperidino]-1-propanol [(+/-)[11C]1], was synthesized as a new subtype-selective PET radioligand for NMDA receptors. The in vitro binding studies using rat brain slices demonstrated that (+/-)[11C]1 shows an extremely high-specific binding to the NR2B subunit of NMDA receptors. In contrast to the in vitro binding, the in vivo binding to mouse and monkey brains showed no apparent specific localization of the radioactivity in any of the brain regions. Metabolism and physicochemical properties such as the lipophilicity of (+/-)[11C]1 seemed unlikely to affect the in vivo (+/-)[11C]1 binding. Among the various endogenous ligands acting at the NMDA receptors, polyamines (spermine and spermidine) and divalent cations (Mg(2+,) Zn(2+,) and Ca(2+)) strongly inhibited the in vitro (+/-)[11C]1 binding. Thus, the present studies point to the possibility that the polyamines and cations behave as endogenous inhibitors for (+/-)[11C]1 binding, leading to the loss of the specific binding in vivo.

Radiosyntheses of two positron emission tomography probes: [11C]Oseltamivir and its active metabolite [11C]Ro 64-0802.

Oseltamivir phosphate (Tamiflu, 1.H(3)PO(4) is an orally active anti-influenza drug, which is hydrolyzed by esterase to its carboxylate metabolite Ro 64-0802 (2) with potent activity inhibiting neuraminidase. In this study, for the first time, we synthesized carbon-11-labeled oseltamivir ([(11)C]1) and Ro 64-0802 ([(11)C]2) as two novel positron emission tomography probes and demonstrated that [(11)C]1 had twofold higher radioactivity concentration in the mouse brains than [(11)C]2.

Determination of radioactivity in infant, juvenile and adult rat brains after injection of anti-influenza drug [11C]oseltamivir using PET and autoradiography

Oseltamivir phosphate (Tamiflu(®)) is an orally active anti-influenza drug, which is hydrolyzed to its metabolite Ro 64-0802 inhibiting the influenza virus with potent activity. The abnormal behavior of young influenza patients associated with the use of oseltamivir has developed to a social problem in countries where Tamiflu is often prescribed. It is important to determine the amount of oseltamivir in the brain and to elucidate the relationship between its presence and neuropsychiatric side effects. The aim of this study was to determine the radioactivity in the infant, juvenile and adult rat brains after injection of [(11)C]oseltamivir into the rats using PET and autoradiography. After injection of this radioligand, the highest radioactivity was found in the infant brain and the radioactivity level decreased with age. Ex vivo autoradiography on the infant brain displayed a relatively higher radioactivity in the cerebellum than that in the cerebrum. Pretreatment with cyclosporin A (an inhibitor for P-glycoprotein) increased the brain radioactivity. These results give helpful insights into elucidating why the neuropsychiatric side effects of oseltamivir occur in young patients.

Efficient and reproducible synthesis of [1-11C]acetyl chloride using the loop method.

[1-(11)C]Acetyl chloride ([(11)C]AcCl), an important [(11)C]acylating agent, was synthesized by reacting [(11)C]CO(2) with methylmagnesium bromide coated on the inner surface of a polyethylene loop (loop method). By optimizing the reaction conditions and synthesis parameters, [1-(11)C]phenylacetate and [1-(11)C]benzylacetate were produced from [(11)C]AcCl in high radiochemical yield and specific activity.

Use of a novel radiometric method to assess the inhibitory effect of donepezil on acetylcholinesterase activity in minimally diluted tissue samples

Background and purpose:  Cholinesterase inhibitors have been widely used for the treatment of patients with dementia. Monitoring of the cholinesterase activity in the blood is used as an indicator of the effect of the cholinesterase inhibitors in the brain. The selective measurement of cholinesterase with low tissue dilution is preferred for accurate monitoring; however, the methods have not been established. Here, we investigated the effect of tissue dilution on the action of cholinesterase inhibitors using a novel radiometric method with selective substrates, N‐[14C]methylpiperidin‐4‐yl acetate ([14C]MP4A) and (R)‐N‐[14C]methylpiperidin‐3‐yl butyrate ([14C]MP3B_R), for AChE and butyrylcholinesterase (BChE) respectively.

Pd2(dba)3/P(MeNCH2CH2)3N·HCl-mediated Stille cross-coupling of [1-11C]acetyl chloride with aryl and heteroaryl stannanes.

INTRODUCTION Developments in the Stille cross-coupling of [1-11C]acetyl chloride with tributylphenylstannane mediated by the Pd2(dba)3/P(MeNCH2CH2)3N·HClsystem are reported. METHODS The reaction conditions for the cross-coupling of [1-11C]acetyl chloride with tributylphenylstannane were optimized, and the reaction scope was investigated. RESULTS The cross-couplings of [1-11C]acetyl chloride with a range of aryl and heteroaryl stannanes were performed with good to excellent radiochemical conversions using the developed method. CONCLUSIONS A highly efficient method for the Stille cross-coupling of [1-11C]acetyl chloride with organostannanes was demonstrated. It is anticipated that our method will be an attractive addition to the carbon-11-labeling procedures available for the synthesis of positron emission tomography probes.