TCS 46b

Synthesis, radiosynthesis and in vivo evaluation of 5-[3-(4-benzylpiperidin-1-yl)prop-1-ynyl]-1,3-dihydrobenzoimidazol-2-[(11)C]one, as a potent NR(1A)/2B subtype selective NMDA PET radiotracer.[Pubmed:14642584]

Bioorg Med Chem. 2003 Dec 1;11(24):5401-8.

Recently, a new series of potent and highly subtype-selective 1-(heteroarylalkynyl)-4-benzylpiperidine antagonists of the NMDA receptors has been described by Pfizer Laboratories. In this series, 5-[3-(4-benzylpiperidin-1-yl)prop-1-ynyl]-1,3-dihydrobenzoimidazol-2-one (1) was identified as a selective antagonist for the NR1(A)/2B subtype, displaying IC(50) values for inhibition of the NMDA responses of 5.3 nM for this subtype (compared to NR1(A)/2A: 35 microM and NR1(A)/2C>100 microM) and was active in rat at a relatively low dosage (10mg/kg po). Derivative 1 has been synthesized in four chemical steps in good overall yield and labelled with carbon-11 at its benzoimidazolone ring using [(11)C]phosgene. The pharmacological profile of [(11)C]-1 was evaluated in vivo in rats with biodistribution studies and brain radioactivity monitored with intracerebral radiosensitive beta-microprobes. The brain uptake of [(11)C]-1 was extremely low (0.07% I.D./mL on average at 30 min) and rather uniform across the different brain structures. This in vivo brain regional distribution of [(11)C]-1 did not match with autoradiographic or binding data obtained with other NR2B subtype-selective NMDA ligands. Competition studies with ifenprodil (20 mg/kg, ip, 30 min before the radiotracer injection) failed to demonstrate specific binding of the radiotracer in the brain. In view of these results, and especially considering the low brain penetration of the radiotracer, [(11)C]-1 does not have the required properties for imaging NMDA receptors using positron emission tomography.

Subtype-selective N-methyl-D-aspartate receptor antagonists: synthesis and biological evaluation of 1-(heteroarylalkynyl)-4-benzylpiperidines.[Pubmed:10978188]

J Med Chem. 2000 Sep 7;43(18):3408-19.

4-[4-(4-Benzylpiperidin-1-yl)but-1-ynyl]phenol (8) and 4-[3-(4-benzylpiperidin-1-yl)prop-1-ynyl]phenol (9) are potent NR1A/2B receptor antagonists (IC(50) values 0.17 and 0.10 microM, respectively). Administered intraperitoneally, they both potentiated the activity of L-DOPA in the unilaterally 6-hydroxydopamine-lesioned (6-OHDA) rat, a model of Parkinson's disease. However, compound 9 was not active orally, likely due to rapid first-pass metabolism of the phenol moiety. The phenol was replaced by several bicyclic heterocyclic systems containing an NH group to function as a H-bond donor in the hope that these would be less likely to undergo rapid metabolism. In general, indoles, indazoles, benzotriazoles, indolones, and isatins gave analogues with weaker NR1A/2B activity than the parent phenols, while benzimidazolones and benzimidazolinones gave equipotent or more potent analogues. The preference for a para arrangement between the H-bond donor and the linking acetylene moiety was confirmed, and a propyne link was preferred over a butyne link. Substitution on the benzyl group or a 4-hydroxyl group on the piperidine had little effect on NR1A/2B potency; however, 4-hydroxypiperidines demonstrated slightly improved selectivity for NR1A/2B receptors versus alpha-1 adrenergic and dopamine D2 receptor affinity. From this study, 5-[3-(4-benzylpiperidin-1-yl)prop-1-ynyl]-1, 3-dihydrobenzoimidazol-2-one (46b) was identified as a very potent, selective NR1A/2B receptor antagonist (IC(50) value 0.0053 microM). After oral administration at 10 and 30 mg/kg, 46b potentiated the effects of L-DOPA in the 6-OHDA-lesioned rat and seemed to have improved oral bioavailability but lower brain penetration compared to phenol 9.