Synthesis and binding properties of MK-801 isothiocyanates; (+)-3-isothiocyanato-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten- 5,10-imine hydrochloride: a new, potent and selective electrophilic affinity ligand for the NMDA receptor-coupled phencyclidine binding site.
Three new site-directed irreversible (wash-resistant) ligands for the high-affinity phencyclidine (PCP) binding site associated with the N-methyl-D-aspartate (NMDA) receptor were synthesized and their binding characteristics were studied. (+)-3- And (+)-2-isothiocyanato-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cycl ohepten-5,10 - imine hydrochloride ((+)-8a,b.HCl) were prepared in four steps from the corresponding nitro derivatives (+)-4a,b, which were obtained by nitration of (+)-3 (MK-801). In the same way the optical antipode (-)-8a.HCl was synthesized from (-)-3. At a concentration of 100 nM, the 3-isothiocyanate derivative (+)-8a irreversibly labeled approximately 50% of the (+)-[3H]-3 binding sites, compared to 20 microM needed for its optical antipode (-)-8a and the 2-isothiocyanate (+)-8b. The apparent Ki values for reversible inhibition of (+)-[3H]-3 binding by (+)- and (-)-8a and (+)-8b were 37,838, and 843 nM, respectively. In contrast, metaphit (1b) and etoxadrol m-isothiocyanate (2b), two previously reported irreversible ligands for the PCP binding site, label about 50% of the (+)-[3H]-3 binding sites at 100 microM and 250 nM, respectively, with apparent Ki values for reversible inhibition of 535 and 94 nM. Compound (+)-8a is also a selective affinity ligand, displaying little or no irreversible in vitro affinity at 100 microM for opioid, benzodiazepine, muscarinic, and dopamine receptors. At a 25 microM concentration, (+)-8a caused an irreversible 52% reduction of binding to sigma 1-receptors. Compound (+)-8a is the most potent known electrophilic affinity label for the PCP binding site. Its potency and selectivity should enable it to be a valuable tool for the elucidation of the structure and function of the NMDA receptor-associated PCP binding site in the mammalian central nervous system.
Linders
J T
JT
Laboratory of Medicinal Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Monn
J A
JA
Mattson
M V
MV
George
C
C
Jacobson
A E
AE
Rice
K C
KC
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D003461:Crystallography; D016291:Dizocilpine Maleate / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D010622:Phencyclidine / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013861:Thiocyanates / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism
D016194:Receptors, N-Methyl-D-Aspartate; D013861:Thiocyanates; C082820:2-isothiocyanato-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine; C082821:3-isothiocyanato-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine; D016291:Dizocilpine Maleate; D010622:Phencyclidine