ABSTRACT
A novel series of 2- and 9-disubstituted heterocyclic-fused 4-oxo-indeno[1,2-e]pyrazin derivatives was synthesized. One of them, the 9-(1H-tetrazol-5-ylmethyl)-4-oxo-5,10-dihydroimidazo[1,2-a]indeno[1,2-e]pyrazin-2-yl phosphonic acid 4i exhibited a strong and a selective binding affinity for the AMPA receptor (IC50 = 13 nM) and demonstrated potent antagonist activity (IC50 = 6nM) at the ionotropic AMPA receptor. This compound also displayed good anticonvulsant properties against electrically-induced convulsions after ip and iv administration with ED50 values between 0.8 and 1 mg/kg. Furthermore, a strong increase in potency was observed when given iv 3 h before test (ED50 = 3.5 instead of 25.6 mg/kg for the corresponding 9-carboxymethyl-2-carboxylic acid analogue). These data confirmed that there is an advantage in replacing the classical carboxy substituents by their bioisosteres such as tetrazole or phosphonic acid groups.
Subject(s)
Excitatory Amino Acid Antagonists/chemical synthesis , Excitatory Amino Acid Antagonists/pharmacology , Pyrazinamide/pharmacology , alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid/antagonists & inhibitors , Animals , Anticonvulsants/chemical synthesis , Anticonvulsants/pharmacology , Combinatorial Chemistry Techniques , Disease Models, Animal , Excitatory Amino Acid Antagonists/chemistry , Imidazoles/chemical synthesis , Imidazoles/pharmacology , Inhibitory Concentration 50 , Male , Mice , Oocytes/drug effects , Pyrazinamide/analogs & derivatives , Pyrazinamide/chemical synthesis , Pyrazinamide/chemistry , Pyrazines/chemical synthesis , Pyrazines/pharmacology , Receptors, AMPA/antagonists & inhibitors , Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors , Seizures/chemically induced , Seizures/drug therapy , Seizures/prevention & control , Structure-Activity RelationshipABSTRACT
Indeno¿1,2-bpyrazin-2,3-diones have been identified as a novel series of potent ligands on the glycine site of the NMDA receptor. To improve their in vivo activities, an acetic acid-type side chain was introduced to the 5-position, giving water-soluble compounds when formulated as the sodium salt (>10 mg/mL). Introduction of a chlorine atom in the 8-position led to a dramatic improvement of anticonvulsant activity and this was surprising since this change did not improve binding affinity. A plausible explanation is a reduced recognition by a Na(+),K(+)-ATPase active transport system responsible for the excretion of these compounds from the brain and kidney. This promising new chemical series led to the optically active isomer (-)-10i (RPR 118723), a glycine/NMDA antagonist with nanomolar binding affinity and in vivo activity in animal model of convulsions and electrophysiology at doses in the range of 2-3 mg/kg following iv administration.
Subject(s)
Excitatory Amino Acid Antagonists/chemical synthesis , Pyrazines/chemical synthesis , Receptors, Glycine/antagonists & inhibitors , Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors , Animals , Anticonvulsants/chemical synthesis , Anticonvulsants/chemistry , Anticonvulsants/metabolism , Anticonvulsants/pharmacology , Cells, Cultured , Cerebellum/cytology , Cerebral Cortex/metabolism , Excitatory Amino Acid Antagonists/chemistry , Excitatory Amino Acid Antagonists/metabolism , Excitatory Amino Acid Antagonists/pharmacology , In Vitro Techniques , Long-Term Potentiation/drug effects , Mice , Neurons/drug effects , Neurons/physiology , Patch-Clamp Techniques , Pyrazines/chemistry , Pyrazines/metabolism , Pyrazines/pharmacology , Rats , Rats, Sprague-Dawley , Receptors, Glycine/metabolism , Receptors, Glycine/physiology , Receptors, N-Methyl-D-Aspartate/metabolism , Receptors, N-Methyl-D-Aspartate/physiology , StereoisomerismSubject(s)
Acetamides/pharmacokinetics , Cerebral Cortex/metabolism , Pancreas/metabolism , Receptors, Cholecystokinin/antagonists & inhibitors , Acetamides/metabolism , Acetamides/pharmacology , Animals , Cell Membrane/metabolism , Guinea Pigs , Male , Mice , Mice, Inbred Strains , Molecular Structure , Receptors, Cholecystokinin/metabolism , Sincalide/metabolism , Structure-Activity RelationshipABSTRACT
The structures of crystalline D-xylose isomerase (D-xylose ketol-isomerase; EC 5.3.1.5) from Streptomyces rubiginosus and of its complexes with substrate and with an active-site-directed inhibitor have been determined by x-ray diffraction techniques and refined to 1.9-A resolution. This study identifies the active site, as well as two metal-binding sites. The metal ions are important in maintaining the structure of the active-site region and one of them binds C3-O and C5-O of the substrate forming a six-membered ring. This study has revealed a very close contact between histidine and C1 of a substrate, suggesting that this is the active-site base that abstracts a proton from substrate. The mechanism-based inhibitor is a substrate analog and is turned over by the enzyme to give a product that alkylates this same histidine, reinforcing our interpretation. The changes in structure of the native enzyme, the enzyme with bound substrate, and the alkylated enzyme indicate that the mechanism involves an "open-chain" conformation of substrate and that the intermediate in the isomerization reaction is probably a cis-ene diol because the active-site histidine is correctly placed to abstract a proton from C1 or C2 of the substrate. A water molecule binds to C1O and C2O of the substrate and so may act as a proton donor or acceptor in the enolization of a ring-opened substrate.
