The present study aimed to design and synthesize a new series of hybrid compounds with pyrrolidine-2,5-dione and thiophene rings in the structure as potential anticonvulsant and antinociceptive agents. For this purpose, we obtained a series of new compounds and evaluated their anticonvulsant activity in animal models of epilepsy (maximal electroshock (MES), psychomotor (6 Hz), and subcutaneous pentylenetetrazole (scPTZ) seizure tests). To determine the mechanism of action of the most active anticonvulsant compounds (3, 4, 6, 9), their influence on the voltage-gated sodium and calcium channels as well as GABA transporter (GAT) was assessed. The most promising compound 3-(3-methylthiophen-2-yl)-1-(3-morpholinopropyl)pyrrolidine-2,5-dione hydrochloride (4) showed higher ED50 value than those of the reference drugs: valproic acid (VPA) and ethosuximide (ETX) (62.14 mg/kg vs. 252.7 mg/kg (VPA) in the MES test, and 75.59 mg/kg vs. 130.6 mg/kg (VPA) and 221.7 mg/kg (ETX) in the 6 Hz test, respectively). Moreover, in vitro studies of compound 4 showed moderate but balanced inhibition of the neuronal voltage-sensitive sodium (site 2) and L-type calcium channels. Additionally, the antinociceptive activity of the most active compounds (3, 4, 6, 9) was also evaluated in the hot plate test and writhing tests, and their hepatotoxic properties in HepG2 cells were also investigated. To determine the possible mechanism of the analgesic effect of compounds 3, 6, and 9, the affinity for the TRPV1 receptor was investigated.
The focused library of new amides derived from 3,3-diphenyl-2,5-dioxo-pyrrolidin-1-yl-acetic acid (2a-t) and 3,3-diphenyl-propionic acid (3a-t) as potential anticonvulsant agents was synthesized. The final products were obtained in the amidation reaction of the given carboxylic acid (2, 3) with appropriate secondary amines in the presence of carbonyldiimidazole (CDI) as a coupling reagent. The initial anticonvulsant screening was performed in mice intraperitoneally (i.p.) using the "classical" maximal electroshock (MES) and subcutaneous pentylenetetrazole (scPTZ) seizure models, whereas the acute neurological toxicity was determined applying the rotarod test. Additionally, several compounds were studied also in the 6-Hz seizures recognized as the animal model of human pharmacoresistant epilepsy. In this series, compound 3q displayed a broad spectrum of activity across the preclinical seizure models (ED MES = 31.64 mg/kg; ED scPTZ = 75.41 mg/kg, ED 6-Hz (32 mA) = 38.15 mg/kg). Consequently, compound 3q revealed a wider spectrum of protection, higher activity or/and a better safety profile than the commonly used antiepileptic drugs such as phenytoin, ethosuximide, valproic acid, or/and levetiracetam. Notably, the in vitro studies showed that the most possible mechanism of action of 3q may be connected to the interaction with neuronal voltage-sensitive sodium channels (site 2). Other substances were active predominantly in the chemically induced seizures. The results of the current studies indicate that the presence of the pyrrolidine-2,5-dione ring is important but not indispensable for anticonvulsant activity.
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