Valproates are commonly used to treat various forms of epilepsy. Problems accompanying their clinical application include drug resistance, adverse effects, acute and chronic toxicity. Safer anticonvulsants with improved efficacy can be obtained through the chemical modification of valproic acid structure. Thiadiazole-linked amide derivatives of valproates hold great promise because 1,3,4-thiadiazole can improve the drug's bioavailability and reduce its toxicity. The aim of this work was to synthesize a novel amide derivative of valproic acid and 1,3,4-thiadiazole exerting antiepileptic activity. The chemical structure of the synthesized valproate was studied by IR, proton NMR and 13С-NMR-spectroscopy, mass spectroscopy and elemental analysis. The purity and individuality of the compound was confirmed by thin-layer and high-performance liquid chromatography. Its antiepileptic activity was assessed in the test with intraperitoneally injected 250 mg/kg isoniazid and subsequent Probit analysis. The synthesized N-(5-ethyl-1,3,4-thiadiazol-2-yl)-2-propyl pentane amide (valprazolamide) had the following characteristics. ESI + MS: m/z 256.1 [M + H] + ; MRM transitions: m/z 256.1 -m/z 81.0 and m/z 130.1. The valproate exerted antiepileptic activity against isoniazid-induced seizures in mice.In the test with isoniazid, ED 50 of intraperitoneally injected VPZ was 126.8 mg/kg (95% CI: 65.5-245.4). Its therapeutic index was 7.3.

Aim: to adapt the HPLC-MS/MS technique to determining valproic acid and its metabolites in blood plasma for drug therapy monitoring.Materials and Methods: The chromatographic assay was run using an Agilent 1260 Infinity II chromatograph with a Phenomenex synergi Fusion analytical column 4 μm-C18 2×50 mm. The mobile phase consisted of 0.1% ammonium acetate in distilled water and 0.1% ammonium acetate in methanol (10:90 v/v, 0.5 ml/min). The multiple ions monitoring (MIM) mode was used for mass- spectrometric detection of valproic acid at m/z = 143.1, with the negative ion mode. The method  was found applicable over the range from 1 mcg/ml to 200 mcg/ml of valproic acid. For the mass  spectroscopy detection of valproic acid metabolites, the multiple reaction monitoring (MRM mode)  was used. MS identifications of 2-propyl-4-pentanoil-β-О-glucuronide; 2-propyl-4-pentenoic acid,  3-hydroxy-2- propylpentanoic acid, 4-hydroxy-2-propylpentanoic acid, 2-propylglutaric acid and 3- oxo-2-propylpentanoic acid in the negative ion mode were carried out at m/z 319.2→143.2; m/z  140.1→140.1; m/z 159.1→101; m/z 159.1→123.1; m/z 173→129.1 and m/z 157.05→11,  respectively. The method was sensitive over the range from 10 ng/ml to 500 ng/ml of the tested  compounds.Results: The developed technique allows for determining valproic acid and its metabolites in a single sample; thus, the preliminary stage of separate sample preparation can be omitted, which increases the informative value of the assay without increasing its cost.Conclusion: This innovative methodology for the quantification of valproic acid and its metabolites in the blood plasma is expected to facilitate the individual approach to the treatment of patients with epilepsy, thereby increasing the efficacy and safety of the pharmacotherapy.

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In experiments on rats, the effect of valprazolamide, a new antiepileptic agent from the group of amide derivatives of valproic acid, on the brain content of neuroactive amino acids (GABA, glycine, glutamic and aspartic acids) was studied. Detection of amino acids was performed by gas chromatography-mass spectrometry. It was shown that a single intraperitoneal injection of valprazolamide (100 mg / kg) increases the level of GABA and the amide form of glutamic acid, reduces the levels of asparagine, glutamic and aspartic acids in the rat brain.

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