Vol. 18 No. 1(69) (2020)
Published:
2020-03-05
Original Researches
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Noncovalent interactions in crowded olefinic radical cations
Aim. To study the effect of electronic (α- and β-hyperconjugations) and steric (noncovalent interactions) factors on the structures of olefinic radical cations.
Results and discussion. The effect of intramolecular dispersion interactions on the structures of crowded alkenes in the neutral and ionized forms has been studied at the density functional theory (DFT) level with and without dispersion corrections included, as well as at the MP2 theory level with medium size basis sets. The results obtained are compared to the available experimental data. An excellent agreement has been found between the experimental and MP2/DFT-computed geometries of sesquihomoadamantene, adamantylidene adamantane, bis-2,2,5,5-tetramethylcyclopentylidene, bis-D3-homocub-4-ylidene, and bis-CS-homocub-8-ylidene in the neutral and ionized forms. The experimental ionization potentials are better reproduced with the DFT-methods.
Experimental part. The structure and composition of compounds were proved by the methods of 1H and 13C NMR-spectroscopy, and GC-MS-analysis. Elemental analysis was performed for the compounds obtained.
Conclusions. The twisting of the olefinic moieties in the sesquihomoadamantene and adamantylidene adamantane radical cations is determined by the balance between the σ-π-hyperconjugation and residual one-electron π-bonding and is close to that of the prototypical ethylene radical cation (29°). The twisting reaches 55° for the bis-2,2,5,5-tetramethylcyclopentylidene radical cation due to substantial steric repulsions between methyl groups. At the same time, the ionized states of bis-D3-homocub-4-ylidene and bis-CS-homocub-8-ylidene retain their planarity due to β-CC-hyperconjugation and intramolecular dispersion attractions.
Received: 26.12.2019
Revised: 17.01.2020
Accepted: 27.02.2020 -
Esters and amides of 3-R-2,8-dioxo-7,8-dihydro2H-pyrrolo[1,2-a][1,2,4]triazino[2,3-c]quinazolin-5a(6H)-carboxylic(-propanoic) acids: synthesis and biological activity
It is known that carboxyl groups bonded to aryl or hetaryl moieties play a role of the “pharmacophore” fragment in most NSAID molecules. It should be mentioned that the carboxyl group may cause the appearance of toxic effects and is characterized by unsatisfactory pharmacokinetic properties. The structural modification of the carboxyl group, including its bioisosteric replacement, is among the most widely used approaches in medicinal chemistry to improve pharmacodynamic, pharmacokinetic and technological characteristics.
Aim. To develop the synthetic procedures for functional derivatives of 3-R-2,8-dioxo-7,8-dihydro-2Н-pyrrolo[1,2-а][1,2,4]triazino[2,3-с]quinazoline-5а(6Н)-carboxylic(-propanoic) acids, study the effect of the carboxyl group chemical modification on the LOX-inhibiting and antiradical activity as a possible mechanism of the pharmacological activity.
Results and discussion. The synthesis of esters of 3-(2,8-dioxo-3-R1-7,8-dihydro-2H-pyrrolo[1,2-a][1,2,4]triazino[2,3-c]quinazolin-5a(6H)-yl)carboxylic(propanoic) acids was conducted by esterification of the corresponding acids and tandem heterocyclization of 2-(6-R1-2,5-dihydro-5-оxo-1,2,4-triazino-3-yl)anilines with diethyl 4-oxoheptanedioate. The synthesis of amides was conducted by aminolysis of N-acylimidazolides generated in situ. The antiradical and LOX-inhibiting activities of the compounds obtained were studied as possible mechanisms of the anti-inflammatory activity. The series of the compounds revealed the LOX-inhibiting activity that was comparable with the effect of the reference compound – nordihydroguaiaretic acid.
Experimental part. The synthetic procedures were conducted according to the commonly used methods. The purity and the structure of the compounds obtained were proven by modern physicochemical methods (1H and 13C NMR-spectroscopy, LC-MS-spectrometry). The antiradical activity was measured by the ability to scavenge a DPPH-radical. The study of the LOX-inhibiting activity was performed using soybean LOX as an enzyme and linolenic acid as a substrate.
Conclusions. The methods for the synthesis of esters and amides of 2,8-dioxo-3-R1-7,8-dihydro-2H-pyrrolo[1,2-a][1,2,4]triazino[2,3-c]quinazolin-5a(6H)-carboxilic(propanoic) acids have been developed. The abovementioned transformations were conducted by alcoholysis of generated in situ acyl halides and aminolysis of N-acylimidazolides, respectively. The more efficient approach for the synthesis of the target esters via condensation of 2-(6-R1-2,5-dihydro-5-oxo-1,2,4-triazino-3-yl)anilines with diethyl 4-oxoheptanedioate has been proposed. It has been found that the highest radical scavenging and LOX-inhibiting activities are characteristic for hetarylpropanoic acids that contain electron withdrawing substituents in position 3, as well as fluorine atoms in positions 11 and 12. The chemical modification of the carboxylic group in most cases results in a decrease or the loss of the activity.
Received: 10.01.2019
Revised: 04.02.2020
Accepted: 27.02.2020 -
ESI-MS fragmentation pathways of some 1,2,4-triazole-3-thiones, the intermediate compounds in the synthesis of active pharmaceutical ingredients
Aim. To determine the fragmentation pathways of eight 1,2,4-triazole-3-thiones, which are intermediate products in the synthesis of active pharmaceutical ingredients of potential and registered pharmaceutical formulations.
Results and discussion. HPLC-MS analysis of eight 1,2,4-triazole-3-thiones, which are intermediate products in the synthesis of salts of 1,2,4-triazolylthioacetate acids, has been carried out; the mass spectra of the compounds to be analyzed have been registered in ESI-mode with different fragmentor voltage (0, 100, 200 V). The fragmentation pathways and patterns of ion decay for compounds to be analyzed have been proposed.
Experimental part. Agilent 1260 Infinity HPLC System with Agilent 6120 mass spectrometer were used. HPLC-MS conditions: column – 4,6 × 30 mm, reversible phase Zorbax SB C18, 1.8 μm, 40 oC; mobile phase – 0.1 % HCOOH in H2O and 0.1 % HCOOH in СH3CN in isocratic mode (50:50, v/v); the flow rate – 0.4 mL/min; ion source – API-ES; positive polarity; drying gas – nitrogen (rate – 10 L/min); the capillary voltage – 4000 V; scanning in the range of m/z 100 – 1000.
Conclusions. For the first time it has been interpreted the mass spectra of 1,2,4-triazole-3-thiones series, the intermediate compounds in the synthesis of active pharmaceutical ingredients of pharmaceutical formulations. The fragmentation pathways and patterns of eight 1,2,4-triazole-3-thiones have been shown.
Received: 06.09.2019
Revised: 20.01.2020
Accepted: 27.02.2020 -
Reactions of Cookson’s diketone with potassium halides in the polyphosphoric acid medium
Aim. To study the rearrangement of Cookson’s diketone by the action of potassium halides under conditions of polyphosphoric acid catalysis.
Results and discussion. Chemical behaviour of Cookson’s diketone (CS-trishomocubane-8,11-dione) in the reactions with potassium halides (KCl, KBr, KI) in the polyphosphoric acid (PPA) medium have been studied. When treated with the KI/PPA mixture Cookson’s diketone undergoes reduction leading to tetracyclo[6.3.0.0.4,11.05,9]undecane-2,7-dione. The use of KBr instead of KI leads to formal addition of HBr to the cyclobutane ring of CS-trishomocubane-8,11-dione and gives 3-bromotetracyclo[6.3.0.04,11.05,9]undecane-2,7-dione. The general scheme of the cycle opening mechanism has been proposed. In the case of using the KCl/PPA mixture the reaction does not occur.
Experimental part. The structure and composition of compounds were proved by the methods of 1H and 13C NMR-spectroscopy, and also X-ray diffraction analysis. Elemental analysis was performed for the compounds obtained.
Conclusions. It has been shown that hydrohalic acids generated in situ under the reaction conditions do not induce the rearrangement of Cookson’s diketone to the D3-trishomocubane system. The cyclobutane ring opening and reduction take place instead.
Received: 12.12.2019
Revised: 10.01.2020
Accepted: 27.02.2020 -
The study of the neurotropic activity of the pyrrolopyrimidin-4-ones rearrangement products under the action of phosphorus oxychloride
Aim. To synthesize the annelated 4-aminopyridines and study the biological activity of one of products.
Results and discussion. In the laboratory of the Research Institute of Biomedical Problems of the Dnipropetrovsk Medical Academy the studies of the effect of 2,3,3-trimethyl-2,3,5,6,7,8-hexahydro-1H-pyrrolo[3,4-b]quinolin-9-amine on the neuroactivity in the “open field” model have been conducted. According to the results of the experiment it has been found that in two hours after the administration of the oil solution of the compound the indices of the motor activity of mice are significantly reduced.
Experimental part. 2,3,3-Trimethyl-2,3,5,6,7,8-hexahydro-1H-pyrrolo[3,4-b]quinolin-9-amine and 2,3,6,7,7-pentamethyl-6,7-dihydro-5H-pyrrolo[3,4-b]pyridin-4-amine were obtained by the rearrangement of the corresponding pyrrolopyrimidin-4-ones under the action of the excess of phosphorus oxychloride in toluene. The initial pyrrolopyrimidin-4-ones were synthesized by the condensation of 4-amino-1,2,2-trimethyl-2,5-dihydro-1H-pyrrole-3-carbonitrile with ketones. The structure of all compounds obtained was confirmed by 1H NMR-spectroscopy, mass spectrometry and elemental analysis.
Conclusions. The neurotropic activity has been detected for the oil solution of 2,3,3-trimethyl-2,3,5,6,7,8-hexahydro-1H-pyrrolo[3,4-b]quinolin-9-amine on the “open field” model. It has been found that the aqueous solution of this compound does not exhibit the neurotropic activity regardless of the administered dose. Taking into account the presence of the neurotropic activity further research in this field is a promising way to search novel bioactive molecules among 4-aminopyridine derivatives, which are structural analogs of the drug Tacrine.
Received: 26.12.2019
Revised: 20.01.2020
Accepted: 27.02.2020 -
Domino-reactions of 3-methyl-5-aminopyrazole with 1-phenyl-3-(4-alkoxyphenyl)pyrazole-4-carbaldehydes and 2,2-dimethyl-1,3-dioxane-4,6-dione
Aim. To synthesize 1-phenyl-3-(4-alkoxyphenyl)pyrazole-4-carbaldehydes and determine the direction of their interaction in the three-component condensation with 3-methyl-5-aminopyrazole and 2,2-dimethyl-1,3-dioxane-4,6-dione.
Results and discussion. A series of 1-phenyl-3-(4-alkoxyphenyl)pyrazole-4-carbaldehydes was synthesized from arylhydrazone by the Vilsmeier–Haak reaction. The domino-reactions of these aldehydes with 3-methyl-5-aminopyrazole and 2,2-dimethyl-1,3-dioxane-4,6-dione lead to pyrazolo[3,4-b]pyridone systems.
Experimental part. The synthesis of 1-phenyl-3-(4-alkoxyphenyl)pyrazole-4-carbaldehyde was carried out by formylation of arylhydrazones under the conditions of the Vilsmeier–Haack reaction with the yield of 55 – 88 %. Refluxing in 2-propanol equimolar amounts of these aldehydes, 3-methyl-5-aminopyrazole and 2,2-dimethyl-1,3-dioxane-4,6-dione gave 3-methyl-4-(1',3'-diarylpyrazol-4'-yl)tetrahydropyrazolo[3,4-b]pyridin-6-ones with the yield of 48 – 75 %. The structure and composition of all substances synthesized were proven by 1H NMR, IR-spectra and elemental analysis.
Conclusions. It has been found that the reactions of 1,3-diaryl substituted pyrazole-4-carbaldehydes with 3-methyl-5-aminopyrazole and 2,2-dimethyl-1,3-dioxane-4,6-dione are regioselective and lead to the formation of pyrazolo[3,4-b]pyridone systems. This orientation of the process corresponds to the interaction of the β-carbon atom of the probable intermediate, which is formed at the first stage of the reaction from dioxandione and aldehyde, with the carbon nucleophilic center in the aminoazole molecule, and then the exocyclic amino group in the heterylamine attacks the C=O group in the dioxane-4,6-dione fragment. -
Luminescent properties of substituted 4-aminophthalimides: computations vs. experiment
Aim. To perform a combined experimental and computational study on the luminescent properties of practically important class of organic dyes – 4-aminophthalimides.
Results and discussion. The absorption and fluorescence spectra of 4-aminophthalimide derivatives in polar protic and aprotic solvents were computed and matched vs. the experimental data. The changes in emission spectra are mainly related to the NH2-group derivatization. The methyl substitution of amide hydrogen causes a batochromic shift of about 7 nm in the absorption peak and a negligible hypsochromic shift in the fluorescence peak, while introducing alkyl substituents to the amine moiety causes bathochromic shifts in absorption and emission peaks of 30 – 40 nm and 10 – 60 nm, respectively.
Experimental part. Absorption and emission wavelengths were computed by the standard algorithm based on the ground state geometry optimization (equilibrium solvation), vertical excitation with nonequilibrium solvation, and the TD-DFT geometry optimization of the excited state structures. A reliable hybrid B3LYP functional was used in combination with DZ and TZ-quality basis sets.
Conclusions. The computed absorption wavelengths are in excellent agreement with the experimental data and are only slightly solvent-dependent. At the same time, the discrepancy with the experiment for Stokes shifts reaches about 20 % at IEF-PCM-TD-B3LYP/6-31G(d). However, the general tendency for both absorption and fluorescence wavelengths is identical for all solvents within one molecule.
Received: 24.12.2019
Revised: 31.01.2020
Accepted: 27.02.2020 -
Application of thin layer chromatography in the analysis of efavirenz
Aim. To carry out the integrated study of visualization conditions of efavirenz on TLC-plates with aplication of standard and particular colored reagents, and the chromatographic behavior of efavirenz using standard mobile phases.
Results and discussion. It has been shown that such widely used color reagents as UV-light, Erdmann reagent, Froehde reagent, Liebermann reagent, sulfuric acid, Marquis reagent, Mandelin reagent, acidified iodoplatinate solution, iodine vapor can be used for efavirenz detection on chromatographic plates. Efavirenz gives the positive detection results with reagents used in the TLC-screening of extracts from the biological material for substances of basic, acid and neutral nature. The chromatographic mobility of efavirenz has been studied in 17 solvents systems; the systems are used as standard mobile phases according to the recommendations of the International Association of Forensic Toxicologists for TLC-screening of organic compounds of acid, neutral and basic nature, and as well as in the general TLC-screening of organic substances in the Ukrainian forensic toxicological laboratories.
Experimental part. The chromatographic plates Sorbfil® PTLC-IIH-UV and Merck® TLC Silica gel 60G were used as thin layers.
Conclusions. The behavior of efavirenz when developing on TLC-plates with two types of a substrate (plastic and glass) and with/without a luminophor with commonly used colored reagents has been studied. The Rf values of efavirenz under chromatographing conditions in the standard solvent systems used for TLC-screening of organic compounds of acid, neutral and basic nature have been set.
Received: 17.12.2019
Revised: 12.01.2020
Accepted: 27.02.2020
