Browsing by Author "Shivachev B."

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    Ammonium hydrogen (RS)-[(5-methyl-2-oxo-1,3-oxazolidin-3-yl)methyl]phospho- nate
    (2010-01-22) Todorov P.; Naydenova E.; Nikolova R.; Shivachev B.
    In the title compound, NH4+·C 5H9NO5P-, the five-membered methyl-oxazolidin-2-one unit is disordered over two positions, the major component having a site occupancy of 0.832 (9). A three-dimensional network of O-H⋯O and N-H⋯O hydrogen bonds stabilizes the crystal structure.
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    Hepatotoxicity and antioxidant activity of some new N,N′-disubstituted benzimidazole-2-thiones, radical scavenging mechanism and structure-activity relationship
    (2018-03-01) Anastassova N.; Mavrova A.; Yancheva D.; Kondeva-Burdina M.; Tzankova V.; Stoyanov S.; Shivachev B.; Nikolova R.
    A new method for the synthesis of 1,3-disubstituted benzimidazole derivatives was developed using aza-Michael addition. The target compounds were synthesized in good yields and purity and tested on isolated hepatocytes for their toxicity and antioxidant activity. The antioxidant properties of the substances with lowest toxicity were evaluated using oxidative stress induced by tert-butyl hydroperoxide (tert-BOOH). Some of them as methyl 3-[3-(3-methoxy-3-oxopropyl)-5-benzoyl-2-thioxo-2,3-dihydro-1H-benzimidazol-1-yl]propanoate 10 and 1,3-bis[3-(hydrazinooxy)-3-oxopropyl]-5-benzoyl-1,3-dihydro-2H-benzimidazole-2-thione 15 exhibited statistically significant cytoprotective and antioxidant effects which were similar to those of quercetin. In order to estimate the influence of the structure on the biological properties, structural characterization of the studied compounds was performed by X-ray diffraction analysis and DFT methods. On the basis of the calculated reaction enthalpies of hydrogen atom abstraction (HAT mechanism) and single-electron transfer (SET mechanism) the mechanisms of the antioxidant action of the tested compounds were studied. Subsequently it was established that the HAT mechanism governs the radical scavenging of 10 and 15 in the lipid phase, while the SET mechanism is preferred in water medium for 10 and competitive to HAT for 15.
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    Structure, conformation and hydrogen bonding of two amino-cycloalkanespiro-5-hydantoins
    (2009-01-09) Todorov P.; Petrova R.; Naydenova E.; Shivachev B.
    The crystal structures of 3-amino-cycloheptanespiro-4′- imidazolidine-2′,5′-dione (I) {systematic name: 3-amino-1,3-diazaspiro[4.6] undecane-2,4-dione} and 3-amino-cyclooctanespiro-4′- imidazolidine-2′,5′-dione (II) {systematic name: 3-amino-1,3-diazaspiro[4.7] dodecane-2,4-dione}, have been determined. In both compounds the polar hydantoin groups cause molecules to aggregate via N-H⋯O and N-H⋯N interactions, forming a layer structure, in which the cycloalkane rings project outwards from the central, more polar, region. The observed molecular structure is compared with that calculated by density functional theory methods. © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2009.
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    Synthesis and superconducting properties of Nd0.33 Eu0.08Gd0.58Ba2Cu3 Oz materials
    (2008-03-01) Stoyanova-Ivanova A.; Terzieva S.; Shivachev B.; Mikli V.; Vladimirova L.
    We have studied the effect of the ratio of different rare-earth element on the superconducting properties and phase formation of (Nd0.33Eu0.08Gd0.58)Ba2 Cu3Oz ceramic. Bulk NEG samples were prepared using the solid-state reaction process. The superconducting transition for Nd0.33Eu0.08Gd0.58Ba2 Cu3Oz is Tc ≈ 90 K and the value of the critical current density (Jc) is 13.9 A/cm2 at 77 K under zero magnetic fields. This value is twice as high when compared with the (Jc) value of YBCO systems (J3 = 7.31 A/cm2). The obtained bulk sample was used for the production of superconducting Ag-sheathed tapes by OPIT method including hot rolling. The critical current density of the obtained tape (337 A/cm2) is one order higher than the one of the bulk sample. © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2008.
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    Synthesis, crystal structure and biological activity screening of novel N-(α-bromoacyl)-α-amino esters containing valyl moiety
    (2015-01-01) Yancheva D.; Cherneva E.; Quick M.; Mikhova B.; Shivachev B.; Nikolova R.; Djordjevic A.; Untergehrer M.; Jürgenliemk G.; Kraus B.; Smelcerovic A.
    Three novel N-(α-bromoacyl)-α-amino esters: methyl 2-(2-bromo-3-methylbutanamido)pentanoate (1), methyl 2-(2-bromo-3-methylbutanamido)-2-phenylacetate (2) and methyl 2-(2-bromo-3-methylbutanamido)-3-phenylpropanoate (3) were synthesized. Single crystal X-ray diffraction data are reported for compounds 1 and 2. The cytotoxicity, antiinflammatory and antibacterial activity of compounds 1-3 were investigated. Additionally, the physico-chemical properties of studied compounds were calculated and an in silico toxicological study of compounds 1-3 was performed. The low level of cytotoxicity and absence of antibacterial and anti-inflammatory activity of 1-3 in tested concentrations might be a beneficial prerequisite for their incorporation in prodrugs.
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    Two 5-Methoxyindole Carboxylic Acid-Derived Hydrazones of Neuropharmacological Interest: Synthesis, Crystal Structure, and Chemiluminescent Study of Radical Scavenging Properties
    (2024-05-01) Anastassova N.; Hristova-Avakumova N.; Rusew R.; Shivachev B.; Yancheva D.
    Given the importance of molecular structure in pharmacological activity and interaction with biological receptors, we conducted a study on the 3,4-dihydroxybenzaldehyde hydrazone derivative of 5-methoxy-indole carboxylic acid (5MICA) and a newly synthesised analogue bearing a 2-methoxy-4-hydroxyphenyl ring using single-crystal X-ray diffraction. We studied the ability of the two compounds to scavenge hypochlorite ions using luminol-enhanced chemiluminescence and their potential to modulate oxidative damage induced by iron on the biologically significant molecules lecithin and deoxyribose in order to evaluate possible antioxidant and prooxidant effects. The X-ray study revealed highly conserved geometry and limited rotation and deformation freedom of the respective indole and phenyl fragments. Interestingly, a conformational difference between the two independent molecules in the asymmetric unit of 3b was found. The X-ray study revealed a combination of hydrogen bonding interactions, short contacts, and π–π stacking stabilizing the specific three-dimensional packing of the molecules of 3a and 3b in the crystal structures. The three-dimensional packing of the molecules of 3b produced a zigzag layering projected along the c-axis. Both compounds effectively decreased luminol-dependent chemiluminescence in model systems with KO2-produced superoxide. They displayed opposite effects when applied in a xanthine/xanthine oxidase system. The hydrazones of 5MICA do not trigger a prooxidant effect or subsequent toxicity under conditions of iron-induced oxidative stress. The 3,4-dihydroxy-substituted derivative demonstrated excellent radical scavenging properties in all model systems, making it the lead compound for the development of compounds with combined neuroprotective and antioxidant properties.