Georgi M. Dobrikov

Tuning the Excited-State Dynamics of GFP-Inspired Imidazolone Derivatives

The excited-state dynamics of five derivatives of the GFP-chromophore, which differ by the position and nature of their substituents, has been investigated in solvents of various viscosity and polarity and in rigid media using femtosecond-resolved spectroscopy. In polar solvents of low viscosity, like acetonitrile or methanol, the fluorescence decays of all compounds are multiexponential, with average lifetimes of the order of a few picoseconds, whereas in rigid matrices (polymer films and low temperature glasses), they are single exponential with lifetimes of the order of a few nanoseconds and fluorescence quantum yields close to unity. Global analysis of the fluorescence decays recorded at several wavelengths and of the transient absorption spectra reveals the presence of several excited-state populations with slightly different fluorescence and absorption spectra and with distinct lifetimes. These populations are attributed to the existence of multiple ground-state conformers. From the analysis of the dependence of the excited-state dynamics on the solvent and on the nature of the substituents, it follows that the nonradiative deactivation of all these excited chromophores involves an intramolecular coordinate with large amplitude motion. However, depending on the solvent and substituent, additional channels, namely, inter- and intramolecular hydrogen bond assisted nonradiative deactivation, are operative. This allows tuning of the excited-state lifetime of the chromophore. Finally, an ultrafast photoinduced intramolecular charge transfer is observed in polar solvents with one derivative bearing a dimethylaminophenyl substituent.

Chiral β- and γ-aminoalcohols derived from (+)-camphor and (−)-fenchone as catalysts for the enantioselective addition of diethylzinc to benzaldehyde

Abstract The addition of Me 3 SiCN and LiCH 2 CN to (+)-camphor and (−)-fenchone, respectively, followed by reduction leads to chiral β- and γ-aminoalcohols. The enantioselectivities realized using these aminoalcohols as ligands in the addition of Et 2 Zn to benzaldehyde were lower than those obtained using the corresponding δ-aminoalcohols.

Enantiopure antituberculosis candidates synthesized from (-)-fenchone.

The synthesis of new enantiopure N-acyl compounds derived from (-)-fenchone has been performed. The evaluation of their in vitro activity against Mycobacterium tuberculosis H37Rv showed for most of them moderate activity. The structures bearing sulfonamide functionality have comparable activity to ethambutol and possess low cytotoxicity.

Anti-enteroviral triple combination of viral replication inhibitors: activity against coxsackievirus B1 neuroinfection in mice

Background Chemotherapy is an important tool for controlling enterovirus infections, but clinically effective anti-enterovirus drugs do not currently exist, mainly due to the development of drug resistance. We investigated the combination effects of enterovirus replication inhibitors in order to limit this process. In previous studies, we showed the efficacy of consecutive alternating administration of the triple combinations disoxaril/guanidine/oxoglaucine and pleconaril/guanidine/oxoglaucine against coxsackievirus B1 infection in newborn mice. Drug sensitivity tests of the viral brain isolates showed that these drug combinations prevented the development of drug resistance. Methods In the current study, we replaced guanidine-HCl with enteroviral RNA synthesis inhibitor MDL-860 to test the effect of a new triple combination—pleconaril/MDL-860/oxoglaucine—applied via consecutive alternating administration in newborn mice infected subcutaneously with 20 MLD50 of coxsackievirus B1. Results The pleconaril/MDL-860/oxoglaucine combination via consecutive alternating administration showed high activity at the 75 mg/kg MDL-860 dose: a protective effect of 50% and a pronounced suppression of brain virus titers. Moreover, along with prevention of drug resistance, a phenomenon of increased drug sensitivity was established. MDL-860 sensitivity in pleconaril/MDL-860/oxoglaucine increased 8.2 times vs. placebo (29 times vs. monotherapy) on day 7 and oxoglaucine sensitivity—4.9 times vs. placebo (by 6.8 times vs. monotherapy) on day 13. As concerns pleconaril, a demonstrable prevention of drug resistance was registered without increase of drug sensitivity. Daily, simultaneous administration of pleconaril/MDL-860/oxoglaucine showed no protective effects and led to a rapid development of drug resistance. Conclusions These results add new support for using consecutive alternating administration treatment courses to achieve clinically effective chemotherapy of enterovirus infections.

Allosteric Regulation of Phosphatidylinositol 4-Kinase III Beta by an Antipicornavirus Compound MDL-860

MDL-860 is a broad-spectrum antipicornavirus compound discovered in 1982 and one of the few promising candidates effective in in vivo virus infection. Despite the effectiveness, the target and the mechanism of action of MDL-860 remain unknown. Here, we have characterized antipoliovirus activity of MDL-860 and identified host phosphatidylinositol-4 kinase III beta (PI4KB) as the target. MDL-860 treatment caused covalent modification and irreversible inactivation of PI4KB. A cysteine residue at amino acid 646 of PI4KB, which locates at the bottom of a surface pocket apart from the active site, was identified as the target site of MDL-860. This work reveals the mechanism of action of this class of PI4KB inhibitors and offers insights into novel allosteric regulation of PI4KB activity.

Antimycobacterial activity generated by the amide coupling of (-)-fenchone derived aminoalcohol with cinnamic acids and analogues.

Aminoethyl substituted 2-endo-fenchol prepared from (-)-fenchone was used as scaffold for the synthesis of series of 31 amide structures by N-acylation applying cinnamic acids and analogues. The evaluation of their in vitro activity against Mycobacterium tuberculosis H37Rv showed for some of them promising activity-up to 0.2 μg/ml, combined with relatively low cytotoxicity of the selected active compounds.

Synthesis and electronic spectra of new low-molecular weight compounds with possible application in electroluminescent layers

AbstractTwo new low-molecular weight compounds — (Z)-4-(4-(dimethylamino)benzylidene)-1-(9-ethyl-9H-carbazol-3-yl)-2-phenyl-1H-imidazol-5(4H)-one and 2-(6-hydroxyhexyl)-6-(pyrrolidin-1-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione) — with possible application in organic light-emitting devices were synthesized. Their photophysical properties in solution and in polymer films were investigated. The determined relative fluorescence quantum yields in solution for both compounds were 0.003 and 0.51, while those in poly(methyl methacrylate) films were around 0.10 and 1.0, respectively. For 1H-imidazol-5(4H)-one derivative, single-layer organic displays with one emitting layer were prepared by spin-coating technology. The applied voltage was 40 V (AC) with 1–3 KHz frequency. The emission maximum of the experimental AC display structures was at 600–630 nm. For displays with 2-(6-hydroxyhexyl)-6-(pyrrolidin-1-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione) the applied voltage was 60 V (AC) with 6-9 KHz frequency, but its future success will require more appropriate binding polymers. Based on the obtained experimental results, it is concluded that the investigated compounds could be applied for preparation of color electroluminescent structures.

Synthesis of ferrocenylmethylidene and arylidene substituted camphane based compounds as potential anticancer agents

Herein is described the synthesis of (+)-camphor derivatives containing sulfonamide groups, ferrocenylmethylidene or arylidene moieties. The obtained derivatives were tested against seven human cancer cells lines, namely BV-173, K-256a, NB-4, A549, H1299, MCF-7, and MDA-MB231, and two normal human cell lines, HEK293 and HUVEC, in order to determine their activity against malignant cells. Some of them exhibit IC50 values below 10 μM in at least one of the cancer cell lines. Ferrocenylmethylidene ketone 16 can be outlined as the most potent and selective in the current study (IC50 for cancer cells – up to 4.0 μM; IC50 for HEK293 and HUVEC – 68 and 69 μM, respectively). There is a clear trend showing that the presence of a conjugated ferrocenylmethylidene group is essential for the cytotoxicity, however different sulfonamide substituents and derivatization of the carbonyl group can modify the activity. Thus, this class of compounds could have good prospects for further structural optimisation.

Synthesis and anti-enterovirus activity of new analogues of MDL-860

A series of twelve novel compounds, analogues of antiviral agent MDL-860 were synthesized and their antiviral activity was evaluated in vitro against enteroviruses poliovirus 1 (PV1), Coxsackieviruses B1 (CVB1) and Coxsackieviruses B3 (CVB3). Compounds 14, 24 and 25 manifested strong antiviral effects against CVB1 and PV1 (SI values of 405 and 118 for CVB1 and PV1 respectively). In contrast to the wide anti-enteroviral activity of MDL-860, these three compounds were inactive against CVB3. Compounds 14, 24 and 25 along with MDL-860 were tested in vivo in mice infected with CVB1. Marked protective effects of compounds 14 and 24 were established, PI values of 50% and 33.3%, respectively. In addition, almost all of the tested compounds manifested very low toxicity.

Design, synthesis and photophysical study of fluorophore modified noble metal nanoparticles

Metal / dielectric nanostructures, such as metal nanoparticles of different shape (spheres, rods, stars) capped with organic adsorbates, have a strong potential for the development of new materials for nanotechnology. Among these structures, those including monolayer protected clusters of noble metal nanoparticles modified with organic fluorophores are of great interest for the fabrication of new fluorescent bio- and chemical sensors, and for optical devices as well. The nature of the interactions between metals and organic fluorophores is still not totally understood. These interactions, which depend on various factors, including the geometry of the systems, the physicochemical properties of the interacting materials and their environment, often result in an enhancement or a quenching of the emission. The performed investigations comprise design, preparation, characterization and photophysical study of monolayer protected clusters of noble metal nanoparticles modified with newly synthesized organic fluorophore.