Biotransformation of (-)-Isopulegol by Rhodococcus rhodochrous.

The ability of actinobacteria of the genus Rhodococcus to biotransform the monoterpenoid (-)-isopulegol has been established for the first time. R. rhodochrous strain IEGM 1362 was selected as a bacterium capable of metabolizing (-)-isopulegol to form new, previously unknown, 10-hydroxy (2) and 10-carboxy (3) derivatives, which may presumably have antitumor activity and act as respiratory stimulants and cancer prevention agents. In the experiments, optimal conditions were selected to provide the maximum target catalytic activity of rhodococci. Using up-to-date (TEM, AFM-CLSM, and EDX) and traditional (cell size, roughness, and zeta potential measurements) biophysical and microbiological methods, it was shown that (-)-isopulegol and halloysite nanotubes did not negatively affect the bacterial cells. The data obtained expand our knowledge of the biocatalytic potential of rhodococci and their possible involvement in the synthesis of pharmacologically active compounds from plant derivatives.

One-Pot Synthesis of 2-R-Naphtho[2,3-b]thiophene-4,9-diones via Cyclization of 2-(R-Ethynyl)-1,4-naphthoquinones with Na2S2O3.

The concise and efficient one-pot synthesis of 2-R-naphtho[2,3-b]thiophene-4,9-diones from 2-bromo-1,4-naphthoquinone and alkynes has been developed. The reaction proceeds through the formation of 2-(R-ethynyl)-1,4-naphthoquinones, which undergo transformation with Na2S2O3 to 2-R-naphtho[2,3-b]thiophene-4,9-diones via C-H sulfuration, accompanied by the formation of the aromatic Bunte salt, followed by its air oxidation and 5-endo-dig cyclization. The protocol is characterized by simplicity, good tolerance for functional groups, relatively mild conditions, and commercially available starting compounds.

Human Serum Albumin Labelled with Sterically-Hindered Nitroxides as Potential MRI Contrast Agents.

Four albumin-nitroxide conjugates were prepared and tested as metal-free organic radical contrast agents (ORCAs) for magnetic resonance imaging (MRI). Each human serum albumin (HSA) carrier bears multiple nitroxides conjugated via homocysteine thiolactones. These molecular conjugates retain important physical and biological properties of their HSA component, and the resistance of their nitroxide groups to bioreduction was retained or enhanced. The relaxivities are similar for these four conjugates and are much greater than those of their individual components: the HSA or the small nitroxide molecules. This new family of conjugates has excellent prospects for optimization as ORCAs.

Conformational flexibility of fused tetracenedione propellers obtained from one-pot reductive dimerization of acetylenic quinones.

Reductive dimerization of acetylenic anthraquinones provides synthetic access to flexible nonplanar polyaromatics with a tetracenedione core. In solution, these nonplanar, contorted polycycles exist as equilibrating mixtures of two symmetric conformers. The fused tetracenediones are easily reduced and exhibit rich electrochemical behavior.

Base-catalyzed domino cyclization of acetylenes with ketones to functionalized cyclopentenes.

Acetylene reacts with methylaryl(hetaryl)ketones in the presence of 6.5 mol % KOH in DMSO to give diastereoselectively in single operationally functionalized cyclopentenes. This domino cyclization involving two molecules of acetylene and two molecules of ketone proceeds with the formation of four C-C bonds. The complementary assembly of the cyclopentenes with similar functionalities from acetylenes and 1,5-diketones has been developed.

Synthesis of 2,5-bis(spirocyclohexane)-substituted nitroxides of pyrroline and pyrrolidine series, including thiol-specific spin label: an analogue of MTSSL with long relaxation time.

The nitroxides of 7-azadispiro[5.1.5.2]pentadecane and 7-azadispiro[5.1.5.2]pentadeca-14-ene series have been prepared, including thiol-specific methane thiosulfonate spin label for site-directed spin labeling. The effect of spirocyclohexane moieties on chemical and spectral properties has been studied. The obtained temperature dependencies of electron spin relaxation parameters demonstrate that new nitroxides may be suitable for PELDOR distance measurements at 80-120 K. Moreover, the new nitroxides demonstrated much higher stability toward reduction by ascorbate than spirocyclohexane-substituted nitroxides of piperidine series and showed 1.3-3.14 times lower reduction rates compared to corresponding 2,2,5,5-tetramethyl nitroxides.