Synthesis of 5,6-dihydro-4h-1,3-thiazines based on substituted n-phenylthioureas

The reaction of phenyl isothiocyanate with 1,3-amino alcohols was used to synthesize substituted N-phenylthioureas, for which cyclization under the influence of mineral acids to give substituted 5,6-dihydro-4H-1, 3-thiazines was studied.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1433–1437, October, 1992.     

Vibrational spectra and rotational isomerism of simple dialkyl dithioesters and N-acylglycine ethyl dithioesters,thiolesters, and dioxygenesters

Simple dialkyl dithioesters and N-acylglycine ethyl dithioesters have been investigated by Raman, resonance Raman and infrared spectroscopies. Based on the data of isotopic substituted derivatives and a normal coordinate analysis, vibrational assignments have been proposed for methyl dithioacetate. Raman spectra of ethyl dithioacetate(CH₃C(=S)S

CH₂CH₃) and methyl dithiopropionate (CH₃CH₂

C (=S)SCH₃) have provided fundamental knowledge on rotational isomerism about the bonds indicated. Raman, resonance Raman and FTIR spectroscopic studies on N-acylglycine ethyl dithioesters indicated the coexistence of three conformers in solution and a combined x-ray crystallographic-resonance Raman spectroscopic approach has been used to set up precise structure-spectra correlations for these conformers. The corresponding conformational states of N-acylglycine thiolesters and dioxygenesters are also discussed briefly.     

Multi-step application of immobilized reagents and scavengers: a total synthesis of epothilone C

The total synthesis of the cytotoxic antitumour natural product epothilone C has provided a stage for the exploitation and further development of immobilized reagent methods. A stereoselective convergent synthetic strategy was applied, incorporating polymer-supported reagents, catalysts, scavengers and catch-and-release techniques to avoid frequent aqueous work-up and chromatographic purification.     

Synthesis of 5,6-trimethylenetetrahydro-1,3-oxazine-4-spirocyclopentanes and their acyclic precursors

Tricyclic tetrahydro-1,3-oxazines-5,6-trimethylenetetrahydro-1,3-oxazine-4-spirocyclopentanes IV, V, and VII — were synthesized on the basis of 2-(1-isothiocyanatocyclopentyl)cyclopentanone (I). The reductive cyclization of the latter by the action of sodium borohydride leads to oxazinethione V; the acidic hydrolysis of I with subsequent reduction of amino ketone hydrochloride II with sodium borohydride and the reaction of isothiocyanato ketone I with lithium aluminum hydride make it possible to obtain 1,3-amino alcohols III and VI, respectively, which are converted to tetrahydro-1,3-oxazines IV and VII by cyclization with formaldehyde. Pyrimidinethione VIII was synthesized from isothiocyanato ketone I and methylamine. Compounds III–VII are mixtures of stereoisomers with predominance of the cis isomer.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1256–1259, September, 1990.     

Problem space local search for number partitioning

We show how simple and effective metaheuristics can be developed for the number partitioning problem using the problem space approach [1]. In a previous application of local search to number partitioning [2], it was found that the performance of simulated annealing used in conjunction with swap neighborhoods was disappointing relative to the differencing heuristic of Karmarkar and Karp [3]. Using problem space neighborhoods as an alternative to swapping, we empirically demonstrate several orders of magnitude improvement over the differencing algorithm, albeit with greater computation time. This improvement in performance comes as little surprise since a modified version of the differencing heuristic is explicitly embedded in the problem space algorithm.     

The role of biodegradation during bioventing of soil contaminated with jet fuel

The enhancing rem oval of kerosene (jet fuel) from contaminated soil during bioventing resulting from biodegradation was compared to the physical removal by evaporation only on bench-scale columns at the controlled temperature of 20°C (±2.5°C). Carbon dioxide-free air and nitrogen were used as flushing gases, at the constant continuous flow rate of 1 dm³/h. Kerosene concentrations in soil up to 35000 mg/kg were not toxic for indigenous microbial population. Much slower kerosene biodegradation rates observed for soil from a contaminated site, as compared to soil artificialy contaminated with kerosene, were the result of a lower bioavailability of “aged” kerosene, and the presence of compounds that might be persistent or toxic to kerosene-specific degraders. The inhibitory effect of toluene to indigenous microorganisms was found at above 75% of the toluene saturation concentrations in the gas phase. After 29 d, the overall bioventing efficiency was 17–23%, depending on whether CO₂ production or O₂ uptake wasused for caculations, as compared to the removal of 10% when biodegradation was excluded. The increase in efficiency by 50–100% owing to biodegradation would be more spectacular at lowr kerosene concentrations during the “tailing” phase, with diffusionlimited desorption, and much lower evaporation of less volatile constituents. Limitation of bioventing as a result of low bioavailability related to intraparticle sorption of residual contamination is discussed.     

Utilization of laser induced breakdown spectroscopy for investigation of the metal accumulation in vegetal tissues

We report on the development and implementation of analytical methodology for investigating elemental accumulation in different layers within plant leaves, with in-situ spatial resolution mapping, exploiting the technique of LIBS. The spectrochemical analysis of lead-doped leaf samples is demonstrated to develop a real time identification procedure in order to complement other analytical techniques not lending themselves for spatial resolution analysis. Our findings suggest that with elevated levels of Pb within the plants transportation and storage of some nutrition elements is changed.     

Enantioselective organocatalytic reductive amination

The first enantioselective organocatalytic reductive amination reaction has been accomplished. The development of a new chiral phosphoric acid catalyst has provided a convenient strategy for the enantioselective construction of protected primary amines and provided a highly stereoselective method for the reductive amination of heterocyclic amines. A diverse spectrum of ketone and amine substrates can be accommodated in high yield and excellent enantioselectivity. This new protocol realizes a key benefit of reductive amination versus imine reduction, in that ketimines derived from alkyl-alkyl ketones are unstable to isolation, a fundamental limitation that is comprehensively bypassed using this direct organocatalytic reductive amination.