Stereochemistry of Seven-membered Heterocycles: XLIV. Spatial Structure of 4-R-3,5-Dioxabicyclo[5.1.0]octanes

4-R-3,5-Dioxabicyclo[5.1.0]octanes were prepared in good yields by reduction of the corresponding 8,8-dichloro derivatives in a system Li-t-BuOH. According to the data of dynamic ¹H and ¹³CNMR spectroscopy involving experiments in the NOESY mode the formal (R = H) at −93°C in (CD₃)₂CO exists in nearly equally occupied chair forms with endo- and exo-oriented three-membered ring. The like structure were found in the diastereomeric 4-Me(t-Bu)-analogs. The characteristic feature of ¹³C NMR spectra consists in considerable difference in the chemical shifts of the C⁸ atoms (Δδ∼16–17 ppm). The data on epimerization of diastereomers and calculations along AM1 procedure suggest for formal a three-component equilibrium including a twist-form.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 2, 2005, pp. 301–305.Original Russian Text Copyright © 2005 by Fedorenko, Baryshnikov, Khairutdinov, Vafina, Shtyrlin, Klochkov, Klimovitskii.     

Identification of the function of gene lndM2 encoding a bifunctional oxygenase-reductase involved in the biosynthesis of the antitumor antibiotic landomycin E by Streptomyces globisporus 1912 supports the originally assigned structure for landomycinone

The angucycline antibiotic family of the landomycins displays potent antitumor activity. To elucidate early post polyketide synthase (PKS) tailoring steps of the landomycin E biosynthetic pathway in Streptomyces globisporus 1912, the mutant S. globisporus M12 was prepared through gene replacement experiment of lndM2. It encodes an enzyme with putative oxygenase and reductase domains, according to sequencing of the gene and its counterpart lanM2 from S. cyanogenus S136 landomycin A biosynthetic gene cluster. The isolation of the novel shunt products 11-hydroxytetrangomycin and 4-hydroxytetrangomycin along with the well-known angucyclines tetrangomycin and tetrangulol from the culture of S. globisporus M12 provides evidence for the involvement of lndM2 in the early biosynthetic pathway of the landomycins, in particular in the formation of the alicyclic 6-hydroxy function of the landomycin aglycon. We therefore propose LndM2 to be responsible for both hydroxylation of the 6-position and its subsequent reduction. These reactions are necessary before the glycosylation reactions can occur. The results are in agreement with the originally published structure of landomycin but do not support the recently suggested revised structure.     

Generation of new landomycins by combinatorial biosynthetic manipulation of the LndGT4 gene of the landomycin E cluster in S. globisporus

A 3 kb DNA fragment from the Streptomyces globisporus 1912 landomycin E (LaE) biosynthetic gene cluster (lnd) was completely sequenced. Three open reading frames were identified, lndGT4, lndZ4, and lndZ5, whose probable translation products resemble a glycosyltransferase, a reductase, and a hydroxylase, respectively. Studies of generated mutants from disruption and complementation experiments involving the lndGT4 gene allowed us to determine that LndGT4 controls the terminal L-rhodinose sugar attachment during LaE biosynthesis and that LndZ4/LndZ5 are responsible for the unique C11-hydroxylation of the landomycins. Generation of the novel landomycins F, G, and H in the course of these studies provided evidence for the flexibility of lnd glycosyltransferases toward their acceptor substrates and a basis for initial structure-activity relationships within the landomycin family of antibiotics.     

Crystal structure of boron difluoride 3-phenylthiopentane-2,4-dionate. π stacking interactions and luminescence of boron difluoride acetyl acetonates

The crystal structure of boron difluoride 3-phenylthiopentane-2,4-dionate was determined. The relationship between the structure and luminescent properties is traced in the series of boron difluoride acetyl acetonates (acetyl acetonate, phenylacetyl acetonate, and phenylthioacetyl acetonate). The presence of the π stacking interactions in boron difluoride phenylthioacetyl acetonate crystals leads to increased intensity and bathochromic shift of the fluorescence band.     

Optical properties of a new photorecording polymer based on 2,2-difluoro-4-(9-anthracyl)-6-methyl-1,3,2-dioxaborine

The optical properties of a new photorecording polymer based on 2,2-difluoro-4-(9-anthracyl)-6-methyl-1,3,2-dioxaborine have been investigated. This material is found to change its absorption coefficient and refractive index in the visible range under illumination with a wavelength λ = 405.9 nm. This circumstance makes it possible to record static holograms with a spatial frequency up to 2500 lines/mm, a diffraction efficiency above 60%, and a lifetime more than 6 months. A dynamic change in the effective refractive index of this material under 405.9-nm irradiation is found, due to which one can form control optical elements of the light-light type with a modulation frequency up to 50 Hz in it.     

Resource-saving electrochemical processes in manufacture of pigment titanium dioxide

Development directions of the sulfate method for manufacture of titanium dioxide are considered, and alternative solutions for improving its cost efficiency and ecological advisability are suggested. A high-efficiency technology for electrochemical synthesis of a strong reducing agent, Ti₂(SO₄)₃·nH₂O, used instead of waste iron and powdered aluminum is suggested.     

CRYSTAL STRUCTURE AND X-RAY CRYSTALLOGRAPHIC ANALYSIS OF THE BINUCLEAR CLUSTER THIOCYANATE COMPLEX OF NIOBIUM(IV)

Journal of Structural Chemistry - The structure of a binuclear niobium(IV) thiocyanate complex (Bu4N)4[Nb2(μ2-S2)2(NCS)8]·H2O (1·H2O) is studied by X-ray crystallography. Compound...     

Ruthenium-Catalyzed Hydrogenative Degradation of End-of-Life Poly(lactide) to Produce 1,2-Propanediol as Platform Chemical

The chemical recycling of end-of-life polymers can add some value to a future circular economy. In this regard, the hydrogenative degradation of end-of-life PLA was investigated to produce 1,2-propanediol as product, which is a useful building block in polymer chemistry. In more detail, the commercially available Ru-MACHO-BH complex was applied as catalyst to degrade end-of-life PLA efficiently to 1,2-propanediol under mild conditions. After investigations of the reaction conditions a set of end-of-life PLA goods were subjected to degradation.     

Pimprinols A–C,from the terrestrial actinomycete,Streptomyces sp.

A Streptomyces sp. Lv3-13, isolated from the rhizosphere soil of the plant Mespilus germanica, has yielded three new pimprinine derivatives, named pimprinols A–C (1–3) and the unknown (2-aminophenyl)(2-ethyloxazol-5-yl) methanone (4) along with the known compounds 2-ethyl oxazole pimprinine and 2-propyl oxazole pimprinine. The structures of the compounds were elucidated based on spectroscopic methods including UV, HR-ESIMS and 1D, 2D NMR data. Compounds 1–4 were screened for antimicrobial and cytotoxic activities.