Xylochemical Synthesis and Biological Evaluation of Shancigusin C and Bletistrin G

The biological activities of shancigusin C (1) and bletistrin G (2), natural products isolated from orchids, are reported along with their first total syntheses. The total synthesis of shancigusin C (1) was conducted by employing the Perkin reaction to forge the central stilbene core, whereas the synthesis of bletistrin G (2) was achieved by the Wittig olefination followed by several regioselective aromatic substitution reactions. Both syntheses were completed by applying only renewable starting materials according to the principles of xylochemistry. The cytotoxic properties of shancigusin C (1) and bletistrin G (2) against tumor cells suggest suitability as a starting point for further structural variation.     

Polymorphism of LiAg

A phase transition from the cubic CsCl-type structure (Pm-3m space group) into a tetragonal UPb-type structure (I4₁/amd) is observed for the LiAg binary compound at ambient conditions. The crystal structure of the tetragonal modification of the LiAg binary compound was solved by direct methods in SHELXS on the base of structure factors which were extracted from a powder diffraction pattern and refined by SHELXL and the Rietveld method (a = 3.9605(1), c = 8.2825(2) Å, Bragg R-factor = 4.81, Rf-factor = 4.87). Elevated temperatures and/or a small Li-excess versus the equimolar composition favour the cubic structure whereas ambient and lower temperatures and/or a small Li-deficiency stabilize the tetragonal structure. This reconstructive transition is reversible but proceeds slowly.     

Diastereoselectivity is in the Details: Minor Changes Yield Major Improvements to the Synthesis of Bedaquiline**

Bedaquiline is a crucial medicine in the global fight against tuberculosis, yet its high price places it out of reach for many patients. Herein, we describe improvements to the key industrial lithiation-addition sequence that enable a higher yielding and therefore more economical synthesis of bedaquiline. Prioritization of mechanistic understanding and multi-lab reproducibility led to optimized reaction conditions that feature an unusual base-salt pairing and afford a doubling of the yield of racemic bedaquiline. We anticipate that implementation of these improvements on manufacturing scale will be facile, thereby substantially increasing the accessibility of this essential medication.     

Effect of carbon coating process on the structure and electrochemical performance of LiNi<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>O<Subscript>2</Subscript> used as cathode in Li-ion batteries

LiNi_0.5Mn_0.5O₂ powder was synthesized by a coprecipitation method. LiOH.H₂O and coprecipitated [(Ni_0.5Mn_0.5)C₂O₄] precursors were mixed carefully together and then calcined at 900°C. Surface modified cathode materials were obtained by coating LiNi_0.5Mn_0.5O₂ with a thin layer of amorphous carbon using table sugar and starch as carbon source. Both parent and carbon-coated samples have the characteristic layered structure of LiNi_0.5Mn_0.5O₂ as estimated from X-ray diffractometry measurements. Transmission electron microscope showed the presence of C layer around the prepared particles. TGA analysis emphasized and confirmed the presence of C coating around LiNi_0.5Mn_0.5O₂. It is obvious that the carbon coating appears to be beneficial for the electrochemical performance of the LiNi_0.5Mn_0.5O₂. A capacity of about 150 mAh/g is delivered in the voltage range 2.5–4.5 V at current density C/15 for carbon coated LiNi_0.5Mn_0.5O₂ in comparison with about 165 mAh/g obtained for carbon free LiNi_0.5Mn_0.5O₂ at the same current density and voltage window. About 92% and 82% capacity retention was obtained at 50th cycle for coated LiNi_0.5Mn_0.5O₂ using sucrose and starch, respectively; whereas, 75% was retained after only 30th cycle for carbon free LiNi_0.5Mn_0.5O₂. This improvement is mainly attributed to the presence of thin layer of carbon layer that encapsulate the nanoparticles and improve the conductivity and the electrochemical performance of LiNi_0.5Mn_0.5O₂.     

Structure and properties of α-AgFe2(MoO4)3

Silver diiron tris(oxomolybdate), α-AgFe₂(MoO₄)₃, was synthesized in sealed silica tubes at 1050 K and is isostructural to α-NaFe₂(MoO₄)₃, determined by single-crystal X-ray diffraction (space group P?1, a = 6.9320(7) Å, b = 6.9266(6) Å, c = 10.9732(13) Å, α = 81.197(8)°, β = 83.456(9)°, γ = 81.352(8)° at 300 K, Z = 2). The crystal structure is built up from both monomers and edge-sharing dimers of [FeO₆]-octahedra, which are linked with each other by isolated [MoO₄]-tetrahedra to a three-dimensional network. Ag ions are situated on a site with four near oxygen neighbours. Thermal expansion is most pronounced along the c-axis, while the angle α decreases with increasing temperature. Antiferromagnetic ordering is indicated by a sharp maximum in the temperature dependence of magnetization at 21.5(5) K, and a magnetic moment of 5.36(1) μ_B per Fe-ion was derived from the Curie constant in the paramagnetic region. The collinear antiferromagnetic structure with propagation vector k = (0,½,½) and an ordered magnetic moment of 4.62(9) μ_B per Fe-ion were deduced from neutron powder diffraction data and give evidence for an underlying magnetic interaction mechanism, resulting in rather strong and long-ranged couplings. Mössbauer spectroscopy shows a change in the electronic configuration on the two distinct Fe sites between room temperature and 150 K, accompanied by an increase of the average Fe–O distance for one site and a shrinking one for the other as expected for charge ordering in a mixed valence compound with Fe(II) and Fe(III).     

On the complexity of SNP block partitioning under the perfect phylogeny model

Recent technologies for typing single nucleotide polymorphisms (SNPs) across a population are producing genome-wide genotype data for tens of thousands of SNP sites. The emergence of such large data sets underscores the importance of algorithms for large-scale haplotyping. Common haplotyping approaches first partition the SNPs into blocks of high linkage-disequilibrium, and then infer haplotypes for each block separately. We investigate an integrated haplotyping approach where a partition of the SNPs into a minimum number of non-contiguous subsets is sought, such that each subset can be haplotyped under the perfect phylogeny model. We show that finding an optimum partition is -hard even if we are guaranteed that two subsets suffice. On the positive side, we show that a variant of the problem, in which each subset is required to admit a perfect path phylogeny haplotyping, is solvable in polynomial time.