Organocatalytic Tandem Reaction to Construct Six‐Membered Spirocyclic Oxindoles with Multiple Chiral Centres through a Formal [2+2+2] Annulation

An efficient tandem reaction for the asymmetric synthesis of six‐membered spirocyclic oxindoles has been successfully developed through a formal [2+2+2] annulation strategy. The amine‐catalysed stereoselective Michael addition of aliphatic aldehydes to electron‐deficient olefinic oxindole motifs gave chiral C3 components, which were further combined with diverse electrophiles (activated olefins or imines) to afford spirocyclic oxindoles with versatile molecular complexity (up to six contiguous stereogenic centres, high diastereo‐ and enantioselectivities).     

Preparation and application of rifamycin-capped (3-(2-O-β-cyclodextrin)-2-hydroxypropoxy)-propylsilyl-appended silica particles as chiral stationary phase for high-performance liquid chromatography

Rifamycin-capped (3-(2-O-β-cyclodextrin)-2-hydroxypropoxy)-propylsilyl-appended silica particles (RCD-HPS), a new type of substituted β-cyclodextrin-bonded chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC), have been synthesized by the treatment of bromoacetate-substituted-(3-(2-O-β-cyclodextrin)-2-hydroxypropoxy)-propylsilyl-appended silica particles (BACD-HPS) with rifamycin SV in anhydrous acetonitrile. The stationary phase is characterized by means of elemental analysis and Fourier-transform infrared spectroscopy. This new CSP has a chiral selector with two recognition sites: rifamycin and β-cyclodextrin (β-CD). The chromatographic behavior of RCD-HPS was studied with several disubstituted benzenes and some chiral drug compounds under reversed-phase HPLC mobile phase conditions. The results show that RCD-HPS has excellent selectivity for the separation of aromatic positional isomers and enantiomers of chiral compounds due to the cooperative functioning of rifamycin and β-CD.     

Three New Triterpene Saponins from Gynostemma pentaphyllum

Three new dammarane‐type triterpene saponins, 1 – 3 , together with three known compounds, 4 – 6 , were isolated from the aerial parts of Gynostemma pentaphyllum (Thunb.) Makino . By means of chemical and spectroscopic methods, their structures were established as (20S)‐3β,20,21‐trihydroxydammara‐23,25‐diene 3‐O‐[α‐L ‐rhamnopyranosyl‐(1→2)] [β‐D ‐xylopyranosyl‐(1→3)]‐β‐D ‐glucopyranosyl‐21‐O‐β‐D ‐glucopyranoside ( 1 ), (20R,23R)‐3β,20‐dihydroxy‐19‐oxodammar‐24‐en‐21‐oic acid 21,23‐lactone 3‐O‐[α‐L ‐rhamnopyranosyl‐(1→2)] [β‐D ‐xylopyranosyl‐(1→3)]‐α‐L ‐arabinopyranoside ( 2 ), and (21S,23S)‐3β,20ξ,21,26‐tetrahydroxy‐19‐oxo‐21,23‐epoxydammar‐24‐ene 3‐O‐[α‐L ‐rhamnopyranosyl‐(1→2)] [β‐D ‐xylopyranosyl‐(1→3)]‐α‐L ‐arabinopyranoside ( 3 ).     

Theoretical prediction on HBeN− and HNBe− anions using multiconfiguration second‐order perturbation theory

The HBeN^? and HNBe^? anions have been investigated for the first time using the CASSCF, CASPT2, and DFT/B3LYP methods with the contracted atomic natural orbital (ANO) and cc‐pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces were optimized at the CASSCF/ANO and B3LYP/cc‐pVTZ levels. The ground and the first excited states of HBeN^? are predicted to be X²Π and A²Σ⁺ states, respectively. It was predicted that the ground state of HNBe^? is X²Σ⁺ state. The A²Π state of HNBe^? has unique imaginary frequency. A bend local minimum M1 was found along the 1²A″ potential energy surface and the A²Π state of HNBe^? should be the transition state of the isomerization reactions for M1 ? M1. The CASPT2/ANO potential energy curves of isomerization reactions were calculated as a function of HBeN bond angle. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Accumulation of Exopolysaccharides in Liquid Suspension Culture of Nostoc flagelliforme Cells

The liquid suspension culture of dissociated Nostoc flagelliforme cells was investigated. It was found that the growth rate of N. flagelliforme cells and the accumulation of exopolysaccharides (EPS) increased prominently when NaNO₃ and KH₂PO₄ were added in the liquid BG-11culture medium though phosphate had little effect on EPS yield for specific mass of cells. N. flagelliforme cells grew well at 25 °C and neutral pH, however, a lower or higher temperature and weak alkaline can promote EPS accumulation. With the increase of the light intensity, the growth rate of N. flagelliforme cells and the EPS accumulation increase accordingly. When N. flagelliforme cells was cultured in BG-11 medium added with 2.5 g L⁻¹ of NaNO₃ and 0.956 g L⁻¹ of KH₂PO₄ at 25 °C with 60 μmol photon m⁻² s⁻¹ of light intensity, 1.05 g L⁻¹ cell density and 89.9 mg L⁻¹ EPS yield were achieved respectively. Adopting the optimal conditions established in flask culture, the liquid culture of N. flagelliforme cells in 20-L photobioreactor for 16 days was conducted and a maximum biomass of 1.32 g L⁻¹ was achieved, which was about 17.6-fold of that in the initial inoculation. The yield of EPS was 228.56 mg L⁻¹and about 2.23-fold of that in flask culture. Moreover, the polysaccharides’ material was released into the culture medium during cell growth. These released polysaccharides (RPSs), which can be easily recovered from the medium, are favorable for industrial applications.     

Enhancement of Lovastatin Production by Supplementing Polyketide Antibiotics to the Submerged Culture of <Emphasis Type="Italic">Aspergillus terreus</Emphasis>

Feedback inhibition existed in lovastatin biosynthesis from Aspergillus terreus. Exogenous lovastatin and other different polyketide antibiotics biosynthesized by polyketide synthase were supplemented to the cultures of A. terreus to investigate their influences on lovastatin production. Supplementing exogenous lovastatin of 100 mg l⁻¹ at the early stage of fermentation and the fast stage of its biosynthesis resulted in decreases of 76.4% and 20% in final lovastatin production, respectively. However, the fungal cell growth was not affected; the growing cycle was only prolonged in the submerged cultivation. Separate supplementation of the five kinds of polyketide antibiotics such as tylosin, erythromycin, tetracycline, daunorobin, and rifamycin to the cultures resulted in increases of about 20~25% in the final lovastatin production. Especially, supplementing tylosin of 50 mg l⁻¹ at the beginning of lovastatin biosynthesis led to the final lovastatin production of 952.7 ± 24.3 mg l⁻¹, which was improved by 42% and 22% compared with that produced in the control and the original culture, respectively. These results are helpful to understand the regulations on lovastatin biosynthesis and improve the final desired metabolite contents in many antibiotics production.     

Performances of Lactobacillus brevis for Producing Lactic Acid from Hydrolysate of Lignocellulosics

Utilizing all forms of sugars derived from lignocellulosic biomass via various pretreatment and hydrolysis process is a primary criterion for selecting a microorganism to produce biofuels and biochemicals. A broad carbon spectra and potential inhibitors such as furan, phenol compounds and weak acids are two major obstacles that limited the application of dilute-acid hydrolysate of lignocellulosics in lactic acid fermentation. Two strains of bacteria isolated from sour cabbage, S3F4 (Lactobacillus brevis) and XS1T3-4 (Lactobacillus plantrum), exhibited the ability to utilize various sugars present in dilute-acid hydrolysate of biomass. The S3F4 strain also showed strong resistance to potential fermentation inhibitors such as ferulic acid and furfural. Fermentation in flasks by this strain resulted in 39.1 g/l of lactic acid from dilute acid hydrolysates of corncobs that had initial total sugar concentration of 56.9 g/l (xylose, 46.4 g/l; glucose, 4.0 g/l; arabinose, 6.5 g/l). The hydrolysate of corncobs was readily utilized by S3F4 without detoxification, and the lactic acid concentration obtained in this study was higher compared to other reports.     

Improving the cycleability of Si anodes by covalently grafting with 4-carboxyphenyl groups

In this study, the lithium storage capacity of Si nanoparticles is significantly enhanced by grafting with 4-carboxyphenyl groups via diazonium salts. The modified Si anodes exhibit reversible capacities of 1173 and 527 mA h g^?1 at the 1st and 50th cycle, while those of the bare Si electrodes are only 56 and 62 mA h g^?1, respectively. The improved electrochemical performance is supposed to arise from the formation of a robust and flexible solid electrolyte interface on the surfaces of the modified Si nanoparticles.     

Characterization and thermal analysis of thiourea and bismuth trichloride complex

A complex of thiourea and bismuth trichloride has been synthesized. Its composition is Bi₃Cl₉[SC(NH₂)₂]₇. Crystallographic data are a = 7.141(2) Å, b = 8.820(3) Å, c = 16.365(5) Å, α = 99.389(4)°, β = 95.422(4)°, γ = 106.177(4)°, triclinic system. There are the mononuclear anion [BiCl₅SC(NH₂)₂]^2? and the dinuclear cation {Bi₂Cl₄[SC(NH₂)₂]₆}²⁺ with the Bi–Cl–Bi bridge bonds in the complex. The electric conductance of the absolute methanol solution contained the complex indicates that the complex is an ionic compound. Raman spectra indicate that the bismuth ion is coordinated by the sulfur atoms of the thiourea. The thermal analysis verifies the structure of complex. The TG–MASS curves show the structure rearrangement in the complex at about 118 °C. The DSC curves and calculation means that the structure rearrangement is irreversible.