Nickel-iminophosphine-catalyzed [4+2] cycloaddition of enones with allenes: synthesis of highly substituted dihydropyrans

Enones were found to react with allenes intermolecularly in the presence of a catalytic amount of a nickel-iminophosphine complex to provide dihydropyrans via oxidative cyclization of an enone and Ni(0).     

Global attractivity for half-linear differential systems with periodic coefficients

The system to be considered in this paper is

     

Phase behavior of binary bilayer membrane of dipalmitoylphosphatidylcholine and stigmasterol

Journal of Thermal Analysis and Calorimetry - We investigated the phase behavior of a binary bilayer membrane of dipalmitoylphosphatidylcholine (DPPC) and stigmasterol (Stig) as a function of the...     

A Non‐Enzymatic Pathway with Superoxide in Intracellular Terpenoid Synthesis

Non‐C₅‐units terpenoids (norisoprenoids) with an acetonyl group are widely distributed in nature. However, studies on the biosynthesis of norisoprenoids are scarce. Now, the C₃₃ norisoprenoid, (all‐E)‐farnesylfarnesylacetone, was identified from Bacillus spp. and it was elucidated for the first time that superoxide mediates the cleavage of menaquinones (vitamin K) to form norisoprenoids in saponification treatment. From in vivo experiments using gene‐disrupted Bacillus subtilis strains targeted for enzymes responsible for menaquinone biosynthesis and for superoxide dismutase, it was suggested that the non‐enzymatic cleavage (autoxidation) of menaquinone with superoxide resulted in norisoprenoid synthesis in Bacillus cells. Furthermore, the bioactive norisoprenoids, farnesylacetone and phytone, were produced in Bacillus cells by this novel synthesis system.     

Analysis of nucleotides by pressure-assisted capillary electrophoresis-mass spectrometry using silanol mask technique

A method for the determination of nucleotides based on pressure-assisted capillary electrophoresis-electrospray ionization mass spectrometry (PACE-MS) is described. To prevent multi-phosphorylated species from adsorbing onto the fused-silica capillary, silanol groups were masked with phosphate ions by preconditioning the capillary with the background electrolyte containing phosphate. During preconditioning, nebulizer gas was turned off to avoid contamination of MS detector with phosphate ions. To detect nucleotides using the CE positive mode at a pH 7.5, it was necessary to apply air pressure to the inlet capillary during electrophoresis to supplement the electroosmotic flow (EOF) toward the cathode. Moreover, we exchanged the running electrolyte every analysis using the buffer replenishment system to obtain the required reproducibility. Under the optimized conditions, 14 phosphorylated species such as nucleotides, nicotinamide-adenine dinucleotides and coenzyme A (CoA) compounds were well determined in less than 20 min. The relative standard deviations (n=6) of the method were better than 0.9% for migration times and between 1.7% and 8.1% for peak areas. The detection limits for these species were between 0.5 and 1.7 micromol/L with pressure injection of 50 mbar for 30 s (30 nL) at a signal-to-noise ratio of 3. This approach is robust and quantitative compared to the previous method, and its utility is demonstrated by the analysis of intracellular nucleotides and CoA compounds extracted from Escherichia coli wild type, pfkA and pfkB knockout mutants. The methodology was used to suggest that pfkA is the main functional enzyme.     

Design of new bidentate ligands constructed of two Hoechst 33258 units for discrimination of the length of two A3T3 binding motifs

[structure: see text] The aim of this study is to develop bidentate minor-groove binders that bind the double binding motifs cooperatively. The new bidentate ligands (1) have been designed by connecting two Hoechst 33258 units with a polyether linker for cooperative binding with two remote A3T3 sites of DNA. The linker is introduced to the benzimidazole ring so that it is located at the convex side of the Hoechst unit. DNA binding affinity of the ligands was evaluated by measuring surface plasmon resonance (SPR), circular dichroism, and fluorescence spectra. Interestingly, the bidentate ligands (1) did not show affinity to DNA1 with a single A3T3 motif but showed selective affinity to DNA2 with two A3T3 motifs. The Long Bis-H (1L) having a long polyether linker showed specific binding to DNA2(6) with two A3T3 motifs separated by six nonbinding base pairs. The Long Bis-H (1L) has also shown specific binding to the three-way junction DNA4 with two A3T3 motifs. This study has demonstrated that DNA with double binding motifs can be selectively recognized by the newly designed bidentate ligands.     

Isolation,Structure Determination,and Synthesis of Allo‐RA‐V and Neo‐RA‐V,RA‐Series Bicyclic Peptides from Rubia cordifolia L.

Two bicyclic hexapeptides, allo‐RA‐V ( 4 ) and neo‐RA‐V ( 5 ), and one cyclic hexapeptide, O‐seco‐RA‐V ( 6 ), were isolated from the roots of Rubia cordifolia L. Their gross structures were elucidated on the basis of spectroscopic analysis and X‐ray crystallography of compound 5 . The absolute stereochemistry of compounds 4 and 5 were established by their total syntheses, and the absolute stereochemistry of compound 6 by chemical correlation with deoxybouvardin ( 3 ). Comparison of the 3D structures of highly active RA‐VII ( 1 ) with less‐active compounds 4 and 5 suggests that the orientation of the Tyr‐5 and/or Tyr‐6 phenyl rings plays a significant role in their biological activity. The isolation of peptides 4 – 6 , along with compound 3 , and the comparison of their structures seem to indicate that peptide 6 may be the common precursor to bicyclic peptides 3 – 5 in the plant.     

Global asymptotic stability for half-linear differential systems with generalized almost periodic coefficients

The following system considered in this paper:

Global asymptotic stability for half-linear differential systems with generalized almost periodic coefficients

The following system considered in this paper:

$$x' = -\,e(t)x + f(t)\phi_{p^*}(y), \qquad y'= -\,(p-1)g(t)\phi_p(x) - (p-1)h(t)y,$$

where \({p > 1, p^* > 1 (1/p + 1/p^* = 1)}\) and \({\phi_q(z) = |z|^{q-2}z}\) for q = p or q = p ^*. This system is referred to as a half-linear system. The coefficient f(t) is assumed to be bounded, but the coefficients e(t), g(t) and h(t) are not necessarily bounded. Sufficient conditions are obtained for global asymptotic stability of the zero solution. Our results can be applied to not only the case that the signs of f(t) and g(t) change like the periodic function but also the case that f(t) and g(t) irregularly have zeros. Some suitable examples are included to illustrate our results.