Stereoselective Total Synthesis of Hetisine‐type C20‐Diterpenoid Alkaloids: Spirasine IV and XI

The first total synthesis of the architecturally complex hetisine‐type heptacyclic C₂₀‐diterpenoid alkaloids (±)‐spirasine IV and XI is reported. The A/F/G/C tetracyclic skeleton with the challenging N?C6 and C14?C20 linkages was efficiently constructed by an intramolecular azomethine‐ylide‐based 1,3‐dipolar cycloaddition with unusual regioselectivity. SmI₂‐mediated free‐radical addition to the arene moiety without prior dearomatization and a stereoselective intramolecular aldol reaction further enabled rapid access to the hetisine core, providing a bicyclo[2.2.2]octane ring with a new oxygen substitution pattern.     

A Diazido Mannose Analogue as a Chemoenzymatic Synthon for Synthesizing Di‐N‐acetyllegionaminic Acid‐Containing Glycosides

A chemoenzymatic synthon was designed to expand the scope of the chemoenzymatic synthesis of carbohydrates. The synthon was enzymatically converted into carbohydrate analogues, which were readily derivatized chemically to produce the desired targets. The strategy is demonstrated for the synthesis of glycosides containing 7,9‐di‐N‐acetyllegionaminic acid (Leg5,7Ac₂), a bacterial nonulosonic acid (NulO) analogue of sialic acid. A versatile library of α2‐3/6‐linked Leg5,7Ac₂‐glycosides was built by using chemically synthesized 2,4‐diazido‐2,4,6‐trideoxymannose as a chemoenzymatic synthon for highly efficient one‐pot multienzyme (OPME) sialylation followed by downstream chemical conversion of the azido groups into acetamido groups. The syntheses required 10 steps from commercially available d ‐fucose and had an overall yield of 34–52 %, thus representing a significant improvement over previous methods. Free Leg5,7Ac₂ monosaccharide was also synthesized by a sialic acid aldolase‐catalyzed reaction.     

On the eigenvalues of the

We study the nonlinear eigenvalue problem

where , is a bounded smooth domain in . We prove that the first and the second variational eigenvalues of (1) are continuous functions of . Moreover, we obtain the asymptotic behavior of the first eigenvalue as and .

     

Bifurcation problems for the

In this paper we consider the bifurcation problem

in with . We show that a continuum of positive solutions bifurcates out from the principal eigenvalue of the problem

Here both functions and may change sign.

     

Determination of estrogens in wastewater using three-phase hollow fiber-mediated liquid-phase microextraction followed by HPLC

Three-phase hollow fiber-mediated liquid-phase microextraction followed by HPLC was used for the determination of three synthetic estrogens, namely diethylstilbestrol, dienestrol, and hexestrol, in wastewater. Extraction conditions including organic solvent, volume ratio between donor solution and acceptor phase, extraction time, stirring rate, donor phase and acceptor phase were optimized. The target compounds were extracted from a 10 mL aqueous sample at pH 1.5 (donor solution) through a 45 mm in length hollow polypropylene fiber that was immersed in 1-octanol in advance, and then the hollow fiber was filled with 10 microL 0.5 mol/L sodium hydroxide solution (acceptor phase). After a 40 min extraction, the acceptor phase was directly injected into an HPLC system for detection. Under the optimized extraction conditions, a large enrichment factor (more than 300-fold) was achieved for the three estrogens. The determination limit at an S/N of 3 ranged from 0.25 to 0.5 microg/L for the estrogens. The recovery ratio was more than 86% in the determination of these estrogens in wastewater.     

μ2‐Acetato‐κ2O:O′‐tris(μ2‐ferrocenecarboxylato‐κ2O:O′)bis[(N,N‐dimethylformamide‐κO)copper(II)]

The title compound, [Cu₂Fe₃(C₅H₅)₃(C₂H₃O₂)(C₆H₄O₂)₃(C₃H₇NO)₂], belongs to the classic dimeric paddle‐wheel structure type. It is an unusual example in that it contains two different carboxylate groups, viz. ferrocenecarboxylate and acetate. With three ferrocenecarboxylate groups and only one acetate group bridging the two Cu centres, a noncentrosymmetric molecular arrangement results.     

Genome-wide computational analyses of microRNAs and their targets from Canis familiaris

By computational analyses, we identified 357 miRNA candidates from Canis familiaris genome, among which 300 are homology of characterized human miRNAs, the remains are not reported in any other animal. Of the 357 miRNA genes, 142 are organized into 53 clusters, and two clusters locate in the paternally imprinted region. These dog miRNAs may regulate more than 800 possible targets, which are involved in a wide range of cellular processes. Remarkably, miR-186 resides in the eighth intron of its target gene in the same orientation, suggesting a feedback regulation of miRNA on its host gene.     

Synthesis of a novel fluorescent probe based on acridine skeleton used for sensitive determination of DNA

In this study, a novel fluorescent probe of acridine derivative N-((N-(2-dimethylamino)ethyl)acridine-4-carboxamide)-alpha-alanine (N-(ACR-4-CA)-alpha-ALA) was synthesized. The structure of the new compound was characterized by (1)H NMR, MS, elemental analysis, fluorescent and ultraviolet spectra. It was found that DNA had the ability to quench the fluorescence of N-(ACR-4-CA)-alpha-ALA, and the quenched intensity of fluorescence was proportional to the concentration of DNA. A method for DNA determination based on the quenching fluorescence (lambda(ex) = 260 nm, lambda(em) = 451 nm) of N-(ACR-4-CA)-alpha-ALA was established. Under optimal conditions, the linear range is 0.05-2.0 microg mL(-1) for both fish semen (fsDNA) and calf thymus DNA (ctDNA). The corresponding determination limits are 9.1 ng mL(-1) for fsDNA and 8.7 ng mL(-1) for ctDNA, respectively. The results suggested that the interaction mode between N-(ACR-4-CA)-alpha-ALA and DNA was intercalative binding. The intrinsic binding constant was determined and the result showed a large binding constant of N-(ACR-4-CA)-alpha-ALA with DNA.