Titanium(IV) chloride-mediated intramolecular ring enlargement of methylenecyclopropanes with propargylic esters: a concise synthesis of bicyclo[4.2.0]oct-5-ene derivatives

Titanium(IV) chloride-mediated intramolecular ring enlargement of methylenecyclopropanes with propargylic esters has been described in this context, affording the corresponding chlorinated bicyclo[4.2.0]oct-5-ene derivatives in moderate to good yields under mild conditions. The E- and Z-methylenecyclopropanes could all be converted to the corresponding bicyclo[4.2.0]oct-5-enes with moderate to high diastereoselectivities.     

Pd-catalyzed amination as an alternative to nucleophilic aromatic substitution for the synthesis of N-alkyltacrines and analogues

A reliable Pd-catalyzed amination protocol is described for the synthesis of N-alkyltacrines and analogs. The Josiphos ligand CyPFtBu was found to provide optimum yields: 16 examples are given. Compared to the typical high-temperature nucleophilic aromatic substitution (NAS) routes, Pd-catalyzed aminations proceed at significantly lower reaction temperatures, and enable the synthesis of otherwise inaccessible products.     

Development of a Biomimetic Enzyme‐linked Immunosorbent Assay Method for the Determination of Methimazole in Urine Sample

A fast and direct competitive biomimetic enzyme‐linked immunosorbent assay (BELISA) method was developed for the determination of methimazole (MMZ) in urine sample based on a molecularly imprinted film as an artificial antibody. This is the first example to monitor methimazole with a direct competitive biomimetic enzyme‐linked immunosorbent assay (BELISA) method. The imprinted film was directly synthesized on the well surface of MaxiSorp polystyrene 96‐well plate and characterized. The results showed that it exhibited an antibody‐like binding ability, rapid adsorption speed, high stability, which was particularly advantageous and suitable for BELISA development. The BELISA method established in this paper had a higher selectivity for MMZ than for the structurally related compounds and the IC₅₀ (calculated as the concentration giving 50% inhibition of color development) and the detection limit values under optimized experimental conditions were 70 ± 4 μg L^‐1 and 0.9 ± 0.04 μg L^‐1, respectively. The method was applied to the determination of MMZ in spiked urine sample with excellent recoveries ranging from 90% to 95%, and the imprinted film was able to be reused for 20 times without loss of sensitivity. The results obtained by BELISA correlated well with that obtained by the high performance liquid chromatography (HPLC) method.     

A novel eudesmene sesquiterpenoid from <Emphasis Type="Italic">Schisandra sphenanthera</Emphasis> stems

Chemical investigation on the stems of Schisandra sphenanthera has afforded a novel eudesmene-type sesquiterpenoid, schisansphene A (1), and a known compound, alismol (2). Their structures and configurations were elucidated by spectroscopic methods, including 2D NMR techniques.     

Development of Dispersive Liquid‐Liquid Microextraction Based on Solidification of Floating Organic Drop for the Determination of Trace Cobalt in Water Samples

A liquid‐phase microextraction technique was developed using dispersive liquid‐liquid microextraction based on solidification of floating organic drop combined with flame atomic absorption spectrometry, for the extraction and determination of trace amounts of cobalt in water samples. Microextraction efficiency factors, such as the type and volume of extraction and dispersive solvents, pH, extraction time, the chelating agent amount, and ionic strength were investigated and optimized. Under optimum conditions, an enrichment factor of 160 was obtained from 10.0 mL of water sample. The calibration graph was linearin the range of 1.15‐110 μg L^?1 with a detection limit of 0.35 μg L^?1. The relative standard deviation for ten replicate measurements of 10 and 100 μg L^?1 of cobalt were 3.26% and 2.57%, respectively. The proposed method was assessed through the analysis of certified reference water or recovery experiments.     

Simultaneous Determination of Four Sudan Dyes in Egg Yolks by Molecularly Imprinted SPE Coupled with LC-UV Detection

A highly selective molecularly imprinted solid-phase extraction (MISPE) combined with liquid chromatography-ultraviolet detection was developed for the simultaneous isolation and determination of four Sudan dyes (I, II, III and IV) in egg-yolk products. The imprinted microspheres synthesized by suspension polymerization using phenylamine?Cnaphthol as mimic template show high selectivity and affinity to the four kinds of Sudan dyes and were successfully applied as selective sorbents of solid-phase extraction for the simultaneous determination of the four Sudans from egg-yolk samples. Good linearity was obtained in a range of 0.062?C10 ??g g^?1 and the average recoveries of the four Sudans at three spiked levels ranged from 94.1 to 102.5% with the relative standard deviations less than 5.8%. The developed extraction protocol eliminated the effect of template leakage on quantitative analysis and could be applied for the determination of Sudans in complicated food samples.     

New Cytochalasins from the Marine‐Derived Fungus Xylaria sp. SCSIO 156

Two new cytochalasins, 18‐deoxycytochalasin Q ( 1 ) and 21‐O‐deacetylcytochalasin Q ( 2 ), together with four known analogues, cytochalasin Q ( 3 ), 19,20‐epoxycytochalasin Q ( 4 ), 21‐O‐deacetyl‐19,20‐epoxycytochalasin Q ( 5 ), and cytochalasin D ( 6 ), were isolated from the fungus Xylaria sp. SCSIO156 originated from the South China Sea marine sediment. The structures of 1 and 2 were elucidated by MS and 1D‐ and 2D‐NMR data analyses, and comparison with known compounds. The known compounds 3 – 6 were identified by comparison of their MS and NMR data with those reported in the literature. In the in vitro antitumor assay, compounds 2 – 6 showed mild cytotoxicity against three tumor cell lines (MCF‐7, SF‐268, and NCI‐H460).     

Two New Steroidal Saponins from the Fresh Leaves of Agave sisalana

A new furostanol saponin, sisalasaponin C ( 1 ), and a new spirostanol saponin, sisalasaponin D ( 2 ), were isolated from the fresh leaves of Agave sisalana, along with three other known steroidal saponins and two stilbenes. Their structures were identified as (3β,5α,6α,22α,25R)‐3,26‐bis[(β‐D ‐glucopyrano‐ syl)oxy]‐22‐hydroxyfurostan‐6‐yl β‐D ‐glucopyranoside ( 1 ), (3β,5α,25R)‐12‐oxospirostan‐3‐yl 6‐deoxy‐α‐L ‐mannopyranosyl‐(1→4)‐β‐D ‐glucopyranosyl‐(1→3)‐[β‐D ‐xylopyranosyl‐(1→3)‐β‐D ‐glucopyranosyl‐(1→2)]‐β‐D ‐glucopyranosyl‐(1→4)‐β‐D ‐galactopyranoside ( 2 ), (3β,5α,6α,22α,25R)‐22‐methoxyfurostane‐3,6,26‐triyl tris‐β‐D ‐glucopyranoside, cantalasaponin‐1, polianthoside D, (E)‐ and (Z)‐2,3,4′,5‐tetrahydroxystilbene 2‐O‐β‐D ‐glucopyranosides. The last three known compounds were isolated from the fresh leaves of Agavaceae for the first time. The structures of the new compounds were elucidated by detailed spectroscopic analysis, including 1D‐ and 2D‐NMR experiments, and chemical techniques.     

Theoretical study on the smallest endohedral metallofullerenes: TM@C20 (TM = Ce and Gd)

The structure, electronic property, and infrared spectroscopy of endohedral metallofullerenes TM@C₂₀ (TM = Ce and Gd) have been systematically investigated with the aid of the hybrid DFT‐B3LYP functional. It is found that in the endohedral metallofullerenes the average C? C bond lengths are obvious longer than those of empty cage. The frontier orbital analyses show that the endohedral metallofullerene Gd@C₂₀ has the high‐thermodynamic stability. Natural population analysis also tells us that only in the Ce@C₂₀, the Ce atom acts as an electron acceptor with the negative charges, and the 4f orbitals of Ce and Gd atoms have a significant contribution in the formation of chemical bonding. Additionally, the analyses of harmonic vibrational frequencies reveal that when the TM atoms are encapsulated into the C₂₀ cage, the strongest absorption peaks are characterized by a mixture of TM?C bending and C? C stretching vibrations. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011