Thiourea-Quaternary Ammonium Salt Catalyzed Asymmetric 1, 3-Dipolar Cycloaddition of Imino Esters To Construct Spiro[pyrrolidin-3,3'-oxindoles].

A highly enantioselective 1,3-dipolar cycloaddition of imino esters with methyleneindolinones has been realized by using readily available thiourea-quaternary ammonium salts as phase-transfer catalysts, enabling efficient construction of a range of chiral spiro[pyrrolidin-3,3'-oxindoles] in good yields with excellent enantioselectivities under mild conditions.

Collective total synthesis of englerin†A and B, orientalol†E and F, and oxyphyllol: application of the organocatalytic [4+3] cycloaddition reaction.

The concise collective total synthesis of englerin A and B, orientalol E and F, and oxyphyllol has been accomplished in 10-15 steps, with the total synthesis of orientalol E and oxyphyllol being achieved for the first time. The success obtained was enabled by the realization of the [4+3] cycloaddition reaction of 9 and 10. Other features of the synthesis include 1) the intramolecular Heck reaction to access the azulene core, 2) the epoxidation-S(N)2' reduction sequence to access the allylic alcohol, 3) the efficient regioselective and stereoselective formal hydration of the bridging C=C bond in the synthesis of englerins, and 4) the late-stage chemo- and stereoselective C-H oxidation in the synthesis of orientalol E. The total synthesis of these natural products has enabled the structural revision of oxyphyllol and established the absolute stereochemical features of the organocatalytic [4+3] cycloaddition reaction. The identification of 5 as the natural product oxyphyllol, the success in converting 5 to orientalol E, along with the fact that englerins and oxyphyllol were isolated from plants of the same genus Phyllanthus gives support to our proposed biosynthetic pathways. This work may enable detailed biological evaluations of these natural products and their analogues and derivatives, especially of their potential in the fight against renal cell carcinoma (RCC).

Preparation of novel mercury-doped silver nanoparticles film glassy carbon electrode and its application for electrochemical biosensor.

A novel mercury-doped silver nanoparticles film glassy carbon (Ag/MFGC) electrode was prepared in this study. Electrochemical behaviors of cysteine on the Ag/MFGC electrode were investigated by electrochemical impedance spectroscopy and cyclic voltammetry (CV). The results indicated that cysteine could be strongly adsorbed on the surface of the Ag/MFGC electrode to form a thin layer. The doped electrode could catalyze the electrode reaction process of cysteine, and the cysteine displayed a pair of well-defined and nearly reversible CV peaks at the electrode in an acetate buffer solution (pH 5.0). The Ag/MFGC electrode was used for determination of cysteine by differential pulse voltammetry. The linear range was between 4.0x10(-7) and 1.3x10(-5) mol/L, with a detection limit of 1.0x10(-7) mol/L and a signal-to-noise ratio of 3. The relative standard deviation was 2.4% for seven successive determinations of 1.0x10(-5) mol/L cysteine. The determinations of cysteine in synthetic samples and urinal samples were carried out and satisfactory results were obtained. Amperometric application of the Ag/MFGC electrode as biosensors is proposed.