Formal total synthesis of hemibrevetoxin B by a convergent strategy

Concise construction of the trans-fused 7/7/6/6 tetracyclic ether part of hemibrevetoxin B (1) was achieved by a convergent strategy based on coupling reaction of an acyl anion equivalent, reductive cyclization of an α,ε-dihydroxyketone, and introduction of a methyl group at the central ring junction by the Nicolaou method. The resultant tetracyclic ether was transformed into the known intermediate, which was already converted to 1 by the Yamamoto group, thereby completing the formal total synthesis of 1.     

A stereoselective synthesis of (2R,3S)-2-amino-3,4-dihydroxybutyric acid using an ether directed aza-Claisen rearrangement

A new approach for the stereoselective synthesis of (2R,3S)-2-amino-3,4-dihydroxybutyric acid, an α-amino acid from Lyophyllum ulmarium, has been accomplished using an ether directed aza-Claisen rearrangement. On investigation of optimal conditions for this key step it was shown for the first time that Au(I) can be used to catalyse this transformation.     

Synthesis of the fungal natural product (−)-xylariamide A

The first synthesis of the fungal natural product (−)-xylariamide A 1 is reported. N,O-Bis(trimethylsilyl)acetamide induced coupling of d-tyrosine with (E)-but-2-enedioic acid 2,5-dioxo-pyrrolidin-1-yl ester methyl ester 5 produced the dechloro natural product 6, which was subsequently monochlorinated using oxone and KCl to yield synthetic 1. (−)-Xylariamide A 1, (+)-xylariamide A 2 and (−)-dechloroxylariamide A 6 displayed no cytotoxic or antimicrobial activity.     

Biocatalytic process intensification via efficient biocatalyst immobilization,miniaturization, and process integration

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Characterization of silicon nitride particles synthesized in an atmospheric-pressure convection-stabilized arc

Silicon nitride powders were synthesized in an atmospheric-pressure convection-stabilized arc using silicon and ammonia as reactants. The morphology and particle size distributions of the silicon nitride particles were characterized by SEM, TEM, and electron diffraction analyses. The silicon nitride particles collected in the plasma reactor were formed by either gas-condensed phase reactions or chemical vapor reactions. The morphologies of the particles formed by gas-condensed phase reactions consisted of -Si₃N₄ prisms, -Si₃N₄ matte, -Si₃N₄ needles, and spaghetti-like whiskers. For the homogeneously nucleated particles, the morphologies included dendrites, needles, platelets, and amorphous particles. Most of the particles formed were aggregates with particle size distributions ranging from 500 to 1500 Å depending on the location of injection of the reactants.     

Application of Cyclopentadiene and its Derivatives in Natural Product Synthesis

Approaches toward the synthesis of iridoids and 9-isocyanopupukeanane starting from cy-clopentadiene are discussed.     

毛细管气相色谱法同时测定水产品中的多氯联苯和有机氯农药残留量

建立了毛细管气相色谱法同时测定水产品中多氯联苯和有机氯农药的方法，用高氯酸与冰乙酸的混合溶液消化样品，以石油醚提取，浓硫酸净化后，用毛细管气相色谱法测定，方法的回收法为88％－110％，相对标准偏差为8％－19％（n=6)，检出限为0．08－0．60ug/kg，方法简便，快速，结果准确。     

The mechanism of nitrite formation in the radiation-induced oxidation of ammonia in aerated aqueous solutions

The mechanism of the radiation-induced conversion of ammonia to nitrites and nitrates in aerated aqueous solutions has been studied. The formation of the pernitrite ion, O=N-O-O^–, was detected at pH 10.5. The kinetics of its formation and decay were studied, andk _form was estimated at (2.3±0.2)·10⁷ L mol^–1 s^–1. The course of decay obeys first-order kinetics; the rate constant decreases at higher pH. Radiochemical yields of pernitrite, nitrite and nitrate at various pH and initial NH₃ concentrations were determined. A mechanism of ammonia oxidation in aqueous solution is proposed.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 280–283, February, 1993.     

高效液相色谱法测定水产品中四环素类抗生素残留

建立了一种高效液相色谱法测定水产品中土霉素、四环素、去甲基金霉素、金霉素、脱氧土霉素的分析方法。样品用5.0%高氯酸溶液提取,上清液用OasisHLB固相萃取柱净化,用紫外检测器于355nm测定。土霉素、四环素、去甲基金霉素检测限为0.01mg/kg,金霉素、脱氧土霉素检出限为0.02mg/kg。5种药物的回收率在74.8%~89.3%之间,相对标准偏差为3.95%~9.95%。方法适用于水产品中四环素类抗生素残留的检测。     

高效液相色谱法测定水产品中的恶喹酸

建立了高效液相色谱法测定水产品中恶喹酸残留量的方法。样品用二氯甲烷提取后，除去溶剂，用稀盐酸和正己烷处理，去除残渣中的脂肪，再用二氯甲烷萃取，浓缩至干后用甲醇定容。以0.002mol/L磷酸溶液－乙腈－四氢呋喃（体积比为65：20：15）为流动相，在ODS反相色谱柱上分离后，用荧光检测器测定，外标法定量。方法的线性范围为5－5000ng/mL，线性回归方程为A＝9.426c-2.123，相关系数r=0.9988，检出限为1μg/kg，回收率为93.0%-96.0%，相对标准偏差为3.7%-6.2%。