Formal Total Synthesis of Palmerolide A

A formal total synthesis of the 20‐membered marine macrolide, palmerolide A from chiral pool tartaric acid is described. Elaboration of a γ‐hydroxy amide, which is derived from the desymmetrization of tartaric acid amide, and Boord olefination are the pivotal reactions employed for the synthesis of the chiral building blocks, and Stille coupling and ring‐closing metathesis (RCM) are used to assemble the macrolactone.     

中红外、近红外和拉曼光谱法测定商品农药制剂中氰戊菊酯和马拉硫磷的含量

利用近红外、中红外和拉曼光谱法定量分析了商品农药制剂中有效成分氰戊菊酯和马拉硫磷的含量.采用偏最小二乘法(Partial least squares,PLS)建立氰戊菊酯和马拉硫磷的定量模型并进行了优化,用独立检验集对模型适应性进行评价.近红外和中红外法测定氰戊菊酯、马拉硫磷定量模型的相关系数分别是0.9981,0.9994和0.9946,0.9998,外部验证集标准差分别是0.082,0081和0.092,0.075,两种方法的定量效果接近;拉曼法氰戊菊酯和马拉硫磷定量模型的相关系数分别为0.9872和0.9993,外部验证集标准差分别为0.254和0.317,预测精度不及近红外和中红外法高.MIR-ATR,NIR和Raman 3种方法均能满足现场检测农药质量的需要.     

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.     

Density Functional Theory Study on the Adsorption of Dioxygen on Small Pt-Pd Clusters

1 INTRODUCTION The bimetallic nanoclusters are of standing inte- rest since they can exhibit catalytic, electronic and optical properties distinct from those of corre- sponding pure nanoclusters[1～4]. Palladium and pla- tinum, well known for their catalytic properties, are often used as the catalyst in different fuel cells[5～8]. Several experimental results illustrate that for the oxygen reduction reaction (ORR), which is one of the primary reactions taking place in many fuel cells and…     

Synthetic studies on chartelline C: stereoselective construction of the core skeleton

What a core-ker! The title synthesis was achieved using a route featuring an intramolecular Mitsunobu reaction of a nosyl amide, stereoselective construction of the β-lactam, and formation of an enamide moiety by selenoxide elimination. The stereochemistry of the alkylation for the formation of the β-lactam was controlled by a secondary hydroxy group on the ten-membered ring. SEM=2-(trimethylsilyl)ethoxymethyl; TBS=tert-butyldimethylsilyl.     

Sample Injection for Capillary Electrophoresis on a Micro Fabricated Device/On Chip CE Injection

Abstract

Reproducible injection for capillary electrophoresis on a micro device/Lab on chip is not an easy task. Different injection designs (e.g., T‐type, double T‐type, cross) and different injection modes have been applied (pinched injection, gated injection, optically gated injection, pressure/pneumatic injection, double L injection) with various analytes. Problems and properties of the different modes are described.     

Determination of API Gravity and Total and Basic Nitrogen Content by Mid- and Near-Infrared Spectroscopy in Crude Oil with Multivariate Regression and Variable Selection Tools

Abstract

American Petroleum Institute (API) gravity is an important parameter in the crude oil industry and the nitrogen compounds are related to the toxic effects of the oil in refineries and the environment. In this paper, 194 crude oil samples with API gravities ranging from 11.4 to 57.5 were used for the purpose of estimating the physicochemical properties: API gravity, total nitrogen content (TNC) and basic nitrogen content (BNC). Initially, infrared spectra in the mid and near regions (MIR and NIR) were collected, then full-spectral partial least squares (PLS) and the orthogonal projections to latent structures (OPLS) chemometric models were developed and validated, as well as models using interval PLS (iPLS), synergy interval PLS (siPLS) and competitive adaptive reweighted sampling PLS (CARSPLS) as variable selection tools. For API gravity and TNC, the best calibration technique is the NIR CARSPLS with a root mean square error of prediction (RMSEP) values of 0.9 and 0.0275?wt%, respectively. For BNC, the best technique is MIR siPLS with a prediction error of 0.0134?wt%. The results were validated based on the evaluation of the figures of merit, a statistical evaluation of the accuracy, characterization of the systematic error and measurement for errors in the residues. The results were satisfactory considering the high variability of the data and the diversity of the samples, demonstrating suitable applicability for practical analysis.     

天然产物Modhephene的全合成研究进展

综述了近年来天然产物Modhephene的全合成方法,并依据其不同的环化方法分为两大类,对每例合成方法进行了详尽的分析。     

Phosphoric Acid Catalyzed Desymmetrization of Bicyclic Bislactones Bearing an All‐Carbon Stereogenic Center: Total Syntheses of (−)‐Rhazinilam and (−)‐Leucomidine B

In the presence of a catalytic amount of an imidodiphosphoric acid, enantioselective desymmetrization of bicyclic bislactones by reaction with alcohols took place smoothly to afford enantiomerically enriched monoacids having an all‐carbon stereogenic center. Concise catalytic enantioselective syntheses of both (?)‐rhazinilam and (?)‐leucomidine B were subsequently developed using (S)‐methyl 4‐ethyl‐4‐formylpimelate monoacid as a common starting material.     

Synthesis of Pyrrolophenanthridine Alkaloids Based on C(sp3)H and C(sp2)H Functionalization Reactions

Assoanine, pratosine, hippadine, and dehydroanhydrolycorine belong to the pyrrolophenanthridine family of alkaloids, which are isolated from plants of the Amaryllidaceae species. Structurally, these alkaloids are characterized by a tetracyclic skeleton that contains a biaryl moiety and an indole core, and compounds belonging to this class have received considerable interest from researchers in a number of fields because of their biological properties and the challenges associated with their synthesis. Herein, a strategy for the total synthesis of these alkaloids by using C? H activation chemistry is described. The tetracyclic skeleton was constructed in a stepwise manner by C(sp³)? H functionalization followed by a Catellani reaction, including C(sp²)? H functionalization. A one‐pot reaction involving both C(sp³)? H and C(sp²)? H functionalization was also attempted. This newly developed strategy is suitable for the facile preparation of various analogues because it uses simple starting materials and does not require protecting groups.