Molecular structure of N-(2-phenylethyl)amide of α-(1,1-ethylenedioxy)-ethyl γ-hydroxybutyric acid (I) and1H NMR spectra of (I) and N-(p-methoxybenzyl)derivative (III)

The spectroscopic and X-ray investigation of the N-(2-phenylethyl) amide of -(1,1-ethylenedioxy)-ethyl--hydroxybutyric acid are reported. The¹H NMR spectra for the title structure and for the N-(p-methoxybenzyl) amide of -(1,1-ethylenedioxy)-ethyl--hydroxybutyric acid are given. The N-(2-phenylethyl)amide of -(1,1-ethylenedioxy)-ethyl--hydroxybutyric acid, C₁₆H₂₃O₄N, crustallizes in the monoclinic space groupP2 ₁/c witha=21.547(5),b=6.333(2),c=11.822(3) Å and =101.01(2)°. The dioxolane ring has a half-chair conformation with C₂(O3)=2.4° and ||_av=18.2°. The inconsiderable deviations from planarity of the six atoms of the amide group are caused mainly by twist around the C4–N1 bond and out-of-plane bending at the N1 atom ((C4–N1)=4°, X_N =7°, X_c =0.4° ). The amide group plane is nearly coplanar with the phenyl ring. The molecules are connected by two intermolecular hydrogen bonds.     

液相色谱-串联质谱法测定蔬菜和水果中6种新型酰胺类杀菌剂的残留量

建立了蔬菜、水果中啶酰菌胺、氟啶酰菌胺、环氟菌胺、嘧菌胺、双炔酰菌胺和硅噻菌胺6种新型酰胺类杀菌剂残留量的液相色谱-串联质谱(liquid chromatography-tandem mass spectrometry, LC-MS/MS)检测方法。试样经乙腈提取、Florisil固相萃取柱净化、以乙腈和水为流动相梯度洗脱、结合新型核壳型填料色谱柱(Poroshell 120 EC-C₁₈)分离,采用电喷雾正离子扫描、多反应监测模式质谱检测,外标法定量。结果表明:固相萃取结合新型色谱柱分离解决了酰胺类农药分析中基质效应强的难点问题。6种杀菌剂在0.5~100 μg/L范围内线性关系良好,相关系数(r)≥0.9990;对7种蔬菜及3种水果进行0.5、5和50 μg/kg 3个加标水平的回收试验,回收率为65%~124%,相对标准偏差(RSD, n=5)为1%~18%; 6种杀菌剂的方法检出限(S/N≥3)为0.10~0.17 μg/kg。该净化、分离模式显著降低了蔬菜、水果中6种新型酰胺类农药的基质效应,方法简单准确,可满足蔬菜和水果中啶酰菌胺等6种新型酰胺类杀菌剂残留检测的要求。     

A data mining and ab initio study of the interaction between the aromatic and backbone amide groups in proteins

Interactions between aromatic groups and backbone amide groups in protein environments are characterized both through data mining analyses of X‐ray protein structures and through ab initio molecular orbital calculations on a model complex. The data mining analyses of 1029 X‐ray protein structures elucidate the configurational characteristics of the interaction as well as the positions of the interacting moieties involved. On a statistical average, more than seven such interactions occur in a typical protein structure. The configurations of these interactions are restricted with the face‐to‐face orientation as the preferred arrangement. The interaction occurs mainly within a single peptide chain. Both α‐helix and β‐strand secondary structures provide an almost equal number of backbone amides to participate within this interaction. The interaction energy was evaluated with the supermolecular ab initio method at the MP2 level. It is shown that aromatic–amide(backbone) interactions identified in proteins can achieve a stabilization energy of 3.3 kcal/mol. The interaction involves the entirety of the backbone amide rather than only its amine portion. This study concludes that the interaction between aromatic and backbone amide groups is of general significance to protein structure due to its strength and common occurrence. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 44–60, 2000     

Synthesis of 2-Oxazolines from Ring Opening Isomerization of 3-Amido-2-Phenyl Azetidines

Chiral 2-oxazolines are valuable building blocks and famous ligands for asymmetric catalysis. The most common synthesis involves the reaction of an amino alcohol with a carboxylic acid. In this paper, an efficient synthesis of 2-oxazolines has been achieved via the stereospecific isomerization of 3-amido-2-phenyl azetidines. The reactions were studied in the presence of both Brønsted and Lewis acids, and Cu(OTf)₂ was found to be the most effective.     

Cyclic Aromatic Polyamides via the Triphenylphosphite Method

Abstract

5‐tert‐Butyl‐isophthalic acid (TIPA) was polycondensed with three different aromatic diamines by means of triphenylphosphite (TPP) and pyridine. The resulting polyamides were characterized by solution viscosities and MALDI‐TOF mass spectra (m.s.). These m.s. revealed significant fractions of cyclic oligo‐ and polyamides in all samples. In polyamides of high molecular weight, only cycles were detectable (observed up to masses of 13,000 Da). Three poly(amide‐imide)s were prepared by TPP‐mediated polycondensation of trimellitic anhydride (TMA) and three aromatic diamines. Although relatively high molar masses were obtained, the MALDI‐TOF m.s. displayed the peaks of linear chains in addition to those of cyclic polymers. The results together suggest that the side reactions mainly occur at the amino endgroups.     

Convenient Synthesis of 3,5‐Biscarbamoyl‐pyridine Derivatives

An efficient and convenient method for synthesis of 3,5‐bis‐carbamoyl‐2,6‐dimethylpyridine derivatives was achieved in good to excellent yields by reaction of anilines with 3,5‐bis(3′,5′‐dimethyl‐1′‐pyrazolyl‐carbonyl)‐2,6‐dimethylpyridine, in which pyrazoles served as leaving groups. The structures of products were confirmed by spectra data and microanalysis.     

One-pot synthesis of 4-substituted 4-alkoxy-1,4-dihydro-3,1-benzoxazine-2-thiones by the reaction of 2-isothiocyanatobenzoates with organolithiums

An efficient one-pot procedure for the preparation of 4-substituted 4-alkoxy-1,4-dihydro-3,1-benzoxazine-2-thiones from 2-isothiocyanatobenzoates has been developed. Thus, 2-isothiocyanatobenzoates were reacted with organolithiums including lithium enolates of acetates and tertiary acetamides in THF at −78 °C to give the desired products in generally good yields.     

Double asymmetric induction as a mechanistic probe: the doubly diastereoselective conjugate addition of enantiopure lithium amides to enantiopure α,β-unsaturated esters and enantiopure α,β-unsaturated hydroxamates

The doubly diastereoselective conjugate addition of the antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide to a range of enantiopure α,β-unsaturated esters [derived from Corey’s 8-phenylmenthol chiral auxiliary] and enantiopure α,β-unsaturated hydroxamates [derived from our ‘chiral Weinreb amide’ auxiliary (S)-N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine] has been used as a mechanistic probe to determine the reactive conformations of these acceptors.     

Ionic liquid salt bridge based on tributyl(2-methoxyethyl)phosphonium bis(pentafluoroethanesulfonyl)amide for stable liquid junction potentials in highly diluted aqueous electrolyte solutions

A moderately hydrophobic ionic liquid, tributyl(2-methoxyethyl)phosphonium bis(pentafluoroethanesulfonyl)amide ([TBMOEP⁺][C₂C₂N⁻]), shows a very stable liquid junction potential upon contact with an aqueous solution whose ionic strength is as low as 1 μmol dm⁻³. The stability with the maximum excursion of the potential within ±0.5 mV for 30 min is very promising for accurate determination of pH and other single ion activities potentiometrically.