Direct amidation of non-activated carboxylic acid and amine derivatives catalyzed by TiCp2Cl2

This paper described a mild and efficient direct amidation of non-activated carboxylic acid and amine derivatives catalyzed by TiCp₂Cl₂. Arylacetic acid derivatives reacted with different amines to afford the corresponding amides in good to excellent yield except of aniline. Aryl formic acids failed to react with aniline but smoothly reacted with aliphatic amines and benzylamine in moderate to good yield, fatty acids reacting with benzyl and aliphatic amines give amides in good to excellent yield. Chiral amino acids derivatives were transformed into amides without racemization in moderate yield. The possible mechanism of direct amidation catalyzed by TiCp₂Cl₂ was discussed. This catalytic method is very suitable for the amidation of low sterically hindered arylacetic acid, fatty acids with different low sterically hindered amines except aniline, as well as the amidation of aryl formic acid with benzyl and aliphatic amines.     

Diels–Alder Reactions of β-Acylacrylic Acids

The Diels–Alder reaction of β-acylacrylic acids with dienes gave good yields and good regio- or stereoselectivity of the corresponding cycloaddition products with the use of Lewis acids.     

A convenient synthesis of amino acid methyl esters

A series of amino acid methyl ester hydrochlorides were prepared in good to excellent yields by the room temperature reaction of amino acids with methanol in the presence of trimethylchlorosilane. This method is not only compatible with natural amino acids, but also with other aromatic and aliphatic amino acids.     

An extremely simple, convenient and mild one-pot reduction of carboxylic acids to alcohols using 3,4,5-trifluorophenylboronic acid and sodium borohydride

Acyloxyboron intermediates formed in situ from carboxylic acids and 3,4,5-trifluorophenylboronic acids react with sodium borohydride in THF to give alcohols in good to high yields.     

Iodine assisted palladium catalyzed ring opening of bicyclic hydrazines with organoboronic acids: stereoselective synthesis of functionalized cyclopentenes and alkylidene cyclopentenes

A novel reactivity of organoboronic acids with bicyclic hydrazines leading to the stereoselective formation of trans-vicinal disubstituted cyclopentenes in good to excellent yield is discussed. The reaction of cyclopentadiene and fulvene derived azabicyclic alkenes with organoboronic acids afforded the trans-3,4-disubstituted cyclopentenes and alkylidene cyclopentenes in good to excellent yields. The products, having a broad range of substituents, are important intermediates in the synthesis of a number of pharmaceutically important molecules.     

Facile synthesis of methylthiomethyl esters through Pummerer-type rearrangement of carboxylic acids and DMSO under metal-free conditions

A green and cost-effective Pummerer-type rearrangement between readily accessible carboxylic acids and DMSO has been achieved under metal-free conditions in satisfactory to excellent yields. The transformation for the synthesis of valuable methylthiomethyl esters is shown to be a convenient strategy for various (hetero)aromatic acids, α,β-unsaturated carboxylic acids and saturated alkyl carboxylic acids with good functional group tolerance.     

An expedient route for the reduction of carboxylic acids to alcohols employing 1-propanephosphonic acid cyclic anhydride as acid activator

A simple and efficient method for the synthesis of alcohols from the corresponding carboxylic acids is described. Activation of carboxylic acid with 1-propanephosphonic acid cyclic anhydride (T3P) and subsequent reduction using NaBH₄ yield the alcohol in excellent yields with good purity. Reduction of several alkyl/aryl carboxylic acids and N^α-protected amino acids/peptide acids as well as N^β-protected amino acids was successfully carried out to obtain corresponding alcohols in good yields. All the products were fully characterized by ¹H NMR and mass spectral analyses. The procedure is mild, simple and the isolation of the products is easy.     

Simultaneous separation and sensitive determination of free fatty acids in blood plasma by high-performance liquid chromatography

Fatty acids are separated by reversed-phase high-performance liquid chromatography after derivatization with a fluorescence reagent, 4-bromomethyl-7-acetoxycoumarin. Each derivative eluted from a column is successively hydrolysed by mixing it with an alkaline solution, and the produced fluorescence is detected. The derivatives of series of both saturated and unsaturated fatty acids (C6:0--C20:4) are simultaneously separated by a continuous gradient elution method using a methanol-based solvent containing acetonitrile. The quantitative detection of fatty acids is over a range of 5-1000 pmol per derivatization mixture. This method is applicable to the quantitative analysis of free fatty acids in normal human blood samples and blood samples from diabetic patients. Ten microliters of blood plasma are sufficient to carry out the determination. The analytical results show good recovery and good reproducibility. This sensitive method is very useful for the analysis of fatty acids in very low concentrations.     

Resolution of carboxylic acids using copper(I)-promoted removal of propargylic esters under neutral conditions

A method for the optical resolution of carboxylic acids is described. Condensation of racemic carboxylic acids with chiral terminal propargyl alcohols gave separable diastereomeric esters. Chromatographic separation followed by heating the individual diastereomers in methanol with catalytic copper(I) halide regenerated the carboxylic acids in good yields and in enantiomeric ratios of ≥94%. This method is particularly useful for the resolution of carboxylic acids that are incompatible with conventional ester hydrolysis.     

N‐Linked Hydroxylamine Resin: Solid‐Phase Synthesis of Hydroxamic Acids

A novel hydroxylamine resin for solid‐phase synthesis of hydroxamic acids is described. Its facile application is illustrated by the solid‐phase synthesis of various hydroxamic acids. Cleavage is induced under acidic conditions by treatment with trifluoroacetic acid, providing hydroxamic acids in high purity and good yields.     

Formation and reactivity of dianions derived from 2- and 3-thiophencarboxylic acids

Dianions (3) and (6) can be generated in high yield from the corresponding thiophencarboxylic acids with lithium diisopropylamide and react with a number of representative electrophiles to give fair to good yields of 5-substituted-thiophen-2-carboxylic acids and 2-substituted thiophen-3-carboxylic acids respectively.     

聚苯胺修饰电极酸碱示波电位滴定法——Ⅰ.水溶液中的酸碱滴定

示波电位滴定具有终点直观、仪器便宜、操作简便、快速、准确等特点。本文将对氢离子响应敏锐、使用寿命长、制备简单的聚苯胺修饰电极(PAME)^[4,5]应用于酸碱示波电位滴定中,使电位突跃更加明显,化学计量点更易判断(与双铂电极体系比较),可滴定多元弱酸、弱碱、混合酸和混合碱.与pH玻璃电极比较,具有阻抗低,响应灵敏、迅速,终点电位突跃大,不易损坏,不需预处理,制备简单等特点.     

Sequential ethoxycarbonylation, methoximation and tert-butyldimethylsilylation for simultaneous determination of amino acids and carboxylic acids by dual-column gas chromatography

Amino acids (AAs) in alkaline solution were first ethoxycarbonylated with subsequent methoximation of keto acids (KAs). After acidification and solid-phase extraction, tert-butyldimethylsilylation was performed for direct analysis by gas chromatography (GC) on dual-columns with different polarities, which provided simultaneous separation of multiple amino acids, carboxylic acids (CAs) and keto acids, facilitating accurate peak confirmation based on matching with retention index sets characteristic of each analyte. The present method was linear (r2 > or = 0.9955) with good precision (0.1-9.4%) and accuracy (-8.6 to 9.9%), allowing simultaneous screening for diagnostic amino acids along with carboxylic acids and keto acids in urine from a phenylketonuria patient.     

Regioselective openings of 2,3-epoxy acids with organocuprates

Lithium organocuprates react with 3-alkyl-2,3-epoxy acids (glycidic acids) to afford the products of ring-opening in good yield. The regiochemistry of ring-opening is dependent on the stereochemistry of the epoxy acid.     

Synthesis of alpha-fluorocarboxylates from the corresponding acids using acetyl hypofluorite.

alpha-Fluorocarboxylic esters and acids were synthesized in good yields. The corresponding esters and acids were converted to their ketene acetals, and these enol derivatives reacted with AcOF made directly from fluorine. This route circumvents the problems associated with nucleophilic fluorinations such as various eliminations and rearrangements. alpha- and beta-branched carboxylic acid derivatives that cannot be directly fluorinated gave by this electrophilic fluorination the corresponding alpha-fluoro derivatives in good yield. Both the fluorination reaction and the preparation of AcOF are fast and suitable for [18]F incorporation into acids and esters needed for working with PET. alpha-Fluoroibuprofen (20) and methyl 2-fluoro-3,3,3-triphenylpropionate (32) are two examples of this general reaction.     

A mild conversion of arylboronic acids and their pinacolyl boronate esters into phenols using hydroxylamine

Hydroxylamine was found to be a mild reagent for conversion of arylboronic acids and their pinacolyl boronate esters into phenols. This procedure works on most arylboronic acids at room temperature, yielding phenols in moderate to good yields, and efficiently on arylboronates also yielding phenols in good yields.     

Paper disk electrophoresis in the determination of isoelectric points of amino acids

Summary A method is described for studying the mobility of different amino acids in buffer solutions of different p_H using the paper disk electrophoretic apparatus. From the mobility of amino acids the isoelectric point of individual amino acids has been calculated. The results obtained are in good agreement with those obtained by others.     

Convenient Synthesis of a Library of Discrete Hydroxamic Acids Using the Hydroxythiophenol (Marshall) Resin

Several resins have reportedly been used to synthesize hydroxamic acids except for the hydroxythiophenol (Marshall) resin. Herein, we report the use of the Marshall resin to synthesize hydroxamic acids from carboxylic acids and its application to convert a library of 14 discrete aliphatic and aromatic carboxylic acids including N-protected amino acids to their corresponding hydroxamic acids in good yields.     

反相高效液相色谱-蒸发光散射检测法同时测定阿胶中的17种未衍生氨基酸

建立了反相高效液相色谱-蒸发光散射检测法(HPLC-ELSD)同时测定中药阿胶中17种未衍生氨基酸含量的方法。采 用PrevailTMC18色谱柱 (250 mm×4.6 mm i.d., 5 μm)，以乙腈-0.7%三氟醋酸溶液(含5.0 mmol/L七氟丁酸）为流 动相进行线性梯度洗脱，流速为0.8 mL/min，在漂移管温度115 ℃、氮气流量2.5 L/min条件下，在25 min内即可完成 对阿胶中17种氨基酸的分离测定。氨基酸质量浓度为0.073～2.327 g/L时,其峰面积的对数值与质量浓度的对数值线性 关系良好；17种氨基酸的加样回收率为93.5%～104.8%；信噪比为3时,测得氨基酸的最低检测限介于18.2 mg/L与54.6 mg/L之间。该法快速、简便、准确,可作为阿胶中氨基酸的直接测定方法,亦为其他药物中氨基酸的分析提供了参考。     

A convenient route to enantiopure 3-aryl-2,3-diaminopropanoic acids by diastereoselective Mannich reaction of camphor-based tricyclic iminolactone with imines

A novel and convenient route to the asymmetric synthesis of 2,3-diamino acids via Mannich reaction of iminolactones 1a and 1b with N-protected imines has been achieved in good yields (up to 95%) and high diastereoselectivity (dr: >99:1). Hydrolysis of the Mannich adducts under acidic conditions furnished the desired 3-aryl-2,3-diaminopropanoic acids in good yields (up to 85%) with excellent enantiomeric excesses (99% ee).