Extraction and quantitative analysis of 1-aminocyclopropane-1-carboxylic acid in plant tissue by gas chromatography coupled to mass spectrometry

We developed a new method for the determination of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) using quantitative GC-negative chemical ionisation MS as a detection and quantification system, in combination with isotope dilution using [2H4]ACC and an off-line solid-phase extraction. By derivatisation with pentafluorobenzyl bromide, ACC could easily be detected with m/z 280 being the most abundant ion. Determination of this component resulted in a detection limit of 10 fmol and a linear fit in the 100 fmol-100 pmol range. The combination of a rapid, high yield purification method with a stable derivatisation procedure and a sensitive detection method allowed the detection of ACC in samples as low as 100 mg fresh mass.     

Determination of 1-aminocyclopropane-1-carboxylic Acid in Apple and Peach Extracts by High Performance Liquid Chromatography Coupled to a Fluorescence Detector

A new, sensitive, and simple HPLC method was described for the determination of 1-aminocyclopropane-1-carboxylic acid (ACC) in apple and peach extracts. The method was based on the derivatization of ACC with fluorescamine in borate buffer systems of pH 8.0 to yield a highly fluorescent product. The experimental parameters affecting the derivatization reaction efficiency were optimized by fluorimetric analysis. Under optimum derivatization conditions, the derivative product of ACC in apple and peach extracts without extra purification was successfully chromatographed on a C-18 column by HPLC coupled to fluorescence detection. The derivative product of ACC with fluorescamine could be well separated from other concomitant substances or their derivatives that might interfere with the determination of ACC. The linearity of ACC was measured in the range of 23.82–238.82 µg · L^?1 with a good correlation coefficient of 0.9997. Based on signal-to-noise ratio of 3, a low detection limit of 5.0 µg · L^?1 could be reached. The proposed method was applied successfully to the determination of ACC in the crude apple and peach extracts without extra purification with low RSDs of 0.19–1.9% and good recoveries of 90.89–104.4%. The sensitive HPLC quantitative method is of great significance for the investigations of ACC metabolism in plants.     

Expedient solid-phase synthesis of fluorogenic protease substrates using the 7-amino-4-carbamoylmethylcoumarin (ACC) fluorophore

A highly efficient solid-phase synthesis method for the preparation of fluorogenic protease substrates based upon the bifunctional leaving group 7-amino-4-carbamoylmethylcoumarin (ACC) is reported. Methods for the large-scale preparation of the novel fluorogenic leaving-group ACC are provided (Scheme 1). Detailed procedures are also provided for loading a diverse set of amino acids to support-bound ACC in good yields and with minimal racemization. Finally, procedures are included for the preparative synthesis of optimized ACC substrates for HIV-1 protease and plasmin.     

三元环氨基酸的合成工艺改进

以甘氨酸乙酯盐酸盐为原料,经酰氨化、脱水、成环、水解反应合成了三元环氨基酸,总收率达50.4%。其结构经1HNMR,13CNMR,IR和EI-MS确证。     

Synthesis of labeled 1-amino-2-methylenecyclopropane-1-carboxylic acid, an inactivator of 1-aminocyclopropane-1-carboxylate deaminase

1-Amino-2-methylenecyclopropane-1-carboxylic acid (2-methylene-ACC) is an irreversible inhibitor for a bacterial enzyme, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which catalyzes the conversion of ACC to alpha-ketobutyrate and ammonia. The inactivation has been proposed to proceed with the ring scission induced by an addition of an enzyme nucleophile, resulting in the formation of a reactive turnover product that then traps an active-site residue. To gain further insight into this unique enzymatic reaction, the tritiated 2-methylene-ACC was prepared and incubated with ACC deaminase to locate and identify the entrapped amino acid residue. The synthesis of this radiolabeled compound and the results of its incubation with ACC deaminase are reported in this paper.     

Efficient synthesis of methylene exo-glycals: another use of glycosylthiomethyl chlorides

A new approach to the synthesis of methylene exo-glycals is described. Oxidation of glycosylthiolmethyl chloride (GTM-Cl) with mCPBA afforded the corresponding glycosylchloromethyl sulfone in almost quantitative yield, which underwent KOtBu-induced Ramberg-B?cklund rearrangement to furnish the desired methylene exo-glycal in excellent yield.     

An Improved Synthesis,of 3-Aryl Thigphenes Using Phase-Transfer Co-Catalysts

An efficient and facile synthesis of 3-aryl thiophenes From disodium 2-aryl succinates using phosphorus penta sulphide-red phosphorus under phase transfer co-catalyst is reported in near quantitative yield.     

A Novel Synthesis of 1-Aminocyclopropane-1-carboxylic Acid (ACC)

A novel synthetic route of 1-aminocyclopropane-1-carboxylic acid (ACC) has been built via cyclopropanedicarboxylic acid monohydrazide III in moderation to good yield.     

A new quantitative structure-retention relationship model for predicting chromatographic retention time of oligonucleotides

An integrated approach is proposed to predict the chromatographic retention time of oligonucleotides based on quantitative structure-retention relationships(QSRR) models.First,the primary base sequences of oligonucleotides are translated into vectors based on scores of generalized base properties(SGBP),involving physicochemical,quantum chemical,topological,spatial structural properties,etc.;thereafter,the sequence data are transformed into a uniform matrix by auto cross covariance(ACC).ACC accounts for the ...     

ACC对羰基化合物、含苄基化合物及稠环芳烃中活泼碳氢键的选择性氧化

前文曾报道了几种以铵盐或氯化铵为配体与三氧化铬所形成的配合物(CH_3)_3NHCrO_3Cl、(CH_3)_2NH_2CrO_3Cl、CH_3NH_3CrO_3Cl和NH_4CrO_3CI。它们都是高效、温和的醇和肟类选择性氧化剂。其中,NH_4CrO_3Cl(ACC)是最廉价的,具有制备简单、性质稳定、选     

Factors involved in the formation of amorphous and crystalline calcium carbonate: a study of an ascidian skeleton.

The majority of invertebrate skeletal tissues are composed of the most stable crystalline polymorphs of CaCO(3), calcite, and/or aragonite. Here we describe a composite skeletal tissue from an ascidian in which amorphous and crystalline calcium carbonate coexist in well-defined domains separated by an organic sheath. Each biogenic mineral phase has a characteristic Mg content (5.9 and 1.7 mol %, respectively) and concentration of intramineral proteins (0.05 and 0.01 wt %, respectively). Macromolecular extracts from various biogenic amorphous calcium carbonate (ACC) skeletons are typically glycoproteins, rich in glutamic acid and hydroxyamino acids. The proteins from the crystalline calcitic phases are aspartate-rich. Macromolecules extracted from biogenic ACC induced the formation of stabilized ACC and/or inhibited crystallization of calcite in vitro. The yield of the synthetic ACC was 15-20%. The presence of Mg facilitated the stabilization of ACC: the protein content in synthetic ACC was 0.12 wt % in the absence of Mg and 0.07 wt % in the presence of Mg (the Mg content in the precipitate was 8.5 mol %). In contrast, the macromolecules extracted from the calcitic layer induced the formation of calcite crystals with modified morphology similar to that expressed by the original biogenic calcite. We suggest that specialized macromolecules and magnesium ions may cooperate in the stabilization of intrinsically unstable amorphous calcium carbonate and in the formation of complex ACC/calcite tissues in vivo.     

Preparation of N(G)-substituted L-arginine analogues suitable for solid phase peptide synthesis

A high-yielding and concise preparation of N(G)-substituted L-arginine analogues, suitably protected for use in solid phase peptide synthesis, is reported. The synthesis of each analogue employed an activated thiourea intermediate that was converted under mild conditions to the desired L-arginine analogue (10 examples, each in near quantitative yield). Subsequent allyl group removal provided each analogue in a form ideally suited for use in solid phase peptide synthesis.     

Synthesis of novel KDR kinase inhibitors through catalytic reductive cyclization of o-nitrobenzylcarbonyl compounds

An efficient synthesis of o-nitrobenzylcarbonyl compounds is demonstrated through the Swern-type oxidation of readily accessible phenethanol analogues. Reductive cyclization of o-nitrobenzylcarbonyl 3 using catalytic Raney nickel gives 1H-indol-2-yl-1H-quinoline 2 in 95% yield. Hydrolysis of 2 affords the KDR kinase inhibitor 1 in quantitative yield. The examination of the reductive cyclization reaction and optimization of conditions is described.     

Microwave-assisted allylation of acetals with allyltrimethylsilane in the presence of CuBr

We describe the first synthesis of homoallyl ethers from acetals and allyltrimethylsilane using microwave heating and CuBr as a promoter. This method works best for aromatic acetals, giving the corresponding homoallyl ethers in good to quantitative yield.     

Asymmetric synthesis of homochiral dibenzylbutyrolactone lignans by conjugate addition to a chiral butenolide

Addition of sulphur stabilised carbanions to a chiral non-racemic butenolide followed by reaction with an aromatic aldehyde affords a short synthesis of homochiral dibenzylbutyrolactone derivatives. Desulphurisation of the first formed adducts proceeds in almost quantitative yield to afford the parent lignan.     

猪肝酯酶在不对称合成中的应用

猪肝酯酸PLE(Pig Liver Esterase)对双酯具有特殊的不对称水解性,而且可获得高产率和高光学纯的不对称水解产物。本文简要介绍PLE作为一种有效的酶催化剂,在温和的条件下,对双酯的不对称水解反应和在不对称合成中应用的近况。     

Highly enantioselective quinoline synthesis via ene-type cyclization of 1,7-enynes catalyzed by a cationic BINAP-palladium(II) complex

The first highly enantioselective synthesis of a six-membered ring quinoline catalyzed by a cationic BINAP-palladium(II) complex is shown to afford the quinoline products having a quaternary carbon center or a spiro-ring in quantitative yield and >99% ee.     

Facile synthesis of a "ready to use" precursor of porphobilinogen and its amino Acid derivatives

A practical synthesis of porphobilinogen based on the biosynthetic mechanism is described. The crossed Mukayiama aldol reaction is the key step creating the central carbon-carbon bond between the two protected forms of 5-aminolevulinic acids. The optimized sequence gives a crystalline, storable precursor, which can be transformed in high yield into porphobilinogen and bioconjugates thereof. The enzymatic hydrolysis of the precursor produces porphobilinogen in quantitative yield.     

Insight into the molecular mechanism of yeast acetyl-coenzyme A carboxylase mutants F510I,N485G,I69E,E477R,and K73R resistant to soraphen A

Acetyl-coenzyme A carboxylases (ACCs) is the first committed enzyme of fatty acid synthesis pathway. The inhibition of ACC is thought to be beneficial not only for diseases related to metabolism, such as type-2 diabetes, but also for infectious disease like bacterial infection disease. Soraphen A, a potent allosteric inhibitor of BC domain of yeast ACC, exhibit lower binding affinities to several yeast ACC mutants and the corresponding drug resistance mechanisms are still unknown. We report here a theoretical study of binding of soraphen A to wild type and yeast ACC mutants (including F510I, N485G, I69E, E477R, and K73R) via molecular dynamic simulation and molecular mechanics/generalized Born surface area free energy calculations methods. The calculated binding free energies of soraphen A to yeast ACC mutants are weaker than to wild type, which is highly consistent with the experimental results. The mutant F510I weakens the binding affinity of soraphen A to yeast ACC mainly by decreasing the van der Waals contributions, while the weaker binding affinities of Soraphen A to other yeast ACC mutants including N485G, I69E, E477R, and K73R are largely attributed to the decreased net electrostatic (ΔE_ele?+?ΔG_GB) interactions. Our simulation results could provide important insights for the development of more potent ACC inhibitors.     

Machine learning modelling of chemical reaction characteristics: yesterday,today, tomorrow

The synthesis of the desired chemical compound is the main task of synthetic organic chemistry. The predictions of reaction conditions and some important quantitative characteristics of chemical reactions as yield and reaction rate can substantially help in the development of optimal synthetic routes and assessment of synthesis cost. Theoretical assessment of these parameters can be performed with the help of modern machine-learning approaches, which use available experimental data to develop predictive models called quantitative or qualitative structure–reactivity relationship (QSRR) modelling. In the article, we review the state-of-the-art in the QSRR area and give our opinion on emerging trends in this field.