The first total synthesis of sequosempervirin A through an orthoester Claisen rearrangement—ring closing metathesis sequence

The first total synthesis of sequosempervirin A, a norlignan with a unique spirocyclic structure has been accomplished using an orthoester Claisen rearrangement—ring closing metathesis sequence.     

Sequosempervirin A, a novel spirocyclic compound from Sequoia sempervirens

A novel spirocyclic compound (4R)-4-(4-hydroxy-benzyl) spiro [4,5] dec-1-en-8-ol (sequosempervirin A) was isolated from the branches and leaves of Sequoia sempervirens. Its structure and relative stereochemistry were mainly determined by MS, 2D NMR and X-ray means, which is the first naturally occurring norlignan containing one spirocycle with C6 (cyclohexane)-C2-C3-C6 skeleton.     

Structural study of the solutions of acidic polysaccharides

A study was made of the effect of NaCl on the counterion activity coefficient in solutions of acidic polysaccharide sodium salts. The counterion activity coefficient in the sodium salt solutions of polyuronic acids was shown to be determined by electrostatic interactions only. Consequently it can be supposed that the counterion-polyion interaction is also of an electrostatic nature. A method was proposed for determining the distribution patterns of nonionogenic groups along the polyelectrolyte chain. The structural transition ofχ-carrageenan, depending on NaCl concentration, was found to be accompanied by a nonelectrostatic binding of sodium ions by the polysaccharide.     

Mammalian Alkaloids: O-methylation of (S)- and (R)-dideoxynorlaudanosoline-1-carboxylic acid by catechol O-methyltransferase and identification of a yellow pigment obtained at physiological pH

O-Methylation of optically active 3′,4′-dideoxynorlaudanosoline-l-carboxylic acids 1 with O-methyltransferase in vitro afforded almost exclusively the 7-O-methylated acids 3 . A similar result was obtained with the yellow quinonemethide 4A obtained from 1 at neutral or slightly alkaline pH by oxidative decarboxylation and affording the 3,4-dihydroisoquinoline 15 on methylation with catechol O-methyltransferase (COMT). The structure of quinonemethide 4A was determined on the basis of spectral data, by its conversion into isoquinolines of established structure, and by synthesis. Quinonemethide 4A was found to be a weak inhibitor of monoamine oxidase A (MAO A) but not a substrate. Nonenzymatic oxidative decarboxylation of dopamine-derived tetrahydroisoquinoline-l-carboxylic acids to quinonemethides may be a major factor in biochemical experimentation and should be considered in the interpretation of data.     

Proposed Mechanism for Microbial Degradation of Polyacrylate

Abstract

A possible aerobic degradation mechanism for polyacrylate (PA) was examined with acrylic oligomer-utilizing bacteria (Microbacterium sp., Xanthomonas maltophilia, and Acinetobacter sp.), using a model compound (1,3,5-pentane tricarboxylic acid, PTCA). Acyl-coenzyme A synthetase activities were detected with dialyzed cell-free extracts of PTCA-utilizing bacteria toward PTCA, PA 500, and PA 1000. This result suggested that PA is activated by coenzyme A and metabolized via PA-coenzyme A. Metabolic products formed from PTCA were detected in culture filtrates and reaction mixtures of washed cells. Fraction A was detected as a main metabolite by high-performance liquid chromatography. A small amount of fraction B was concomitant with fraction A. Also, another fraction, C, was detected. These intermediate metabolites were characterized by LC-MS as 1,3,5-(1- or 2-pentene)tricarboxylic acid for fractions A and B and as 1,3,5-(2-oxopentane)tricarboxylic acid for fraction C. Fraction A was metabolized far faster than fraction B. Fraction B was thought to be an artifact formed from fraction A under alkaline conditions. Thus PTCA and also PA seemed to be metabolized by the mechanism similar to β-oxidation of fatty acids. The degradation of PTCA by washed cells was slower than that by growing cells and was inhibited by 5 mM NaN₃. This suggests that the metabolism is linked to a respiratory chain of bacteria.     

A high-copy-number plasmid capable of replication in thermophilic cyanobacteria

A 2.5 kb high-copy-number plasmid, pM A4 in thermophilic cyanobacterium Synechococcus sp. M A4 was isolated and characterized to develop a genetic engineering system for thermophilic cyanobacteria. The copy number of pM A4 was determined to be by densitometry about 350/cell. The pM A4 may be a type of rolling-circle plasmid, because a possible rep gene encoding 34 k D-protein and a consensus sequence of a double-stranded origin nick site of rolling circle plasmids were found in the pM A4 sequence. The pM A4 was electro-introduced into another thermophile, Synechococcus sp. MA 19, which is the strongest poly-β-hydroxybutyrate (PHB) accumulator in photoau totrophic organisms. The pM A4 was incorporated and retained in MA 19. These results indicate that pM A4 could be developed as a useful vector for thermophilic cyanobacteria.     

One-step synthesis of amino-dextran-protected gold and silver nanoparticles and its application in biosensors

A sensitive method for the detection of the lectin protein concanavalin A (Con A) was developed using amino-dextran (AD)-protected gold (AD-Au) and silver nanoparticles (AD-Ag) as sensitive optical probes. The AD-Au and AD-Ag nanoparticles were synthesized by directly applying amino-dextran as a reductive and protective reagent. The size of the nanoparticles could be altered by changing the molar ratio of AD to the metal salt. The amino-dextran bound to Con A by forming a 4:1 Au-Con A complex at neutral pH, and the nanoparticles were induced to aggregate by Con A. The absorption intensity of the nanoparticles decreased linearly with as the Con A concentration was increased from 3.85×10^–8 to 6.15×10^–7 M. The Au-Con A complex was dissociated by the disaccharide isomaltose, which has a higher affinities for Con A than Au; this competitive strategy could also be used to detect similar types of saccharides.     

High-performance affinity chromatography of messenger RNA.

A 50-mer of thymidylic acid, (dT)50, was coupled to silica inside prepacked columns using the N-hydroxysuccinimide chemistry. The resulting (dT)50-silica columns were used to resolve oligomers of adenylic acid, (dA)19-24, and to separate poly(A) mRNA (messenger RNA) from Saccharomyces. Oligomers which differed in length by a single nucleotide base were readily resolved. Using either (dT)50- or (dT)18-silica, poly(A) mRNA could be purified in as little as 8 min. The poly(A) mRNA isolated appeared to be full length and could be used directly for T4 RNA ligase and RNAse A and T1 enzymatic reactions. The (dT)50-silica column was used to fractionate total poly(A) mRNA by tail length. While the separation was primarily due to poly(A) tail length, most fractions appeared to contain multiple tail lengths. Whether this represents an intrinsic feature of the RNA or a limitation of the method is discussed. These studies show that polynucleotides in the kilobase size range can be separated rapidly and with good resolution on DNA-silica.     

Identification of Polyethylene by Differential Scanning Calorimetry: Application to forensic science

A forensic sample consisting of melt-recrystallized polymers that was recovered from the scene of a fire in a factory was identified by differential scanning calorimetry. The factory commonly used two kinds of film sheets, A and B, made by different manufacturers. It was necessary to decide whether the forensic sample related to material A or B. The forensic sample and reference samples of materials A and B were subjected to infrared spectroscopy and pyrolysis gas chromatograph mass spectrometry measurements, which revealed their polyethylene nature. The thermal behaviour of the samples was examined by differential scanning calorimetry (DSC) and they were found to be blends of two kinds of polyethylenes, low-density polyethylene and linear low-density polyethylene. The samples could be identified and distinguished from each other via the DSC measurements.This revised version was published online in November 2005 with corrections to the Cover Date.     

Reversed-phase high-performance liquid chromatography of human haemoglobin chains

A reversed-phase high-performance liquid chromatographic method for the separation of human haemoglobin chains has been devised. Using a LiChrospher 100 CH-8/2 column and a ternary eluent (acetonitrile-methanol-0.155 M NaCl, pH 2.7) improved resolution was achieved between (delta beta) Lepore, beta A, beta S, alpha, G gamma and A gamma chains within a 60-min linear gradient. The A gamma T chain can also be separated by increasing the gradient time and decreasing the flow-rate. Silanophilic interactions play an important role in the retention mechanism, and NaCl addition was necessary in order to suppress adsorption on free silanols. Increasing the methanol concentration to 10% caused a slight increase in chain retention, probably owing to solvation of the stationary phase. The recovery was 82% and the reproducibility of retention times was as good as +/- 1.5%. Quantitation of chains is likely to be possible by peak area measurement. Owing to its sensitivity, the proposed method may be useful in the diagnosis of haemoglobinopathies and in the study of haemoglobin variants.     

WYE‐120318, a ring contraction product of methylnaltrexone,and structure revision of coniothyrione

A contracted ring degradation product, WYE‐120318 (compound 2), was discovered during the development phase for methylnaltrexone bromide (compound 1) drug substance. The compound was isolated by high‐performance liquid chromatography fractionation, and its structure was determined by spectroscopic data analyses. WYE‐120318 is formed from methylnaltrexone through a benzyl‐benzilic acid type rearrangement reaction to yield an α‐hydroxy‐cyclopentanecarboxylic acid substructure. The proposed structure and the formation mechanism are confirmed by the synthesis of WYE‐120318 from methylnaltrexone (compound 1). A similar benzyl‐benzilic acid type rearrangement reaction can be envisioned as the biological origin of remisporine A (compound 3), a naturally occurring cyclopentadienyl compound that autocatalytically dimerizes to remisporine B (compound 4). The structure of remisporine A was deduced from its dimer 4. Coniothyione (compound 5) can be considered as the first example of a stable natural product bearing the remisporine A skeleton. However, the regiochemistry of the chlorosubstitution in the coniothyrione structure needs to be revised to compound 6 on the basis of the nuclear magnetic resonance data and biogenesis analysis. Copyright © 2012 John Wiley & Sons, Ltd.     

人类腺苷受体A3亚型拮抗剂的构效关系分析

构建人类腺苷受体A3亚型药效团模型和三维蛋白结构模型用于作用模式研究.以18个来源于文献具有腺苷受体A3亚型拮抗活性的化合物作为训练集,使用HypoGen方法构建药效团模型.通过同源模建和分子动力学模拟构建了人类腺苷受体A3亚型的三维蛋白模型,并利用PROCHECK方法评估该模型的合理性,对所得的结构使用分子对接程序进行作用模式分析,药效团模型和同源模建结果相互匹配较好.使用新药效团模型对MDL药物数据库(MDDR)中包含的约120000个化合物进行虚拟筛选,得到了8个候选化合物,用于进一步的生物学评价和活性测定.本工作对于人类腺苷受体A3亚型拮抗剂的设计和抗哮喘药物的研发具有一定的理论指导和应用价值.     

Surface adsorption of zwitterionic surfactants: n-alkyl phosphocholines characterised by surface tensiometry and neutron reflection

The surface adsorption of n-dodecyl phosphocholine (C12PC) has been characterised by a combined measurement of surface tension and neutron reflectivity. The critical micellar concentration (CMC) was found to be 0.91 mM at 25 degrees C in pure water. At the CMC, the limiting area per molecule (A(cmc)) was found to be 52+/-3 A2 and the surface tension (gamma(cmc)) to be ca. 40.0+/-0.5 mN/m. The parallel study of chain isomer n-hexadecyl phosphocholine (C16PC) showed a decrease of the CMC to 0.012 mM and a drop of gamma(cmc) to 38.1+/-0.5 mN/m. However, A(cmc) for C16PC was found to be 54+/-3 A2, showing that increase in alkyl chain length by four methylene groups has little effect on A(cmc). The almost constant A(cmc) suggested that the limiting area per molecule was determined by the bulky PC head group. It was further found that the surface tension and related key physical parameters did not vary much with temperature, salt addition, solution pH or any combination of these, thus showing that surface adsorption and solution aggregation from PC surfactants is largely similar to the zwitterionic betaine surfactants and is distinctly different from ionic and non-ionic surfactants. The thickness of the adsorbed monolayers measured from both dC12hPC and dC16hPC was found to be 20-22 A at the CMC from neutron reflectivity. Neither A(cmc) nor layer thickness varied with alkyl chain length, indicating that as the alkyl chain length became longer it was further tilted away from the surface normal direction and the layer packing density increased. It was also observed that the thickness of the layer varied little with surfactant concentration, indicating that the average conformational orientation of the alkyl chain remained unchanged against varying surface coverage.     

Adsorption-desorption isotherm hysteresis of beta-lactoglobulin A with a weakly hydrophobic surface.

Adsorption-desorption isotherms of bovine beta-lactoglobulin A (beta-lact A) on a weakly hydrophobic stationary phase (C1-ether) were measured by frontal analysis. The adsorption isotherms obtained at different pH were found to be dramatically different in shape, column capacity and desorption reversibility. At pH 4.5, an S-shaped adsorption isotherm was observed whereas at pH 6.0 a Langmuir isotherm was found. In addition, the desorption isotherm at pH 6.0 was found to overlap with the adsorption isotherm, and the adsorption-desorption process of beta-lact A under this condition could be characterized by a fully reversible Langmuir model. The desorption isotherm at pH 4.5, however, did not retrace the adsorption isotherm, resulting in hysteresis loops. A higher aggregate (tetramer) of beta-lact A is shown to be in an equilibrium with the beta-lact A protomer (dimer) at pH 4.5 whereas the dimer alone is predominant at pH 6.0. It is further shown that changes in the absorption coefficient between the adsorption and the desorption cycles for the tetramer at pH 4.5 can account for the hysteresis. The results demonstrate that pH can be a sensitive parameter in protein adsorption isotherm behavior and ultimately the behavior of species in preparative-scale chromatography.     

A novel peptide from Apis mellifera and solid-phase synthesis of its analogue

A novel peptide designated secapin-1,was purified and characterized from Apis mellifera.The molecular weight of 25 amino acid peptide secapin-1 was found to be 2821.5625 Da by ESI-FTICR-MS.It showed high identity to secapin.The sequence of secapin-1 was determined to be YIINVPPRCPPGSKFVKNKCRVIVP by automatic Edman degradation.A disulfide bond was formed between Cys⁹ and Cys²⁰ residues.In addition,an analogue of secapin-1 was synthesized by solid phase peptide synthesis method.The synthesis product was successfully purified and identified to homogeneity by using a combination of SEC,IEC,and RP-HPLC techniques.     

Synthesis of 2,6-disubstituted piperazines by a diastereoselective palladium-catalyzed hydroamination reaction

A highly diastereoselective intramolecular hydroamination is the key step in a modular synthesis of 2,6-disubstituted piperazines. The requisite hydroamination substrates were prepared in excellent yields by nucleophilic displacement of cyclic sulfamidates derived from amino acids. A variety of alkyl and aryl substituents at the 2-position were tolerated. The stereochemistry of the piperazines was determined to be trans by X-ray crystallography, which also showed the preferred conformation of the 2,6-disubstituted piperazine to be a twist-boat due to A(1,3) strain.     

尿中有机酸的毛细管气相色谱—质谱轮廓分析—用于苯丙酮尿症的诊断

应用毛细管气相色谱-质谱轮廓分析方法,测定了33例2.5～4.5岁健康儿童尿中有机酸种类及含量和8例拟诊为苯丙酮尿症儿童尿中的有机酸,结果表明患儿尿样中苯丙酮酸、苯乙酸、邻羟基苯乙酸、对羟基苯乙酸高于正常值10～470倍。为苯丙酮尿症的确诊提供了可靠方法。     

Sugar-sensitive thin films composed of concanavalin A and sugar-bearing polymers.

Layered thin films composed of concanavalin A (Con A) and sugar-bearing polymers were prepared by a layer-by-layer deposition of Con A and the polymer on a solid surface. The sugar-induced disintegration was studied. Con A-polymer layered films could be successfully prepared using a maltose-bearing polymer (PV-MA), while melibiose- and glucose-bearing polymers (PV-MEA and PV-G) did not afford a layered film, due to a weak affinity of PV-MEA and PV-G to Con A. The Con A/PV-MA layered film was stable in pH 7 and 8 solutions, while in a pH 6 medium the film was slightly unstable. The Con A/PV-MA film was disintegrated upon the addition of sugars in solution owing to a preferential binding of the sugars to the binding site of Con A in the film. The disintegration rate was dependent on the type of sugar and its concentration. The Con A/PV-MA film was disintegrated rapidly upon the addition of methyl alpha-D-mannopyranoside, while the rate was slower upon the addition of the same concentration of D-mannose, D-glucose and methyl alpha-D-glucopyranoside. The present system may be useful for constructing sensitive devices that can release a drug or other functional molecules in response to sugars.     

Potentiometric detection of halides and pseudohalides in anion chromatography

A small piece of silver wire, coated with an insoluble silver salt, can be used as a selective potentiometric detector for halides in ion chromatography. Several coated electrodes were examined by electron microscopy and their response to various anions evaluated in a flow-injection system. A silver/silver chloride was found to be a selective and reproducible detector for chloride, bromide, iodide, thiocyanate and thiosulfate separated by ion chromatography. Calibration curves were non-linear and had slopes ranging from 40 to 60 mV per concentration decade in the range 0.1–2 mM. A working range of 0.05–2 mM was used. This electrode is also satisfactory when gradient elution is used in ion chromatography.     

Absolute structure of prunustatin A, a novel GRP78 molecular chaperone down-regulator

In the course of our screening program for regulators of a molecular chaperone GRP78 expression, we isolated a novel inhibitor of GRP78 expression, designated as prunustatin A, from Streptomyces violaceoniger 4521-SVS3. The planar structure of prunustatin A was determined to be an oxidized type of the neoantimycin family. Its absolute stereochemistry was established to be 2R, 4S, 6S, 7R, 9S, and 29S by analyzing chemically degraded components obtained from the derivative of prunustatin A.