A proton-driven amino acid pump: lipophilic primary ammonium cation—crown ether complex as a new type of anion-transport carrier

A lipophilic primary ammonium cation—crown ether complex was shown to mediate effectively active and passive transport of amino acid derivatives via proton/amino acid anion cotransport as well as anion/amino acid anion countertransport. It may offer a new chemical analog to amino group-containing carrier proteins and a prototype for an anion separation membrane.     

Total synthesis of (-)-stevastelin B

The total synthesis and an unambiguous structure confirmation of stevastelin B 1, a novel 15-membered cyclic depsipeptide, are described; the fatty acid moiety in 1, prepared stereoselectively from L-quebrachitol was converted into the amino carboxylic acid, whose macrolactamization by Shioiri's procedure effectively constructed the cyclic structure of 1.     

Acylation of Amino Acids with Furancarboxylic Acid Chlorides

Acylation of aromatic amino acids with furancarboxylic acid chlorides effectively proceeds in water-acetone medium at pH 8-9. Aliphatic amino acids are acylated at higher pH values, but under these conditions hydrolysis of acid chlorides becomes the main process. Acylation of chlorohydrates of methyl esters of aliphatic amino acids proceeds smoothly in chloroform in the presence of triethylamine. Alkaline hydrolysis of obtained products leads to N-acylated amino acids containing furan heteroring in the acyl radical.     

Interaction of water-soluble amino acid Schiff base complexes with bovine serum albumin: fluorescence and circular dichroism studies

Fluorescence spectroscopy in combination with circular dichroism (CD) spectroscopy were used to investigate the interaction of water-soluble amino acid Schiff base complexes, [Zn(L1,2)(phen)] where phen is 1,10-phenanthroline and H2L1,2 is amino acid Schiff base ligands, with bovine serum albumin (BSA) under the physiological conditions in phosphate buffer solution adjusted to pH 7.0. The quenching mechanism of fluorescence was suggested as static quenching according to the Stern-Volmer equation. Quenching constants were determined using the Stern-Volmer equation to provide a measure of the binding affinity between amino acid Schiff base complexes and BSA. The thermodynamic parameters DeltaG, DeltaH and DeltaS at different temperatures (298, 310 and 318K) were calculated. The results indicate that the hydrophobic and hydrogen bonding interactions play a major role in [Zn(L1)(phen)]-BSA association, whereas hydrophobic and electrostatic interactions participate a main role in [Zn(L2)(phen)]-BSA binding process. Binding studies concerning the number of binding sites and apparent binding constant Kb were performed by fluorescence quenching method. The distance R between the donor (BSA) and acceptor (amino acid Schiff base complexes) has been obtained utilizing fluorescence resonant energy transfer (FRET). Furthermore, CD spectra were used to investigate the structural changes of the BSA molecule with the addition of amino acid Schiff base complexes. The results indicate that the interaction of amino acid Schiff base complexes with BSA leads to changes in the secondary structure of the protein. Fractional contents of the secondary structure of BSA (f(alpha), f(beta), f(turn) and f(random)) were calculated with and without amino acid Schiff base complexes utilizing circular dichroism spectroscopy. Our results clarified that amino acid Schiff base complexes could bind to BSA and be effectively transported and eliminated in the body, which could be a useful guideline for further drug design.     

胆汁酸为载体的肝靶向一氧化氮释放药物的设计与合成

新型肝靶向一氧化氮释放药物对许多肝脏疾病具有较好的治疗作用. 以胆酸和熊去氧胆酸作为药物的载体, 以氨基酸作为联接子, 以氨基酸的α羧基模拟胆酸或熊去氧胆酸分子24位羧基的负电性, 最大限度地保持胆酸或熊去氧胆酸的结构特征, 通过酰胺键将载体与一氧化氮供体硝酸酯偶联, 设计并合成了一系列新型肝靶向一氧化氮释放偶合物, 其结构经元素分析, IR, 1H NMR和MS光谱分析确证. 利用四氯化碳及对乙酰氨基酚所致小鼠急性肝损伤模型研究化合物对小鼠急性肝损伤的修复作用.     

A New Methodology for Synthesis of 1,2-Epoxy Alkane with the Linear Aliphatic Olefins in Presence of Molecular Oxygen

The linear aliphatic olefins, such as 1-octene, 1-decene, 1-dodecene and 1-tetradecene, were effectively epoxidized with molecular oxygen catalyzed by the amino acid Schiffbase manganese complex (Sal-Phe-Mn). The products of the reaction was 1, 2-epoxy alkane     

Site-specific incorporation of photo-cross-linker and bioorthogonal amino acids into enteric bacterial pathogens

Enteric bacterial pathogens are known to effectively pass through the extremely acidic mammalian stomachs and cause infections in the small and/or large intestine of human hosts. However, their acid-survival strategy and pathogenesis mechanisms remain elusive, largely due to the lack of tools to directly monitor and manipulate essential components (e.g., defense proteins or invasive toxins) participating in these processes. Herein, we have extended the pyrrolysine-based genetic code expansion strategy for encoding unnatural amino acids in enteric bacterial species, including enteropathogenic Escherichia coli , Shigella , and Salmonella . Using this system, a photo-cross-linking amino acid was incorporated into a Shigella acid chaperone HdeA (shHdeA), which allowed the identification of a comprehensive list of in vivo client proteins that are protected by shHdeA upon acid stress. To further demonstrate the application of our strategy, an azide-bearing amino acid was introduced into a Shigella type 3 secretion effector, OspF, without interruption of its secretion efficiency. This site-specifically installed azide handle allowed the facile detection of OspF's secretion in bacterial extracellular space. Taken together, these bioorthogonal functionalities we incorporated into enteric pathogens were shown to facilitate the investigation of unique and important proteins involved in the pathogenesis and stress-defense mechanisms of pathogenic bacteria that remain exceedingly difficult to study using conventional methodologies.     

Aluminum-catalyzed asymmetric alkylations of pyridyl-substituted alkynyl ketones with dialkylzinc reagents

Alkylations of pyridyl-substituted ynones with Et2Zn and Me2Zn, promoted by amino acid-based chiral ligands in the presence of Al-based alkoxides, afford tertiary propargyl alcohols efficiently in 57% to >98% ee. Two easily accessible chiral ligands are identified as optimal for reactions of the two dialkylzinc reagents. Catalytic alkylations with Et2Zn require a chiral ligand carrying two amino acid moieties (valine and phenylalanine) along with a p-trifluoromethylphenylamide C-terminus. In contrast, reactions with Me2Zn are most effectively promoted in the presence of a chiral ligand containing a single amino acid (benzyl cysteine), capped by an n-butylamide. Enantiomerically enriched tertiary alcohols bearing a pyridyl and an alkyne substituent can be functionalized in a variety of manners to furnish a wide range of difficult-to-access acyclic and heterocyclic structures; two noteworthy examples are Cu-catalyzed protocols for conversion of tertiary propargyl alcohols to enantiomerically enriched tetrasubstituted allenes and bicyclic amides that bear an N-substituted quaternary carbon stereogenic center. Mechanistic models that account for the trends and enantioselectivity levels are provided.     

Enantiomeric separation of amino acids derivatized with 7-fluoro-4-nitrobenzoxadiazole by capillary liquid chromatography/tandem mass spectrometry

Pre-column derivatization allowed stacking amino acid enantiomers on C18 reversed-phase micro extraction columns, thus facilitating sample loading in capillary HPLC/tandem mass spectrometry. Two tagging reagents, i.e. 7-fluoro-4-nitrobenzoxadiazole (NBD-F) and 1-fluoro-2,4-dinitrobenzene (DNB-F) were evaluated. Both of them reacted readily with amino acids at an elevated temperature, resulting in derivatives that were effectively stacked and suitable for a sensitive MS/MS detection as well. Separation of the tagged enantiomers on a teicoplanin chiral stationary phase (CSP) with mobile phases compatible with MS detection was investigated. NBD-amino acid enantiomers (12 pairs) tested were all base-line resolved. However, the efforts to separate DNB-F tagged amino acid enantiomers on this CSP were not successful. Separation conditions including pH, organic modifiers, and column dimension were studied. All the NBD-amino acids studied could be sensitively detected by MS/MS detection set in the negative ion mode, but only a few including NBD-Asp, BND-Glu, NBD-Ser, and NBD-Thr were detected in the positive ion mode. Thus, the selectivity for enantiomeric determination of excitatory amino acids (e.g. Asp and Glu) was further improved by choosing MS/MS detection in the positive ion mode.     

SchiffBase Dinuclear Complex Catalyst for Oxidation of Cyclohexene with Molecular Oxygen

In the past decades, the oxidation of hydrocarbons by transition metal complexes has been studied extensively. The current progress of the research on synthetic quasiporphyrin catalysts has led to the development of several systems that are able to reproduce the hene-enzyme mediated oxygenation and oxidation reactions[1]. In our group[2,51, the mononuclear complexes of amino acid Schiff base have been synthesized and their catalytic oxidation has been studied. In this paper, two dinuclear complexes, such as Salicylidence-β-alanine-Co(II)-Cu(II) and Salicylidence-β-alanine-Co(II)Mn(II), were prepared with amino acid Schiff bases and metal ions. In the presence of these dinuclear complexes, cyclohexene was effectively oxidized under 1 atm of molecular oxygen without any coreductants. The allylic hydroperoxide was obtained as an important product, which suggested a clear allylic pathway of oxidation of cyclohexene.     

An efficient synthesis of 2-amino-3-cyano-2-pyrrolin-4-ones, via the corresponding open chain tautomers (aminoacetylmalononitriles)

Malononitrile has been found to be acylated effectively using N-protected glycines by simultaneous activation of an amino acid carbonyl group and a malononitrile methylene group using carbonyl diimidazole (CDI). The corresponding aminoacetonitriles were isolated as enols and/or as their tautomeric forms, 2-amino-3-cyano-2-pyrrolin-4-ones.     

Creation of a productive, highly enantioselective nitrilase through gene site saturation mutagenesis (GSSM)

Gene site saturation mutagenesis (GSSM) technology is applied for the directed evolution of a nitrilase. The nitrilase effectively catalyzes the desymmetrization of the prochiral substrate 3-hydroxyglutaronitrile to afford (R)-4-cyano-3-hydroxybutyric acid, a precursor to the valuable cholesterol-lowering drug Lipitor. The discovered wild-type enzyme effectively performs the reaction at the industrially relevant 3 M substrate concentration but affords a product enantiomeric excess of only 87.6% ee. Through GSSM, a mutagenesis technique that effects the combinatorial saturation of each amino acid in the protein to each of the other 19 amino acids, combined with a novel high-throughput mass spectroscopy assay, a number of improved variants were identified, the best of which is the Ala190His mutant that yields product enantiomeric excess of 98.5% at 3 M substrate loading and a volumetric productivity of 619 g L-1 d-1.     

pH and reduction sensitive bio-based polyamides derived from renewable dicarboxylic acid monomers and cystine amino acid

New reduction biodegradable and pH-sensitive linear nonpeptidic polyamides were synthesized by interfacial polycondensation of diamines and cystine amino acid with dicarbonyl dichlorides derived from renewable dicarboxylic acids. The polymer degradability by glutathione is enhanced by the introduction of disulfide linkages, and the response to pH change is enhanced by introducing pendant carboxylic acid functions. The results of pH sensitivity tests indicated that protonation–deprotonation of the carboxylic acid group at about pH of 4.1 with cation exchange capacity 4.5?meq?g^?1 and the disulfide bonds in polyamides were effectively cleaved.     

Tetrafluoroboric acid, a useful deprotecting reagent in peptide synthesis

We have found that tetrafluoroboric acid (HBF4) in trifluoroacetic acid (TFA) in the presence of thioanisole cleaves various protecting groups currently used in peptide synthesis. HBF4 in TFA cleaves an amino acid amide from 4-methylbenzhydrylamine resin more effectively than trifluoromethanesulfonic acid in TFA. Lamprey gonadotropin-releasing hormone (a 10-residue peptide amide) was synthesized using 1 M HBF4-thioanisole in TFA by both solution-phase and solid-phase methods.     

Supersecondary structure prediction using Chou's pseudo amino acid composition

Supersecondary structures (SSSs) are the building blocks of protein 3D structures. Accurate prediction of SSSs can be one important step toward building a tertiary structure from the specified secondary structure. How to improve the accuracy of prediction of SSSs by effectively incorporating the sequence order effects is an important and challenging problem. Based on a different form of Chou's pseudo amino acid composition, a novel approach for feature representation of SSSs is proposed. Amino acid basic compositions, dipeptide components, and amino acid composition distribution are incorporated to represent the compositional features of proteins. Each supersecondary structural motif is characterized as a vector of 36 dimensions. In addition, we propose a novel prediction system by using SVM and IDQD algorithm as classifiers. Our method is trained and tested on ArchDB40 dataset containing 3088 proteins. The highest overall accuracy for the training dataset and the independent testing dataset are 77.7 and 69.4%, respectively. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011     

Synthese de polymeres a proprietes pharmacologiques: Introduction de sequence peptidique en chaine laterale

Amino acids have been introduced on to the side-chains of a polymer. Two schemes have been studied: the first involves the synthesis of a monomer containing the amino acid drug moiety and subsequent polymerization; the second depends upon chemical modification of a polymer with the amino acid drug moiety. The drugs used in this study are steroids (cholesterol testosterone). The amino acid moieties introduced on to the side-chains are L-lysine. The preparation of the drug containing the amino acid is done by reacting the chloroformate derivative of the steroid with the amine function of the lysine subsequent to the blocking of the amino acid as a copper complex. The methacrylic monomer is obtained by reacting methacryloyl chloride with the drug amino acid moiety. The polymers were characterized by i.r., NMR (¹H and ¹³C) and GPC. Pharmacological tests are being performed to observe the effect due to the hydrolysis of the drug or the amino acid drug in living organisms.     

Synthesis and specific biodegradation of novel polyesteramides containing amino acid residues

Novel polyesteramides were synthesized from p‐nitrophenyl esters of sebacic or adipic acids and diamines containing α‐amino acid ester groups. The optimal polymerization condition was 60 °C in N,N‐dimethylformamide. The structures of these polymers were confirmed by IR and NMR. The number‐average molecular weights of these polyesteramides ranged from 2280 to 23,600 (except for the polymers containing glycine residues), depending on the nature of the amino acid used. The biodegradability of the polyesteramides was investigated by in vitro hydrolysis with proteases and a lipase as catalysts in borate buffer solutions. The results indicated that the polymers containing L ‐phenylalanine were hydrolyzed most effectively by α‐chymotrypsin, subtilisin Carlsberg, and subtilisin BPN′. The polyesteramides containing other amino acid residues also underwent hydrolysis to different extents, reflecting the substrate specificity of the proteases. Lipase had almost no effect on the hydrolytic degradation of these polyesteramides. The polymers containing glycine residues were hardly decomposed by any of the enzymes used. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1318–1328, 2001     

Application of polyelectrolyte complexes as novel pseudo-stationary phases in MEKC

Polyacrylic acid (PAA) and polymethacrylic acid (PMAA) with carboxyl groups partially blocked by dodecyltrimethylammonium bromide (DTAB) and tetrabutylammonium bromide (TBAB) were tested as new pseudo-stationary phases in micellar electrokinetic chromatography (MEKC). The separation of was examined using PAA and PMAA. Excellent resolution of the substituted phenols and derivatized amino acids was demonstrated using additives of PAA-DTAB polyelectrolyte complex in the running phosphate buffer. It was found that the capacity factors were proportional to the concentration of the complex PAA/DTAB. Critical micelle concentration was effectively zero. It was found that the migration times and efficiency of separation of phenols and derivatives of amino acids depended on the type of polymers and alkyltrimethylammonium salts used.     

QUALITATIVE UNTERSUCHUNGEN ZUR PHOTOLYSE EINFACHER DIPEPTIDE

Abstract— The photolyses of eight chromatographical pure dipeptides were studied. They were irradiated by the total spectrum of a high pressure mercury lamp. The resulting products were separated by electrophoresis and identified by paper chromatography. It was found that the carbonyl group of the N-terminal amino acid was eliminated in a dipeptide; an amine and an amino acid were found as primary products. This reaction is accompanied by a second reaction, the decarboxylation of the C-terminal amino acid. Possible mechanisms of these reactions are discussed.     

生物芯片表面氨基硅烷化修饰

本文以无水乙醇为溶剂、3-氨基丙基三乙氧基硅烷(APTES)为修饰试剂、醋酸为催化剂,采用浸泡法,对生物芯片玻璃基片表面进行了氨基硅烷化修饰,得到了一种基片表面氨基修饰的制备方法。着重研究了制备过程中浸泡时间、APTES的浓度、酸处理的时间和羟基化的时间对基片噪声的影响。通过对以上工艺参数的逐步优化,基片噪声逐渐减小,最小值为193。通过对最佳修饰条件下得到的基片进行DNA点样和杂交测试可知,此方法制备得到的基片能够有效结合基因探针,且杂交清洗后信号强度可达17000以上,信噪比在110以上。由X射线光电子能谱分析可知,采用浸泡法可以获得表面氨基修饰的生物芯片基片。最后通过对修饰前后基片透过率的比较可知,修饰过程对透过率影响很小,且透过率在91%以上,从而保证了后续杂交信号与微阵列噪声检测的准确性。