A Biocatalytic Cascade for Versatile One‐Pot Modification of mRNA Starting from Methionine Analogues

Methyltransferases have proven useful to install functional groups site‐specifically in different classes of biomolecules when analogues of their cosubstrate S‐adenosyl‐l ‐methionine (AdoMet) are available. Methyltransferases have been used to address different classes of RNA molecules selectively and site‐specifically, which is indispensable for biophysical and mechanistic studies as well as labeling in the complex cellular environment. However, the AdoMet analogues are not cell‐permeable, thus preventing implementation of this strategy in cells. We present a two‐step enzymatic cascade for site‐specific mRNA modification starting from stable methionine analogues. Our approach combines the enzymatic synthesis of AdoMet with modification of the 5′ cap by a specific RNA methyltransferase in one pot. We demonstrate that a substrate panel including alkene, alkyne, and azido functionalities can be used and further derivatized in different types of click reactions.     

Effects of Active‐Site Modification and Quaternary Structure on the Regioselectivity of Catechol‐O‐Methyltransferase

Catechol‐O‐methyltransferase (COMT), an important therapeutic target in the treatment of Parkinson's disease, is also being developed for biocatalytic processes, including vanillin production, although lack of regioselectivity has precluded its more widespread application. By using structural and mechanistic information, regiocomplementary COMT variants were engineered that deliver either meta‐ or para‐methylated catechols. X‐ray crystallography further revealed how the active‐site residues and quaternary structure govern regioselectivity. Finally, analogues of AdoMet are accepted by the regiocomplementary COMT mutants and can be used to prepare alkylated catechols, including ethyl vanillin.     

Studies on the Synthesis of Di‐ and Trisaccharide Analogues of Moenomycin A. Modifications in Unit E and in the Lipid Part

Routes allowing the synthesis of moenomycin analogues with one modified sugar component and with new lipid parts were developed (see 10c, 12c, 16b , and 20b in Schemes 2–4). It is anticipated that such analogues will be useful for studying the mode of action of the moenomycin‐type transglycosylase inhibitors in detail and for preparing analogues with improved pharmacokinetic properties.     

Methyltransferase‐Directed Labeling of Biomolecules and its Applications

Methyltransferases (MTases) form a large family of enzymes that methylate a diverse set of targets, ranging from the three major biopolymers to small molecules. Most of these MTases use the cofactor S‐adenosyl‐l ‐Methionine (AdoMet) as a methyl source. In recent years, there have been significant efforts toward the development of AdoMet analogues with the aim of transferring moieties other than simple methyl groups. Two major classes of AdoMet analogues currently exist: doubly‐activated molecules and aziridine based molecules, each of which employs a different approach to achieve transalkylation rather than transmethylation. In this review, we discuss the various strategies for labelling and functionalizing biomolecules using AdoMet‐dependent MTases and AdoMet analogues. We cover the synthetic routes to AdoMet analogues, their stability in biological environments and their application in transalkylation reactions. Finally, some perspectives are presented for the potential use of AdoMet analogues in biology research, (epi)genetics and nanotechnology.     

Bioelectrochemical detection of L-lactate respiration using genetically modified Hansenula polymorpha yeast cells overexpressing flavocytochrome b2

In general, L-lactate respiration is difficult to detect in living yeast cells due to the small activity of L-lactate oxidizing enzymes within the mitochondria. Genetically modified cells of methylotrophic yeast Hansenula polymorpha overproducing L-lactate:cytochrome c-oxidoreductase (EC 1.1.2.3, also known as flavocytochrome b₂, FC b₂) were physically immobilized by means of a dialysis membrane onto various types of electrode materials in order to investigate the possibility of electrochemically detecting L-lactate respiration. It could be shown that in the case of genetically modified Hansenula polymorpha cells in contrast to cells from the parental strain, enhanced L-lactate-dependent respiration could be detected. Due to overproduction of FC b₂ the O₂ reduction current is decreased upon addition of L-lactate to the electrolyte solution. The electron transfer pathway in the L-lactate-dependent respiration process involves a cascade over three redox proteins, FC b₂, cytochrome c and Complex-IV, starting with L-lactate oxidation and ending with oxygen reduction. By means of selective inhibition of Complex IV with CN⁻, lactate respiration could be proven for causing the decrease in the O₂ reduction.     

手性化合物组合修饰剂对CdSe纳米晶荧光性能的影响及标记大肠杆菌的研究

以手性化合物L-青霉胺、D-青霉胺、L-半胱氨酸为单一修饰剂或组合成双修饰剂,合成不同修饰剂修饰的CdSe纳米晶。对最佳合成条件如配料比,反应pH值,回流温度,回流时间进行了优化,对CdSe纳米晶发光强度及稳定性进行了系统研究。结果发现双修饰剂修饰的纳米晶比单修饰剂修饰的纳米晶荧光强度高,稳定性好;双修饰剂中第二修饰剂的空间位阻小的修饰效果好;不同手性修饰剂之间能以稳定方式结合的修饰效果好。研究了CdSe纳米晶对生物大分子的识别,仅发现核酸对CdSe纳米晶有明显的作用,用CdSe纳米晶作为荧光探针对大肠杆菌进行标记。     

HY Zeolite Modified by Liquid Silane Deposition and Its Catalytic Activity in Selective tert-Butylation of Naphthalene

HY zeolites were modified by chemical liquid deposition with i-C₄H₉Si(OC₂H₅)₃, followed by hydrothermal treatment. The samples were characterized by X-ray diffraction, N₂ adsorption and pulse mass analysis to investigate the influence on framework structure, specific surface area, pore diameter and adsorption behaviors. The catalytic performances of HY zeolite and the modified samples in the alkylation of naphthalene with tert-butyl alcohol were also evaluated. The results showed the modification of HY zeolite did not change framework structure but increased specific surface area, decreased average pore diameter, and reduced the size of pore opening. Catalytic activity of the modified HY zeolite catalyst for tert-butylation of naphthalene was decreased compared with that of HY zeolite catalyst while shape-selectivity of 2,6-di-tert-butylnaphthalene (2,6-DTBN) was increased obviously, the highest 2,6-DTBN/2,7-DTBN ratio of 6.62 obtained.     

锶助剂对铂锡催化剂正丁烷脱氢催化性能的影响

负载型ＰｔＳｎ／Ａｌ２Ｏ３催化剂已广泛地应用于工业生产中［１］，人们正尝试着添加不同助剂以改变催化剂的反应性能。文献的工作主要集中在研究铂锡催化剂中添加助剂对载体表面酸性的调变作用。在烃类重整催化剂中，加入氟、氯等元素可增强载体的表面酸性［２］，提高...     

Reduction of the IgE-binding ability and maintenance of immunogenicity of gamma-irradiated Dermatophagoides farinae

House dust mites, Dermatophagoides farinae (DF) and Dermatophagoides pteronyssinus, are major allergens in the most common indoor allergen and are important risk factor for asthma. The modified antigen has been studied to treat allergic disorder. This study was carried out to measure possibility of modified allergen using gamma irradiation to treat allergy such as asthma. DF solutions (2 mg/ml) as target allergen were irradiated with Co-60 at 50 and 100 kGy. Conformational alternation of irradiated DF was observed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Levels of anti-irradiated DF mouse IgGs (sub-isotypes) against intact DF were measured similar to that of anti-intact DF IgGs. The binding abilities of house dust mite-allergic patients’ IgE were reduced depending on radiation dose, and irradiation could inhibit the binding ability of patients’ IgE more than 40%. This study has shown that the binding ability of IgE was reduced by conformational alteration by irradiation and the irradiated DF had epitopes capable to induce immunogeniciy.     

A novel 8,4′-oxyneolignan diglycoside from Ligusticum sinensis

A novel 8,4’-oxyneolignan diglycoside,named ligusinenoside d(1),was isolated from the rhizomes of Ligusticum sinensis, together with five known analogues 2-6.The absolute configurations of 1 and 2 were elucidated by means of enzymatic hydrolysis and spectroscopic data.     

Preparation of 4- and 6-desphenyl analogues of (−)-clausenamide and alternative synthesis of (+)-epi-clausenamide

4- and 6-desphenyl analogues of(-)-clausenamide,6 and 7,were prepared in optical active form from commercially available D-pyroglutamic acid and the known racemic pyrrolidinone 13,respectively.In order to confirm the absolute stereochemistry of(+)-and (-)-7,intermediate 19b was transferred into the(+)-epi-clausenamide 8.     

Asymmetric hydrogenation of acetophenone catalyzed by cinchonidine stabilized Ir/SiO2

A series of silica (SiO₂) supported iridium catalysts stabilized by cinchona alkaloids was prepared and applied in the heterogeneous asymmetric hydrogenation of acetophenone. Cinchona alkaloids exhibited a marked ability to stabilize and disperse the Ir particles. In the presence of (1S,2S)-diphenylethylenediamine ((1S,2S)-DPEN)) as chiral modifier, the cinchonidine (CD) stabilized catalyst 5%Ir/2CD-SiO₂ exhibited excellent catalytic performance in the asymmetric hydrogenation of acetophenone in MeOH. Under the optimum conditions, the ee value of (R)-phenylethanol achieved 79.8% and no other product was produced, a higher enantioselectivity than that reported up to now for acetophenone hydrogenation catalyzed by the supported metal catalysts modified by chiral reagents. In particular, a synergistic effect between (1S,2S)-DPEN and CD was observed, which significantly accelerated the reaction rate and enhanced the enantioselectivity. The catalyst can be reused several times without a significant loss of activity and enantioselectivity.     

Engineered SAM Synthetases for Enzymatic Generation of AdoMet Analogs with Photocaging Groups and Reversible DNA Modification in Cascade Reactions

Methylation and demethylation of DNA, RNA and proteins has emerged as a major regulatory mechanism. Studying the function of these modifications would benefit from tools for their site‐specific inhibition and timed removal. S‐Adenosyl‐L‐methionine (AdoMet) analogs in combination with methyltransferases (MTases) have proven useful to map or block and release MTase target sites, however their enzymatic generation has been limited to aliphatic groups at the sulfur atom. We engineered a SAM synthetase from Cryptosporidium hominis (PC‐ChMAT) for efficient generation of AdoMet analogs with photocaging groups that are not accepted by any WT MAT reported to date. The crystal structure of PC‐ChMAT at 1.87 Å revealed how the photocaged AdoMet analog is accommodated and guided engineering of a thermostable MAT from Methanocaldococcus jannaschii. PC‐MATs were compatible with DNA‐ and RNA‐MTases, enabling sequence‐specific modification (“writing”) of plasmid DNA and light‐triggered removal (“erasing”).     

Photocatalytic activity of N-doped TiO2: photocatalytic synthesis of o-aminophenol at room temperature

The photocatalytic synthesis of o-aminophenol in methanol was investigated with N-doped TiO₂ nanoparticles under UV-light irradiation. The catalytic quantities of N-doped TiO₂ prepared by a simple modified sol–gel process with urea as nitrogen source rapidly reduced o-nitrophenol to the corresponding amine at room temperature.     

Sugar Puckering Drives G-Quadruplex Refolding: Implications for V-Shaped Loops

A DNA G-quadruplex adopting a (3+1) hybrid structure was modified in two adjacent syn positions of the antiparallel strand with anti-favoring 2′-deoxy-2′-fluoro-riboguanosine (^FrG) analogues. The two substitutions promoted a structural rearrangement to a topology with the 5′-terminal G residue located in the central tetrad and the two modified residues linked by a V-shaped zero-nucleotide loop. Strikingly, whereas a sugar pucker in the preferred north domain is found for both modified nucleotides, the ^FrG analogue preceding the V-loop is forced to adopt the unfavored syn conformation in the new quadruplex fold. Apparently, a preferred C3′-endo sugar pucker within the V-loop architecture outweighs the propensity of the ^FrG analogue to adopt an anti glycosidic conformation. Refolding into a V-loop topology is likewise observed for a sequence modified at corresponding positions with two riboguanosine substitutions. In contrast, 2′-F-arabinoguanosine analogues with their favored south-east sugar conformation do not support formation of the V-loop topology. Examination of known G-quadruplexes with a V-shaped loop highlights the critical role of the sugar conformation for this distinct structural motif.     

Nonnucleoside HIV-1 Reverse Transcriptase Inhibitors, Part 4[1]. Synthesis and Anti-HIV Activity of N-1-β-Carbonyl-6-naphthyl-methyl Analogues of HEPT

Summary.  A series of 6-naphthylmethyl substituted HEPT analogues bearing a β-carbonyl and a terminal phenyl ring or ester groups on the N-1 side chain of uracil were synthesized, and the in vitro anti-HIV activity was evaluated. Most of these HEPTs were considerably less potent and selective or inactive, only a few compounds showed moderate or high activity against HIV-1. The results demonstrated that the anti-HIV-1 activity of 6-naphthylmethyl substituted HEPT analogues was diminished or eliminated when the β-oxygen of N-1 side chain was replaced by a carbonyl group.     

α-氨基膦酸(酯)不对称合成研究进展

α-氨基膦酸作为天然氨基酸的含磷类似物, 具有广泛的生物活性, 详细介绍了使用手性辅助基团诱导和手性催化剂催化两种方法不对称合成光学活性α-氨基膦酸(酯)的最新研究进展.     

CF_x-Ru复合阴极材料的制备及在锂一次电池中的应用（英文）

首次采用简单的原位化学改性方法合成了CFx-Ru复合阴极材料并应用于锂一次电池。与原始CFx材料相比,CFx-Ru在5C的放电倍率下放电容量、放电电压平台和最大功率密度可分别高达605 mAh·g^-1、2 V、8727 W·kg^-1。通过X射线衍射、X射线光电子能谱、扫描电子显微镜和透射电子显微镜对阴极材料结构、化学环境和形貌进行了研究。研究发现,在CFx-Ru复合材料中,nF/nC和C-F2键与C-F共价键的峰面积比都有所降低,这可能是由于RuO2与CFx材料表面或边缘的CF2惰性基团反应所致。这种原位化学反应消耗了非活性的CF2,产生了导电元素钌,并由于气相产物的演化而增加了比表面积。这些特性有助于改善阴极材料的电化学性能。电化学阻抗谱和N2吸附-脱附测试结果也进一步证实了改性材料拥有较大的比表面积和优异的电导率。     

High pressure pyrolysis of n-heptane

Pyrolysis of n-heptane was investigated in a tubular reactor in the temperature range of 793–953 K and pressure range of 0.1–2.93 MPa. At all conditions, the main products were methane, ethylene, ethane, propylene, 1-butene, 1-pentene and 1-hexene. With an increase in pressure, the selectivities of hydrogen, methane, ethylene and propylene decreased and that of propane, n-butane and 1-butene increased. To explain the product distribution at high pressure, the Rice–Kossiakoff theory was modified by including the bimolecular reactions of alkyl radicals with the parent hydrocarbon. The initial product selectivities, calculated using the modified R–K mechanism, were in good agreement with the experimental selectivities. The overall kinetics of n-heptane pyrolysis was determined by non-linear analysis. The optimum values of the kinetic parameters at each pressure were determined by minimizing the difference between the calculated and experimental conversions. At each pressure, the reaction order was close to unity and the activation energy ranged between 209 and 219 kJ mol⁻¹.