A novel and efficient method for cleavage of phenacylesters by magnesium reduction with acetic acid

[reaction: see text] In the present study, we use magnesium turnings as a new deprotection reagent for the phenacyl group during orthogonal organic synthesis in the presence of other esters and sensitive protecting groups. By applying the new magnesium turnings/acetic acid deprotection method, phenacyl group can be more easily combined with other protecting groups that are not compatible with the zinc/acetic acid method.     

Enantio- and diastereoselective Michael reaction of 1,3-dicarbonyl compounds to nitroolefins catalyzed by a bifunctional thiourea

We synthesized a new class of bifunctional catalysts bearing a thiourea moiety and an amino group on a chiral scaffold. Among them, thiourea 1e bearing 3,5-bis(trifluoromethyl)benzene and dimethylamino groups was revealed to be highly efficient for the asymmetric Michael reaction of 1,3-dicarbonyl compounds to nitroolefins. Furthermore, we have developed a new synthetic route for (R)-(-)-baclofen and a chiral quaternary carbon center with high enantioselectivity by Michael reaction. In these reactions, we assumed that a thiourea moiety and an amino group of the catalyst activates a nitroolefin and a 1,3-dicarbonyl compound, respectively, to afford the Michael adduct with high enantio- and diastereoselectivity.     

Convergence behavior of the density-matrix renormalization group algorithm for optimized orbital orderings

The density-matrix renormalization group algorithm has emerged as a promising new method in ab initio quantum chemistry. However, many problems still need to be solved before this method can be applied routinely. At the start of such a calculation, the orbitals originating from a preceding quantum chemical calculation must be placed in a specific order on a one-dimensional lattice. This ordering affects the convergence of the density-matrix renormalization group iterations significantly. In this paper, we present two approaches to obtain optimized orderings of the orbitals. First, we use a genetic algorithm to optimize the ordering with respect to a low total electronic energy obtained at a predefined stage of the density-matrix renormalization group algorithm with a given number of total states kept. In addition to that, we derive orderings from the one- and two-electron integrals of our test system. This test molecule is the chromium dimer, which is known to possess a complicated electronic structure. For this molecule, we have carried out calculations for the various orbital orderings obtained. The convergence behavior of the density-matrix renormalization group iterations is discussed in detail.     

Analysis of electron delocalization in aromatic systems: individual molecular orbital contributions to para-delocalization indexes (PDI)

Our research group has recently defined two new aromaticity indexes based on the analysis of electron delocalization in aromatic species using the quantum theory of atoms-in-molecules. One of these indexes is the para-delocalization index (PDI) that measures the electronic delocalization between para-related carbon atoms in six-membered rings. In this paper, we show that this index can be partitioned into individual molecular orbital contributions. We have applied this PDI decomposition to several polycyclic aromatic hydrocarbons showing that this partitioning provides new insight into the origin of aromaticity.     

New route for stabilizing silicon fullerenes

Motivated by the recent synthesis of silica-coated silicon nanotubes, we here present the structural models of their counterparts, silica-coated silicon fullerenes, which can be considered as arising from a structurally stable building block, Si3O2. By performing density functional theory calculations we show that the silica-coated silicon fullerenes possess high energetic and thermal stabilities and point group symmetries as well as large energy gaps. The present results indicate that coating silica on silicon clusters would be a new way for stabilizing silicon fullerenes, which is expected to find potential allocations in nanotechnology.     

Escherichia coli O86 O-antigen biosynthetic gene cluster and stepwise enzymatic synthesis of human blood group B antigen tetrasaccharide

Previous study showed that some Gram-negative bacteria possess human blood group activity. Among them, Escherichia coli O86 has high blood group B activity and weak blood group A activity. This is due to the cell surface O-antigen structure, which resembles that of human blood group B antigen. In this study, we sequenced the entire E. coli O86 antigen gene cluster and identified all the genes responsible for O-antigen biosynthesis by sequence comparative analysis. The blood group B-like antigen in E. coli O86 O-polysaccharide was synthesized by sequentially employing three glycosyltransferases identified in the gene cluster. More importantly, we identified a new bacterial glycosyltransferase (WbnI) equivalent to human blood group transferase B (GTB). The enzyme substrate specificity and stepwise enzymatic synthesis of blood group B-like antigen revealed that the biosynthetic pathway of B antigen is essentially the same in E. coli O86 as in humans. This new finding provides a model to study the specificity and structure relationship of blood group transferases and supports the hypothesis of anti-blood group antibody production by bacterial stimulation.     

Small Cause,Great Impact: Modification of the Guanidine Group in the RGD Motif Controls Integrin Subtype Selectivity

Due to its unique role as a hydrogen‐bond donor and its positive charge, the guanidine group is an important pharmacophoric group and often used in synthetic ligands. The chemical modification of the guanidine group is often considered to destroy its function. Herein, we show that the N‐methylation, N‐alkylation, or N‐acylation of the guanidine group can be used to modify the receptor subtype specificity of the integrin ligand cilengitide. Using the αvβ6/α5β1‐biselective ligand c(isoDGRkphg) and the αvβ6‐specific ligand c(FRGDLAFp(NMe)K(Ac) as examples, we show that the binding affinities of the ligands can be fine‐tuned by this method to enhance the selectivity for αvβ6. Furthermore, we describe a new strategy for the functionalization of integrin ligands. By introducing longer N‐alkylguanidine and N‐acylguanidine groups, we are able to simultaneously identify a hitherto unknown anchoring point and enhance the subtype selectivity of the ligand.     

Synthesis and biological evaluation of 20-hydroxytriptonide and its analogues

20-Hydroxytriptonide was synthesized from readily accessible l-abietic acid in 22 linear steps, which features a Barton reaction carried out under air atmosphere to install the C20-hydroxy group. Meanwhile, we also synthesized (5R)-5-hydroxytriptolide's probable metabolite product. Preliminary structure–activity relationship studies revealed that C20-angular methyl group might play a key role in maintaining the electronic properties of the whole molecule, which was essential for retaining the cytotoxic activity and might easily and inevitably be affected by the introduction of a new group.     

Explorations into new reaction chemistry

This Review describes the basic concepts that have guided our exploration of new chemical reactions by giving examples of results from my research group. Our strategy of carrying out research is to investigate three to four different topics at a time so we can gather as many results as possible. These may at first appear unrelated to each other but may have the potential to be united into a greater hypothesis after repeated feedback. Three scenarios from our research are presented: the "oxidative-reductive condensation reaction" devised in 1960, which after an interval of nearly 40 years brought forth the new concept of using compounds of structure Ph(2)POR as reducing reagents; the "TiCl(4)-aldol reaction" of 1973 that eventually led to the present "base-promoted aldol reaction" through a chain of ideas; and the "glycosylation reaction using fluorosugars" from 1984 which recently bloomed into "stereocontrolled glycosylation". Thus, it can be said that by reviewing what we had done before, we were able to expand on it to achieve new outcomes.     

A General Synthesis of α-Substituted Acrylic Esters

During a study of synthetic approaches to various naturally-occurring sesquiterpenes lactones, we developed a new synthesis of the α-methylene-γ-butyrolactone group.¹ This new sequence suggested that it might be applicable to the general synthesis of α-methylenecarbonyl compounds.² This report describes the application to a general synthesis of α-substituted acrylic esters.     

Formation of benzylamines from triazene compounds via a 1,2-proton shift

A new approach to benzylamines using triazene compounds has been developed that is facilitated by the lithiation of aryltriazenes followed by treatment with an electrophile. The regioselectivity of the reaction can be controlled by means of the substituents in the aryl group. The reaction contains the following steps: intramolecular carbon-carbon bond formation involving lithiation of an alkyl group on a 3-nitrogen atom; a 1,2-proton shift; and the subsequent release of nitrogen gas. Through the use of a deuterated triazene, we were able to determine that the reaction proceeds through a 1,2-proton shift.     

New structural motif of 18 valence electron molecules with a planar tetracoordinate heavier group 14 center: Unique stabilization effect of a π‐type skeleton

Proposing new valence electron counting rules and new structural motifs are both very important in chemistry. In this work, we unexpectedly found that by introducing a π‐type skeleton YCCY (Y = Al/Ga/In/Tl), a total of sixteen novel planar tetracoordinate heavier group 14 species, that is, ptM (M = Si/Ge/Sn/Pb) in neutral, can be designed as global minima. The underlying bonding situation contrasts sharply both with the well‐known 18ve‐ptC and the limited 18ve‐ptM, for which there is little multiple bonding character within the skeleton. The fact that each YCCY (Y = Al/Ga/In/Tl) can stabilize all heavier group 14 atoms in a planar tetracoordinate fashion strongly demonstrates the universality of such a π‐type skeleton. The present work firmly demonstrates that introducing the π‐type ligand skeleton can effectively enrich the planar tetracoordinate chemistry with the heavier group atoms.     

Tuning the optical properties of BODIPY dye through Cu(I) catalyzed azide-alkyne cycloaddition (CuAAC) reaction

Borondipyrromethenes(BODIPY) are a class of fluorescent dyes whose fluorescence quantum yields are generally high and independent of the solvent.In this paper,we report the synthesis of a new type of BODIPY compound that carries an azido group on the 3-position of the pyrrole core.The azido group quenches the fluorescence of the dye due to its weak electron-donating effect.The fluorescence of the BODIPY dye can be switched on after reacting with alkynes via a Cu(Ⅰ) catalyzed azide-alkyne cycloaddition(CuAAC) reaction.We further demonstrate that this azido-BODIPY compound can be used in the cell imaging applications.     

Guidelines to design new spin crossover materials

This review focuses on new families of spin crossover (SCO) complexes based on polynitrile anions as new anionic ligands or on polyazamacrocycles as neutral macrocyclic ligands. We have shown that the structural and electronic characteristics (original coordination modes and high electronic delocalization) of the polynitrile anions can be tuned by slight chemical modifications such as substitution of functional groups or variation of the negative charge to design new discrete or polymeric SCO systems.In our ongoing work on the design of new molecular systems based on new ligands that can be fine-tuned via chemical modifications, another promising way which has been recently developed in our group concerns the use of new neutral polydentate ligands which are able to tune the ligand field energy around the metal centre. Here we report some recent original Fe(II) SCO complexes based on such polydentate ligands.     

Antimicrobial Poly(2‐methyloxazoline)s with Bioswitchable Activity through Satellite Group Modification

Biocides are widely used for preventing the spread of microbial infections and fouling of materials. Since their use can build up microbial resistance and cause unpredictable long‐term environmental problems, new biocidal agents are required. In this study, we demonstrate a concept in which an antimicrobial polymer is deactivated by the cleavage of a single group. Following the satellite group approach, a biocidal quaternary ammonium group was linked through a poly(2‐methyloxazoline) to an ester satellite group. The polymer with an octyl‐3‐propionoate satellite group shows very good antimicrobial activity against Gram‐positive bacterial strains. The biocidal polymer was also found to have low hemotoxicity, resulting in a high HC₅₀/MIC value of 120 for S. aureus. Cleaving the ester satellite group resulted in a 30‐fold decrease in antimicrobial activity, proving the concept valid. The satellite group could also be cleaved by lipase showing that the antimicrobial activity of the new biocidal polymers is indeed bioswitchable.     

Design and Synthesis of 1-Benzyl-3-(a-hydroxy-(un)substituted benzylidene)pyrrolidine-2,4-diones as Potential Herbicides

The inhibitors of 4-hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) are an new kind of herbicides.[1]Generally, in structure, potent herbicides of this kind must possess: (1) a tricarbonyl methane structure and one of the three carbonyl groups must be a subustituted benzoyl group; (2) the compound must be able to enolise so that the enolate is capable of inhibiting HPPD enzyme by competitive combination with Fe2+, the reaction center of HPPD enzyme.[2]Recently, we noticed that the 3-acyltetramic acids form an expanding group of antibiotics and pigments from micro-organisms,[3] they display a range of biological activities[4] and all of this kind compounds possess all of the characters mentioned above. Tests of their antimicrobial activities indicated that the structure of the acyl substituent at the 3-position was important to many typical antibiotics.[4～6] These characters stimulated us to study this kind of compounds so as to discover new herbicides. In this report, we synthesized a series of compounds 3 and tested their herbicidal activities to investigate their structure-activity relationships.     

Structural studies of heparan sulfate hexasaccharides: new insights into iduronate conformational behavior

There is a growing opinion that the conformational dynamics within HS chains is critical to their observed biological activities. Investigations into HS conformational dynamics are problematic, given the structural complexity and heterogeneity of HS chains. However, this goal will be more obtainable once we understand the important roles HS sequence/sulfation patterns play in determining the conformational dynamics of iduronate units. This is the first study to compare isomers of N-sulfated oligosaccharides, with respect to the conformational versatility of their internal iduronates. Characterization by NMR spectroscopy of two HS oligosaccharides derived from porcine mucosal HS enabled the measurement of iduronate coupling constants, while under the influence of different flanking saccharide sequences. By fitting our coupling constant data to a new set of theoretical coupling constants, calculated using explicit water molecular dynamic simulations, we are able to offer new insights into the role sequence/sulfation patterns play in influencing iduronate conformational behavior. Fitting of experimental data, using our new theoretically derived coupling constants, suggests that replacement of the N-sulfate group to the reducing side of IdoUA by an N-acetyl group has little effect on the balance of IdoUA conformational equilibrium. Fitting of coupling constants for sequences GlcNS-IdoUA(2S)-GlcNS and GlcNS(6S)-IdoUA(2S)-GlcNS suggests that the flanking 6-O-sulfate group alters the balance of the IdoUA(2S) equilibrium more toward the (2)S0 conformation. There is also the suggestion that a cooperative effect may exist for N- and 6-O sulfation. These observations could be the key to understanding the important regulatory function attributed to 6-O-sulfation within HS chains.     

反应碰撞的动力学李代数描述

提出一种李代数方法描述分子反应碰撞问题．给出了含有主要动力学参量的S-矩阵元、分子碰撞跃迁几率以及反应体系能量统计平均值随时间演化的解析表达式．讨论了一个简单排斥势场中的原子-双原子分子共线反应体系，以阐明这种新方法的要点。     

General equation for size nanocharacterization of the core-shell nanoparticles by X-ray photoelectron spectroscopy

Nanocharacterization is essential for nanoengineering of new types of core-shell (c-s) nanoparticles, which can be used to design new devices for photonics, electronics, catalysis, medicine, etc. X-ray photoelectron spectroscopy (XPS) has been widely used to study the elemental composition of the c-s nanoparticles. However, the physical and chemical properties of a c-s nanoparticle dramatically depend on the sizes of its core and shell. We therefore propose a general equation for the XPS intensity of a c-s nanoparticle, which is based on an analytical model. With this equation, XPS can now also be used for nanocharacterization of the core and shell sizes of the c-s nanoparticles (with a diameter smaller than or equal to the XPS probing depth of approximately 10 nm). To validate the new equation with experimental XPS data, we first determine the average shell thickness of a group of c-s nanoparticles by comparing the XPS intensity of reference bare cores to that of the c-s nanoparticles. Then we study the growth kinetics of the cores and shells of another group of c-s nanoparticles where the shells are obtained by oxidation.     

Ba2CdMoO6及新化合物—Sr2CdMoO6晶体结构的研究

自从对Sr_2CaWO_6的相变和晶体结构研究以后,引起了我们对该类型化合物A_2~ⅡB~ⅡB~ⅥO_6的兴趣(A~Ⅱ=Ba~( 2),Sr~( 2);B~Ⅱ=Ca~( 2),Cd~( 2),Fe~( 2),Co~( 2),…;B~Ⅵ=W~( 6),Mo~( 6)),它们属于复杂的钙钛矿型结构,且具有一定的规律性。据文献[2]报导Ba_2CaWO_6属立方晶系,而文献[1]报导Sr_2CaWO_6低温相属正交晶系。在元素周期表中Mo和W同属于ⅥB族,它们的化学性质相似,二元素的离子半径也非常相近,Cd和Ca虽不同族,但离子半径很相近,化合价相同。为此,本文用Mo~( 6)代替W~( 6),Cd~( 2)代替Ca~( 2)来研究Ba_2CdMoO_6和Sr_2CdMoO_6的晶体结构。文献[3]对Ba_2CdMoO_6做了简单的报导,但Sr_2CdMoO_6则未见报导。