Stereoselective Synthesis of Fluorinated Galactopyranosides as Potential Molecular Probes for Galactophilic Proteins: Assessment of Monofluorogalactoside–LecA Interactions

The replacement of hydroxyl groups by fluorine atoms on hexopyranoside scaffolds may allow access to invaluable tools for studying various biochemical processes. As part of ongoing activities toward the preparation of fluorinated carbohydrates, a systematic investigation involving the synthesis and biological evaluation of a series of mono- and polyfluorinated galactopyranosides is described. Various monofluorogalactopyranosides, a trifluorinated, and a tetrafluorinated galactopyranoside have been prepared using a Chiron approach. Given the scarcity of these compounds in the literature, in addition to their synthesis, their biological profiles were evaluated. Firstly, the fluorinated compounds were investigated as antiproliferative agents using normal human and mouse cells in comparison with cancerous cells. Most of the fluorinated compounds showed no antiproliferative activity. Secondly, these carbohydrate probes were used as potential inhibitors of galactophilic lectins. The first transverse relaxation-optimized spectroscopy (TROSY) NMR experiments were performed on these interactions, examining chemical shift perturbations of the backbone resonances of LecA, a virulence factor from Pseudomonas aeruginosa. Moreover, taking advantage of the fluorine atom, the ¹⁹F NMR resonances of the monofluorogalactopyranosides were directly monitored in the presence and absence of LecA to assess ligand binding. Lastly, these results were corroborated with the binding potencies of the monofluorinated galactopyranoside derivatives by isothermal titration calorimetry experiments. Analogues with fluorine atoms at C-3 and C-4 showed weaker affinities with LecA as compared to those with the fluorine atom at C-2 or C-6. This research has focused on the chemical synthesis of “drug-like” low-molecular-weight inhibitors that circumvent drawbacks typically associated with natural oligosaccharides.     

Unexpected relative aqueous solubilities of a phosphotyrosine analogue and two phosphonate derivatives

Phosphotyrosine (pTyr) is an essential component of biological signaling, often being a determinant of protein-protein interactions. Accordingly, a number of drug discovery efforts targeting signal transduction pathways have included phosphotyrosine and analogues as essential components of the lead compounds. Toward the goal of improved biological efficacy, the phosphonate and difluoro phosphonate analogues of pTyr have been employed in inhibitor design because of their stability to hydrolysis and enhanced binding affinity in certain cases. To quantitate the contribution of aqueous solubility of pTyr, phosphonomethyl phenylalanine (Pmp), and difluorophosphonomethyl phenylalanine (F(2)Pmp) to their relative binding affinities, free energy perturbation calculations were undertaken on the mimetics phenol phosphate (PP), benzyl phosphonate (BP), and difluorobenzyl phosphonate (F(2)BP), including development of empirical force field parameters compatible with the CHARMM all-atom force fields. Notably, it is shown that the most favorably solvated compound of the series is BP, followed by PP, with F(2)BP the least favorably solvated for both the mono- and dianionic forms of the compounds. The molecular origin of this ordering is shown to be due to changes in charge distribution, in the comparatively larger size of the fluorine atoms, as well as in differences of local solvation between PP and BP. The implications of the differences in aqueous solubility toward the relative binding potencies of pTyr-, Pmp-, and F(2)Pmp-containing peptide ligands are discussed. Our results indicate that one general principle explaining the efficacy of selective fluorination to enhance binding affinities may lie in the ability of fluorine atoms to increase the hydrophobicity of a ligand while maintaining its capability to form hydrogen bonds.     

2-氰基-3-甲硫基-3-取代甲氨基丙烯酸酯类化合物的合成及其除草活性

A series of 2-cyano-3-methylthio-3-substituted methylaminoacrylates were synthesized as herbicidal inhibitors of photosystem Ⅱ （PSⅡ） electron transport, in order to estimate the effect of fluorine atom, pyridyl group, chirality and ester chain on activity. The important intermediate 2-fluoro-5-aminomethylpyridine was synthesized with high yield. The bioassay results showed that most of rifle compounds had high herbicidal activity in postemergence treatment. The introduction of an a-methyl into the 3-substituted methylamino could improve the activity notably. The replacement of hydrogen by chlorine or fluorine group and phenyl by pyridyl group showed different effects, and at the same time, the ester chain affected the activity too.     

新型二氟甲基磷酸类酪氨酸蛋白磷酸酯酶1B抑制剂的分子动力学模拟和结合自由能计算

通过分子对接建立了一系列含二氟甲基磷酸基团(DFMP)或二氟甲基硫酸基团(DFMS)的抑制剂与酪氨酸蛋白磷酸酯酶1B(PTP1B)的相互作用模式, 并通过1 ns的分子动力学模拟和molecular mechanics/generalized Born surface area (MM/GBSA)方法计算了其结合自由能. 计算获得的结合自由能排序和抑制剂与靶酶间结合能力排序一致; 通过基于主方程的自由能计算方法, 获得了抑制剂与靶酶残基间相互作用的信息, 这些信息显示DFMP/DFMS基团的负电荷中心与PTP1B的221位精氨酸正电荷中心之间的静电相互作用强弱决定了此类抑制剂的活性, 进一步的分析还显示位于DFMP/DFMS基团中的氟原子或其他具有适当原子半径的氢键供体原子会增进此类抑制剂与PTP1B活性位点的结合能力.     

Structural effects of fluorine substitution in proteins

The consequences of substitution of fluorine for the para hydrogen of a phenylalanine residue in ribonuclease-S were investigated by conformational energy calculations using the AMBER force field. Both the fluorine-containing protein and the corresponding nonfluorinated material were subjected to conformational adjustment through energy minimization and the minimum energy structures so defined were compared. Fluorine substitution leads to small alterations in many atomic positions in the protein, with adjustments at at sites more than 0.5 nm from the fluorine appearing to be somewhat larger than those within the immediate vicinity of the fluorine. Several atoms proximate to the fluorine atom were observed to move toward the fluorine while others in the same vicinity move away. The greater bulk of the fluorine atom and the strongly different electronic properties of fluorine compared to hydrogen thus appear to be insufficient to cause a consistent, unidirectional change in nearest-neighbor interactions upon introduction of a fluorine atom into a protein structure. Virtually all changes in atomic positions that are predicted by these calculations would be barely detectable by a crystallographic study with a resolution of 0.2 nm.     

Synthesis of Some Dialkyl Bromo-Substituted Benzyl Phosphonates

Arbuzov reaction of bromo-substituted benzyl bromides and trialkyl phosphites in benzene gave high yields of dialkyl bromo-substituted benzyl phosphonates, and —CH₂CH₂CH₂CH₃). The structural assignments of these phosphonates were confirmed by ¹H nmr, ¹³C nmr, ir and mass spectral analysis.     

Selectfluor: Mechanistic Insight and Applications

The replacement of hydrogen atoms with fluorine substituents in organic substrates is of great interest in synthetic chemistry because of the strong electronegativity of fluorine and relatively small steric footprint of fluorine atoms. Many sources of nucleophilic fluorine are available for the derivatization of organic molecules under acidic, basic, and neutral conditions. However, electrophilic fluorination has historically required molecular fluorine, whose notorious toxicity and explosive tendencies limit its application in research. The necessity for an electrophilic fluorination reagent that is safe, stable, highly reactive, and amenable to industrial production as an alternative to very hazardous molecular fluorine was the inspiration for the discovery of selectfluor. This reagent is not only one of the most reactive electrophilic fluorinating reagents available, but it is also safe, nontoxic, and easy to handle. In this Review we document the many applications of selectfluor and discuss possible mechanistic pathways for its reaction.     

Reactions of azoles with tetrachloro-1,2-difluoroethane and 1,2-dichlorodifluoroethylene

Tetrachloro-1,2-difluoroethane reacted with pyrazole and imidazole sodium salts to give mixtures of the corresponding N-(1,2,2-trichloro-1,2-difluoroethyl) derivatives and (E)-1,2-difluoro-1,2-dihetarylethenes. (E)-1,2-Difluoro-1,2-di(3,5-dimethyl-1H-pyrazol-1yl)ethene was also obtained as a result of replacement of chlorine atoms in 1,2-dichloro-1,2-difluoroethene. Analogous reaction with more nucleophilic imidazole involved replacement of not only chlorine but also fluorine atoms in 1,2-dichloro-1,2-difluoroethene, yielding tetraimidazolyl-substituted ethylene.     

Selectfluor: mechanistic insight and applications

The replacement of hydrogen atoms with fluorine substituents in organic substrates is of great interest in synthetic chemistry because of the strong electronegativity of fluorine and relatively small steric footprint of fluorine atoms. Many sources of nucleophilic fluorine are available for the derivatization of organic molecules under acidic, basic, and neutral conditions. However, electrophilic fluorination has historically required molecular fluorine, whose notorious toxicity and explosive tendencies limit its application in research. The necessity for an electrophilic fluorination reagent that is safe, stable, highly reactive, and amenable to industrial production as an alternative to very hazardous molecular fluorine was the inspiration for the discovery of selectfluor. This reagent is not only one of the most reactive electrophilic fluorinating reagents available, but it is also safe, nontoxic, and easy to handle. In this Review we document the many applications of selectfluor and discuss possible mechanistic pathways for its reaction.     

Synthesis of Triazole‐Linked Amino Acid‐Aryl C‐Glycoside Hybrids via Click Chemistry as Novel PTP1B Inhibitors

Triazolyl phenylalanine and tyrosine‐aryl C‐glycoside hybrids were readily synthesized via microwave‐assisted Cu(I)‐catalyzed azide‐alkyne 1,3‐dipolar cycloaddition in high yields. Successive enzymatic assay identified the synthesized glycoconjugates as novel PTP1B inhibitors with low micromole‐ranged inhibitory activity and at least several‐fold selectivity over other homologous PTPs tested. In addition, the benzyl groups on glucosyl moiety were found crucial toward PTP1B inhibition.     

Mass spectrometric investigation of polyfluorinated C60. Evidence for the existence of C60F2n (n = 0–30)

Electron-capture negative ion chemical ionization (EC-NICI) and field desorption (FD) mass spectrometric techniques were utilized to examine polyfluorinated C₆₀. Two different samples from the same preparation, one prior to sublimation and the other sublimed material, were investigated. From the raw non-sublimed product in EC-NCI six series of ions corresponding to different numbers of attached oxygen atoms were obtained, which are represented by the formula [C₆₀F_2nO_m]^?, where n ranged from 0 to 30 and m from 0 to 5. The sublimed material in EC-NICI produced the same six series of ions with up to 48 fluorine atoms attached to C₆₀. The field desorption of the same sample produced similar results, but the signal-to-noise ratios of the spectra were low. Both samples, in the two different techniques examined, yielded C₆₀F₆₀ ions with only an even number of fluorine atoms attached. The present investigation, for the first time, provides direct experimental evidence for the existence of higher fluorinated C₆₀ up to C₆₀F₆₀ and multiple oxides of polyfluoro-C₆₀ with up to five oxygen atoms attached.     

Synthesis of β-chloro-α-aminophosphonate derivatives via the regioselective ring opening of unactivated aziridine-2-phosphonates

Abstract

A series of unactivated racemic and chiral aziridine-2-phosphonates were synthesized by modified Gabriel-Cromwell reaction. Ring opening reaction of the synthesized phosphonates by gaseous HCl provided access to a wide range of biologically interesting novel β-chloro-α-aminophosphonates. All reactions toward each of the above-mentioned products can be conducted regioselectively in high yields.     

Organoruthenium Antagonists of Human A3 Adenosine Receptors

Human A₃ adenosine receptor (hA₃AR) is a membrane‐bound G protein‐coupled receptor implicated in a number of severe pathological conditions, including cancer, in which it acts as a potential therapeutic target. To derive structure–activity relationships on pyrazolo–triazolo–pyrimidine (PTP)‐based A₃AR antagonists, we developed a new class of organometallic inhibitors through replacement of the triazolo moiety with an organoruthenium fragment. The objective was to introduce by design structural diversity into the PTP scaffold in order to tune their binding efficacy toward the target receptor. These novel organoruthenium antagonists displayed good aquatic stability and moderate binding affinity toward the hA₃ receptor in the low micromolar range. The assembly of these complexes through a template‐driven approach with selective ligand replacement at the metal center to control their steric and receptor‐binding properties is discussed.     

Solid-phase synthesis and biochemical studies of O-boranophosphopeptides and O-dithiophosphopeptides

Signal transduction cascades maintain control over important cellular processes such as cell growth and differentiation by orchestrating protein phosphorylation and dephosphorylation. Specific control of these processes in vivo and in vitro can be achieved with peptide analogues that mimic the binding properties of phosphoproteins. We present here the solid-phase synthesis of two novel classes of phosphopeptide mimetics, O-boranophosphopeptides and O-dithiophosphopeptides, derivatized on tyrosine, serine, and threonine. The use of H-phosphonate and H-phosphonothioate monoesters containing the base labile 9-fluorenemethyl protecting group was key to the synthesis of both phosphopeptide mimetics. O-Boranophosphopeptides were synthesized by condensing O-(9-fluorenemethyl)-H-phosphonate to the peptide hydroxylic component (tyr, ser, or thr) followed by oxidation with borane complexes. Similarly, the synthesis of O-dithiophosphopeptides used the O-(9-fluorenemethyl)-H-phosphonothioate synthon and oxidation with elemental sulfur. Base elimination of the Fmol protecting group and cleavage from the solid support with concentrated ammonium hydroxide afforded the boranophosphopeptide and dithiophosphopeptide target compounds. Ac-YIIPLPG-NH2, having either dithiophosphoryl tyrosine or boranophosphoryltyrosine but no sequence specificity for Yersinia protein tyrosine phosphatase (PTP), was found to competitively inhibit this enzyme with KI values of 430 +/- 50 and 670 +/- 50 microM, respectively. In addition, both phosphopeptide analogues were resistant toward Yersinia PTP enzymatic hydrolysis. Under conditions (pH 8.0) where the phosphopeptide was rapidly dephosphorylated, the boranophosphopeptide hydrolyzed slowly (t1/2 = 15 h) and the dithiophosphopeptide was completely stable over 24 h.     

Development of activity-based probes with tunable specificity for protein tyrosine phosphatase subfamilies

Herein we describe the development of activity-based probes toward protein tyrosine phosphatase (PTP) subfamilies. A novel phosphotyrosine analog serving as the latent trapping unit has been designed and explored. It allows addition of various amino acid residues to its C- and N-termini to extend the recognition element. As a proof-of-concept, we have synthesized three tripeptide probes, which carry the phosphotyrosine analog in the middle position and a leucinamide residue at the C-terminus. The three tripeptide probes differed only in their N-terminal amino acid (Glu, Phe, and Lys). The labeling properties of these probes were determined and the results showed the newly synthesized probes could selectively label PTPs in an activity-dependent manner. In addition, the probes’ target specificity was also shown to be influenced by the amino acid residues flanking the phosphotyrosine analog.     

Inhibitors of Protein Tyrosine Phosphatases: Next‐Generation Drugs?

The protein tyrosine phosphatases (PTPs) constitute a family of closely related key regulatory enzymes that dephosphorylate phosphotyrosine residues in their protein substrates. Malfunctions in PTP activity are linked to various diseases, ranging from cancer to neurological disorders and diabetes. Consequently, PTPs have emerged as promising targets for therapeutic intervention in recent years. In this review, general aspects of PTPs and the development of small-molecule inhibitors of PTPs by both academic research groups and pharmaceutical companies are discussed. Different strategies have been successfully applied to identify potent and selective inhibitors. These studies constitute the basis for the future development of PTP inhibitors as drugs.     

From Graphene to Carbon Nanotubes: Variation of the Electronic States and Nonlinear Optical Responses

From the same piece of graphene sheet, (3, 3) and (6, 0) carbon nanotube clips were obtained on the basis of the different manners of rolling. The nature of the electronic state varies differently with different manners of rolling and is significantly affected by zigzag edges. The intermediate structures formed during the rolling process were functionalized with fluorine and oxygen atoms to investigate the electronic states and nonlinear optical (NLO) responses. Passivation of the intermediate structures with fluorine neither changes the nature of electronic states and nor improves the NLO responses. In constrast, passivation with oxygen enhances the NLO properties and changes the electronic states of the structures upon passivating at the open zigzag edges.     

Discovery of a new phosphotyrosine mimetic for PTP1B using breakaway tethering

Protein tyrosine phosphatases play important roles in many signaling cascades involved in human disease. The identification of druglike inhibitors for these targets is a major challenge, and the discovery of suitable phosphotyrosine (pY) mimetics remains one of the key difficulties. Here we describe an extension of tethering technology, "breakaway tethering", which is ideally suited for discovering such new chemical entities. The approach involves first irreversibly modifying a protein with an extender that contains both a masked thiol and a known pY mimetic. The extender is then cleaved to release the pY mimetic, unmasking the thiol. The resulting protein is screened against a library of disulfide-containing small molecule fragments; any molecules with inherent affinity for the pY binding site will preferentially form disulfides with the extender, allowing for their identification by mass spectrometry. The ability to start from a known substrate mimimizes perturbation of protein structure and increases the opportunity to probe the active site using tethering. We applied this approach to the anti-diabetic protein PTP1B to discover a pY mimetic which belongs to a new molecular class and which binds in a novel fashion.     

The Crystal Structure of 5,5′,7,7′-tetramethyl-3,3′,9-triethyl thiacarbocyanine perchlorate

The crystal structure of the title compound has been determined by X-ray crystallographic analysis from diffractometer data. The compound is found to exist in the crystalline state as the mono-cis isomer (a). The conjugated chain is in a folded configuration and the two sulfur atoms are on opposing sides. It is the first time such a mono-cis isomer has been analysed by X-ray crystallography.     

α-(1,3,4-噻二唑-5-基)氨基烃基膦酸酯的合成及生物活性

以5-氨基-2-巯基的席夫碱与亚磷酸二乙酯反应, 合成了15个新的α-(1,3,4-噻二唑-5-基)氨基烃基膦酸酯, 初步的生物活性测试表明部分目标化合物具有较好的植物生长调节活性, 其中2,4-二氯苯甲醛、呋喃甲醛和吲哚甲醛的席夫碱生成的α-氨基烃基膦酸酯具有较好的生长素活性.