Reduction products of the alkaloid norfluorocurarine

The alkaloid norfluorocurarine was reduced under various conditions to produce the novel bisindoline derivative 2,16-dihydro-19-oxo-C-dihydrotoxiferine and the previously known natural derivatives deoxydihydro-, deoxytetrahydro-, and tetrahydronorfluorocurarine. The structures of the synthesized compounds were identified using IR and UV spectroscopy; of newly produced 2,16-dihydro-19-oxoC-dihydrotoxiferine and deoxydihydronorfluorocurarine, also by x-ray structure analysis. Determination of the absolute configuration of N(α)-methylfluorocurarine chloride dihydrate by x-ray methods enabled the configuration of the 3S,7R,15S asymmetric centers in norfluorocurarine and 2S,3S,7R,15S in deoxydihydronorfluorocurarine to be determined. Also, the absolute configuration of 2,16-dihydro-19-oxoC-dihydrotoxiferine was determined as 2S,3S,7R,15R,16R in one part of the bisindoline and 3'S,7'R,15'S in the other.     

Cyclization vs. cyclization/dimerization in o-amidostilbene radical cation cascade reactions: the amide question

The n-butyramido, isobutyramido, benzamido, and furancarboxamido functions profoundly modulate the electronics of the stilbene olefinic and NH groups and the corresponding radical cations in ways that influence the efficiency of the cyclization due presumably to conformational and stereoelectronic factors. For example, isobutyramido- stilbene undergoes FeCl(3) promoted cyclization to produce only indoline, while n-butyramidostilbene, under the same conditions, produces both indoline and bisindoline.     

Reaction of the fischer base with nitro- and bromo-substituted o-hydroxycinnamaldehydes

The Fischer base reacts with -ethyl-5-nitro-, 5-bromo-, and 3,5-dibromo-2-hydroxy-cinnamaldehydes to give bisindoline spirochromans, with 3-bromo-5-nitro-2-hydroxy-cinnamaldehyde to give a mixture of a spirochroman and a monoindoline merocyanine, and with 3,5-dinitro-2-hydroxycinnamaldehyde to give only a merocyanine. The monoindoline merocyanines obtained do not display a tendency to undergo intramolecular cyclization to give spiro-2H-oxocines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 775–778, June, 1984.     

A FeCl3-promoted highly atropodiastereoselective cascade reaction: synthetic utility of radical cations in indolostilbene construction

The FeCl₃-promoted oxidative cyclization/coupling of acetamidostilbenes possessing 3-methoxy, 4-methoxy and 3,5-methoxy substitutions (21), (22) and (23) is described. Only 3,5-substitution gave rise to novel indolostilbenes, each possessing two stereogenic axes (axially chiral but racemic dimers (39) and (40)). The 4-methoxy substituted acetamidostilbenes, by contrast, yielded the bisindoline dimer (36).     

Reaction of Fischer's base with o-hydroxycinnamaldehydes

On the basis of a study of the PMR spectra and alternative synthesis it was established that the dicondensed products of the reaction of Fischer's base with o-hydroxycinnamaldehydes are not oxocine derivatives, as was previously assumed, but rather are bisindoline spirochromans that are identical to the products of the reaction of vinylogs of Fischer's base with salicylaldehydes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 352–355, March, 1982.     

A tandem highly stereoselective FeCl3-promoted synthesis of a bisindoline: synthetic utility of radical cations in heterocyclic construction

A conceptually distinctive stereoselective construction of the novel dimer, N-[N′-acetyl-7,7′-bis-(3,4-dimethoxy-phenyl)-7,8,7′,8′-tetrahydro-N′H-[8,8′]biindolyl-N-yl]-ethanone 25 (bisindoline) is described below. These structures, which include 7-(3,4-dimethoxyphenyl)-indoline 24 (veratryl indoline), were obtained by the tactical combination of palladium-catalysed coupling which produced 10-acetamido-3,4-dimethoxystilbene 9, followed by FeCl₃ induced oxidative cyclization/dimerization. All new structures were fully characterized by 1- and 2D NMR spectroscopy, (proton, carbon-13, COSY, HMBC, HMQC) and mass spectrometry. Configurational assignments were further supported by semi-empirical AM1 calculations. Mechanistic interpretations, consistent with our results, are discussed.     

Exploring the Trans‐Cleavage Activity of CRISPR‐Cas12a (cpf1) for the Development of a Universal Electrochemical Biosensor

An accurate, rapid, and cost‐effective biosensor for the quantification of disease biomarkers is vital for the development of early‐diagnostic point‐of‐care systems. The recent discovery of the trans‐cleavage property of CRISPR type V effectors makes CRISPR a potential high‐accuracy bio‐recognition tool. Herein, a CRISPR‐Cas12a (cpf1) based electrochemical biosensor (E‐CRISPR) is reported, which is more cost‐effective and portable than optical‐transduction‐based biosensors. Through optimizing the in vitro trans‐cleavage activity of Cas12a, E‐CRIPSR was used to detect viral nucleic acids, including human papillomavirus 16 (HPV‐16) and parvovirus B19 (PB‐19), with a picomolar sensitivity. An aptamer‐based E‐CRISPR cascade was further designed for the detection of transforming growth factor β1 (TGF‐β1) protein in clinical samples. As demonstrated, E‐CRISPR could enable the development of portable, accurate, and cost‐effective point‐of‐care diagnostic systems.     

Identification and Role of a 6‐Deoxy‐4‐Keto‐Hexosamine in the Lipopolysaccharide Outer Core of Yersinia enterocolitica Serotype O:3

The outer core (OC) region of Yersinia enterocolitica serotype O:3 lipopolysaccharide is a hexasaccharide essential for the integrity of the outer membrane. It is involved in resistance against cationic antimicrobial peptides and plays a role in virulence during early phases of infection. We show here that the proximal residue of the OC hexasaccharide is a rarely encountered 4‐keto‐hexosamine, 2‐acetamido‐2,6‐dideoxy‐D ‐xylo‐hex‐4‐ulopyranose (Sugp) and that WbcP is a UDP‐GlcNAc‐4,6‐dehydratase enzyme responsible for the biosynthesis of the nucleotide‐activated form of this rare sugar converting UDP‐2‐acetamido‐2‐deoxy‐D ‐glucopyranose (UDP‐D ‐GlcpNAc) to UDP‐2‐acetamido‐2,6‐dideoxy‐D ‐xylo‐hex‐4‐ulopyranose (UDP‐ Sugp). In an aqueous environment, the 4‐keto group of this sugar was present in the 4‐dihydroxy form, due to hydration. Furthermore, evidence is provided that the axial 4‐hydroxy group of this dihydroxy function was crucial for the biological role of the OC, that is, in the bacteriophage and enterocoliticin receptor structure and in the epitope of a monoclonal antibody.     

Loss of PEG chain in routine SDS‐PAGE analysis of PEG‐maleimide modified protein

SDS‐PAGE represents a quick and simple method for qualitative and quantitative analysis of protein and protein‐containing conjugates, mostly pegylated proteins. PEG‐maleimide (MAL) is frequently used to site‐specifically pegylate therapeutic proteins via free cysteine residue by forming a thiosuccinimide structure for pursuing homogeneous products. The C–S linkage between protein and PEG‐MAL is generally thought to be relatively stable. However, loss of intact PEG chain in routine SDS‐PAGE analysis of PEG‐maleimide modified protein was observed. It is a thiol‐independent thioether cleavage and the shedding of PEG chain exclusively happens to PEG‐MAL modified conjugates although PEG‐vinylsulfone conjugates to thiol‐containing proteins also through a C–S linkage. Cleavage kinetics of PEG40k‐MAL modified ciliary neurotrophic factor showed this kind of degradation could immediately happen even in 1 min incubation at high temperature and could be detected at physiological temperature and pH, although the rate was relatively slow. This may provide another degradation route for maleimide‐thiol conjugate irrespective of reactive thiol, although the specific mechanism is still not very clear for us. It would also offer a basis for accurate characterization of PEG‐MAL modified protein/peptide by SDS‐PAGE analysis.     

Novel Photodynamic Effect of a Psoralen‐Conjugated Oligonucleotide for the Discrimination of the Methylation of Cytosine in DNA

DNA methylation and demethylation significantly affect the deactivation and activation processes of gene expression significantly. In particular, C‐5‐methylation of cytosine in the CpG islands is important for the epigenetic modification in genes, which plays a key role in regulating gene expression. The determination of the location and frequency of DNA methylation is important for the elucidation of the mechanisms of cell differentiation and carcinogenesis. Here we designed a psoralen‐conjugated oligonucleotide (PS‐oligo) for the discrimination of 5‐methylcytosine (5‐mC) in DNA. The cross‐linking behavior of psoralen derivatives with pyrimidine bases, such as thymine, uracil and cytosine has been well discussed, but there are no reports which have examined whether cross‐linking efficiency of psoralen with cytosine would be changed with or without C‐5 methylation. We found that the cross‐linking efficiency of PS‐oligo with target‐DNA containing 5‐mC was greatly increased compared to the case of target‐DNA without 5‐mC, approximately seven‐fold higher. Here we report a new aspect of the photocross‐linking behavior of psoralen with 5‐mC that is applicable to a simple, sequence‐specific and quantitative analysis for the discrimination of 5‐mC in DNA, which can be applicable to study the epigenetic behavior of gene expressions.     

Nanoscopic Visualization of Cross‐Linking Density in Polymer Networks with Diarylethene Photoswitches

The in situ nanoscopic imaging of soft matter polymer structures is of importance to gain knowledge of the relationship between structure, properties, and functionality on the nanoscopic scale. Cross‐linking of polymer chains effects the viscoelastic properties of gels. The correlation of mechanical properties with the distribution and amount of cross‐linkers is relevant for applications and for a detailed understanding of polymers on the molecular scale. We introduce a super‐resolution fluorescence‐microscopy‐based method for visualizing and quantifying cross‐linker points in polymer systems. A novel diarylethene‐based photoswitch with a highly fluorescent closed and a non‐fluorescent open form is used as a photoswitchable cross‐linker in a polymer network. As an example for its capability to nanoscopically visualize cross‐linking, we investigate pNIPAM microgels as a system known with variations in internal cross‐linking density.     

Dielectric studies of tetraaryl and triaryl polycarbonates and comparisons with bisphenol A‐polycarbonate

The relative permittivity, loss, and breakdown strength are reported for a commercial sample of bisphenol A‐polycarbonate (comm‐BPA‐PC) and a purified sample of the same polymer (rp‐BPA‐PC) as well as for two new polycarbonates having low molecular cross‐sectional areas, namely a copolymer of tetraaryl polycarbonate and BPA‐PC (TABPA‐BPA‐PC) and a triaryl polycarbonate homopolymer (TriBPA‐PC). The glass transition temperatures of the new polymers are higher than the T_g of BPA‐PC (187 and 191 °C vs. 148 °C). Relative permittivity and loss measurements were carried out from 10 to 10⁵ Hz over a wide temperature range, and results for the α‐ and γ‐relaxation regions are discussed in detail. For the α‐relaxation, the isochronal peak position, T_α, scales approximately with T_g. On the other hand, the peak temperature for the γ‐relaxation is approximately constant, independent of T_g. Also, in contrast to what is observed for α, γ exhibits a strong increase in peak height as temperature/frequency increases and a significant difference is found between Arrhenius plots determined from isochronal and isothermal data analyses. Next, the γ‐relaxation region for comm‐BPA‐PC and associated activation parameters show strong history/purity effects. The activation parameters also depend on the method of data analysis. The results shed light on discrepancies that exist in the literature for BPA‐PC. The shapes of the γ loss peaks and hence glassy‐state motions for all the polymers are very similar. However, the intensities of the TriBPA‐PC and TABPA‐BPA‐PC γ peaks are reduced by an amount that closely matches the reduced volume fraction of carbonate units in the two new polymers. Finally, for comm‐BPA‐PC, the breakdown strength is strongly affected by sample history and this is assumed to be related to volatile components in the material. It is found that the breakdown strengths for TriBPA‐PC and TABPA‐BPA‐PC are relatively close to that for rp‐BPA‐PC with the value for TriBPA‐PC being slightly larger than that for rp‐BPA‐PC or the value usually reported for typical capacitor grade polycarbonate. Finally, it is shown that the real part of the relative permittivity remains relatively constant from low temperatures to T_g. Consequently, based on the dielectric properties, TriBPA‐PC and TABPA‐BPA‐PC should be usable in capacitors to at least 50 °C higher than BPA‐PC. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

A CIEF‐LIF method for simultaneous analysis of multiple protein kinases and screening of inhibitors

Here, a CIEF‐LIF method for multiple protein kinase simultaneous analysis and inhibitors throughput screening with fast rate and low cost is presented. Comparing with CZE, CIEF‐LIF exhibited great focusing ability and high separation efficiency for substrate and phosphorylated peptides, and is applicable for multiple kinases simultaneous analysis regardless of their substrate peptides compositions and charge statuses. Thus, highly sensitive analysis for cyclic adenosine 3’, 5’‐monophosphate‐dependent protein kinase (PKA) and cyclin‐dependent kinase 1 (CDK1) was achieved in CIEF‐LIF analysis with detection sensitivity up to 1.25 mU/μL and 0.4 mU/μL, respectively, two magnitudes higher than that of CZE and comparable with that in nanomaterials or green fluorescent protein‐based kinase assay. Moreover, the inhibition effect of inhibitors on multiple kinases could be simultaneously readout in a single electrophoretic run, with half maximal inhibitory concentration of H‐89 for PKA and Ro‐3306 for CDK1 calculated as 37.0 and 35.9 nM, respectively, consistent with literatures reported. The CIEF‐LIF also exhibited strong anti‐interference ability in human breast cancer cell lysates analysis and simulators such as forskolin and 3‐isobutyl‐1‐methylxantine assessment. Therefore, CIEF‐LIF is desirable for future biological application and clinical diagnostics and drug discovery.     

In Vitro Biosynthesis of the Nonproteinogenic Amino Acid Methoxyvinylglycine

Oxyvinylglycines are a family of nonproteinogenic amino acids featuring an essential vinyl ether conferring mechanism‐based inhibition of pyridoxal phosphate enzymes. The gene clusters for a few oxyvinylglycines are known, yet the biosynthetic origin of the vinyl ether is elusive. The in vitro biosynthesis of methoxyvinylglycine or l ‐2‐amino‐4‐methoxy‐trans‐3‐butenoic acid (AMB) is reported. It is shown that AMB is made from glutamate as an alanyl‐AMB dipeptide and the rationale is provided for the N‐term Ala. Using a chemical capture method, the order and timing of the modifications on non‐ribosomal peptide synthetase (NRPS)‐bound substrates was determined, including a cryptic hydroxylation of the Glu β‐carbon. Eliminating this hydroxy group likely generates a key α,β‐dehydroamino acid intermediate that facilitates decarboxylation. This work sheds light on vinyl ether biosynthesis and uncovers new NRPS chemistry.     

Synthesis of Honeycomb‐Structured Beryllium Oxide via Graphene Liquid Cells

Using high‐resolution transmission electron microscopy and electron energy‐loss spectroscopy, we show that beryllium oxide crystallizes in the planar hexagonal structure in a graphene liquid cell by a wet‐chemistry approach. These liquid cells can feature van‐der‐Waals pressures up to 1 GPa, producing a miniaturized high‐pressure container for the crystallization in solution. The thickness of as‐received crystals is beyond the thermodynamic ultra‐thin limit above which the wurtzite phase is energetically more favorable according to the theoretical prediction. The crystallization of the planar phase is ascribed to the near‐free‐standing condition afforded by the graphene surface. Our calculations show that the energy barrier of the phase transition is responsible for the observed thickness beyond the previously predicted limit. These findings open a new door for exploring aqueous‐solution approaches of more metal‐oxide semiconductors with exotic phase structures and properties in graphene‐encapsulated confined cells.     

Electrooxidation of Nitrite Mediated by Cu‐x‐Tetraaminophenylporphyrin (x=2, 3, and 4) Glassy Carbon‐Modified Electrodes: Effect of Substituent Position

A study of glassy carbon electrodes modified with poly‐Cu‐x‐tetraaminophenylporphyrin (TAPP) (x=2, 3, and 4) toward the electrooxidation of nitrite is reported. The position of the amino group influences the degree of electropolymerization and the response toward the electrooxidation of nitrite. The influence of pH on the electrocatalytic oxidation of nitrite was also studied, finding that the activity is strongly pH‐dependent. For each system (polymeric porphyrins, poly‐Cu‐2‐TAPP, poly‐Cu‐3‐TAPP, and poly‐Cu‐4‐TAPP), the behavior of the modified electrode as amperometric nitrite sensor was studied at the best pH response, finding a linear correlation over a wide range of concentrations for poly‐Cu‐3‐TAPP. With poly‐Cu‐2‐TAPP, the range is smaller, and there is no linear relationship for poly‐Cu‐4‐TAPP. The plot of I_p vs. the square root of the scan rate shows a linear relationship for all the polymer systems, indicating that the electrooxidation of nitrite in the modified electrodes is a process controlled by diffusion. The Tafel slope was calculated, indicating that the determining step in the electrooxidation of nitrite varies depending on the position of the substituent, showing a dramatic change in the nature of the active sites.     

Assessing the performance of density functional theory for the dynamic polarizabilities of amino acids: Treatment of correlation and role of exact exchange

The theoretical determination of electric response properties of the biological systems is a field where the application of density functional theory (DFT) appears to be quite promising. In this work, the performance of 41 density functional methods is evaluated in predicting dynamic polarizabilities of an experimental benchmark set of 20 proteinogenic amino acids. The behavior of a large number of density functionals, including various types of the local spin density approximation (LSDA), generalized gradient approximation (GGA), meta‐GGA (m‐GGA), hybrid‐GGA (h‐GGA), hybrid meta‐GGA (hm‐GGA), and range‐separated hybrid‐GGA (rsh‐GGA), has been assessed for the purpose. Analyzing the results of our DFT benchmarking, we found that these computationally economical methods show very diverse predictive capability and a careful selection of DFT functionals is very important in the polarizability calculations. Considering the role of exchange, correlation, dispersion and long‐range corrections, it turned out that in the LSDA class, SVWN3 gives better results than SPL and SVWN5 toward the reference values. Of the GGA methods, OPBE outperforms all other functionals. The M06‐L is the best method of m‐GGA class. The B3LYP and TPSSh are the best functionals of h‐GGA and hm‐GGA lineages, respectively. Finally, CAM‐B3LYP is the best method of rsh‐GGA functionals that predicts the most accurate polarizability for amino acids by a large margin with respect to others. Overall, the best performing functionals turn out to be hm‐GGAs TPSSh, TPSS1KCIS, M05, tau‐HCTHhyb, and h‐GGA B3LYP. Hopefully, the results of this investigation might provide the useful guidance to propose a new exchange‐correlation functional for calculating the optical properties of biomolecular materials. © 2013 Wiley Periodicals, Inc.     

Scavenger Receptor A‐Mediated Targeting of Carboxylated Polyrotaxanes to Macrophages and the Impacts of Supramolecular Structure

Because macrophages are involved in the pathology of many diseases, targeting delivery of therapeutic molecules to macrophages is important issue. Polyrotaxanes (PRXs) composed of multiple cyclodextrins threaded with a linear polymer were utilized as a therapeutic agent for metabolic disease and for regulating cellular metabolism. For targeting delivery of PRXs to macrophages, carboxyethyl ether group‐modified PRXs (CEE‐PRXs) are designed for promoting interaction to macrophage scavenger receptor class A (SR‐A). The cellular internalization of anionic CEE‐PRXs in SR‐A‐positive macrophage‐like cells (RAW264.7) is remarkably higher than that of nonionic PRX, whereas the cellular internalization efficiency in SR‐A‐negative cells is comparable between anionic and nonionic PRX. Furthermore, the molecular weight of axle polymer and the number of CEE groups modified on PRX are found to be the predominant factors governing cellular internalization efficiency in SR‐A‐positive RAW264.7 cells. Thus, CEE‐PRXs are a promising design for targeting delivery of PRXs to macrophages.     

Expeditious and Divergent Total Syntheses of Aspidosperma Alkaloids Exploiting Iridium(I)‐Catalyzed Generation of Reactive Enamine Intermediates

A new approach for the divergent total syntheses of (±)‐vincaminorine, (±)‐N‐methylquebrachamine, (±)‐quebrachamine, (±)‐minovine and (±)‐vincadifformine, each in less than 10 linear steps starting from a single δ‐lactam building block, is reported. Key to our route design is the late‐stage generation of reactive enamine functionality from stable indole‐linked δ‐lactams via a highly chemoselective iridium(I)‐catalyzed reduction. The efficiently formed secodine intermediates subsequently undergo either a formal Diels–Alder cycloaddition or a competitive Michael addition/reduction to access aspidosperma‐type alkaloids in excellent diastereoselectivities. Product selectivity could be controlled by changing the indole N‐protecting group in the reductive cyclization precursors. An asymmetric variant of this synthetic strategy for the synthesis of (+)‐20‐epi‐ibophyllidine is also described.