Synthetic entries to 6-fluoro-7-substituted indole derivatives

Three practical synthetic entries of functionalized 6-fluoro-7-substituted indole derivatives were developed in connection with the preparation of 7-fluoro-8-substituted-1,3,4,9-tetrahydropyrano[3,4-b]indole-1-acetic acid derivatives 11 . The first route, which permits group modification about position 8 of the pyranoindole skeleton, employs 2-bromo-3-fluoroaniline ( 18 ) as a key intermediate, the preparation of which was achieved by either a novel ortho metalation of 15 or via the intermediacy of 22 . The second route utilizes 32 to append a terminally functionalized three carbon side chain onto the indole template and in addition leads to 43 from 40 . The third route to the 7-fluoro-8-substituted-pyranoindole skeleton complements route two in that the synthetic pathway exploits 32 in a nucleophilic fashion to construct a terminally functionalized two carbon appendage onto the indole nucleus.     

Fluorescent and electroactive cyclic assemblies from perylene tetracarboxylic acid bisimide ligands and metal phosphane triflates

Tetraaryloxy-substituted perylene tetracarboxylic acid bisimides with one or two 4-pyridyl receptor substituents at the imide functionality were synthesized and employed in transition metal directed self-assembly with Pd(II) and Pt(II) phosphane triflates. Upon mixing of the components, quantitative formation of functional molecular square-type complexes containing four dye molecules and model complexes of a 2:1 (perylene bisimide ligand:transition metal ion) stoichiometry was observed. The isolated metallosupramolecular squares were characterized by 1H and 31P [1H] NMR spectroscopy as well as conventional electrospray ionization (ESI) and ESI-FTICR mass spectrometry, which gave evidence for the structure and the high stability of these giant cyclic dye assemblies (molecular weight (3a) 8172, Pt-Pt corner diagonal ca. 3.4 nm). Studies of the optical absorption and fluorescence properties and the electrochemistry and spectroelectrochemistry of both the perylene bisimide ligands and the perylene bisimide metal complexes show that Pt(II) coordination does not interfere with the optical and electrochemical properties of the perylene bisimide ligands; this gives squares with high fluorescence quantum yields (phiF (3a)=0.88) and three fully reversible redox couples. The latter could be unambiguously related to quantitative formation of perylene bisimide radical cations (E1/2 = +0.93 V vs. Fc/Fc+), radical anions (E1/2= - 1.01 V vs. Fc/Fc+), and dianions (E1/2 = -1.14 V vs. Fc/Fc+); these redox reactions change the charge state of the cyclic assembly from +12 to zero. In contrast, Pd(II) coordination influenced the electrochemical properties of the assembly because of an irreversible palladium reduction at E1/2= -1.15 V versus Fc/Fc+. Finally, dynamic ligand exchange processes between different metallosupramolecular assemblies were investigated by multinuclear NMR and electrospray mass spectrometry. These studies confirmed the reversible nature of the pyridine-Pt(II)/Pd(II) coordination process.     

Completely automated, highly error-tolerant macromolecular structure determination from multidimensional nuclear overhauser enhancement spectra and chemical shift assignments

The major rate-limiting step in high-throughput NMR protein structure determination involves the calculation of a reliable initial fold, the elimination of incorrect nuclear Overhauser enhancement (NOE) assignments, and the resolution of NOE assignment ambiguities. We present a robust approach to automatically calculate structures with a backbone coordinate accuracy of 1.0-1.5 A from datasets in which as much as 80% of the long-range NOE information (i.e., between residues separated by more than five positions in the sequence) is incorrect. The current algorithm differs from previously published methods in that it has been expressly designed to ensure that the results from successive cycles are not biased by the global fold of structures generated in preceding cycles. Consequently, the method is highly error tolerant and is not easily funnelled down an incorrect path in either three-dimensional structure or NOE assignment space. The algorithm incorporates three main features: a linear energy function representation of the NOE restraints to allow maximization of the number of simultaneously satisfied restraints during the course of simulated annealing; a method for handling the presence of multiple possible assignments for each NOE cross-peak which avoids local minima by treating each possible assignment as if it were an independent restraint; and a probabilistic method to permit both inactivation and reactivation of all NOE restraints on the fly during the course of simulated annealing. NOE restraints are never removed permanently, thereby significantly reducing the likelihood of becoming trapped in a false minimum of NOE assignment space. The effectiveness of the algorithm is demonstrated using completely automatically peak-picked experimental NOE data from two proteins: interleukin-4 (136 residues) and cyanovirin-N (101 residues). The limits of the method are explored using simulated data on the 56-residue B1 domain of Streptococcal protein G.     

Kinetische Untersuchungen der Dimerisierung von Cyclopentadien

Zusammenfassung Es wurde die Kinetik der Umwandlung von Cyclopentadien in -Dicyclopentadien in den Medien Toluol, -Dicyclopentadien und in reiner, flüssiger Phase untersucht.Der Umsatz ist eine bimolekulare Reaktion.Der Geschwindigkeitskoeffizient der Reaktion in Toluol wurde auf viskosimetrischem Wege bestimmt. Bei 25° C istk=6,7·10^–5 Liter Mol^–1 Minuten^–1.Kryoskopische Bestimmungen ergaben für den Geschwindigkeitskoeffizienten der Reaktion in -Dicyclopentadien bei 25° Ck=1,1·10^–4 Liter Mol^–1 Minuten^–1.Der Temperaturkoeffizient des Geschwindigkeitskoeffizienten dieser Reaktion pro 10° ist 2,3, die Aktivierungsenergie 15500 cal.Es wurde der Nachweis erbracht, daß die Dimerisierung von Cyclopentadien auch in reiner flüssiger Phase eine bimolekulare Reaktion ist und daß der stetige Anstieg des Geschwindigkeitskoeffizienten auf die Umwandlung des Mediums von Cyclopentadien in Dicyclopentadien zurückzuführen ist.Der Geschwindigkeitskoeffizient der Dimerisierung des Cyclopentadiens in reiner flüssiger Phase ist bei 25° Ck=3,3·10^–5 Liter Mol^–1 Minuten^–1.     

Chiral separation of halogenated amino acids by ligand-exchange capillary electrophoresis

The chiral separation of halogenated amino acids by ligand-exchange CE is described. Halogenated amino acids attracted increasing interest in recent years because of their physiological activities. Different chiral selectors, as there are L-4-hydroxyproline, L-histidine, and N-alkyl derivatives of L-4-hydroxyproline in form of their copper(II) complexes, are compared for their chiral recognition ability for halogenated amino acids. The influence of various parameters, such as selector concentration, pH, organic modifier, and field strength, on the resolution was investigated. All halogenated amino acids investigated were baseline-separated under optimized conditions.     

Die durch Silberionen katalysierte Umlagerung von Propargyl-phenyläther

It is known that propargyl-phenylethers rearrange at about 200° to 2 H-chromenes [1–4]. It is shown that this rearrangement occurs in benzene or chloroform at lower temperatures (20–80°) in the presence of silver-tetrafluoroborate (or-trifluoracetate). The ethers examined are presented in Scheme 1. Thus in chloroform at 61° in the presence of AgBF₄, phenyl-propargylether ( 3 ) yields 2 H-chromene ( 13 ). With 0.78 molar equivalents AgBF₄ in benzene at 80° the same ether 3 yields a 3:1 mixture of 2-methyl-cumaron ( 14 ) and 2 H-chromene ( 13 ). From 1′-methylpropargyl-phenylether ( 4 ) and 2′-butinyl-3,5-dimethylphenylether ( 5 ) under similar conditions the corresponding chromenes 16 and 17 resp. are obtained. Rearrangement of propargyl- and 2′-butinyl-1-methyl-2-naphthylether ( 6 and 7 resp.) in benzene at 80° in the presence of AgBF₄ gives the corresponding allenyl-naphthalenones 18 and 19 resp. Treatment of propargyl- and 2′-butinyl-mesityl-ether ( 8 and 9 resp.), and propargyl- and l′-methylpropargyl- 2 , 6 -dimethyl-phenylether ( 10 and 11 resp.) in benzene at 80° with AgRF, yields as the only product the corresponding 3 -allenyl-phenols 21 , 22 , 24 and 25 (Scheme 3). It is shown that in the presence of μ-dichlor-dirhodiuni (1)-tetracarbonyl in benzene a t 80° the ether 4 rearranges to 2-methyl-2H-chromene (16). However with this catalyst the predominant reaction is a cleavage to phenol. No reaction was observed when ethers 3 and 12 , (Scheme 7 ) were treated with the tris-(trimethylsily1)-ester of vanadic acid in benzene a t 80° (see also [8]). By analogy with the known mechanism for thc silver catalysis of the reversible propargylesterl/allenylester rearrangement [S], the silver (1)ion is assumed to form a pre-equilibrium π-complex with the C, C-triplebond of the substrate. This complex then undergoes a [3s, 3s]-sigmatropic rearrangement (Scheme 2). In the case of the others 6 , 7 and 12 the resulting allenyldienones were isolated. The 2,G-dimethyl substituted ethers 8 , 9 , 10 and 11 resp. first give the usual allenyl- dienones (Scheme 3). These then undergo a novel silver catalysed dienon-phenol-rearrangement (Sclzenzu4) to give the 3-allenylphenols 21 , 22 , 24 and 25 . Thc others 3 , 4 and 5 with free ortho positions presumably rearrange first to the non-isolated 2-allenyl-phenols 15 , 42 and 43 resp.(Scheme 7). These then rearrange, either thermally or by silver (1)ion catalysis to the 2H-chromenes 13 , 16 and 17 resp. The rate of the rearrangement of 2-allenylphenol ( 15 ) to 13 at room temperature in benzene or chloroform is approximately doubled when silver ions are present as catalyst.     

Some remarks concerning the M.I.T. public-key cryptosystem

Let a messageM be encrypted by raisingM to a powere moduloR, whereR ande are integers which are made public. The recipient of this encrypted form ofM can decipher it by raising the cipher text to a powerd moduloR. Only the recipient knows the values of the two large primesp ₁,p ₂ such thatR=p ₁ p ₂; consequently, only he knowsd, ase is preselected such that (e, (p ₁ – 1)(p ₂ – 1))=1 anded 1 (mod (p ₁ – 1)(p ₂ – 1)).Recently several attacks have been made on the proposed security of this cryptosystem under iteration of the encryption procedure. In this paper we discuss methods of selecting the primesp ₁,p ₂ and the encryption exponente such that the possibility of breaking this cryptosystem by using an iteration procedure is minimized. Several numerical results are also presented.     

A Polyclonal Selex Aptamer Library Directly Allows Specific Labelling of the Human Gut Bacterium Blautia producta without Isolating Individual Aptamers

Recent studies have demonstrated that changes in the abundance of the intestinal bacterium Blautia producta, a potential probiotic, are closely associated with the development of various diseases such as obesity, diabetes, some neurodegenerative diseases, and certain cancers. However, there is still a lack of an effective method to detect the abundance of B. producta in the gut rapidly. Especially, DNA aptamers are now widely used as biometric components for medical testing due to their unique characteristics, including high chemical stability, low production cost, ease of chemical modification, low immunogenicity, and fast reproducibility. We successfully obtained a high-affinity nucleic acid aptamer library (B.p-R14) after 14 SELEX rounds, which efficiently discriminates B. producta in different analysis techniques including fluorometric suspension assays or fluorescence microscopy from other major gut bacteria in complex mixtures and even in human stool samples. These preliminary findings will be the basis towards aptamer-based biosensing applications for the fast and reliable monitoring of B. producta in the human gut microbiome.     

Precise Quantification of Molybdate In Vitro by the FRET-Based Nanosensor ‘MolyProbe’

Molybdenum (Mo) is an essential trace element in all kingdoms of life. Mo is bioavailable as the oxyanion molybdate and gains biological activity in eukaryotes when bound to molybdopterin, forming the molybdenum cofactor. The imbalance of molybdate homeostasis results in growth deficiencies or toxic symptoms within plants, fungi and animals. Recently, fluorescence resonance energy transfer (FRET) methods have emerged, monitoring cellular and subcellular molybdate distribution dynamics using a genetically encoded molybdate-specific FRET nanosensor, named MolyProbe. Here, we show that the MolyProbe system is a fast and reliable in vitro assay for quantitative molybdate determination. We added a Strep-TagII affinity tag to the MolyProbe protein for quick and easy purification. This MolyProbe is highly stable, resistant to freezing and can be stored for several weeks at 4 °C. Furthermore, the molybdate sensitivity of the assay peaked at low nM levels. Additionally, The MolyProbe was applied in vitro for quantitative molybdate determination in cell extracts of the plant Arabidopsis thaliana, the fungus Neurospora crassa and the yeast Saccharomyces cerevisiae. Our results show the functionality of the Arabidopsis thaliana molybdate transporter MOT1.1 and indicate that FRET-based molybdate detection is an excellent tool for measuring bioavailable Mo.     

2,9-Diazadibenzoperylene and 2,9-Dimethyldibenzoperylene-1,3,8,10-tetratriflates: Key to Functionalized 2,9-Diazaperopyrenes

The synthesis of 2,9-diaza-1,3,8,10-tetratriflato-dibenzoperylene (DDP 3 a ) and corresponding 2,9-dimethyl-1,3,8,10-tetratriflato-dibenzoperylene (DBP 3 b ) has been developed at multigram scale via reduction of one of the industrially most important high-performance dyes, perylene-3,4,9,10-tetracarboxylic diimide (PTCDI), and of the corresponding dihydroxy peropyrenequinone precursor. The focus of this paper is on the reactivity pattern of 3 a as key intermediate towards highly functionalized 2,9-diazadibenzopyrelenes (DDPs) obtained via catalytic substitution of four triflate by aryl, heteroaryl, alkynyl, aminyl, and O-phosphanyl substituents. The influence of electron-donating substituents (OSiMe₃, OPt-Bu₂, N-piperidinyl), electron-withdrawing (OTf, 3,5-bis-trifluoromethyl-phenyl), and of electron-rich π-conjugated (2-thienyl, 4-tert-butylphenyl, trimethylsilyl-ethynyl) substituents on optoelectronic and structural properties of these functionalized DDPs has been investigated via XRD analyses, UV/Vis, PL spectroscopy, and by electroanalytical CV. These results were correlated to results of DFT and TD-DFT calculations. Thus, functionalized DPPs with easily tunable HOMO and LUMO energies and gap became available via a new and reliable synthetic strategy starting from readily available PTCDI.