Highly Productive Oxidative Biocatalysis in Continuous Flow by Enhancing the Aqueous Equilibrium Solubility of Oxygen

We report a simple, mild, and synthetically clean approach to accelerate the rate of enzymatic oxidation reactions by a factor of up to 100 when compared to conventional batch gas/liquid systems. Biocatalytic decomposition of H₂O₂ is used to produce a soluble source of O₂ directly in reaction media, thereby enabling the concentration of aqueous O₂ to be increased beyond equilibrium solubility under safe and practical conditions. To best exploit this method, a novel flow reactor was developed to maximize productivity (g product L^?1 h^?1). This scalable benchtop method provides a distinct advantage over conventional bio‐oxidation in that no pressurized gas or specialist equipment is employed. The method is general across different oxidase enzymes and compatible with a variety of functional groups. These results culminate in record space‐time yields for bio‐oxidation.     

Rapid Photoactuation of a DNA Nanostructure using an Internal Photocaged Trigger Strand

A reconfigurable DNA nano‐tweezer is reported that can be switched between a closed and open state with a brief pulse of UV light. In its initial state, the tweezer is held shut using a hairpin with a single‐stranded poly‐A loop. Also incorporated in the structure is a poly‐T trigger strand bearing seven photocaged residues. Upon illumination with 365 nm light, the cages are removed and the trigger strand hybridizes to the loop, opening the tweezer and increasing the distance between its arms from 4 to 18 nm. This intramolecular process is roughly 60 times faster than adding an external trigger strand, and provides a mechanism for the rapid interconversion of DNA nanostructures with light.     

Selective,C-3 Friedel-Crafts acylation to generate functionally diverse,acetylated Imidazo[1,2-a]pyridine derivatives

Carbon-carbon bonds are integral for pharmaceutical discovery and development. Frequently, CC bond reactions utilize expensive catalyst/ligand combinations and/or are low yielding, which can increase time and expenditures in pharmaceutical development. To enhance CC bond formation protocols, we developed a highly efficient, selective, and combinatorially applicable Friedel-Crafts acylation to acetylate the C-3 position of imidazo[1,2-a]pyridines. The reaction, catalyzed by aluminum chloride, is both cost effective and more combinatorial friendly compared to acetylation reactions requiring multiple, stoichiometric equivalents of AlCl₃. The protocol has broad application in the construction of acetylated imidazo[1,2-a]pyridines with an extensive substrate scope. All starting materials are common and the reaction requires inexpensive, conventional heating methods for adaptation in any laboratory. Further, the synthesized compounds are predicted to possess GABA activity through a validated, GABA binding model. The developed method serves as a superior route to generate C-3 acetylated imidazo[1,2-a]pyridine building-blocks for combinatorial synthetic efforts.     

Assessment of the regioselectivity in the condensation reaction of unsymmetrical o-phthaldialdehydes with alanine

One approach for the synthesis of isoindolinones, a privileged bioactive heterocyclic core structure, involves a condensation reaction of o-phthaldialdehydes with a suitable nitrogen-containing nucleophile. This fascinating reaction is revisited here in the context of the use of o-phthaldialdehydes that contain additional substituents in the aromatic ring leading to a detailed analysis of the regioselectivity of the reaction. Eleven monosubstituted o-phthaldialdehydes were synthesised and reacted with alanine. The regioselectivity observed across the eleven substrates led to the design of a disubstituted substrate that reacted with very high control. A gram-scale reaction followed by esterification gave one major regioisomer in high yield. In addition, the regioselectivity observed on reaction of two novel monodeuterated substrates led to an increased mechanistic understanding.     

Zur Mikrochemie der seltenen Erden

Zusammenfassung Scandium gibt mit Alizarin-3-sulfonat ein in verdünnter Essigsäure schwer lösliches Scandiumalizarin-3-sulfonat, während die übrigen seltenen Erden in nicht zu konzentrierten Lösungen nicht ausfallen. Scandium kann auf diese Weise zusammen mit Thorium, das ebenfalls eine schwer lösliche Verbindung gibt, ineiner Operation von den übrigen seltenen Erden abgetrennt werden, auch wenn nur geringe Mengen Scandium vorhanden sind.Mit Cochenilletinktur geben die seltenen Erden und die Zirkonverbindungen violette, Thoriumsalze dagegen blaue Lösungen. Die violetten Lösungen der Ceriterden von Lanthan bis Samarium werden durch verdünnte Essigsäure orangerot gefärbt, indem die ursprüngliche Farbe der Cochenilletinktur wieder hergestellt wird. Bei den Terbin- und Erbinerden und Zirkon ruft erst konzentriertere Essigsäure einen Farbumschlag nach rot hervor und erst ganz konzentrierte Essigsäure bewirkt Farbumschlag nach orangerot.

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Summary Scandium gives with alizarine-3-sulphonate a precipitate of the scandium salt, difficultly soluble in dilute acetic acid, whilst the remaining rare earths are not precipitated, provided the solutions are not unduly concentrated. Scandium, together with thorium, which also forms a sparingly soluble compound, may be separated in this way by a single operation from the other rare earths, even if only small quantities of scandium are present.The rare earths and zirconium compounds yield violet solutions with tincture of cochineal, whereas thorium salts give blue solutions. The violet solutions of the cerite earths from lanthanum to samarium become reddish-orange on the addition of dilute acetic acid, the original colour of the cochineal tincture being restored. In the case of the terbium and erbium earths and zirconium strong acetic acid is necessary in order to bring about a change of colour to red, and a change to the original reddish-orange only results when quite concentrated acetic acid is used.

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Résumé Le scandium donne avec l'alizarine-3-sulfonate un sel difficilement soluble dans l'acide acétique dilué, tandis que les autres terres rares ne sont pas précipitées dans des solutions diluées. On peut, de cette manière, en une seule opération, séparer le scandium et le thorium (qui, lui aussi, donne un composé peu soluble) des autres terres rares, même en présence de très petites quantités de scandium.Les terres rares et les combinaisons de zirconium donnent des solutions violettes avec la teinture de cochenille, les sels de thorium, par contre, donnent des solutions bleues. Les solutions violettes des terres cérites du lanthane au samarium deviennent rouge-orangé par adjonction d'acide acétique dilué; parallèlement, la couleur originelle de la teinture de cochenille réapparait.Quand on a affaire à des terres de terbium et d'erbium et au zirconium, seul l'emploi d'acide acétique plus concentré amène le virage au rouge, tandis qu'il faut de l'acide acétique absolument concentré pour faire virer au rouge.

     

Anion induced and inhibited circumrotation of a [2]catenane

The first example of a catenane capable of performing circumrotation via an anion switching methodology is described; of particular interest is a conformational locking mechanism which results from chloride coordination in the catenane binding cavity.     

Catalytic aerobic oxidation of substituted 8-methylquinolines in Pd(II)-2,6-pyridinedicarboxylic acid systems

The ability of Pd(II) complexes derived from 2,6-pyridinedicarboxylic acids to catalyze homogeneous regioselective aerobic oxidation of 5- and 6-substituted 8-methylquinolines in AcOH-Ac(2)O solution to produce corresponding 8-quinolylmethyl acetates in high yield was demonstrated; corresponding 8-quinoline carboxylic acids are minor reaction products.