DNA vs. Mirror-Image DNA: A Universal Approach to Tune the Absolute Configuration in DNA-Based Asymmetric Catalysis

Terpyridine-Cu(ii) targeting human telomeric DNA to produce highly stereospecific G-quadruplex DNA metalloenzyme

The cofactors commonly involved in natural enzymes have provided the inspiration for numerous advances in the creation of artificial metalloenzymes. Nevertheless, to design an appropriate cofactor for a given biomolecular scaffold or vice versa remains a challenge in developing efficient catalysts in biochemistry. Herein, we extend the idea of G-quadruplex-targeting anticancer drug design to construct a G-quadruplex DNA metalloenzyme. We found that a series of terpyridine-Cu(ii) complexes (CuLn) can serve as excellent cofactors to dock with human telemetric G-quadruplex DNA. The resulting G-quadruplex DNA metalloenzyme utilising CuL1 catalyzes an enantioselective Diels-Alder reaction with enantioselectivity of >99% enantiomeric excess and about 73-fold rate acceleration compared to CuL1 alone. The terpyridine-Cu(ii) complex cofactors demonstrate dual functions, both as an active site to perform catalysis and as a structural regulator to promote the folding of human telemetric G-quadruplex DNA towards excellent catalysts.

Octahedral Chiral-at-Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions

Octahedral iridium(III) complexes containing two bidentate cyclometalating 5-tert-butyl-2-phenylbenzoxazole (IrO) or 5-tert-butyl-2-phenylbenzothiazole (IrS) ligands in addition to two labile acetonitrile ligands are demonstrated to constitute a highly versatile class of asymmetric Lewis acid catalysts. These complexes feature the metal center as the exclusive source of chirality and serve as effective asymmetric catalysts (0.5-5.0 mol % catalyst loading) for a variety of reactions with α,β-unsaturated carbonyl compounds, namely Friedel-Crafts alkylations (94-99% ee), Michael additions with CH-acidic compounds (81-97% ee), and a variety of cycloadditions (92-99% ee with high d.r.). Mechanistic investigations and crystal structures of an iridium-coordinated substrates and iridium-coordinated products are consistent with a mechanistic picture in which the α,β-unsaturated carbonyl compounds are activated by two-point binding (bidentate coordination) to the chiral Lewis acid.

Asymmetric Lewis acid catalysis directed by octahedral rhodium centrochirality

A rhodium-based asymmetric catalyst is introduced which derives its optical activity from octahedral centrochirality. Besides providing the exclusive source of chirality, the rhodium center serves as a Lewis acid by activating 2-acyl imidazoles through two point binding and enabling a very effective asymmetric induction mediated by the propeller-like C2-symmetrical ligand sphere. Applications to asymmetric Michael additions (electrophile activation) as well as asymmetric α-aminations (nucleophile activation) are disclosed, for which the rhodium catalyst is found to be overall superior to its iridium congener. Due to its straightforward proline-mediated synthesis, high catalytic activity (catalyst loadings down to 0.1 mol%), and tolerance towards moisture and air, this novel class of chiral-at-rhodium catalysts will likely to become of widespread use as chiral Lewis acid catalysts for a large variety of asymmetric transformations.

DNA-cellulose: an economical, fully recyclable and highly effective chiral biomaterial for asymmetric catalysis

We report here the first generation of a DNA-based catalyst bound to a cellulose matrix. The chiral biomaterial is commercially available, trivial to use, highly selective and fully recyclable.

Characterisation of the interactions between substrate, copper(ii) complex and DNA and their role in rate acceleration in DNA-based asymmetric catalysis

High effective molarity is responsible for the significant increase of binding of substrates to copper(ii) complexes in DNA-based catalysis.

DNA based multi-copper ions assembly using combined pyrazole and salen ligandosides

The DNA structure is an ideal building block for the construction of functional nano-objects. In this direction, metal coordinating base pairs (ligandosides) are an appealing tool for the future specific functionalization of such nano-objects. We present here a study, in which we combine the metal ion coordinating pyrazole ligandoside with the interstrand crosslinking salen ligandoside system. We show that both ligandosides, when combined, are able to create stable multi-copper ion complexing DNA double helix structures in a cooperative fashion.

DNA-Based Asymmetric Catalysis: Role of Ionic Solvents and Glymes

Recently, DNA has been evaluated as a chiral scaffold for metal complexes to construct so called 'DNA-based hybrid catalysts', a robust and inexpensive alternative to enzymes. The unique chiral structure of DNA allows the hybrid catalysts to catalyze various asymmetric synthesis reactions. However, most current studies used aqueous buffers as solvents for these asymmetric reactions, where substrates/products are typically suspended in the solutions. The mass transfer limitation usually requires a long reaction time. To overcome this hurdle and to advance DNA-based asymmetric catalysis, we evaluated a series of ionic liquids (ILs), inorganic salts, deep eutectic solvents (DES), glymes, glycols, acetonitrile and methanol as co-solvents/additives for the DNA-based asymmetric Michael addition. In general, these additives induce indistinguishable changes to the DNA B-form duplex conformation as suggested by circular dichroism (CD) spectroscopy, but impose a significant influence on the catalytic efficiency of the DNA-based hybrid catalyst. Conventional organic solvents (e.g. acetonitrile and methanol) led to poor product yields and/or low enantioselectivities. Most ILs and inorganic salts cause the deactivation of the hybrid catalyst except 0.2 M [BMIM][CF3COO] (95.4% ee and 93% yield) and 0.2 M [BMIM]Cl (93.7% ee and 89% yield). Several other additives have also been found to improve the catalytic efficiency of the DNA-based hybrid catalyst (control reaction without additive gives >99% ee and 87% yield): 0.4 M glycerol (>99% ee and 96% yield at 5 °C or 96.2% ee and 83% yield at room temperature), 0.2 M choline chloride/glycerol (1:2) (92.4% ee and 90% yield at 5 °C or 94.0% ee and 88% yield at room temperature), and 0.5 M dipropylene glycol dimethyl ether (>99% ee and 87% yield at room temperature). The use of some co-solvents/additives allows the Michael addition to be performed at a higher temperature (e.g. room temperature vs 5 °C) and a shorter reaction time (24 h vs 3 days). In addition, we found that a brief pre-sonication (5 min) of DNA in MOPS buffer prior to the reaction could improve the performance of the DNA-based hybrid catalyst. We have also shown that this DNA-based catalysis method is suitable for a variety of different substrates and relatively large-scale reactions. In conclusion, a judicious selection of benign co-solvents/additives could improve the catalytic efficiency of DNA-based hybrid catalyst.

Amplification by nucleic acid-templated reactions

Nucleic acid-templated reactions that proceed with turnover provide a means for signal amplification, which facilitates the use and detection of biologically occurring DNA/RNA molecules.