Applications of Bacteria Decorated with Synthetic DNA Constructs.

The advent of DNA nanotechnology has revolutionized the way DNA has been perceived. Rather than considering it as the genetic material alone, DNA has emerged as a versatile synthetic scaffold that can be used to create a variety of molecular architectures. Modifying such self-assembled structures with bio-molecular recognition elements has further expanded the scope of DNA nanotechnology, opening up avenues for using synthetic DNA assemblies to sense or regulate biological molecules. Recent advancements in this field have lead to the creation of DNA structures that can be used to modify bacterial cell surfaces and endow the bacteria with new properties. This mini-review focuses on the ways by which synthetic modification of bacterial cell surfaces with DNA constructs can expand the natural functions of bacteria, enabling their potential use in various fields such as material engineering, bio-sensing, and therapy. The challenges and prospects for future advancements in this field are also discussed.

Insights into the Mechanism of Aluminum-Catalyzed Halodefluorination.

Aluminum has been reported to catalyze halodefluorination reactions, where aliphatic fluorine is substituted with a heavier halogen. Although it is known that stoichiometric aluminum halide can perform this reaction, the role of catalytic aluminum halide and organyl alane reagents is not well understood. We investigate the mechanism of the halodefluorination reaction using catalytic aluminum halide and stoichiometric trimethylsilyl halide. We explore the use of B(C6F5)3 as a catalyst to benchmark pathways where aluminum acts either as a Lewis acid catalyst in cooperation with trimethylsilyl halide or as an independent halodefluorination reagent which is subsequently regenerated by trimethylsilyl halide. Computational and experimental results indicate that aluminum acts as an independent halodefluorination reagent and that reactivity trends observed between different halide reagents can be attributed to relative barriers in halide delivery to the organic fragment, which is the rate-limiting step in both the aluminum halide- and B(C6F5)3-catalyzed pathways.

Nucleophilic Substitution of Aliphatic Fluorides via Pseudohalide Intermediates.

A method for aliphatic fluoride functionalization with a variety of nucleophiles has been reported. Carbon-fluoride bond cleavage is thermodynamically driven by the use of silylated pseudohalides TMS-OMs or TMS-NTf2 , resulting in the formation of TMS-F and a trapped aliphatic pseudohalide intermediate. The rate of fluoride/pseudohalide exchange and the stability of this intermediate are such that little rearrangement is observed for terminal fluoride positions in linear aliphatic fluorides. The ability to convert organofluoride positions into pseudohalide groups allows facile nucleophilic attack by a wide range of nucleophiles. The late introduction of the nucleophiles also allows for a wide range of functional-group tolerance in the coupling partners. Selective alkyl fluoride mesylation is observed in the presence of other alkyl halides, allowing for orthogonal synthetic strategies.

Recent methods for the synthesis of α-acyloxy ketones.

The present review provides a broad description of the methods reported for the synthesis of α-acyloxy ketones and some of their derivatives. α-Acyloxy ketones and their derivatives are vital synthetic intermediates and are ubiquitous as biochemical constituents of living organisms, biologically active natural products and pharmaceuticals. Due to their biological importance, new methods for their synthesis are being continuously developed and documented in the recent past. However, the chemical literature lacks a comprehensive summary on the synthetic methodologies targeting α-acyloxy ketones. In an attempt to fill this void, this review discusses their synthetic procedures developed over time. The synthetic approaches are systematically classified based on the substrates used. The mechanistic details for certain critical cases are also discussed. In the past, preparation of α-acyloxy ketones was reported from functionalized ketones like α-haloketones and diazo esters. Later on, among the reactions that formed the acyloxy ketones, oxidative coupling of ketones with carboxylic acids both under metal and metal-free conditions made their synthesis simple and versatile. Specifically, in the last decade, many oxidative coupling reactions emerged as a powerful tool for the synthesis of α-acyloxy ketones. Quite recently, acyloxy ketones' synthesis has been reported from commercially available alkenes and alkynes through oxidative addition reactions. Subsequently, the mechanistic details for these coupling reactions became interesting to many organic chemists. The asymmetric version of the title compounds hails from their enzymatic resolution to metal catalysed chiral synthesis. Besides, the synthesis of acyloxy ketones from epoxides, alcohols and enamides using various oxidative reagents has also been documented.

I2-mediated regioselective C-3 azidation of indoles.

An unprecedented synthesis of novel 3-azido indoles has been developed using I2 and NaN3 in high yields and excellent regioselectivity. The reaction proceeds under metal-free conditions at room temperature. Essentially, an umpolung in reactivity at the C-3 position of indole has been achieved by the activation of indoles with I2.

N-Heterocyclic Carbene Catalyzed Oxidative Coupling of Alkenes/α-Bromoacetophenones with Aldehydes: A Facile Entry to α,ß-Epoxy Ketones.

A novel, N-heterocyclic carbene (NHC) catalyzed direct oxidative coupling of styrenes with aldehydes has been described for the synthesis of α,ß-epoxy ketones in good yields. This unprecedented regioselective oxidative coupling employs NBS/DBU/DMSO (DBU=1,8-diazabicyclo [5.4. 0] undec-7-ene, DMSO=dimethylsulfoxide, NBS=N-bromosuccinimide) as an oxidative system at ambient conditions. Additionally, first NHC-catalyzed Darzens reaction of α-bromoketones and aldehydes under mild reaction conditions has also been described. Interestingly, mechanistic studies have revealed the preferred reactivity of NHC with alkene/α-bromoketone rather than aldehydes, thus proceeding via the ketodeoxy Breslow intermediate.

CuCN-mediated cascade cyclization of 4-(2-bromophenyl)-2-butenoates: a high-yield synthesis of substituted naphthalene amino esters.

A new method of CuCN-mediated one-pot cyclization of 4-(2-bromophenyl)-2-butenoates leading to efficient synthesis of substituted naphthalene amino esters including phenanthrene aromatic structural units is described. Deuterium labeling studies establish that this one-pot cascade cyclization proceeds through isomerization of olefin, intramolecular C-C bond cyclization, and aromatization as the key intermediates, all occurring in a single step.

Chemically programmable bacterial probes for the recognition of cell surface proteins.

Common methods to label cell surface proteins (CSPs) involve the use of fluorescently modified antibodies (Abs) or small-molecule-based ligands. However, optimizing the labeling efficiency of such systems, for example, by modifying them with additional fluorophores or recognition elements, is challenging. Herein we show that effective labeling of CSPs overexpressed in cancer cells and tissues can be obtained with fluorescent probes based on chemically modified bacteria. The bacterial probes (B-probes) are generated by non-covalently linking a bacterial membrane protein to DNA duplexes appended with fluorophores and small-molecule binders of CSPs overexpressed in cancer cells. We show that B-probes are exceptionally simple to prepare and modify because they are generated from self-assembled and easily synthesized components, such as self-replicating bacterial scaffolds and DNA constructs that can be readily appended, at well-defined positions, with various types of dyes and CSP binders. This structural programmability enabled us to create B-probes that can label different types of cancer cells with distinct colors, as well as generate very bright B-probes in which the multiple dyes are spatially separated along the DNA scaffold to avoid self-quenching. This enhancement in the emission signal enabled us to label the cancer cells with greater sensitivity and follow the internalization of the B-probes into these cells. The potential to apply the design principles underlying B-probes in therapy or inhibitor screening is also discussed here.

Regioselective Oxo-Amination of Alkenes and Enol Ethers with N-Bromosuccinimide-Dimethyl Sulfoxide Combination: A Facile Synthesis of α-Amino-Ketones and Esters.

An unprecedented conversion of alkenes and enol ethers to the corresponding α-imido carbonyl compounds with excellent regioselectivity and yields has been developed. This oxo-amination process employs readily available N-bromosuccinimide (NBS) and secondary amines as N-sources and dimethyl sulfoxide (DMSO) as the oxidant and also leads to the production of amino alcohols in a single step on reduction, thus broadening the scope of this operationally simple reaction. For the first time, the formation of reactive Me2S(+)-O-Br species generated by the interaction of NBS with DMSO has been proven.

I2-catalyzed regioselective oxo- and hydroxy-acyloxylation of alkenes and enol ethers: a facile access to α-acyloxyketones, esters, and diol derivatives.

I2-catalyzed oxo-acyloxylation of alkenes and enol ethers with carboxylic acids providing for the high yield synthesis of α-acyloxyketones and esters is described. This unprecedented regioselective oxidative process employs TBHP and Et3N in stoichiometric amounts under metal-free conditions in DMSO as solvent. Additionally, I2-catalysis allows the direct hydroxy-acyloxylation of alkenes with the sequential addition of BH3·SMe2 leading to monoprotected diol derivatives in excellent yields.