Optimized Properties and Synthesis of Photoactivatable Diazoketorhodamines Facilitate and Enhance High-Throughput Single-Molecule Tracking.

Photoactivatable (PA) rhodamine dyes are widely used in single-molecule tracking (SMT) and a variety of other fluorescence-based imaging modalities. One of the most commonly employed scaffolds uses a diazoketone to lock the rhodamine in the nonfluorescent closed form, which can be activated with 405 nm light. However, poor properties of previously reported dyes require significant washing, which can be resource- and cost-intensive, especially when performing microscopy in a large scale and high-throughput fashion. Here, we report improved diazoketorhodamines that perform exceptionally well in single-molecule tracking microscopy. We also report on the optimization of an improved synthetic method for further iteration and tailoring of diazoketorhodamines to the requirements of a specific user.

Nickel-catalyzed asymmetric reductive cross-coupling of α-chloroesters with (hetero)aryl iodides.

An asymmetric reductive cross-coupling of α-chloroesters and (hetero)aryl iodides is reported. This nickel-catalyzed reaction proceeds with a chiral BiOX ligand under mild conditions, affording α-arylesters in good yields and enantioselectivities. The reaction is tolerant of a variety of functional groups, and the resulting products can be converted to pharmaceutically-relevant chiral building blocks. A multivariate linear regression model was developed to quantitatively relate the influence of the α-chloroester substrate and ligand on enantioselectivity.

Photoaffinity Labeling and Quantitative Chemical Proteomics Identify LXRß as the Functional Target of Enhancers of Astrocytic apoE.

Utilizing a phenotypic screen, we identified chemical matter that increased astrocytic apoE secretion in vitro. We designed a clickable photoaffinity probe based on a pyrrolidine lead compound and carried out probe-based quantitative chemical proteomics in human astrocytoma CCF-STTG1 cells to identify liver x receptor ß (LXRß) as the target. Binding of the small molecule ligand stabilized LXRß, as shown by cellular thermal shift assay (CETSA). In addition, we identified a probe-modified peptide by mass spectrometry and proposed a model where the photoaffinity probe is bound in the ligand-binding pocket of LXRß. Taken together, our findings demonstrated that the lead chemical matter bound directly to LXRß, and our results highlight the power of chemical proteomic approaches to identify the target of a phenotypic screening hit. Additionally, the LXR photoaffinity probe and lead compound described herein may serve as valuable tools to further evaluate the LXR pathway.

Sulfonamide Synthesis via Calcium Triflimide Activation of Sulfonyl Fluorides.

A method using calcium triflimide [Ca(NTf2)2] as a Lewis acid to activate sulfonyl fluorides toward nucleophilic addition with amines is described. The reaction converts a wide array of sterically and electronically diverse sulfonyl fluorides and amines into the corresponding sulfonamides in good yield.

Progress toward the total synthesis of N-methylwelwitindolinone B isothiocyanate.

Progress toward the welwitindolinone alkaloid N-methylwelwitindolinone B isothiocyanate is reported. A key reaction to synthesize the [4.3.1] bicycle embedded in the core of the molecule is a furan type 2 intramolecular Diels-Alder reaction with a tetrasubstituted dienophile, which sets the two vicinal quaternary centers present in the natural product. The sterically encumbered cycloaddition precursor was synthesized using a Horner-Wadsworth-Emmons reaction followed by a Suzuki cross-coupling reaction. Finally, introduction of the secondary alkyl chloride was achieved by a regio- and diastereoselective opening of a [2.2.1] oxobicycloheptane functionality.

Origins of regio- and stereochemistry in type 2 intramolecular N-acylnitroso Diels-Alder reactions: a computational study of tether length and substituent effects.

Quantum mechanical calculations have been used to investigate type 2 intramolecular N-acylnitroso Diels-Alder reactions. Experimentally observed regioselectivities and diastereoselectivities of these reactions have been reproduced using B3LYP/6-31+G(d) DFT calculations. The factors that govern selectivity (i.e., tether length, tether substitution and diene substitution) were systematically investigated. Tethers less than 6 carbon atoms lead to 1,3-regioisomers due to conformational restrictions. Substituents on the tether lead to diastereoselective outcomes dictated by transannular interactions in the transition states. The modest diastereoselectivity of diene-substituted substrates is rationalized as arising from reduction of eclipsing interactions in the flattened diene transition states. This method should prove valuable for planning syntheses involving type 2 intramolecular Diels-Alder reactions.

Electric-field-induced wetting and dewetting in single hydrophobic nanopores.

The behaviour of water in nanopores is very different from that of bulk water. Close to hydrophobic surfaces, the water density has been found to be lower than in the bulk, and if confined in a sufficiently narrow hydrophobic nanopore, water can spontaneously evaporate. Molecular dynamics simulations have suggested that a nanopore can be switched between dry and wet states by applying an electric potential across the nanopore membrane. Nanopores with hydrophobic walls could therefore create a gate system for water, and also for ionic and neutral species. Here, we show that single hydrophobic nanopores can undergo reversible wetting and dewetting due to condensation and evaporation of water inside the pores. The reversible process is observed as fluctuations between conducting and non-conducting ionic states and can be regulated by a transmembrane electric potential.

Copper(II)-catalyzed room temperature aerobic oxidation of hydroxamic acids and hydrazides to acyl-nitroso and azo intermediates, and their Diels-Alder trapping.

CuCl(2), in the presence of a 2-ethyl-2-oxazoline ligand, is an effective catalyst for the room temperature, aerobic oxidation of hydroxamic acids and hydrazides, to acyl-nitroso and azo dienophiles respectively, which are efficiently trapped in situ via both inter- and intramolecular hetero-Diels-Alder reactions with dienes. Both inter- and intramolecular variants of the Diels-Alder reaction are suitable under the reaction conditions using a variety of solvents. Under the same conditions, an acyl hydrazide was also oxidized to give an acyl-azo dienophile which was trapped intramolecularly by a diene.

Microwave assisted synthesis of bridgehead alkenes.

A new, concise method to synthesize triene precursors for the type 2 intramolecular Diels-Alder reaction has been developed. Microwave irradiation of the trienes provides a convenient method for the synthesis of bridgehead alkenes. Higher yields, shorter reaction times, and lower reaction temperatures provide a general and efficient route to this interesting class of molecules.