A Universal Procedure for the [18F]Trifluoromethylation of Aryl Iodides and Aryl Boronic Acids with Highly Improved Specific Activity

Herein, we describe a valuable method for the introduction of the [¹⁸F]CF₃ group into arenes with highly improved specific activity by the reaction of [¹⁸F]trifluoromethane with aryl iodides or aryl boronic acids. This [¹⁸F]trifluoromethylation reaction is the first to be described in which the [¹⁸F]CF₃ products are generated in actual trace amounts and can therefore effectively be used as PET tracers. The method shows broad scope with respect to possible aryl iodide and aryl boronic acid substrates, as well as good to excellent conversion. In particular, the [¹⁸F]trifluoromethylation of boronic acids was found to outperform [¹⁸F]trifluoromethylation reactions of halogenated aryl precursors with regard to conversion, reaction conditions, and kinetics.     

A Breast Cancer Stem Active Cobalt(III)-Cyclam Complex Containing Flufenamic Acid with Immunogenic Potential

The cytotoxic and immunogenic-activating properties of a cobalt(III)-cyclam complex bearing the non-steroidal anti-inflammatory drug, flufenamic acid is reported within the context of anti-cancer stem cell (CSC) drug discovery. The cobalt(III)-cyclam complex 1 displays sub-micromolar potency towards breast CSCs grown in monolayers, 24-fold and 31-fold greater than salinomycin (an established anti-breast CSC agent) and cisplatin (an anticancer metallopharmaceutical), respectively. Strikingly, the cobalt(III)-cyclam complex 1 is 69-fold and 50-fold more potent than salinomycin and cisplatin towards three-dimensionally cultured breast CSC mammospheres. Mechanistic studies reveal that 1 induces DNA damage, inhibits cyclooxygenase-2 expression, and prompts caspase-dependent apoptosis. Breast CSCs treated with 1 exhibit damage-associated molecular patterns characteristic of immunogenic cell death and are phagocytosed by macrophages. As far as we are aware, 1 is the first cobalt complex of any oxidation state or geometry to display both cytotoxic and immunogenic-activating effects on breast CSCs.     

Activity and Enantioselectivity of the Hydroxynitrile Lyase MeHNL in Dry Organic Solvents

Water concentration affects both the enantioselectivity and activity of enzymes in dry organic media. Its influence has been investigated using the hydrocyanation of benzaldehyde catalyzed by hydroxynitrile lyase cross‐linked enzyme aggregate (MeHNL‐CLEA) as a model reaction. The enzyme displayed higher enantioselectivity at higher water concentration, thus suggesting a positive effect of enzyme flexibility on selectivity. The activity increased on reducing the solvent water content, but drastic dehydration of the enzyme resulted in a reversible loss of activity.     

Multicomponent synthesis of 2-imidazolines

[reaction: see text] A multicomponent reaction (MCR) between amines, aldehydes, and isocyanides bearing an acidic alpha-proton gives easy access to a diverse range of highly substituted 2-imidazolines. The limitations of the methodology seem to be determined by the reactivity of the isocyanide and by the steric bulk on the in situ generated imine rather than by the presence of additional functional groups on the imine. Less reactive isocyanides, for example p-nitrobenzyl isocyanide 25a, react successfully with amines and aldehydes, using a catalytic amount of silver(I) acetate. Some of the resulting p-nitrophenyl-substituted 2-imidazolines undergo air oxidation to the corresponding imidazoles. Differences in reactivity of the employed isocyanides are explained with use of DFT calculations. Difficult reactions with ketones instead of aldehydes as the oxo-compound in this MCR are promoted by silver(I) acetate as well.     

High‐Throughput Reaction Optimisation and Activity Screening of Ferrocene‐Based Lewis Acid–Catalyst Complexes by Using Continuous‐Flow Reaction Detection Mass Spectrometry

Optimising synthetic conversions and assessing catalyst performance is a tedious and laborious endeavour. Herein, we present an automated alternative to the commonly applied sequential approaches that are used to increase catalyst discovery process efficiencies by increasing the number of entities that can be tested. This new approach combines conversion of the reactants and determination of product formation into a single comprehensive reaction detection system that can be operated with minimal catalyst and reactant consumption. With this approach, rudimentary reaction conditions can be quickly optimised and the same system can then be used to screen for the optimal homogenous catalyst in a selected solution‐phase synthetic conversion. The system, which is composed of standard HPLC components, can be used to screen catalyst libraries at a repetition rate of five minutes and can be run unsupervised. The sensitive mass spectrometric detection that is implemented in the reaction detection methodology can be used for the simultaneous monitoring of reactants, catalysts and product ions. In the experiments, the three‐component reaction that gives a substituted 2‐imidazoline was optimised. Afterwards, the same method was used to assess a library of ferrocene‐based Lewis acid catalysts for performance in the aforementioned conversion in six different solvents. We demonstrate the feasibility of using this methodology to directly compare the performance results obtained in different solvents by calibrating the solvent‐specific MS responses.     

A Multicomponent Reaction Towards N‐(Cyanomethyl)amides

Diversity‐oriented synthesis : The multicomponent reaction of α‐isocyano amides, aldehydes or ketones, and amines affords N‐(cyanomethyl)amides, presenting the fourth class of products from this combination of reagents (see scheme). The scope of the reaction is very broad and various functional groups are tolerated. The outcome of the reaction can also be directed to the formation of 2H‐2‐imidazolines by Ag^I catalysis.

     

Asymmetric Synthesis of Tetracyclic Pyrroloindolines and Constrained Tryptamines by a Switchable Cascade Reaction

The interrupted Fischer indole synthesis of arylhydrazines and biocatalytically generated chiral bicyclic imines selectively affords either tetracyclic pyrroloindolines or tricyclic tryptamine analogues depending on the reaction conditions. We demonstrate that the reaction is compatible with a variety of functional groups. The products are obtained in high optical purity and in reasonable to good yield. We present a plausible reaction mechanism to explain the observed reaction outcome depending on the stoichiometry of the acid mediator. To demonstrate the synthetic utility of our method, pharmaceutically relevant examples of both product classes were synthesized in highly efficient reaction sequences, including a phenserine analogue as a potential cholinesterase inhibitor and constrained tryptamine derivatives as selective inhibitors of the 5‐HT₆ serotonin receptor and the TRPV1 ion channel.     

Trityl Isocyanide as a Mechanistic Probe in Multicomponent Chemistry: Walking the Line between Ugi‐ and Strecker‐type Reactions

Herein, we describe the versatile application of triphenylmethyl (trityl) isocyanide in multicomponent chemistry. This reagent can be employed as a cyanide source in the Strecker reaction and as convertible isocyanide in the preparation of N‐acyl amino acids by Ugi 4CR/detritylation and free imidazo[1,2‐a]pyridin‐3‐amines by a Groebke–Blackburn–Bienaymé 3CR condensation/deprotection protocol. The mechanisms of these three classical MCRs intersect at the common N‐trityl nitrilium ion intermediate, whose predictable reactivity can be exploited towards chemoselective transformations.     

A flexible six-component reaction to access constrained depsipeptides based on a dihydropyridinone core

Highly functionalized and conformationally constrained depsipeptides based on a dihydropyridin-2-one core are prepared by the combination of a four- and a three-component reaction. The synthesis combines a one-pot Horner-Wadsworth-Emmons/cyclocondensation sequence leading to isonitrile-functionalized DHP-2-ones with an isonitrile-based Passerini multicomponent reaction (MCR). Substituents could be independently varied at six different positions. The two MCRs could also be performed as a one-pot procedure, simplifying the protocol and leading to a new and highly variable six-component process.