Electrochemical recycling of polymeric materials

Polymeric materials play a pivotal role in our modern world, offering a diverse range of applications. However, they have been designed with end-properties in mind over recyclability, leading to a crisis in their waste management. The recent emergence of electrochemical recycling methodologies for polymeric materials provides new perspectives on closing their life cycle, and to a larger extent, the plastic loop by transforming plastic waste into monomers, building blocks, or new polymers. In this context, we summarize electrochemical strategies developed for the recovery of building blocks, the functionalization of polymer chains as well as paired electrolysis and discuss how they can make an impact on plastic recycling, especially compared to traditional thermochemical approaches. Additionally, we explore potential directions that could revolutionize research in electrochemical plastic recycling, addressing associated challenges.

Computational Predictive and Electrochemical Detection of Metabolites (CP-EDM) of Piperine

In this article, we introduce a proof-of-concept strategy, Computational Predictive and Electrochemical Detection of Metabolites (CP-EDM), to expedite the discovery of drug metabolites. The use of a bioactive natural product, piperine, that has a well-curated metabolite profile but an unpredictable computational metabolism (Biotransformer v3.0) was selected. We developed an electrochemical reaction to oxidize piperine into a range of metabolites, which were detected by LC-MS. A series of chemically plausible metabolites were predicted based on ion fragmentation patterns. These metabolites were docked into the active site of CYP3A4 using Autodock4.2. From the clustered low-energy profile of piperine in the active site, it can be inferred that the most likely metabolic position of piperine (based on intermolecular distances to the Fe-oxo active site) is the benzo[d][1,3]dioxole motif. The metabolic profile was confirmed by comparison with the literature, and the electrochemical reaction delivered plausible metabolites, vide infra, thus, demonstrating the power of the hyphenated technique of tandem electrochemical detection and computational evaluation of binding poses. Taken together, we outline a novel approach where diverse data sources are combined to predict and confirm a metabolic outcome for a bioactive structure.

Polymer up-cycling by mangana-electrocatalytic C(sp3)-H azidation without directing groups

The chemical up-cycling of polymers into value-added materials offers a unique opportunity to place plastic waste in a new value chain towards a circular economy. Herein, we report the selective up-cycling of polystyrenes and polyolefins to C(sp3)-H azidated materials under electrocatalytic conditions. The functionalized polymers were obtained with high retention of mass average molecular mass and high functionalization through chemo-selective mangana-electrocatalysis. Our strategy proved to be broadly applicable to a variety of homo- and copolymers. Polyethylene, polypropylene as well as post-consumer polystyrene materials were functionalized by this approach, thereby avoiding the use of hypervalent-iodine reagents in stoichiometric quantities by means of electrocatalysis. This study, hence, represents a chemical oxidant-free polymer functionalization by electro-oxidation. The electrocatalysis proved to be scalable, which highlights its unique feature for a green hydrogen economy by means of the hydrogen evolution reaction (HER).

Synthesis of Bridged Oxabicycles via Cascade Reactions involving O-Acyloxocarbenium Ion Intermediates

Compared to related electrophilic species, O-acyloxocarbenium ions (AOIs) have been much less utilized in organic synthesis due to the lack of an efficient formation method. Here, we present a facile and simple approach for the generation of AOI from ester and acetal groups. Based on our AOI system with a pendant nucleophile, we obtained a unique bridged bicyclic system via an epoxonium-like transition state. The proposed mechanism is based on experimental and computational studies.

Collective Asymmetric Total Synthesis of C-11 Oxygenated Cephalotaxus Alkaloids

While numerous studies pertaining to the total synthesis of Cephalotaxus alkaloids have been reported, only two strategies have been reported to date for the successful synthesis of the C-11 oxygenated subset, due to the additional synthetic challenge posed by the remote C-11 stereocenter. Herein, we report the collective asymmetric total synthesis of C-11 oxygenated Cephalotaxus alkaloids using a chiral proline both as a starting material and as the only chirality source. A tetracyclic advanced intermediate was synthesized in a highly stereoselective manner from l-proline in 8 steps involving sequential chirality transfer steps such as a diastereoselective N-alkylation, stereospecific Stevens rearrangement and intramolecular Friedel-Crafts reaction via an unusual O-acyloxocarbenium intermediate. From a common intermediate, the asymmetric total synthesis of six C-11 oxygenated Cephalotaxus alkaloids was completed by a series of oxidation state adjustments.

Dialling-In New Reactivity into the Shono-Type Anodic Oxidation Reaction

This Personal Account describes the author's groups' research in the field of electrosynthetic anodic oxidation, beginning with initial trial and error attempts with the Shono oxidation. Early setbacks with complex rotameric amide mixtures, provided the ideal environment for the discovery of the Oxa-Shono reaction-O_sp ² -C_sp ³ bond cleavage of esters-providing two useful products in one-step: aldehyde selective oxidation level products and a mild de-esterification method to afford carboxylic acids in the process. The development of the Oxa-Shono reaction provided the impetus for the discovery of other electrically propelled-N_sp ² -C_sp ² and N_sp ² -C_sp ³ -bond breaking reactions in bioactive amide and sulfonamide systems. Understanding the voltammetric behaviour of the molecule under study, switching between controlled current- or controlled potential- electrolysis, and restricting electron flow (the reagent), affords exquisite control over the reaction outcomes in batch and flow. Importantly, this bio-inspired advance in electrosynthetic dealkylation chemistry mimics the metabolic outcomes observed in nature.

Voltammetric Behaviour of Drug Molecules as a Predictor of Metabolic Liabilities

Electron transfer plays a vital role in drug metabolism and underlying toxicity mechanisms. Currently, pharmaceutical research relies on pharmacokinetics (PK) and absorption, distribution, metabolism, elimination and toxicity (ADMET) measurements to understand and predict drug reactions in the body. Metabolic stability (and toxicity) prediction in the early phases of the drug discovery and development process is key in identifying a suitable lead compound for optimisation. Voltammetric methods have the potential to overcome the significant barrier of new drug failure rates, by giving insight into phase I metabolism events which can have a direct bearing on the stability and toxicity of the parent drug being dosed. Herein, we report for the first time a data-mining investigation into the voltammetric behaviour of reported drug molecules and their correlation with metabolic stability (indirectly measured via t½), as a potential predictor of drug stability/toxicity in vivo. We observed an inverse relationship between oxidation potential and drug stability. Furthermore, we selected and prepared short- (<10 min) and longer-circulation (>2 h) drug molecules to prospectively survey the relationship between oxidation potential and stability.

A novel exchange method to access sulfated molecules

Organosulfates and sulfamates are important classes of bioactive molecules but due to their polar nature, they are both difficult to prepare and purify. We report an operationally simple, double ion-exchange method to access organosulfates and sulfamates. Inspired by the novel sulfating reagent, TriButylSulfoAmmonium Betaine (TBSAB), we developed a 3-step procedure using tributylamine as the novel solubilising partner coupled to commercially available sulfating agents. Hence, in response to an increasing demand for complementary methods to synthesise organosulfates, we developed an alternative sulfation route based on an inexpensive, molecularly efficient and solubilising cation exchanging method using off-the-shelf reagents. The disclosed method is amenable to a range of differentially substituted benzyl alcohols, benzylamines and aniline and can also be performed at low temperature for sensitive substrates in good to excellent isolated yield.

Electrochemically induced oxidative S–O coupling: synthesis of sulfonates from sulfonyl hydrazides and N-hydroxyimides or N-hydroxybenzotriazoles

A variety of sulfonates were synthesized from sulfonyl hydrazides and N-hydroxy compounds via electrochemically induced oxidative S–O bond formation.