Metal-Free Electrocatalytic Diacetoxylation of Alkenes

1,2-Dioxygenation of alkenes leads to a structural motif ubiquitous in organic synthons, natural products and active pharmaceutical ingredients. Straightforward and green synthesis protocols starting from abundant raw materials are required for facile and sustainable access to these crucial moieties. Especially industrially abundant aliphatic alkenes have proven to be arduous substrates in sustainable 1,2-dioxygenation methods. Here, we report a highly efficient electrocatalytic diacetoxylation of alkenes under ambient conditions using a simple iodobenzene mediator and acetic acid as both the solvent and an atom-efficient reactant. This transition metal-free method is applicable to a wide range of alkenes, even challenging feedstock alkenes such as ethylene and propylene, with a broad functional group tolerance and excellent faradaic efficiencies up to 87 %. In addition, this protocol can be extrapolated to alkenoic acids, resulting in cyclization of the starting materials to valuable lactone derivatives. With aromatic alkenes, a competing mechanism of direct anodic oxidation exists which enables reaction under catalyst-free conditions. The synthetic method is extensively investigated with cyclic voltammetry.     

Electrochemical AFM on surface grafted poly(ferrocenylsilanes)

Ethylenesulfide and trimethylenesulfide end‐functionalized poly(ferrocenyldimethylsilanes) (ES‐PFS and TMS‐PFS) with different degrees of polymerization were prepared via anionic ring‐opening polymerization. Molecular characterization of ES‐PFS was carried out by using ¹H‐NMR, GPC, FTIR, and elemental analysis. Thin films of ES‐PFS were prepared by immersing gold(111) substrates into 1.0 mg/ml solutions of the polymers in toluene. The polymeric films were characterized by FTIR, XPS, and contact angle measurements. Thicknesses of the grafted films were measured by SPR. Thicknesses determined by SPR and the theoretically calculated values are in a reasonable agreement. The morphology of the films was studied by tapping mode AFM. The electrochemical behavior of the films was monitored by cyclic voltammetry (CV). CVs show two reversible redox peaks, indicating a stepwise oxidation of the iron atoms in the polymer chains. Scanning Electrochemical Force Microscopy (SEFM) allowed us to study in situ the morphological changes occurring in the film upon electrochemical oxidation or reduction. AFM images indicated that in the oxidized form the chains were stretched due to electrostatic repulsion.     

The Role of Cytochrome P450 AbyV in the Final Stages of Abyssomicin C Biosynthesis

Abyssomicin C and its atropisomer are potent inhibitors of bacterial folate metabolism. They possess complex polycyclic structures, and their biosynthesis has been shown to involve several unusual enzymatic transformations. Using a combination of synthesis and in vitro assays we reveal that AbyV, a cytochrome P450 enzyme from the aby gene cluster, catalyses a key late-stage epoxidation required for the installation of the characteristic ether-bridged core of abyssomicin C. The X-ray crystal structure of AbyV has been determined, which in combination with molecular dynamics simulations provides a structural framework for our functional data. This work demonstrates the power of combining selective carbon-13 labelling with NMR spectroscopy as a sensitive tool to interrogate enzyme-catalysed reactions in vitro with no need for purification.