Biocatalytic production of bicyclic β-lactams with three contiguous chiral centres using engineered crotonases

YesThere is a need to develop asymmetric routes to functionalised β-lactams, which remain the most important group of antibacterials. Here we describe biocatalytic and protein engineering studies concerning carbapenem biosynthesis enzymes, aiming to enable stereoselective production of functionalised carbapenams with three contiguous chiral centres. Structurallyguided substitutions of wildtype carboxymethylproline synthases enable tuning of their C-N and C-C bond forming capacity to produce 5-carboxymethylproline derivatives substituted at C-4 and C-6, from amino acid aldehyde and malonyl-CoA derivatives. Use of tandem enzyme incubations comprising an engineered carboxymethylproline synthase and an alkylmalonylCoA forming enzyme (i.e. malonyl-CoA synthetase or crotonyl-CoA carboxylase reductase) can improve stereocontrol and expand the product range. Some of the prepared 4,6-disubstituted-5-carboxymethylproline derivatives are converted to bicyclic β-lactams by carbapenam synthetase catalysis. The results illustrate the utility of tandem enzyme systems involving engineered crotonases for asymmetric bicyclic β-lactam synthesis

Nonenzymatic Direct Assay of Hydrogen Peroxide at Neutral pH Using the Eu3Tc Fluorescent Probe

A detailed study is presented on the use of an easily accessible probe (the europium–tetracycline 3:1 complex; referred to as Eu3Tc) for determination of hydrogen peroxide (HP). Eu3Tc undergoes a 15-fold increase in luminescence intensity on exposure to an excess of HP. Data are given on the time dependence of the reaction, on the pH dependence of the absorption and emission spectra of both the probe and its complex with HP, and on the effect of stoichiometry between Eu3+ and Tc on selectivity and signal change. HP can be quantified in aqueous solution of pH 6.9 over a 2–400 μM concentration range with a limit of detection of 960 nM. The assay is validated using standard additions, and mean recoveries are found to be between 97.0 and 101.8%. Species that interfere in concentrations below 1 mM include phosphate, copper(II), fluoride and citrate. The addition of detergents causes the response curves towards HP to shift to higher HP concentrations. The method is critically assessed with respect to other common optical methods for determination of HP

Hydrogen-Free Alkene Reduction in Continuous Flow

The first continuous hydrogenation that requires neither H[subscript 2] nor metal catalysis generates diimide by a novel reagent combination. The simple flow reactor employed minimizes residence time by enabling safe operation at elevated temperature.Novartis (Firm