The first catalytic intermolecular aldehyde-ketone coupling via acyl phosphonate is reported. Acyl phosphonates are potent acyl anion precursors, which generate acyl anion equivalents under the influence of cyanide anion via phosphonate-phosphate rearrangement. These anions readily react with activated ketones to form acyloin type coupling in 41-95% yields.
We report the electrochemical cofactor regeneration for electroenzymatic reduction as a promising alternative to the enzymatic recycling due to the avoidance of couple products. In the mediated electron transfer reaction appropriate redox mediators for the cofactor reduction are necessary. We have synthesized different redox mediators-based on rhodium complexes-and have screened their electrochemical performance at different pH values and concentrations. Suitable mediators have been tested in the presence of the cofactor NAD + and then additionally in the presence of D-sorbitol dehydrogenase (DSDH) from Rhodobacter sphaeroides. The electroenzymatically generated product was analyzed by HPLC. As result of the screening some mediator species were identified which enable an efficient electrochemical cofactor reduction.Biofunctionalization of metal surfaces is widely used in the field of analytical applications especially in clinical diagnostics or for biofuel cells. 1-3 But electrochemical cofactor regeneration can also be important for preparative applications like synthesis of enantiomerically pure fine chemicals as synthons in the pharmaceutical industry. Especially for the preparative conversion with dehydrogenases, which implies a mediated electron transfer from the enzyme to the electrode, a cofactor and a redox mediator are necessary. The redox mediator decreases the potential for the NAD + reduction which amounts to about −1.0 V vs. NHE at bare electrodes without mediator. 4 For preparative syntheses only catalytic amounts of the cofactor NAD + /NADH are necessary which can be recycled in an enzymatic way. 5 A promising alternative represents the electrochemical cofactor regeneration which is already extensively known for the electrochemical re-oxidation of NADH by the functionalization of metal surfaces with biomolecules in the research of biosensors and biofuel cells 6-9 but only few mediators for reduction of NAD + are known. Numerous mediators likely to oxidize NADH (i.e., NAD + regeneration) have been reported. 10 For example, the regeneration of NAD + cofactor by a nitro fluorenone redox mediator was intensively investigated by Mano and co-workers. [11][12][13] In this case, the redox mediator was covalently bound to a gold surface and the cofactor was attached to the mediator by electrostatic forces via calcium bridges. This has been notably applied in the field of bioelectrocatalysis using a modified variant of a dehydrogenase for electroenzymatic oxidation reactions 14 on the basis of a cysteine modified galactitol dehydrogenase from Rhodobacter spaeroides, which was directly immobilized onto a gold surface, leading to successful electrochemical regeneration of the cofactor.On the other hand, elaborating redox mediators enabling the onestep transfer of two electrons (or one hydride) to NAD + species to regenerate directly the active form of the reduced cofactor (i.e., 1,4-NADH) is not an easy task as such mediator should react with NAD + and not transferring directly the electrons (or hydride ion) t...
a-Halogenated aldimines have emerged as an important class of synthetic intermediates. The stability and reactivity of a-halo aldimines can vary greatly depending on the nitrogen protecting group. A general synthesis of stable, chiral a-halo-N-sulfonimines can be isolated upon treatment with a mild base. Enantioenriched a-chloro aldehydes can be employed to afford aldimine precursors with no erosion of optical purity. Both the enantioenriched aldi-mine precursor and the isolated aldimine can react with an alkynyllithium nucleophile to give trans-bchloroamine products with excellent dr. Ring closure affords the enantioenriched trans-aziridine, demonstrating the potential for this approach in complex molecule synthesis. Scheme 1. Formation of a-amido sulfone 1.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.