Cofactor switch: Development of A Nad+-dependent cascade for the production of ursodeoxycholic acid (UDCA)

The employment of alcohol dehydrogenases in cascade reactions is often limited by the different cofactor specificity of the enzymes involved: the employment of additional cofactor regeneration systems and the excess amount of sacrificial substrates frequently increase the environmental impact and the costs of biocatalytic processes. Additionally, a NADP+-dependent process is generally less desirable, inasmuch this cofactor is more expensive, unstable and less naturally available than NAD+, leading to an increase of the process costs. Nowadays, protein engineering offers the possibility to switch the cofactor dependency of enzymes introducing few targeted mutation1. Please click Additional Files below to see the full abstract

Photoenzymatic epoxidation of styrenes

Two-component-diffusible-flavomonooxygenases are versatile biocatalysts for selective epoxidation-, hydroxylation- or halogenation reactions. Their complicated molecular architecture can be simplified using photochemical regeneration of the catalytically active, reduced FADH 2 prosthetic group. In this contribution we provide the proof-of-concept and characterization for the direct regeneration of the styrene monooxygenase from Pseudomonas. </p

A highly efficient, green and recoverable catalytic system for the epoxidation of fatty esters and biodiesel with H2O2

A highly efficient and green strategy for the epoxidation of fatty esters, combining a green oxidant (aqueous hydrogen peroxide) and a recyclable catalyst (a seleninic acid derivative) is presented. The possibility of integrating renewable solvents derived from glycerol in the productive cycle of biodiesel commodities is also explored. Fluorinated solvents (both commercial and glycerol-derived) play a double key role on this methodology: on the one hand, they strongly accelerate epoxidation reaction with respect to common non-fluorinated solvents and, on the other hand, some of them allow catalyst recycling. Mono- and polyunsaturated fatty esters, as well as soy biodiesel have been epoxidized with excellent yields and selectivities towards epoxide under the optimal conditions and with minimum catalyst loads.Financial support from the European Union (project Solvsafe, NMP2-CT-2005-011774) and the Spanish MCIMM (projects CTQ2008-05138 and Consolider Ingenio 2010 CSD 2006-0003) is gratefully acknowledged. M. de Torres thanks the Gobierno de Aragón for a grant. G. Jiménez-Osés acknowledges Gobierno de la Rioja for a Postoctoral Fellowship.Peer reviewe

A Photo-Enzymatic Cascade to Transform Racemic Alcohols into Enantiomerically Pure Amines

The consecutive photooxidation and reductive amination of various alcohols in a cascade reaction were realized by the combination of a photocatalyst and several enzymes. Whereas the photocatalyst (sodium anthraquinone-2-sulfonate) mediated the light-driven, aerobic oxidation of primary and secondary alcohols, the enzymes (various &#969;-transaminases) catalyzed the enantio-specific reductive amination of the intermediate aldehydes and ketones. The system worked in a one-pot one-step fashion, whereas the productivity was significantly improved by switching to a one-pot two-step procedure. A wide range of aliphatic and aromatic compounds was transformed into the enantiomerically pure corresponding amines via the photo-enzymatic cascade

Efficient immobilisation of Rh-MonoPhos on the aluminosilicate AlTUD-1

Rhodium-MonoPhos was successfully immobilised by ionic interactions on aluminosilicate AlTUD-1. The resulting new heterogeneous catalyst can be used in water and showed excellent enantioselectivity and activity in the asymmetric hydrogenation of methyl-2-acetamidoacrylate.

Glycerol-based solvents as green reaction media in epoxidations with hydrogen peroxide catalysed by bis[3,5-bis(trifluoromethyl)-diphenyl] diselenide

A family of glycerol-based solvents, consisting of eighteen 1,3-dialkoxy-2-propanols and 1,2,3-trialkoxypropanes, both symmetrically and unsymmetrically substituted at terminal positions, has been tested as new solvents in cyclooctene epoxidation with hydrogen peroxide, using a diselenide catalyst, but also without a catalyst. A quantitative relationship between the reactivity and solvent polarity properties has been developed through statistical linear regression analyses, and the predictive ability of the resulting equation has been demonstrated.Financial support from the European Union (project Solvsafe, NMP2-CT-2005-011774) and the Spanish MCIMM (projects CTQ2008-05138 and Consolider Ingenio 2010 CSD 2006-0003) is gratefully acknowledged. H. Garcia-Marin thanks the Gobierno de Aragón and Caja de Ahorros de la Inmaculada for grants.Peer reviewe

Probing the enantioselectivity of Bacillus subtilis esterase BS2 for tert. alcohols

The activity and enantioselectivity of several mutants of the esterase BS2 from Bacillus subtilis have been investigated. In the enzymatic hydrolysis of α,α-disubstituted cyanohydrin acetates, a class of tert. alcohol esters, they were active but not selective. In contrast to this result similar tert. acetylenic alcohol esters were hydrolysed with high E-values (>100). The difference in reactivity has been studied by molecular dynamics studies. The computer model suggested that the source of the observed difference in reactivity between the two very similar tert. alcohol esters lies in the ability of the cyanohydrins to form hydrogen bonds to water molecules—even when the substrate is in the active site.

Mechanism of Laccase¿TEMPO-Catalyzed Oxidation of Benzyl Alcoho

The oxidation of benzyl alcohol by air, catalyzed by the organocatalyst TEMPO and the enzyme laccase has been investigated. To establish the kinetically significant pathways and corresponding kinetic parameters, a series of experiments is conducted with synthesized stable oxidized and reduced forms of the organocatalyst, the oxoammonium cation, and hydroxylamine. The time course of TEMPO and its oxidized and reduced derivatives is monitored off line by a combination of GC analysis, UV/Vis spectroscopy, EPR spectroscopy, and FTIR spectroscopy. TEMPO is found to be regenerated through noncatalyzed comproportionation of the oxoammonium cation with hydroxylamine. A kinetic model is presented based on the experimentally determined kinetically significant pathways. The time dependences of the concentrations of the three redox states of TEMPO and benzyl alcohol are adequately described by the model. The results provide new leads for the development of a practical process for a combined laccase–TEMPO-catalyzed selective oxidation of alcohol

Microbial-catalysed resolution of sterically demanding cyanohydrins

Mycelia containing carboxyl-esterases, a novel source of enzymes, have been investigated in the hydrolytic kinetic resolution of one type of tert-alcohols, α,α-disubstituted cyanohydrins. This class of enzymes was found to be both active and selective towards these tert-alcohols, giving E-values as high as 42.