Kinetic Resolution of sec -Thiols by Enantioselective Oxidation with Rationally Engineered 5-(Hydroxymethyl)furfural Oxidase

Cooperative chemoenzymatic and biocatalytic cascades to access chiral sulfur compounds bearing C(sp3)-S stereocentres

Biocatalysis has been widely employed for the generation of carbon-carbon/heteroatom stereocentres, yet its application in chiral C(sp3)-S bond construction is rare and limited to enzymatic kinetic resolutions. Herein, we describe the enantioselective construction of chiral C(sp3)-S bonds through ene-reductase biocatalyzed conjugate reduction of prochiral vinyl sulfides. A series of cooperative sequential/concurrent chemoenzymatic and biocatalytic cascades have been developed to access a broad range of chiral sulfides, including valuable β-hydroxysulfides bearing two adjacent C(sp3)-S and C(sp3)-O stereocentres, in a stereoconvergent manner with good to excellent yields (up to 96%) and enantioselectivities (up to >99% ee). Notably, this biocatalytic strategy allows to overcome the long-standing shortcomings of catalyst poisoning and C(sp2)/C(sp3)-S bond cleavage faced in transition-metal-catalyzed hydrogenation of vinyl sulfides. Finally, the potential of this methodology is also exemplified by its broader application in the stereoconvergent assembly of chiral C(sp3)-N/O/Se bonds with good to excellent enantioselctivities.

Multistep Biooxidation of 5-(Hydroxymethyl)furfural to 2,5-Furandicarboxylic Acid with H2O2 by Unspecific Peroxygenases

5-(Hydroxymethyl)furfural (HMF) is a key platform chemical derived from renewable biomass sources, holding great potential as starting material for the synthesis of valuable compounds, thereby replacing petrochemical-derived counterparts. Among these valorised compounds, 2,5-furandicarboxylic acid (FDCA) has emerged as a versatile building block. Here we demonstrate the biocatalytic synthesis of FDCA from HMF via a one-pot three-step oxidative cascade performed via two operative steps under mild reaction conditions employing two unspecific peroxygenases (UPOs) using hydrogen peroxide as the only oxidant. The challenge of HMF oxidation by UPOs is the chemoselectivity of the first step, as one of the two possible oxidation products is only a poor substrate for further oxidation. The unspecific peroxygenase from Marasmius oreades (MorUPO) was found to oxidize 100 mM of HMF to 5-formyl-2-furoic acid (FFCA) with 95 % chemoselectivity. In the sequential one-pot cascade employing MorUPO (TON up to 13535) and the UPO from Agrocybe aegerita (AaeUPO, TON up to 7079), 100 mM of HMF were oxidized to FDCA reaching up to 99 % conversion and yielding 861 mg isolated pure crystalline FDCA, presenting the first example of a gram scale biocatalytic synthesis of FDCA involving UPOs.

Glucose Oxidase, an Enzyme "Ferrari": Its Structure, Function, Production and Properties in the Light of Various Industrial and Biotechnological Applications

Glucose oxidase (GOx) is an important oxidoreductase enzyme with many important roles in biological processes. It is considered an "ideal enzyme" and is often called an oxidase "Ferrari" because of its fast mechanism of action, high stability and specificity. Glucose oxidase catalyzes the oxidation of β-d-glucose to d-glucono-δ-lactone and hydrogen peroxide in the presence of molecular oxygen. d-glucono-δ-lactone is sequentially hydrolyzed by lactonase to d-gluconic acid, and the resulting hydrogen peroxide is hydrolyzed by catalase to oxygen and water. GOx is presently known to be produced only by fungi and insects. The current main industrial producers of glucose oxidase are Aspergillus and Penicillium. An important property of GOx is its antimicrobial effect against various pathogens and its use in many industrial and medical areas. The aim of this review is to summarize the structure, function, production strains and biophysical and biochemical properties of GOx in light of its various industrial, biotechnological and medical applications.

Enzymatic strategies for asymmetric synthesis

Enzymes, at the turn of the 21st century, are gaining a momentum. Especially in the field of synthetic organic chemistry, a broad variety of biocatalysts are being applied in an increasing number of processes running at up to industrial scale. In addition to the advantages of employing enzymes under environmentally friendly reaction conditions, synthetic chemists are recognizing the value of enzymes connected to the exquisite selectivity of these natural (or engineered) catalysts. The use of hydrolases in enantioselective protocols paved the way to the application of enzymes in asymmetric synthesis, in particular in the context of biocatalytic (dynamic) kinetic resolutions. After two decades of impressive development, the field is now mature to propose a panel of catalytically diverse enzymes for (i) stereoselective reactions with prochiral compounds, such as double bond reduction and bond forming reactions, (ii) formal enantioselective replacement of one of two enantiotopic groups of prochiral substrates, as well as (iii) atroposelective reactions with noncentrally chiral compounds. In this review, the major enzymatic strategies broadly applicable in the asymmetric synthesis of optically pure chiral compounds are presented, with a focus on the reactions developed within the past decade.

The multipurpose family of flavoprotein oxidases

This chapter represents a journey through flavoprotein oxidases. The purpose is to excite the reader curiosity regarding this class of enzymes by showing their diverse applications. We start with a brief overview on oxidases to then introduce flavoprotein oxidases and elaborate on the flavin cofactors, their redox and spectroscopic characteristics, and their role in the catalytic mechanism. The six major flavoprotein oxidase families will be described, giving examples of their importance in biology and their biotechnological uses. Specific attention will be given to a few selected flavoprotein oxidases that are not extensively discussed in other chapters of this book. Glucose oxidase, cholesterol oxidase, 5-(hydroxymethyl)furfural (HMF) oxidase and methanol oxidase are four examples of oxidases belonging to the GMC-like flavoprotein oxidase family and that have been shown to be valuable biocatalysts. Their structural and mechanistic features and recent enzyme engineering will be discussed in details. Finally we give a look at the current trend in research and conclude with a future outlook.

Biocatalytic Enantioselective Oxidation of Sec-Allylic Alcohols with Flavin-Dependent Oxidases

The oxidation of allylic alcohols is challenging to perform in a chemo- as well as stereo-selective fashion at the expense of molecular oxygen using conventional chemical protocols. Here, we report the identification of a library of flavin-dependent oxidases including variants of the berberine bridge enzyme (BBE) analogue from Arabidopsis thaliana (AtBBE15) and the 5-(hydroxymethyl)furfural oxidase (HMFO) and its variants (V465T, V465S, V465T/W466H and V367R/W466F) for the enantioselective oxidation of sec-allylic alcohols. While primary and benzylic alcohols as well as certain sugars are well known to be transformed by flavin-dependent oxidases, sec-allylic alcohols have not been studied yet except in a single report. The model substrates investigated were oxidized enantioselectively in a kinetic resolution with an E-value of up to >200. For instance HMFO V465S/T oxidized the (S)-enantiomer of (E)-oct-3-en-2-ol (1 a) and (E)-4-phenylbut-3-en-2-ol with E>200 giving the remaining (R)-alcohol with ee>99% at 50% conversion. The enantioselectivity could be decreased if required by medium engineering by the addition of cosolvents (e. g. dimethyl sulfoxide).

Nonconventional regeneration of redox enzymes - a practical approach for organic synthesis?

Oxidoreductases have become useful tools in the hands of chemists to perform selective and mild oxidation and reduction reactions. Instead of mimicking native catalytic cycles, generally involving costly and unstable nicotinamide cofactors, more direct, NAD(P)-independent methodologies are being developed. The promise of these approaches not only lies with simpler and cheaper reaction schemes but also with higher selectivity as compared to whole cell approaches and their mimics.

Hot off the Press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as mollebenzylanol A from Rhododendron molle.