Formate Oxidase (FOx) from Aspergillus oryzae: One Catalyst Enables Diverse H2 O2 -Dependent Biocatalytic Oxidation Reactions.

An increasing number of biocatalytic oxidation reactions rely on H2 O2 as a clean oxidant. The poor robustness of most enzymes towards H2 O2 , however, necessitates more efficient systems for in situ H2 O2 generation. In analogy to the well-known formate dehydrogenase to promote NADH-dependent reactions, we here propose employing formate oxidase (FOx) to promote H2 O2 -dependent enzymatic oxidation reactions. Even under non-optimised conditions, high turnover numbers for coupled FOx/peroxygenase catalysis were achieved.

A Photoenzymatic NADH Regeneration System.

A photoenzymatic NADH regeneration system was established. The combination of deazariboflavin as a photocatalyst with putidaredoxin reductase enabled the selective reduction of NAD+ into the enzyme-active 1,4-NADH to promote an alcohol dehydrogenase catalysed stereospecific reduction reaction. The catalytic turnover of all the reaction components was demonstrated. Factors influencing the efficiency of the overall system were identified.

Identification of some Bioactive Metabolites in a Fractionated Methanol Extract from Ipomoea aquatica (Aerial Parts) through TLC, HPLC, UPLC-ESI-QTOF-MS and LC-SPE-NMR Fingerprints Analyses.

INTRODUCTION: The plant species Ipomoea aquatica contains various bioactive constituents, e.g. phenols and flavonoids, which have several medical uses. All previous studies were executed in Asia; however, no reports are available from Africa, and the secondary metabolites of this plant species from Africa are still unknown. OBJECTIVE: The present study aims finding suitable conditions to identify the bioactive compounds from different fractions. METHODOLOGY: Chromatographic fingerprint profiles of different fractions were developed using high-performance liquid chromatography (HPLC) and then these conditions were transferred to thin-layer chromatography (TLC). Subsequently, the chemical structure of some bioactive compounds was elucidated using ultra-performance liquid chromatography-quadrupole time of flight-tandem mass spectrometry (UPLC-QTOF-MS) and liquid chromatography-solid phase extraction-nuclear magnetic resonance (LC-SPE-NMR) spectroscopy. RESULTS: The HPLC fingerprints, developed on two coupled Chromolith RP-18e columns, using a gradient mobile phase (methanol/water/trifluoroacetic acid, 5:95:0.05, v/v/v), showed more peaks than the TLC profile. The TLC fingerprint allows the identification of the types of chemical constituents, e.g. flavonoids. Two flavonoids (nicotiflorin and ramnazin-3-O-rutinoside) and two phenolic compounds (dihydroxybenzoic acid pentoside and di-pentoside) were tentatively identified by QTOF-MS, while NMR confirmed the structure of rutin and nicotiflorin. CONCLUSION: The HPLC and TLC results showed that HPLC fingerprints give more and better separated peaks, but TLC helped in determining the class of the active compounds in some fractions. Bioactive constituents were identified as well using MS and NMR analyses. Two flavonoids and two phenolic compounds were tentatively identified in this species for the first time, to the best of our knowledge. Copyright © 2017 John Wiley & Sons, Ltd.

Biocatalytic Oxidation Reactions: A Chemist's Perspective.

Oxidation chemistry using enzymes is approaching maturity and practical applicability in organic synthesis. Oxidoreductases (enzymes catalysing redox reactions) enable chemists to perform highly selective and efficient transformations ranging from simple alcohol oxidations to stereoselective halogenations of non-activated C-H bonds. For many of these reactions, no "classical" chemical counterpart is known. Hence oxidoreductases open up shorter synthesis routes based on a more direct access to the target products. The generally very mild reaction conditions may also reduce the environmental impact of biocatalytic reactions compared to classical counterparts. In this Review, we critically summarise the most important recent developments in the field of biocatalytic oxidation chemistry and identify the most pressing bottlenecks as well as promising solutions.

Rapid chemoenzymatic route to glutamate transporter inhibitor l-TFB-TBOA and related amino acids.

The complex amino acid (l-threo)-3-[3-[4-(trifluoromethyl)benzoylamino]benzyloxy]aspartate (l-TFB-TBOA) and its derivatives are privileged compounds for studying the roles of excitatory amino acid transporters (EAATs) in regulation of glutamatergic neurotransmission, animal behavior, and in the pathogenesis of neurological diseases. The wide-spread use of l-TFB-TBOA stems from its high potency of EAAT inhibition and the lack of off-target binding to glutamate receptors. However, one of the main challenges in the evaluation of l-TFB-TBOA and its derivatives is the laborious synthesis of these compounds in stereoisomerically pure form. Here, we report an efficient and step-economic chemoenzymatic route that gives access to enantio- and diastereopure l-TFB-TBOA and its derivatives at multigram scale.

Bis(2-amino-5-benzyl-3-eth-oxy-carbonyl-4,5,6,7-tetra-hydro-thieno[3,2-c]pyridin-5-ium) bis-(4-meth-oxy-phen-yl)di-phos-phon-ate.

The asymmetric unit of the title salt, 2C17H21N2O2S(+)·C14H14O7P2 (2-), contains half of a centrosymmetric bis-(4-meth-oxy-phen-yl)di-phospho-nate anion and one 2-amino-5-benzyl-3-eth-oxy-carbonyl-4,5,6,7-tetra-hydro-thieno[3,2-c]pyri-din-5-ium cation. In the anion, the O atoms of the di-phospho-nate group are disordered over two positions with equal occupancies. In the cation, the ethyl group is disordered over two orientations with a refined occupancy ratio of 0.753 (5):0.247 (5), and the tetra-hydro-pyridinium ring adopts a distorted half-chair conformation. In the crystal, the ions are linked by C-H⋯O, N-H⋯O and C-H⋯S hydrogen bonds into a three-dimensional network.

N'-[(E)-(Furan-2-yl)methyl-idene]-2-[4-(2-methyl-prop-yl)phen-yl]propano-hydrazide.

In the title mol-ecule, C18H22N2O2, the furan and benzene rings form a dihedral angle of 70.17 (14)°. In the crystal, strong N-H⋯O and weak C-H⋯O hydrogen bonds link the mol-ecules into chains running parallel to [010].

Studies on organophosphorus compounds. Part 1: synthesis and in vitro antimicrobial activity of some new pyrimido[5',4':5,6]pyrano[2,3-d][1,3,2]thiazaphosphinine compounds.

2,4-Bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide (Lawesson's reagent, LR) reacted with pyrano[2,3-d]pyrimidine-2,4-(1H,3H)-dione derivatives in boiling acetonitrile to afford various pyrimido[5',4':5,6]pyrano[2,3-d][1,3,2]thiazaphosphinine derivatives. The structures of the target compounds were characterized by elemental analysis and spectral data. The biological activities of all synthesized compounds were tested against various microorganisms by the disk diffusion method. In general, the newly synthesized compounds showed good inhibitory effects against most of the applied microorganisms.

3-Amino-1-phenyl-1H-benzo[f]chromene-2-carbonitrile.

In the title compound, C20H14N2O, the phenyl ring is almost normal to the naphthalene ring system with a dihedral angle of 86.72 (9)°. The 4H-pyran ring fused with the naphthalene ring system has a boat conformation. In the crystal, mol-ecules are linked into a helical supra-molecular chain along the b axis via N-H⋯N hydrogen bonds. The chains are consolidated into a three-dimensional architecture by C-H⋯π inter-actions.

2-(4-Oxo-3-phenyl-1,3-thia-zolidin-2-yl-idene)propanedi-nitrile.

In the title compound, C12H7N3OS, the five-membered 1,3-thia-zolidine ring is nearly planar [maximum deviation = 0.032 (2) Å] and makes a dihedral angle of 84.14 (9)° with the phenyl ring. In the crystal, mol-ecules are linked by C-H⋯N hydrogen bonds into infinite chains along [-101]. C-H⋯π inter-actions contribute to the arrangement of the mol-ecules into layers parallel to (101).

Diethyl 3,4-dimethyl-thieno[2,3-b]thio-phene-2,5-dicarboxyl-ate.

In the title compound, C14H16O4S2, the thieno[2,3-b]thio-phene ring systems are planar [maximum deviation = 0.008 (2) Å]. The mol-ecular conformation is stabilized by intra-molecular C-H⋯O hydrogen bonds, while the crystal packing is stabilized by C-H⋯O, C-H⋯π and π-π stacking [centroid-centroid distance = 3.6605 (14) Å] inter-actions, which lead to supra-molecular layers in the ab plane.

4-Phenyl-1H-1,5-benzodiazepin-2(3H)-one.

In the title compound, C15H12N2O, the phenyl ring makes a dihedral angle of 32.45 (9)° with the benzene ring of the 1,5-benzodiazepin-2-one unit. The seven-membered ring adopts a boat conformation with the methyl-ene group as the prow and the fused benzene-ring C atoms as the stern. In the crystal, inversion dimers linked by pairs of N-H⋯O hydrogen bonds generate R2(2)(8) loops. The dimers are further linked by C-H⋯O hydrogen bonds, so forming a column along the a-axis direction.

2-[(Phenyl-carbamo-yl)amino]-butyl N-phenyl-carbamate.

In the title compound, C(18)H(21)N(3)O(3), the terminal phenyl rings make a dihedral angle of 86.3 (5)°. In the crystal, mol-ecules are linked by N-H⋯O hydrogen bonds into chains along [001], forming parallel C(4) and R(1) (2)(6) graph-set motifs.

(Z)-3-(2-Hy-droxy-eth-yl)-2-(phenyl-imino)-1,3-thia-zolidin-4-one.

In the title compound, C(11)H(12)N(2)O(2)S, the thia-zole and phenyl rings are inclined at 56.99 (6)° to one another. The thia-zole ring is planar with an r.m.s. deviation for the five ring atoms of 0.0274 Å. The presence of the phenyl-imine substituent is confirmed with the C=N distance to the thia-zole ring of 1.2638 (19) Å. The mol-ecule adopts a Z conformation with respect to this bond. The -OH group of the hy-droxy-ethyl substituent is disordered over two positions with relative occupancies 0.517 (4) and 0.483 (4). In the crystal, O-H⋯O hydrogen bonds, augmented by C-H⋯N contacts, form dimers with R(2) (2)(11) rings and generate chains along the b axis. Parallel chains are linked in an obverse fashion by weak C-H⋯S hydrogen bonds. C-H⋯O hydrogen bonds together with C-H⋯π contacts further consolidate the structure, stacking mol-ecules along the b axis.

2-Amino-4-(4-meth-oxy-phen-yl)-5-oxo-5,6,7,8-tetra-hydro-4H-chromene-3-carbonitrile 1,4-dioxane hemisolvate.

In the crystal structure of the title compound, C(17)H(16)N(2)O(3)·0.5C(4)H(8)O(2), pairs of N-H⋯N hydrogen bonds link mol-ecules into dimers with R(2) (2)(12) motifs, which are connected by N-H⋯O hydrogen bonds, forming a supra-molecular array in the ab plane. The 1,4-dioxane ring, which lies about an inversion center, adopts a chair conformation.

Chemoenzymatic Hunsdiecker-Type Decarboxylative Bromination of Cinnamic Acids.

In this contribution, we report chemoenzymatic bromodecarboxylation (Hunsdiecker-type) of α,ß-unsaturated carboxylic acids. The extraordinarily robust chloroperoxidase from Curvularia inaequalis (CiVCPO) generated hypobromite from H2O2 and bromide, which then spontaneously reacted with a broad range of unsaturated carboxylic acids and yielded the corresponding vinyl bromide products. Selectivity issues arising from the (here undesired) addition of water to the intermediate bromonium ion could be solved by reaction medium engineering. The vinyl bromides so obtained could be used as starting materials for a range of cross-coupling and pericyclic reactions.

Structure of the Reductase Domain of a Fungal Carboxylic Acid Reductase and Its Substrate Scope in Thioester and Aldehyde Reduction.

The synthesis of aldehydes from carboxylic acids has long been a challenge in chemistry. In contrast to the harsh chemically driven reduction, enzymes such as carboxylic acid reductases (CARs) are considered appealing biocatalysts for aldehyde production. Although structures of single- and didomains of microbial CARs have been reported, to date no full-length protein structure has been elucidated. In this study, we aimed to obtain structural and functional information regarding the reductase (R) domain of a CAR from the fungus Neurospora crassa (Nc). The NcCAR R-domain revealed activity for N-acetylcysteamine thioester (S-(2-acetamidoethyl) benzothioate), which mimics the phosphopantetheinylacyl-intermediate and can be anticipated as the minimal substrate for thioester reduction by CARs. The determined crystal structure of the NcCAR R-domain reveals a tunnel that putatively harbors the phosphopantetheinylacyl-intermediate, which is in good agreement with docking experiments performed with the minimal substrate. In vitro studies were performed with this highly purified R-domain and NADPH, demonstrating carbonyl reduction activity. The R-domain was able to accept not only a simple aromatic ketone but also benzaldehyde and octanal, which are typically considered to be the final product of carboxylic acid reduction by CAR. Also, the full-length NcCAR reduced aldehydes to primary alcohols. In conclusion, aldehyde overreduction can no longer be attributed exclusively to the host background.

Biocatalytic Aromaticity-Breaking Epoxidation of Naphthalene and Nucleophilic Ring-Opening Reactions.

Aromatic hydroxylation reactions catalyzed by heme-thiolate enzymes proceed via an epoxide intermediate. These aromatic epoxides could be valuable building blocks for organic synthesis giving access to a range of chiral trans-disubstituted cyclohexadiene synthons. Here, we show that naphthalene epoxides generated by fungal peroxygenases can be subjected to nucleophilic ring opening, yielding non-racemic trans-disubstituted cyclohexadiene derivates, which in turn can be used for further chemical transformations. This approach may represent a promising shortcut for the synthesis of natural products and APIs.

Chemoenzymatic Halocyclization of 4-Pentenoic Acid at Preparative Scale.

The scale-up of chemoenzymatic bromolactonization to 100 g scale is presented, together with an identification of current limitations. The preparative-scale reaction also allowed for meaningful mass balances identifying current bottlenecks of the chemoenzymatic reaction.

Chemoenzymatic Halocyclization of γ,δ-Unsaturated Carboxylic Acids and Alcohols.

Invited for this month's cover is the group of Prof. Dr. Frank Hollmann at Delft University of Technology in the Netherlands. The Front Cover shows the vanadium-dependent haloperoxidase from the marine organism Curcuvaria inaequalis, which efficiently activates halides as hypohalites that can then initiate spontaneous halo-lactonization and halo-etherification reactions. The Communication itself is available at 10.1002/cssc.201902240.