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).

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.

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.

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.

(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.

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 γ,δ-Unsaturated Carboxylic Acids and Alcohols.

A chemoenzymatic method for the halocyclization of unsaturated alcohols and acids by using the robust V-dependent chloroperoxidase from Curvularia inaequalis (CiVCPO) as catalyst has been developed for the in situ generation of hypohalites. A broad range of halolactones and cyclic haloethers are formed with excellent performance of the biocatalyst.

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.

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.

Photobiocatalytic synthesis of chiral secondary fatty alcohols from renewable unsaturated fatty acids.

En route to a bio-based chemical industry, the conversion of fatty acids into building blocks is of particular interest. Enzymatic routes, occurring under mild conditions and excelling by intrinsic selectivity, are particularly attractive. Here we report photoenzymatic cascade reactions to transform unsaturated fatty acids into enantiomerically pure secondary fatty alcohols. In a first step the C=C-double bond is stereoselectively hydrated using oleate hydratases from Lactobacillus reuteri or Stenotrophomonas maltophilia. Also, dihydroxylation mediated by the 5,8-diol synthase from Aspergillus nidulans is demonstrated. The second step comprises decarboxylation of the intermediate hydroxy acids by the photoactivated decarboxylase from Chlorella variabilis NC64A. A broad range of (poly)unsaturated fatty acids can be transformed into enantiomerically pure fatty alcohols in a simple one-pot approach.

Triclinic and monoclinic polymorphs of meso-(E,E)-1,1'-[1,2-bis(4-chlorophenyl)ethane-1,2-diyl]bis(phenyldiazene): the high-yield synthesis of an unexpected product, concomitant polymorphism and configurational disorder.

Pyrazolidine-3,5-diones and their derivatives exhibit a wide range of biological activities. Seeking to explore the effect of combining a hydrocarbyl ring substituent, as present in sulfinpyrazone (used to treat gout), with a chlorinated aryl ring, as present in muzolimine (a diuretic), we explored the reaction between 1-phenylpyrazolidine-3,5-dione and 4-chlorobenzaldehyde under mildly basic conditions in the expectation of producing the simple condensation product 4-(4-chlorobenzylidene)-1-phenylpyrazolidine-3,5-dione. However, the reaction product proved to be meso-(E,E)-1,1'-[1,2-bis(4-chlorophenyl)ethane-1,2-diyl]bis(phenyldiazene), C26H20Cl2N4, and a tentative mechanism is proposed. Crystallization from ethanol produces two concomitant polymorphs, i.e. a triclinic form, (I), in the space group P-1, and a monoclinic form, (II), in the space group C2/c. In both polymorphs, the molecules lie across centres of inversion, but in (II), the molecules are subject to whole-molecule disorder equivalent to configurational disorder with occupancies of 0.6021 (19) and 0.3979 (19). There are no hydrogen bonds in the crystal structure of polymorph (I), but the molecules of polymorph (II) are linked by C-H...π(arene) hydrogen bonds into complex chains, which are further linked into sheets by C-H...N interactions.

Crystal structure of 3-amino-1-(4-hy-droxy-phen-yl)-1H-benzo[f]chromene-2-carbo-nitrile.

In the title compound, C20H14N2O2, the hy-droxy-benzene ring is almost perpendicular to the mean plane of the naphthalene ring system, making a dihedral angle of 85.56 (4)°. The 4H-pyran ring fused with the naphthalene ring system has a flattened boat conformation. In the crystal, O-H⋯N and N-H⋯O hydrogen bonds link the mol-ecules into a supra-molecular layer in the bc plane; N-H⋯π inter-actions also contribute to this arrangement. The layers are linked by weak by C-H⋯π and π-π [inter-centroid separation = 3.8713 (7) Å] inter-actions.