Stereoselective Bioreduction of α-diazo-ß-keto Esters.

Diazo compounds are versatile reagents in chemical synthesis and biology due to the tunable reactivity of the diazo functionality and its compatibility with living systems. Much effort has been made in recent years to explore their accessibility and synthetic potential; however, their preparation through stereoselective enzymatic asymmetric synthesis has been scarcely reported in the literature. Alcohol dehydrogenases (ADHs, also called ketoreductases, KREDs) are powerful redox enzymes able to reduce carbonyl compounds in a highly stereoselective manner. Herein, we have developed the synthesis and subsequent bioreduction of nine α-diazo-ß-keto esters to give optically active α-diazo-ß-hydroxy esters with potential applications as chiral building blocks in chemical synthesis. Therefore, the syntheses of prochiral α-diazo-ß-keto esters bearing different substitution patterns at the adjacent position of the ketone group (N3CH2, ClCH2, BrCH2, CH3OCH2, NCSCH2, CH3, and Ph) and in the alkoxy portion of the ester functionality (Me, Et, and Bn), were carried out through the diazo transfer reaction to the corresponding ß-keto esters in good to excellent yields (81-96%). After performing the chemical reduction of α-diazo-ß-keto esters with sodium borohydride and developing robust analytical conditions to monitor the biotransformations, their bioreductions were exhaustively studied using in-house made Escherichia coli overexpressed and commercially available KREDs. Remarkably, the corresponding α-diazo-ß-hydroxy esters were obtained in moderate to excellent conversions (60 to >99%) and high selectivities (85 to >99% ee) after 24 h at 30 °C. The best biotransformations in terms of conversion and enantiomeric excess were successfully scaled up to give the expected chiral alcohols with almost the same activity and selectivity values observed in the enzyme screening experiments.

Continuous multistep synthesis of 2-(azidomethyl)oxazoles.

An efficient three-step protocol was developed to produce 2-(azidomethyl)oxazoles from vinyl azides in a continuous-flow process. The general synthetic strategy involves a thermolysis of vinyl azides to generate azirines, which react with bromoacetyl bromide to provide 2-(bromomethyl)oxazoles. The latter compounds are versatile building blocks for nucleophilic displacement reactions as demonstrated by their subsequent treatment with NaN3 in aqueous medium to give azido oxazoles in good selectivity. Process integration enabled the synthesis of this useful moiety in short overall residence times (7 to 9 min) and in good overall yields.

Lithium chloride-mediated stereoselective synthesis of cyclopropanecarboxamides from γ,δ-epoxy malonates through a domino cyclopropanation/lactonization/aminolysis process.

The stereoselective synthesis of novel multifunctionalized cyclopropanes from γ,δ-epoxy malonates and amines mediated by LiCl under mild conditions was carried out. This domino reaction involves the initial cyclopropanation via intramolecular ring-opening of γ,δ-epoxy malonates through the cooperative catalysis of LiCl (acting as a Lewis acid) and a Brønsted base (a primary or, in selected cases, a secondary amine). The sequential events consisted of lactonization and aminolysis of the lactone ring, which ultimately furnished cyclopropanecarboxamides with different substitution patterns in good isolated yields. In all cases, a quaternary stereogenic center could be perfectly assembled, with a single diastereoisomer being obtained. This method proceeds with high atom economy, is remarkably modular and operationally simple, and tolerates a variety of functional groups. The involvement of readily available starting materials, the broad scope, and the use of a sustainable solvent (methanol or ethanol) at ambient temperature make this domino process highly effective. A reaction mechanism is proposed on the basis of the experimental observations involving the preparation and reactivity of cyclopropylidene lactones as possible intermediates of the domino process.

Allylic thiocyanates as a new class of antitubercular agents.

TB is a global public health emergency in which new drugs are desperately needed. Herein we report on the synthesis of a diverse panel of 41 aryl allylic azides, thiocyanates, isothiouronium salts, and N,N'-diacetylisothioureas that were evaluated for their in vitro activity against replicating and non-replicating Mycobacterium tuberculosis (Mtb) H(37)Rv and toxicity to VERO cells. We found a selective group of new and promising compounds having good (micromolar) to excellent (sub-micromolar) potency against replicating Mtb H(37)Rv. Allylic thiocyanates bearing halophenyl (halo=2-Br, 4-Br, 4-Cl, 4-F), 4-methylphenyl and 2-naphthyl moieties were the most active as antitubercular agents. In particular, the 2-bromophenyl-substituted thiocyanate showed MIC=0.25 µM against replicating Mtb, MIC=8.0 µM against non-replicating Mtb and IC(50)=32 µM in the VERO cellular toxicity assay.

In vitro evidence that the anti-inflammatory effect of synthetic cinnamate-derived dienes is directly linked to a macrophage repolarization.

The inflammatory process is a mammalian physiological reaction against infectious agents or injuries. Among the cells involved, the macrophages have a highlighted role during this process. Depending on the inflammatory context, they can polarize into pro- or anti-inflammatory profiles (M1 and M2). In this context, compounds derived from cinnamic acid have demonstrated strong evidence of anti-inflammatory activity; however, the mechanism responsible for this effect remains unclear. In this study, we investigated the anti-inflammatory activity of five cinnamate-derived dienes of synthetic origin. The compounds that did not demonstrate significant cytotoxicity were tested to assess anti-inflammatory activity (NOx ) in RAW 264.7 cells stimulated with LPS. Then, the selected compound (diene 1) was evaluated as to its ability to inhibit the secretion of pro-inflammatory cytokines (IL-1ß, TNF-α, INF-γ, MCP-1, and IL-6) and increase the production of anti-inflammatory cytokines (IL-13, IL-4, and IL-10). Finally, diene 1 was able to reduce the expression of TLR4 and increase the phagocytic activity of the macrophages. Gathering these results together, we conclude that diene 1 showed an important anti-inflammatory effect, and this effect is linked to its immunomodulatory characteristic. Since the M1 markers were reduced at the same time, M2 markers were increased by the treatment of the macrophages with diene 1.

Nucleophilic ring-opening of epoxide and aziridine acetates for the stereodivergent synthesis of ß-hydroxy and ß-amino γ-lactams.

A highly regio- and stereoselective synthesis of novel ß,γ-disubstituted γ-lactams with either an anti or syn relative configuration was developed from readily available epoxide and aziridine acetates. The key steps include the regio- and diastereocontrolled nucleophilic ring-opening of these three-membered heterocycles followed by mild reductive cyclization of the γ-azido ester intermediate. The method was also extended to an asymmetric synthesis of (4R,5S)-4-hydroxy-5-phenylpyrrolidin-2-one from a chiral epoxide acetate. The main features of this versatile synthesis of functionalized γ-lactams include the involvement of inexpensive reagents and mild conditions together with high chemical efficiency.

Mechanism of intramolecular catalysis in the hydrolysis of alkyl monoesters of 1,8-naphthalic acid.

Hydrolysis of alkyl 1,8-naphthalic acid monoesters 1a-d is subject to highly efficient intramolecular nucleophilic catalysis by the neighboring COOH group. The reactivity for the COOH reaction depends on the leaving group pK(a), with values of ß(LG) of -0.50, consistent with a mechanism involving rate determining breakdown of tetrahedral addition intermediates. The release of the steric strain of the peri-substitiuents in the highly reactive alkyl 1,8-naphthalic acid monoesters is fundamental to understand the observed special reactivity in this intramolecular reaction. DFT calculations show how the proton transfers involved in the cleavage of the neutral ester can be catalyzed by solvent water, thus facilitating the departure of poor alkoxide leaving groups.

5-O-Acetyl-d-ribono-1,4-lactone.

The title compound, C(7)H(10)O(6), was obtained from a regioselective enzyme-catalysed acyl-ation of d-ribono-1,4-lactone. The five-membered ring of the acyl-ated sugar shows an envelope conformation. In the crystal, the mol-ecules are linked by inter-molecular O-H⋯O hydrogen-bonds, forming a one-dimensional polymeric structure parallel to [010]. In addition, packing analysis shows stacking along the b axis.

Structure-based design of δ-lactones for new antifungal drug development: susceptibility, mechanism of action, and toxicity.

Dermatophytes are the etiological agents of cutaneous mycoses, including the prevalent nail infections and athlete's foot. Candida spp. are opportunistic and emerging pathogens, causing superficial to deeper infections related to high mortality rates. As a consequence of prolonged application of antifungal drugs, the treatment failures combined with multidrug-resistance have become a serious problem in clinical practice. Therefore, novel alternative antifungals are required urgently. δ-Lactones have attracted great interest owing to their wide range of biological activity. This article describes the antifungal activity of synthetic δ-lactones against yeasts of the genus Candida spp. and dermatophytes (through the broth microdilution method), discusses the pathways by which the compounds exert this action (toward the fungal cell wall and/or membrane), and evaluates the toxicity to human leukocytes and chorioallantoic membrane (by the hen's egg test-chorioallantoic membrane). Two of the compounds in the series presented broader spectrum of antifungal activity, including against resistant fungal species. The mechanism of action was related to damage in the fungal cell wall and membrane, with specific target action dependent on the type of substituent present in the δ-lactone structure. The damage in the fungal cell was corroborated by electron microscopy images, which evidenced lysed and completely altered cells after in vitro treatment with δ-lactones. Toxicity was dose dependent for the viability of human leukocytes, but none of the compounds was mutagenic, genotoxic, or membrane irritant when evaluated at higher concentrations than MIC. In this way, δ-lactones constitute a class with excellent perspectives regarding their potential applications as antifungals.

Metal-free artificial nucleases based on simple oxime and hydroxylamine scaffolds.

Hydrolysis of DNA is of increasing importance in biotechnology and medicine. In this Letter, we present the DNA-cleavage potential of metal-free hydroxylamines and oximes as new members of nucleic acid cleavage agents.

(E,E)-Methyl 2-[(3-nitrobenzylidene)-aminomethyl]-3-phenylpropenoate.

The mol-ecule of the title compound, C(18)H(16)N(2)O(4), adopts a T-shaped conformation with E stereochemistry for the imine double bond. The (3-nitro-benzyl-idene)amino fragment is almost planar, the mean planes of phenyl ring and nitro group forming a dihedral angle of 8.9 (3)°. In the 3-phenyl-acryloyl unit, the acrylic ester fragment is also almost planar, with the phenyl ring twisted by 41.44 (7)°. In the crystal, the mol-ecules are linked by C-H⋯O hydrogen-bond inter-actions into chains running parallel to [01].

A Novel Tetrasubstituted Imidazole as a Prototype for the Development of Anti-inflammatory Drugs.

Although inflammation is a biological phenomenon that exists to protect the host against infections and/or related problems, its unceasing activation results in the aggravation of several medical conditions. Imidazoles, whether natural or synthetic, are molecules related to a broad spectrum of biological effects, including anti-inflammatory properties. In this study, we screened eight novel small molecules of the imidazole class synthesized by our research group for their in vitro anti-inflammatory activity. The effect of the selected molecules was confirmed in an in vivo inflammatory model. We also analyzed whether the effects were caused by inhibition of nuclear factor kappa B (NF-κB) transcription factor transmigration. Of the eight imidazoles tested, methyl 1-allyl-2-(4-fluorophenyl)-5-phenyl-1H-imidazole-4-acetate (8) inhibited nitric oxide metabolites and pro-inflammatory cytokine (TNF-α, IL-6, and IL-1ß) secretion in J774 macrophages stimulated with LPS. It also attenuated leukocyte migration and exudate formation in the pleural cavity of mice challenged with carrageenan. Furthermore, imidazole 8 reverted the oxidative stress pattern triggered by carrageenan in the pleural cavity by diminishing myeloperoxidase, superoxide dismutase, catalase, and glutathione S-transferase activities and reducing the production of nitric oxide metabolites and thiobarbituric acid-reactive substances. Finally, these effects can be attributed, at least in part, to the ability of this compound to prevent NF-κB transmigration. In this context, our results demonstrate that imidazole 8 has promising potential as a prototype for the development of a new anti-inflammatory drug to treat inflammatory conditions in which NF-κB and oxidative stress play a prominent role. Graphical Abstract ᅟ.

Crystal structure of 5-O-benzoyl-2,3-O-iso-propyl-idene-d-ribono-1,4-lactone.

In the title compound, C15H16O6, obtained from the acyl-ation reaction between 2,3-O-iso-propyl-idene-d-ribono-1,4-lactone and benzoyl chloride, the known absolute configuration for the lactone moiety of the ester substituent has been confirmed. The five-membered rings of the bicyclic lactone-dioxolane moiety both show envelope conformations and form a dihedral angle of 19.82 (7)° between the lactone ring and the benzene ring. In the crystal, mol-ecules of the acyl-ated sugar are linked by very weak inter-molecular C-H⋯O inter-actions, forming a three-dimensional network.

Chemo-, regio- and stereoselective Heck arylation of allylated malonates: mechanistic insights by ESI-MS and synthetic application toward 5-arylmethyl-γ-lactones.

We describe herein a general method for the controlled Heck arylation of allylated malonates. Both electron-rich and electron-poor aryldiazonium salts were readily employed as the aryl-transfer agents in good yields and in high chemo-, regio-, and stereoselectivity without formation of decarboxylated byproducts. Reaction monitoring via ESI-MS was used to support the formation of chelated Pd species through the catalytic cycle. Additionally, some Heck adducts were successfully used in the total synthesis of pharmacologically active γ-lactones.

Structure-activity relationships of novel inhibitors of glyceraldehyde-3-phosphate dehydrogenase.

3D QSAR studies were performed on a library of 120 GAPDH inhibitors, including a series of coumarins, flavonoids, and nucleosides. The VolSurf method was successfully used to calculate surface descriptors for protein-ligand affinity and binding site of the enzyme. PCA/PLS analyses have permitted the evaluation of the structural features crucial for potency, selectivity, and favorable pharmacokinetic properties, and are important for the design of new ligands.