Cooperative Triple Catalysis Enables Deaminative α-Indolmethylation of Carbonyl Compounds with Gramines.

α-Functionalization of carbonyl compounds is an important reaction in synthetic chemistry. However, the development of novel synthetic strategies to realize this reaction is challenging. This study describes the α-indolmethylation of carbonyl compounds using cooperative copper, amine, and hydrogen-bond catalysis. This reaction provides a novel and efficient strategy for developing indolmethylated carbonyl compounds by deaminative coupling of gramines.

Transition-Metal-Free Base-Promoted Deaminative Coupling of Gramines with Aminomaleimides.

The direct utilization of amines for C-C bond formation without prefunctionalization remains a significant challenge. Herein, we report the base-promoted deaminative coupling of gramines with aminomalaimides under redox-neutral conditions. In this operationally simple reaction, a series of indolmethyl-substituted aminomaleimides that emitted fluorescence were synthesized in good-to-excellent yields. Biological evaluation revealed that some products exhibited antiproliferative activity against human cancer cell lines.

Design, synthesis and evaluation of halogenated phenazine antibacterial prodrugs targeting nitroreductase enzymes for activation.

It is of great importance to develop new strategies to combat antibiotic resistance. Our lab has discovered halogenated phenazine (HP) analogues that are highly active against multidrug-resistant bacterial pathogens. Here, we report the design, synthesis, and study of a new series of nitroarene-based HP prodrugs that leverage intracellular nitroreductase (NTR) enzymes for activation and subsequent release of active HP agents. Our goals of developing HP prodrugs are to (1) mitigate off-target metal chelation (potential toxicity), (2) possess motifs to facilitate intracellular, bacterial-specific HP release, (3) improve water solubility, and (4) prevent undesirable metabolism (e.g., glucuronidation of HP's phenol). Following the synthesis of HP-nitroarene prodrugs bearing a sulfonate ester linker, NTR-promoted release experiments demonstrated prodrug HP-1-N released 70.1% of parent HP-1 after 16 hours (with only 6.8% HP-1 release without NTR). In analogous in vitro experiments, no HP release was observed for control sulfonate ester compounds lacking the critical nitro group. When compared to parent HP compounds, nitroarene prodrugs evaluated during these studies demonstrate similar antibacterial activities in MIC and zone of inhibition assays (against lab strains and clinical isolates). In conclusion, HP-nitroarene prodrugs could provide a future avenue to develop potent agents that target antibiotic resistant bacteria.

Copper-Mediated C4-Benzylations of 5-Aminopyrazoles with 3-Indoleacetic Acids.

Herein, we present a copper-mediated C4-benzylation of 5-aminopyrazoles with 3-indoleacetic acids. Various benzylated 5-aminopyrazoles are prepared in good-to-excellent yields under basic and ligand-free conditions in the presence of copper acetate. Moreover, this benzylation method is applicable to other substrates, including naphthylamine, 2-aminochromen-4-one, and enamines. Some products exhibit antiproliferative activities against cancer cell lines. In addition, the C4-benzylated products are cyclized into 1H-pyrazolo[4',3':6,7]azepino[3,4-b]indoles with aldehydes via one-pot two-step processes; notably, the cyclized products exhibit fluorescence emissions with large Stokes shifts.

Design, Synthesis, and Evaluation of Carbonate-Linked Halogenated Phenazine-Quinone Prodrugs with Improved Water-Solubility and Potent Antibacterial Profiles.

Pathogenic bacteria have devastating impacts on human health as a result of acquired antibiotic resistance and innate tolerance. Every class of our current antibiotic arsenal was initially discovered as growth-inhibiting agents that target actively replicating (individual, free-floating) planktonic bacteria. Bacteria are notorious for utilizing a diversity of resistance mechanisms to overcome the action of conventional antibiotic therapies and forming surface-attached biofilm communities enriched in (non-replicating) persister cells. To address problems associated with pathogenic bacteria, our group is developing halogenated phenazine (HP) molecules that demonstrate potent antibacterial and biofilm-eradicating activities through a unique iron starvation mode of action. In this study, we designed, synthesized, and investigated a focused collection of carbonate-linked HP prodrugs bearing a quinone trigger to target the reductive cytoplasm of bacteria for bioactivation and subsequent HP release. The quinone moiety also contains a polyethylene glycol group, which dramatically enhances the water-solubility properties of the HP-quinone prodrugs reported herein. We found carbonate-linked HP-quinone prodrugs 11, 21-23 to demonstrate good linker stability, rapid release of the active HP warhead following dithiothreitol (reductive) treatment, and potent antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus epidermidis, and Enterococcus faecalis. In addition, HP-quinone prodrug 21 induced rapid iron starvation in MRSA and S. epidermidis biofilms, illustrating prodrug action within these surface-attached communities. Overall, we are highly encouraged by these findings and believe that HP prodrugs have the potential to address antibiotic resistant and tolerant bacterial infections.

Copper-Mediated Cyclization of o-Hydroxyaryl Enaminones with 3-Indoleacetic Acids toward the Synthesis of 3-Indolmethyl-Chromones.

Here, we describe a copper-mediated tandem decarboxylative coupling/annulation protocol of o-hydroxyaryl enaminones with 3-indoleacetic acids. A series of 3-indolmethyl-chromones were afforded in up to 97% yield. A one-pot method for 3-indolmethyl-chromones from o-hydroxy acetophenones, N, N-dimethylformamide dimethyl acetal, and 3-indoleacetic acids was also developed. Derivatization of the products was conducted to provide various indolmethyl-substituted pyrimidines. Moreover, a biological evaluation revealed that some compounds had anti-influenza viral activities.

A new method for C(sp2)-H sulfonylmethylation with glyoxylic acid and sodium sulfinates.

We herein describe a C4 sulfonylmethylation of pyrazol-5-amines with glyoxylic acid and sodium sulfinates. The reaction only needed water as a solvent, and it featured mild reaction conditions, simple operation, and high regioselectivity. Various C4 sulfonylmethylated pyrazol-5-amines were obtained in good to excellent yields. Moreover, this sulfonylmethylation method was applicable for C(sp2)-H sulfonylmethylation of other substrates such as enamines, indoles, and antipyrines by adding a catalyst and changing the solvent. Biological evaluation revealed that some products had antiproliferative activity against cancer cell lines.

Development of a High-Throughput, Compound-Multiplexed Fluorescence Polarization Assay to Identify ATG5-ATG16L1 Protein-Protein Interaction Inhibitors.

Macroautophagy is a catabolic process wherein cytosolic cargo is engulfed in an autophagosome that fuses with a lysosome to degrade the cargo for recycling. Autophagy maintains cellular homeostasis and is involved in a myriad of illnesses ranging from cancer to neurodegenerative diseases, but its therapeutic potential remains elusive due to a lack of potent and specific autophagy modulators. To identify specific inhibitors of early autophagy, a target-based, compound-multiplexed, fluorescence polarization, high-throughput screen that targets the ATG5-ATG16L1 protein-protein interaction was developed. This interaction is critical for the formation of LC3-II, which is involved in phagophore maturation, and its disruption should inhibit autophagy. This assay is based on the polarization of light emitted by a fluorescent rhodamine tag conjugated to a peptide corresponding to the N-terminal region of ATG16L1 (ATG16L1-N). It was confirmed that this peptide binds specifically to ATG5, and the assay was validated by rapidly screening 4800 molecules through compound multiplexing. Through these initial screening efforts, a molecule was identified that disrupts the ATG5-ATG16L1 protein-protein interaction with micromolar potency, and this molecule will serve as a starting point for chemical optimization as an autophagy inhibitor.

Multiple Chemical Features Impact Biological Performance Diversity of a Highly Active Natural Product-Inspired Library.

A systematic, diversity-oriented synthesis approach was employed to access a natural product-inspired flavonoid library with diverse chemical features, including chemical properties, scaffold, stereochemistry, and appendages. Using Cell Painting, the effects of these diversity elements were evaluated, and multiple chemical features that predict biological performance diversity were identified. Scaffold identity appears to be the dominant predictor of performance diversity, but stereochemistry and appendages also contribute to a lesser degree. In addition, the diversity of chemical properties contributed to performance diversity, and the driving chemical property was dependent on the scaffold. These results highlight the importance of key chemical features that may inform the creation of small-molecule, performance-diverse libraries to improve the efficiency and success of high-throughput screening campaigns.

Systematic Diversity-Oriented Synthesis of Reduced Flavones from γ-Pyrones to Probe Biological Performance Diversity.

Diversity-oriented synthesis (DOS) has historically focused on the development of small-molecule collections with considerable chemical diversity with the hypothesis that chemical diversity will lead to diverse biological activities. We took a systematic approach to DOS to develop a focused library of reduced flavones from γ-pyrones with diversity of appendage, stereochemistry, and chemical properties to determine which features of small molecules are most predictive of biological performance diversity. The effects of these systematic modifications on biodiversity were determined using Cell Painting and cytotoxicity assays to compare the results of multiple methods of assessment. We observed that a greater fraction of sp3 hybridized atoms (fsp3) does not always lead to enhanced biodiversity, that stereochemistry and appendage diversity both contribute to biodiversity, and that lipophilicity of the pyrone class of compounds correlates with biodiversity. These results will contribute to the development of a general algorithm to predict which chemical features should be considered during the synthesis of DOS libraries to create biological performance-diverse collections of small molecules for probe and drug discovery.

A photochemical flow reactor for large scale syntheses of aglain and rocaglate natural product analogues.

Herein, we report the development of continuous flow photoreactors for large scale ESIPT-mediated [3+2]-photocycloaddition of 2-(p-methoxyphenyl)-3-hydroxyflavone and cinnamate-derived dipolarophiles. These reactors can be efficiently numbered up to increase throughput two orders of magnitude greater than the corresponding batch reactions.