A new metal-free near-infrared fluorescent probe based on nitrofuran for the detection and bioimaging of carbon monoxide releasing molecule-2 in vivo.

As a stable donor for releasing controlled amounts of CO, carbon monoxide releasing molecule-2 (CORM-2) is a new type of therapeutic drug that contributes to exploring the pathophysiological effects of CO. The accurate detection of CORM-2 in biological systems is of great significance for controlling its dosage as a therapeutic drug and elucidating the reaction mechanisms of CO, but currently there is a lack of metal-free near-infrared fluorescent probes. Herein, a new metal-free near-infrared fluorescent probe based on nitrofuran which could selectively identify CORM-2 was designed and it has been successfully applied in living cells, zebrafish and mice. After reacting with CORM-2, both the color and fluorescence signal of the solution are restored, which is ascribed to the reduction of the nitro group. The spectroscopic probe DXPN shows high sensitivity to CORM-2 with a low detection limit of 87 nM and near-infrared fluorescence emission of 712 nm. Notably, this is the first time that paper chips are being used as a carrier to detect CORM-2 through fluorescence signals instead of the traditional liquid phase detection mode of fluorescent probes. These superior properties of the probe make it a promising and reliable tool for exploring the role played by CORM-2 in biological systems.

ADAM17 mediates ectodomain shedding of the soluble VLDL receptor fragment in the retinal epithelium.

Very low-density lipoprotein receptor (VLDLR) is a multifunctional transmembrane protein. Beyond the function of the full-length VLDLR in lipid transport, the soluble ectodomain of VLDLR (sVLDLR) confers anti-inflammatory and antiangiogenic roles in ocular tissues through inhibition of canonical Wnt signaling. However, it remains unknown how sVLDLR is shed into the extracellular space. In this study, we present the first evidence that a disintegrin and metalloprotease 17 (ADAM17) is responsible for sVLDLR shedding in human retinal pigment epithelium cells using pharmacological and genetic approaches. Among selected proteinase inhibitors, an ADAM17 inhibitor demonstrated the most potent inhibitory effect on sVLDLR shedding. siRNA-mediated knockdown or CRISPR/Cas9-mediated KO of ADAM17 diminished, whereas plasmid-mediated overexpression of ADAM17 promoted sVLDLR shedding. The amount of shed sVLDLR correlated with an inhibitory effect on the Wnt signaling pathway. Consistent with these in vitro findings, intravitreal injection of an ADAM17 inhibitor reduced sVLDLR levels in the extracellular matrix in the mouse retina. In addition, our results demonstrated that ADAM17 cleaved VLDLR only in cells coexpressing these proteins, suggesting that shedding occurs in a cis manner. Moreover, our study demonstrated that aberrant activation of Wnt signaling was associated with decreased sVLDLR levels, along with downregulation of ADAM17 in ocular tissues of an age-related macular degeneration model. Taken together, our observations reveal the mechanism underlying VLDLR cleavage and identify a potential therapeutic target for the treatment of disorders associated with dysregulation of Wnt signaling.

First-generation structure-activity relationship studies of 2,3,4,9-tetrahydro-1H-carbazol-1-amines as CpxA phosphatase inhibitors.

Genetic activation of the bacterial two-component signal transduction system, CpxRA, abolishes the virulence of a number of pathogens in human and murine infection models. Recently, 2,3,4,9-tetrahydro-1H-carbazol-1-amines were shown to activate the CpxRA system by inhibiting the phosphatase activity of CpxA. Herein we report the initial structure-activity relationships of this scaffold by focusing on three approaches 1) A-ring substitution, 2) B-ring deconstruction to provide N-arylated amino acid derivatives, and 3) C-ring elimination to give 2-ethylamino substituted indoles. These studies demonstrate that the A-ring is amenable to functionalization and provides a promising avenue for continued optimization of this chemotype. Further investigations revealed that the C-ring is not necessary for activity, although it likely provides conformational constraint that is beneficial to potency, and that the (R) stereochemistry is required at the primary amine. Simplification of the scaffold through deconstruction of the B-ring led to inactive compounds, highlighting the importance of the indole core. A new lead compound 26 was identified, which manifests a ∼30-fold improvement in CpxA phosphatase inhibition over the initial hit. Comparison of amino and des-amino derivatives in bacterial strains differing in membrane permeability and efflux capabilities demonstrate that the amine is required not only for target engagement but also for permeation and accumulation in Escherichia coli.

Consequences of Depsipeptide Substitution on the ClpP Activation Activity of Antibacterial Acyldepsipeptides.

The acyldepsipeptide (ADEP) antibiotics operate through a clinically unexploited mechanism of action and thus have attracted attention from several antibacterial development groups. The ADEP scaffold is synthetically tractable, and deep-seated modifications have produced extremely potent antibacterial leads against Gram-positive pathogens. Although newly identified ADEP analogs demonstrate remarkable antibacterial activity against bacterial isolates and in mouse models of bacterial infections, stability issues pertaining to the depsipeptide core remain. To date, no study has been reported on the natural ADEP scaffold that evaluates the sole importance of the macrocyclic linkage on target engagement, molecular conformation, and bioactivity. To address this gap in ADEP structure-activity relationships, we synthesized three ADEP analogs that only differ in the linkage motif (i.e., ester, amide, and N-methyl amide) and provide a side-by-side comparison of conformational behavior and biological activity. We demonstrate that while replacement of the naturally occurring ester linkage with a secondary amide maintains in vitro biochemical activity, this simple substitution results in a significant drop in whole-cell activity. This study provides direct evidence that ester to amide linkage substitution is unlikely to provide a reasonable solution for ADEP instability.

Tunable Heck-Mizoroki Reaction of Dibromonaphthalene Diimide with Aryl Ethylenes: Design, Synthesis, and Characterization of Coplanar NDI-Based Conjugated Molecules.

Rational design of coplanar NDI-based conjugated molecules was achieved by covalently connecting naphthalene diimide (NDI) units with aryl (Ar) groups through vinylene (V) linkers via Heck-Mizoroki reaction. Two series of products, diolefination products (ArVNDIVAr) and hydroxylated and mono-olefination products (HONDIVAr), can be obtained, respectively, in moderate to excellent yields (45-90%) under controlled conditions, in which catalyst and base play the key roles. Density functional theory calculation discloses the outstanding planarity of the two types of products. Large bathochromic shifts are observed in both the absorbance and photoluminescence spectra of the HONDIVAr (144 and 229 nm) and ArVNDIVAr (180 and 242 nm) π-systems. Bathochromic shifts can be adjusted within the broad wavelength range by introducing 4'-substituents, either electron-withdrawing group (NO2) or electron-donating group (NMe2), in the phenyl group of aryl ethylenes. ArVNDIVArs show bigger bathochromic shifts than HONDIVArs.

A metal-free yne-addition/1,4-aryl migration/decarboxylation cascade reaction of alkynoates with Csp(3)-H centers.

A metal-free cascade reaction of aryl alkynoates with five different types of radical precursors (R-H) through an yne-addition/1,4-aryl migration/decarboxylation process was reported, which allowed facile and convenient access to functionalized vinyl products with "R" and protons located at the identical carbon of the formed double bond.

Palladium-Catalyzed Alkynylation of Morita-Baylis-Hillman Carbonates with (Triisopropylsilyl)acetylene on Water.

Direct alkynylation of Morita-Baylis-Hillman carbonates with (triisopropylsilyl)acetylene catalyzed by a Pd(OAc)2-NHC complex was developed "on water" to give the corresponding 1,4-enynes. The significant effects of water amount in the solvent on further transformations of 1,4-enynes were investigated.

A Pd(0)-catalyzed direct dehydrative coupling of terminal alkynes with allylic alcohols to access 1,4-enynes.

A direct dehydrative coupling of terminal alkynes with allylic alcohols catalyzed by Pd(PPh3)4 with an N,P-ligand assisted by Ti(OiPr)4 has been developed. The coupling reaction tolerates various functional groups, providing a valuable synthetic tool to access 1,4-enynes.

The application of tandem aza-wittig reaction to synthesize artemisinin-guanidine hybrids and their anti-tumor activity.

Three series of novel artemisinin-guanidine hybrids 4a-4f, 8a-8h and 9a-9h have been facilely synthesized via four-component reaction (aza-Wittig reaction) and evaluated for their anti-tumor activities against A549, HT-29 and MDA-MB-231 cell lines in vitro. All of the tested compounds showed enhanced anti-tumor activities with IC(50) values ranging from 0.02 µM to 12.0 µM as compared to DHA (dihydroartemisinin). Among them, artemisinin derived dimers, compounds 9b (IC(50) = 0.05 µM), 9d (IC(50) = 0.06 µM) and 9f (IC(50) = 0.02 µM) were found to be most active against HT29 cells.

Anti-tumor activity of new artemisinin-chalcone hybrids.

In an attempt to develop potent and selective anti-tumor agents, three new series of artemisinin-chalcone hybrids 10a-10g, 11a-11g and 12a-12h were designed, synthesized and screened for their anti-tumor activity against five cell lines (HT-29, A549, MDA-MB-231, HeLa and H460) in vitro. Among compounds 10a-g and 11a-11g, most of them displayed enhanced activity and good selectivity toward HT-29 and HeLa cell lines with IC(50) values ranging from 0.12 to 0.85 µM as compared with DHA (dihydroartemisinin). Compounds 10a and 11a are most active toward HeLa cells with IC(50) values of 0.12 and 0.19 µM. The results revealed that the presence of chalcone moiety is beneficial to their activity and selectivity. In addition, compounds 12a-12h containing a 'reversed chalcone' moiety showed only slight improvement in activity than those of DHA.