Fengrong Xu

Rational Design, Green Synthesis, and Initial Evaluation of a Series of Full-Color Tunable Fluorescent Dyes Enabled by the Copper-Catalyzed N-Arylation of 6-Phenyl Pyridazinones and Their Application in Cell Imaging

There is widespread interest in the application, optimization, and evolution of the transition-metal-catalyzed arylation of N-heteroarenes to discover full-color tunable fluorescent core frameworks. Inspired by the versatile roles of pyridazinone in organic synthesis and medicinal chemistry, herein, we report a simple and efficient copper-catalyzed cross-coupling reaction for the N-functionalization of pyridazinones in neat water. To achieve the efficient conversion of pyridazinones and organic halides in aqueous phase, a series of copper-salen complexes composed of different Schiff base ligands were investigated by rational design. A final choice of fine-tuned hydrophilicity balanced with lipophilicity among the candidates was confirmed, which affords excellent activity towards the reaction of a wide range of pyridazinones and organic halides. More importantly, the products as N-substituted pyridazinones were synthesized rationally by this methodology as full-color tunable fluorescent agents (426-612 nm). The N2 position of pyridazinones was modified by different aryl group such as benzothiazole, N,N-dimethylaniline, 3-quinoline, 4-isoquinoline and 2-thiophene, resulting in a series of full-color tunable fluorescent reagents. Meanwhile, the effects of electron-donating and electron-withdrawing groups of the 6-substituted phenyl ring have also been investigated to optimize the fluorescent properties. These fluorescent core frameworks were studied in several cell lines as fluorescent dyes. Different colors from blue to red were observed by using fluorescence microscopy and confocal microscopy.

Relay Catalysis by a Multifunctional Cu Catalyst in a Tandem Dehydro-/Dehalogenation Sequence along with N-Arylation

A Cu-catalyzed tandem dehydrogenation/dehalogenation sequential reaction along with N-arylation has been developed for the synthesis of pyridazinone derivatives in an aerobic and aqueous environment. To achieve the transformation of three chemical bonds in a one-pot reaction, a multifunctional copper catalyst was used which afforded excellent activity, high selectivity, and recyclability. The catalytic system consists of a water-soluble Cusalen complex and Na2CO3 in neat water and an air atmosphere.

The Discovery of Novel β‐Secretase Inhibitors: Pharmacophore Modeling, Virtual Screening, and Docking Studies

This article describes the identification of two small molecular inhibitors for β‐secretase by integrating virtual screening with fluorescence resonance energy transfer bioassay. A ligand‐based pharmacophore model was developed, and the sequential virtual screening of ZINC database was performed using the acquired pharmacophore model and molecular docking. Biological evaluation of 10 virtual hits led to the identification of two novel inhibitors with IC50 values of 4.76 and 0.31 μm, respectively. These two moderate inhibitors could represent new potentials for the development of anti‐Alzheimer’s disease agents.

Substituted 3-Benzylcoumarins as Allosteric MEK1 Inhibitors: Design, Synthesis and Biological Evaluation as Antiviral Agents

In order to find novel antiviral agents, a series of allosteric MEK1 inhibitors were designed and synthesized. Based on docking results, multiple optimizations were made on the coumarin scaffold. Some of the derivatives showed excellent MEK1 binding affinity in the appropriate enzymatic assays and displayed obvious inhibitory effects on the ERK pathway in a cellular assay. These compounds also significantly inhibited virus (EV71) replication in HEK293 and RD cells. Several compounds showed potential as agents for the treatment of viral infective diseases, with the most potent compound 18 showing an IC50 value of 54.57 nM in the MEK1 binding assay.

Synthesis, in vitro Biological Evaluation and Molecular Docking Studies of Benzimidamides as Potential BACE1 Inhibitors

A series of 3, 5‐disubstituted benzimidamides were synthesized and biologically evaluated as potential BACE1 inhibitors. Both the targeted compounds (benzimidamides) and the synthetic intermediates (benzonitriles) were tested for their BACE1 inhibitory activities in a cell‐free FRET assay. All the synthesized benzimidamides were active as BACE1 inhibitors and compound 6d showed the lowest IC50 value of 3.35 μm. Molecular docking study proposed a binding mode, which would help to the further optimization on 6d to achieve more potent, BBB penetrant BACE1 inhibitors.

Discovery of 3-benzyl-1,3-benzoxazine-2,4-dione analogues as allosteric mitogen-activated kinase kinase (MEK) inhibitors and anti-enterovirus 71 (EV71) agents

Enterovirus 71 (EV71) is a kind of RNA virus and one of the two causes of Hand, foot and mouth disease (HFMD). Inhibitors that target key components of Ras/Raf/MEK/ERK pathway in host cells could impair replication of EV71. A series of 3-benzyl-1,3-benzoxazine-2,4-diones were designed from a specific MEK inhibitor G8935, by replacing the double bond between C3 and C4 within the coumarin scaffold with amide bond. One compound (9f) showed submicromolar inhibitory activity among the 12 derivatives. Further optimization on 9f led to two active compounds (9k and 9m) with nanomolar bioactivities (55nM and 60nM). The results of enzymatic assays also demonstrated that this series of compounds were allosteric inhibitors of unphosphorylated MEK1. The binding mode of compound 9k was predicted by molecular dynamic simulation and the key interactions were same as published MEK1/2 allosteric inhibitors. In the cell-based assays, compounds 9k and 9m could effectively suppress the ERK1/2 pathway, expression of EV71 VP1, and EV71 induced cytopathic effect (CPE) in rhabdomyosarcoma (RD) cells.

Rational Design of Fluorescent Phthalazinone Derivatives for One- and Two-Photon Imaging.

Phthalazinone derivatives were designed as optical probes for one- and two-photon fluorescence microscopy imaging. The design strategy involves stepwise extension and modification of pyridazinone by 1) expansion of pyridazinone to phthalazinone, a larger conjugated system, as the electron acceptor, 2) coupling of electron-donating aromatic groups such as N,N-diethylaminophenyl, thienyl, naphthyl, and quinolyl to the phthalazinone, and 3) anchoring of an alkyl chain to the phthalazinone with various terminal substituents such as triphenylphosphonio, morpholino, triethylammonio, N-methylimidazolio, pyrrolidino, and piperidino. Theoretical calculations were utilized to verify the initial design. The desired fluorescent probes were synthesized by two different routes in considerable yields. Twenty-two phthalazinone derivatives were synthesized and their photophysical properties were measured. Selected compounds were applied in cell imaging, and valuable information was obtained. Furthermore, the designed compounds showed excellent performance in two-photon microscopic imaging of mouse brain slices.

Development of novel proteasome inhibitors based on phthalazinone scaffold

In this study we designed a series of proteasome inhibitors using pyridazinone as initial scaffold, and extended the structure with rational design by computer aided drug design (CADD). Two different synthetic routes were explored and the biological evaluation of the phthalazinone derivatives was investigated. Most importantly, electron positive triphenylphosphine group was first introduced in the structure of proteasome inhibitors and potent inhibition was achieved. As 6c was the most potent inhibitor of proteasome, we examined the structure-activity relationship (SAR) of 6c analogs.

Synthesis, bioactivity, docking and molecular dynamics studies of furan-based peptides as 20S proteasome inhibitors.

Proteasome inhibitors are promising compounds for a number of therapies, including cardiovascular and eye diseases, diabetes, and cancers. We previously reported a series of furan‐based peptidic inhibitors with moderate potencies against the proteasome β5 subunit, hypothesizing that the C‐terminal furyl ketone motif could form a covalent bond with the catalytic residue, threonine 1. In this context, we describe further optimizations of the furan‐based peptides, and a series of dipeptidic and tripeptidic inhibitors were designed and synthesized, aiming at improved potency and better solubility. Most of the tripeptidic inhibitors demonstrated improved potency and selectivity as β5 subunit inhibitors in both enzymatic and cellular assays, and good antineoplastic activities in various tumor cell lines were also observed. However, no inhibitory effects were observed for the dipeptidic compounds, which led us to presume that a noncovalent binding mode is adopted. Docking studies and molecular dynamics simulations were carried out to verify this presumption, with results showing that the distance between the furyl ketone motif and Thr1 is slightly too long to form covalent bond.

Synthesis and Biological Evaluations of 3-Benzothiazol-2-yl Coumarin Derivatives as MEK1 Inhibitors

In order to discover novel MEK inhibitors, a series of 3-(benzothiazol-2-yl) coumarin derivatives have been synthesized following our earlier study of 3-benzyl coumarin derivatives. The target compounds were obtained by con- densation, cyanation, hydrolyzation and esterification starting from o-hydroxy benzaldehydes and benzothiazole-2- acetonitrile. The cyanation reaction could only occur when there were electron with drawing groups at C3 position of cou- marin scaffold. All the synthesized compounds showed weak binding and inhibition potencies to phosphorylated MEK1 but obvious inhibitory effect to unphosphorylated MEK1, suggesting that compounds inhibition to MEK1 is mainly due to the inhibition of npMEK1 rather than pMEK1. The most potent compound 3 was with an inhibition rate of 60.7% at 1 µM in the RAF-MEK cascading assay. Molecular docking studies revealed that the pocket occupation and structure hydro- phobicity may be important for activity. These results can contribute to further optimization on coumarin scaffold and led to the design of novel coumarin derivatives as more potent MEK1 inhibitors.