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.

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.

A ruthenium-catalyzed switchable N–H/C–H alkenylation reaction of 6-phenyl-(dihydro)pyridazin-3(2H)-ones triggered by a nitrogen/oxygen atmosphere was developed. To achieve switchable modification of the two important sites of the widely used pharmacophore, a simple and efficient procedure containing two optimized ruthenium catalytic systems was utilized, which afforded excellent activity, high selectivity, and good tolerance of a wide range of functional groups.

A copper-catalyzed cascade dehydrogenative and dehalogenative reaction of halogenated 6-phenyl-4,5-dihydropyridazin-3(2H)-ones to 6-phenylpyridazin-3(2H)-ones has been developed. Moreover, the catalytic system consisting of copper(II) acetate/sodium carbonate/pyridine exhibits high reactivity and selectivity with oxygen as the terminal oxidant.

A simple and efficient procedure for the synthesis of pyridazin-3(2H)-ones through copper-catalyzed dehydrogenation of a single C–C bond of 4,5-dihydropyridazin-3(2H)-ones to a C=C bond with oxygen as the terminal oxidant is described. Functional groups including hydroxy, carboxylic, bromo, chloro, cyano, nitro and alkoxy were all tolerated under the reaction conditions. Moreover, this methodology was applied to the preparation of a series of structurally similar N-substituted 6-phenylpyridazinone compounds containing fluorine. The dehydrogenation reactions exhibit good yields and selectivity.

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.

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.

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.