Rhodamine-Based Cyclic Hydroxamate as Fluorescent pH Probe for Imaging of Lysosomes.

Monitoring the microenvironment within specific cellular regions is crucial for a comprehensive understanding of life events. Fluorescent probes working in different ranges of pH regions have been developed for the local imaging of different pH environments. Especially, rhodamine-based fluorescent pH probes have been of great interest due to their ON/OFF fluorescence depending on the spirolactam ring's opening/closure. By introducing the N-alkyl-hydroxamic acid instead of the alkyl amines in the spirolactam of rhodamine, we were able to tune the pH range where the ring opening and closing of the spirolactam occurs. This six-membered cyclic hydroxamate spirolactam ring of rhodamine B proved to be highly fluorescent in acidic pH environments. In addition, we could monitor pH changes of lysosomes in live cells and zebrafish.

Stereoselective synthesis of 1,6-diazecanes by a tandem aza-Prins type dimerization and cyclization process.

We report the stereocontrolled synthesis of 1,6-diazecanes via a tandem aza-Prins type reaction of N-acyliminium ions with allylsilanes. It involves an aza-Prins type dimerization and cyclization in a single-step operation. This reaction represents the first example of 10-membered N-heterocycle synthesis using an aza-Prins reaction. Also, the interesting formation of an unusual tetracyclic compound through further cyclization of 1,6-diazecane and bicyclic compounds by the intramolecular cyclization of linear allylsilane are described. This tandem aza-Prins protocol provides a new synthetic strategy for the direct synthesis of medium-sized nitrogen heterocycles.

Rhodamine-based cyclic hydrazide derivatives as fluorescent probes for selective and rapid detection of formaldehyde.

We describe fluorescent probes to detect formaldehyde (FA) in aqueous solutions and cells. The probes rapidly respond to FA in aqueous solutions and have great selectivity toward FA over other biologically relevant analytes. The results of cell studies reveal that probe 1 can be utilized to monitor endogenous and exogenous FA in live cells.

Discovery of ß-Arrestin Biased Ligands of 5-HT7R.

Though many studies have been published about therapeutic potentials of selective 5-HT7R ligands, there have been few biased ligands of 5-HT7R. The development of potent and selective biased ligands of 5-HT7R would be of great help in understanding the relationship between pharmacological effects and G protein/ß-arrestin signaling pathways of 5-HT7R. In order to identify 5-HT7R ligands with biased agonism, we designed and synthesized a series of tetrahydroazepine derivatives 1 and 2 with arylpyrazolo moiety or arylisoxazolo moiety. Through several biological evaluations such as binding affinity, selectivity profile, and functions in G protein and ß-arrestin signaling pathways, 3-(4-chlorophenyl)-1,4,5,6,7,8-hexahydropyrazolo[3,4- d]azepine 1g was discovered as the ß-arrestin biased ligand of 5-HT7R. In an electroencephalogram (EEG) test, 1g increased total non-rapid eye movement (NREM) sleep time and decreased total rapid eye movement (REM) sleep time.

Discovery of benzimidazole derivatives as modulators of mitochondrial function: A potential treatment for Alzheimer's disease.

In this study, we designed a library of compounds based on the structures of well-known ligands of the 18 kDa translocator protein (TSPO), one of the putative components of the mPTP. We performed diverse mitochondrial functional assays to assess their ability to restore cells from Aß-induced toxicity in vitro and in vivo. Among tested compounds, compound 25 effectively improved cognitive function in animal models of AD. Given the excellent in vitro and in vivo activity and a favorable pharmacokinetic profile of compound 25, we believe that it can serve as a promising lead compound for a potential treatment option for AD.

5-HT7 receptor modulators: Amino groups attached to biphenyl scaffold determine functional activity.

5-HT7 receptor (5-HT7R) agonists and antagonists have been reported to be used for treatment of neuropathic pain and depression, respectively. In this study, as a novel scaffold for 5-HT7R modulators, we designed and prepared a series of biphenyl-3-yl-methanamine derivatives with various amino groups. Evaluation of functional activities as well as binding affinities of the title compounds identified partial agonists (EC50 = 0.55-3.2 µM) and full antagonists (IC50 = 5.57-23.1 µM) depending on the amino substituents. Molecular docking study suggested that the ligand-based switch in functional activity from agonist to antagonist results from the size of the amino groups and thereby different binding modes to 5-HT7R. In particular, interaction of the ligand with Arg367 of 5-HT7R is shown to differentiate agonists and antagonists. In the pharmacophore model study, two distinct pharmacophore models can tell whether a ligand is an agonist or an antagonist. Taken together, this study provides valuable information for designing novel compounds with selective agonistic or antagonistic properties against 5-HT7R.

Novel N-acyl-carbazole derivatives as 5-HT7R antagonists.

To discover a novel 5-HT7R antagonist for treatment of depression, we designed N-acyl-carbazole derivatives which were synthesized and biologically evaluated against 5-HT7R. Among total 30 compounds synthesized, four compounds 27-30 showed good binding affinities with Ki values of <100 nM. The compound 28, 1-(9H-carbazol-9-yl)-6-(4-(2-methoxyphenyl)piperazin-1-yl)hexan-1-one, showed good selectivity over other serotonin receptor subtypes and turned out to be a novel selective 5-HT7R antagonist following functional assays. The compound 28 showed moderate activity on hERG channel and good stability in microsomal stability test. The compound 28 exhibited a good pharmacokinetic profile with 67.8% oral bioavailability and good penetration to the brain. The compound 28 was also tested in in vivo depression animal model and showed antidepressant effect in the forced swimming test. Therefore, the selective 5-HT7R antagonist 28 can be considered as a good lead for discovery of novel 5-HT7R antagonists as antidepressants.

Fluorescent Probes Based on Rhodamine Hydrazides and Hydroxamates.

Rhodamine hydrazides and hydroxamates derived from hydrazines and hydroxylamines have been applied as fluorescent chemosensors. Reaction-based irreversible probes based on the specific chemical reactions of reactive target species have been developed and applied in bio-imaging studies. The strong chelation frames provided by the rhodamine hydrazides and hydroxamates have been utilized for the monitoring of metal ions, amino acids, and reactive acid derivatives. This Personal Account focuses on our perspective of developing fluorescent probes based on rhodamine hydrazides and hydroxamates.

Design, synthesis, in vitro antiproliferative evaluation, and kinase inhibitory effects of a new series of imidazo[2,1-b]thiazole derivatives.

Design and synthesis of a new series of 5,6-diarylimidazo[2,1-b]thiazole derivatives possessing terminal aryl sulfonamide moiety are described. Their in vitro antiproliferative activities against a panel of 57 human cancer cell lines of nine different cancer types were tested at the NCI. Compounds 8a, 8b, 8n, 8q, 8t, and 8u showed the highest mean % inhibition values over the 57 cell line panel at 10 µM, and they were further tested in 5-dose testing mode to determine their IC50 values. Among the six compounds, compound 8u possessing terminal para-hydroxybenzenesulfonamido moiety and ethylene linker showed the highest potency. It demonstrated superior potency than Sorafenib against eight different cell lines, and was equipotent to Sorafenib against COLO 205 colon cancer cell line. Its IC50 values over NCI-H460 non-small cell lung cancer cell line and MCF7 breast cancer cell line were 0.845 µM and 0.476 µM, respectively. Compounds 8a, 8b, 8q, 8t, and 8u showed high selectivity indices towards cancer cells over L132 normal lung cell line. Compound 8u showed potential inhibitory effects over the components of ERK pathway. Its IC50 value over V600E-B-RAF and C-RAF kinases were 39.9 nM and 19.0 nM, respectively.

Synthesis of novel dihydropyridothienopyrimidin-4,9-dione derivatives.

A novel molecular scaffold, dihydropyridothienopyrimidin-4,9-dione, was synthesized from benzylamine or p-methoxybenzylamine in six steps involving successive ring closure to form a fused ring system composed of dihydropyridone, thiophene and pyrimidone. The pharmacological versatility of the dihydropyridothenopyrimidin-4,9-dione scaffold was demonstrated by inhibitory activity against metabotropic glutamate receptor subtype 1 (mGluR1), which shows that the title compounds can serve as an interesting scaffold for the discovery of potential bioactive molecules for the treatment of human diseases.

Novel thienopyrimidinones as mGluR1 antagonists.

There has been much attention to discover mGluR1 antagonists for treating various central nervous system diseases such as seizures and neuropathic pain. Thienopyrimidinone derivatives were designed, synthesized, and biologically evaluated against mGluR1. Among the synthesized compounds, 3-(4-methoxyphenyl)-7-(o-tolyl)thienopyrimidin-4-one 30 exhibited the most potent inhibitory activity with an IC50 value of 45 nM and good selectivity over mGluR5. Also, the selective mGluR1 antagonist 30 showed marginal hERG channel activity (IC50 = 9.87 µM), good profiles to CYP isozymes, and a good pharmacokinetic profile. Overall, the compound 30 was identified as a selective mGluR1 antagonist with a good pharmacokinetic profile, which is probably devoid of cardiac side effect and drug-drug interactions. Therefore, the compound 30 can be expected to be broadly used as mGluR1 antagonistic chemical probe in in vitro and in vivo study for investigating CNS diseases.

Novel N-biphenyl-2-ylmethyl 2-methoxyphenylpiperazinylalkanamides as 5-HT7R antagonists for the treatment of depression.

5-HT7 receptor (5-HT7R) is a promising target for the treatment of depression and neuropathic pain. 5-HT7R antagonists exhibited antidepressant effects, while the agonists produced strong anti-hyperalgesic effects. In our efforts to discover selective 5-HT7R antagonists or agonists, N-biphenylylmethyl 2-methoxyphenylpiperazinylalkanamides 1 were designed, synthesized, and biologically evaluated against 5-HT7R. Among the synthesized compounds, N-2'-chlorobiphenylylmethyl 2-methoxyphenylpiperazinylpentanamide 1-8 showed the best binding affinity with a Ki value of 8.69nM and it was verified as a novel antagonist according to functional assays. The compound 1-8 was very selective over 5-HT1DR, 5-HT2AR, 5-HT3R, 5-HT5AR and 5-HT6R and moderately selective over 5-HT1AR, 5-HT1BR and 5-HT2CR. The novel 5-HT7R antagonist 1-8 exhibited an antidepressant effect at a dose of 25mg/kg in the forced swimming test in mice and showed a U-shaped dose-response curve which typically appears in 5-HT7R antagonists such as SB-269970 and lurasidone.

Aryl biphenyl-3-ylmethylpiperazines as 5-HT7 receptor antagonists.

The 5-HT7 receptor (5-HT7 R) is a promising therapeutic target for the treatment of depression and neuropathic pain. The 5-HT7 R antagonist SB-269970 exhibited antidepressant-like activity, whereas systemic administration of the 5-HT7 R agonist AS-19 significantly inhibited mechanical hypersensitivity and thermal hyperalgesia. In our efforts to discover selective 5-HT7 R antagonists or agonists, aryl biphenyl-3-ylmethylpiperazines were designed, synthesized, and biologically evaluated against the 5-HT7 R. Among the synthesized compounds, 1-([2'-methoxy-(1,1'-biphenyl)-3-yl]methyl)-4-(2-methoxyphenyl)piperazine (28) was the best binder to the 5-HT7 R (pKi =7.83), and its antagonistic property was confirmed by functional assays. The selectivity profile of compound 28 was also recorded for the 5-HT7 R over other serotonin receptor subtypes, such as 5-HT1 R, 5-HT2 R, 5-HT3 R, and 5-HT6 R. In a molecular modeling study, the 2-methoxyphenyl moiety attached to the piperazine ring of compound 28 was proposed to be essential for the antagonistic function.

Rhodamine cyclic hydrazide as a fluorescent probe for the detection of hydroxyl radicals.

A new rhodamine fluorescent probe for monitoring ˙OH has been developed based on the oxidative C-H abstraction reaction of rhodamine cyclic hydrazide. The probe exhibits excellent selectivity for ˙OH with virtually no interference by other ROS/RNS species. Fluorescent imaging of A549 and RAW264.7 cells is also successfully demonstrated to detect intracellular ˙OH in live cells.

Discovery of aryl-biphenyl-2-ylmethylpiperazines as novel scaffolds for 5-HT(7) ligands and role of the aromatic substituents in binding to the target receptor.

It has been reported that 5-HT(7) receptors are promising targets of depression and neuropathic pain. 5-HT(7) receptor antagonists have exhibited antidepressant-like profiles, while agonists have represented potential therapeutics for pain. In the course of our ongoing efforts to discover novel 5-HT(7) modulators, we designed an arylpiperazine scaffold with a substituted biphenyl-2-ylmethyl group. A series of biphenyl-2-yl-arylpiperazinylmethanes were then prepared, which showed a broad spectrum of binding affinities to the 5-HT(7) receptor depending upon the substituents attached to the biphenyl and aryl functionalities. Among those synthesized compounds, the compounds 1-24 and 1-26 showed the best binding affinities to the 5-HT(7) receptor with K(i) values of 43.0 and 46.0 nM, respectively. Structure-activity relationship study in conjunction with molecular docking study proposed that the 5-HT(7) receptor might have two distinctive hydrophobic binding sites, one specific for aromatic 2-OCH(3) substituents within the arylpiperazine and the other for biphenyl methoxy group.

Novel pyrimidoazepine analogs as serotonin 5-HT(2A) and 5-HT(2C) receptor ligands for the treatment of obesity.

Obesity is one of the most serious public health problems worldwide in the 21st century. Current therapeutic treatment for obesity is mostly focused on preventive measures involving dietary control and physical exercises in combination with anti-obesity medications. However, most of these anti-obesity medications have little or no effect on weight loss, and some cases have demonstrated fatal side effects. Due to the urgent need for highly potent and selective anti-obesity agents, the serotonin receptors (5-HTR) have been the focus of much interest as a novel therapeutic target. In this report, we have developed pyrimidoazepine analogs targeting the 5-HT2A and 5-HT2C receptors and evaluated their biological activity in vitro and in vivo as novel anti-obesity agents. We were able to identify 6p as the most potent 5-HT2A and 5-HT2C ligand in vitro (IC50 = 3 nM and 2.3 nM, respectively), and this compound also demonstrated the greatest potency in vivo. In an acute obesity model, mice treated with 6p showed significant decrease in body weight gain and food intake over approximately 77-94% compared to a control group. In a chronic obesity model, mice treated with 6p also showed a marked decrease in food intake and body weight gain.

Rhodamine triazole-based fluorescent probe for the detection of Pt(2+).

A rhodamine triazole-based fluorescent chemosensor has been developed for the selective detection of platinum ions in aqueous solutions. The rhodamine 6G hydroxamate linked with a propargyl group is converted to the corresponding triazole by a "click" reaction. The dual binding unit composed of a hydroxamate and a triazole shows high selectivity and sensitivity toward Pt(2+) over a range of other metal ions in water. The fluorescent probe is applied to monitor cisplatin in aqueous solutions.

Rhodamine-sugar based turn-on fluorescent probe for the detection of cysteine and homocysteine in water.

A new turn-on fluorescent probe utilizing the "chemosensing ensemble" method is developed to detect thiol-containing amino acids. A complex of Au(+) and a rhodamine hydroxylamine having 2-deoxyribose can selectively detect cysteine and homocysteine in water.

Synthesis of aminoquinazoline derivatives and their antiproliferative activities against melanoma cell line.

The synthesis of a novel series of aminoquinazoline derivatives 1a-r and their antiproliferative activities against A375 human melanoma cell line were described. Among them, six compounds showed superior antiproliferative activities to Sorafenib as a reference compound. In particular, the representative compound 1q bearing chromen-4-one moiety exhibited excellent antiproliferative activity (IC(50)=0.006 µM) and good selectivity over HS27 fibroblast cell line.