Thiophene Ring-opening Reactions III: One-Pot Synthesis and Antitumor Activity of 1,3,4-Thiadiazoline-Benzothiazolo[3,2-b]pyridazine Hybrids†.

INTRODUCTION: The preparation of model 6-chloro-5-nitrothieno[2,3-c]pyridazines incorporating (2'-halo-5'-nitrophenyl) entity is described. Interaction of these substrates with N'-(aryl)benzothiohydrazides, in the presence of triethylamine, followed a formal [4+1] annulation, furnishing the respective 1,3,4-thiadiazoline-benzothiazolo [3,2-b]pyridazine hybrids directly. This one-pot synthesis implies thiophene ring-opening and two consecutive intramolecular cyclizations. The structures of the synthesized new hybrids are supported by MS, NMR, and IR spectral data and further confirmed by single-crystal X-ray diffraction. These hybrids exhibit antiproliferative activity with notable selectivity against solid tumor cell lines (IC50: 4-18 µM). AIMS: This study aimed at exploring the scope and applicability of thiophene ring-opening reaction towards the synthesis of new thiadiazoline-[fused]tricyclic conjugates. BACKGROUND: α-Chloro-ß-nitrothienopyridazine underwent ring-opening upon reacting with N'-(aryl)benzothiohydrazides generating 1,3,4-thiadiazoline-benzothiazolo[3,2-b]pyridazines. OBJECTIVE: This new thiophene ring-opening reaction is applied to the one-pot synthesis of thiadiazoline-benzothiazolo[3,2-b]pyridazine couples. METHOD: A direct interaction of α-chloro-ß-nitrothienopyridazine with N'-(aryl)benzothio-hydrazide at room temperature for 1-2 h occurred. RESULT: a-Chloro-ß-nitrothieno[2,3-c]pyridazines are suitable substrates for the facile synthesis of thiadiazoline-benzothiazolo[3,2-b]pyridazine hybrids. CONCLUSION: This novel ring-opening reaction proceeds via formal [4+1] annulation and provides a versatile approach to various conjugated and/or fused five-membered heterocycles.

Development and Biological Evaluation of a Photoactivatable Small Molecule Microtubule-Targeting Agent.

Photoremovable protecting groups added to bioactive molecules provide spatial and temporal control of the biological effects. We present synthesis and characterization of the first photoactivatable small-molecule tubulin inhibitor. By blocking the pharmacophoric OH group on compound 1 with photoremovable 4,5-dimethoxy-2-nitrobenzyl moiety we developed the photocaged prodrug 2 that had no effect in biological assays. Short UV light exposure of the derivative 2 or UV-irradiation of cells treated with 2 resulted in fast and potent inhibition of tubulin polymerization, attenuation of cell viability, and apoptotic cell death, implicating release of the parent active compound. This study validates for the first time the photoactivatable prodrug concept in the field of small molecule tubulin inhibitors. The caged derivative 2 represents a novel tool in antitubulin approaches.

Cytotoxic activity of the novel heterocyclic compound G-11 is primarily mediated through intrinsic apoptotic pathway.

Natural and chemically synthesized heterocyclic compounds have been explored for their potential use as anticancer agents. We had synthesized non-natural heterocyclic analogs and evaluated their anti-tumor activity by measuring effect on cell proliferation and induction of apoptosis in different cell lines. Previously, we identified a pyrazole-containing compound (G-11) showing cytotoxic effect towards leukemia and lymphoma cell lines. In this study, we further investigated the mechanistic aspects of anticancer properties of G-11 in HL-60 cell line. We demonstrated that cytotoxic effect of G-11 is mediated by caspase-dependent apoptosis. However, the involvement of mitochondrial dysfunction induced by G-11 was independent of caspases. G-11 triggered generation of ROS, caused disruption of mitochondrial transmembrane potential, increased release of cytochrome c to the cytosol, and altered the expression of Bcl-2 and Bax proteins. These results suggest significant involvement of intrinsic apoptotic pathway. This study comprehensively details the possible mechanisms of action of a novel heterocyclic compound which could find its potential use as an anticancer agent.

Self Organizing Map-Based Classification of Cathepsin k and S Inhibitors with Different Selectivity Profiles Using Different Structural Molecular Fingerprints: Design and Application for Discovery of Novel Hits.

The main step in a successful drug discovery pipeline is the identification of small potent compounds that selectively bind to the target of interest with high affinity. However, there is still a shortage of efficient and accurate computational methods with powerful capability to study and hence predict compound selectivity properties. In this work, we propose an affordable machine learning method to perform compound selectivity classification and prediction. For this purpose, we have collected compounds with reported activity and built a selectivity database formed of 153 cathepsin K and S inhibitors that are considered of medicinal interest. This database has three compound sets, two K/S and S/K selective ones and one non-selective KS one. We have subjected this database to the selectivity classification tool 'Emergent Self-Organizing Maps' for exploring its capability to differentiate selective cathepsin inhibitors for one target over the other. The method exhibited good clustering performance for selective ligands with high accuracy (up to 100 %). Among the possibilites, BAPs and MACCS molecular structural fingerprints were used for such a classification. The results exhibited the ability of the method for structure-selectivity relationship interpretation and selectivity markers were identified for the design of further novel inhibitors with high activity and target selectivity.

Synthesis and antibacterial activity of some novel 4-oxopyrido[2,3-a]phenothiazines.

A series of substituted 4-oxopyrido[2,3-a]phenothiazine-3-carboxylic acids (6a-d) were prepared via cyclization of the corresponding ethyl 7-(arylthioxy)-8-nitro(or azido)-4-oxoquinoline-3-carboxylates (3a-d/4a-d), followed by hydrolysis of the resultant esters (5a-d). Among these tetracyclics, compound 6a with unsubstituted terminal benzo-ring D was the most active against representative Gram-positive and Gram-negative bacterial strains. These compounds were also active against methicillin-resistant Staphylococcus aureus (MRSA), with very low toxicity to normal cells. Virtual screening using ligand-protein docking modeling predicted that the compounds 6a-d are potential inhibitors of the topoisomerase IV enzyme and that hydrophobic interactions and hydrogen bonds are the major molecular interactions between these compounds and the residues of the active site of topoisomerase IV.

Design synthesis and antibacterial activity studies of new thiadiazoloquinolone compounds.

Abstract New 9-(alkyl/aryl)-4-fluoro-6-oxo[1,2,5]thiadiazolo[3,4-h]quinoline-5-carboxylic acids and their esters were designed and synthesized. A detailed discussion of the reactions utilized in the preparation of the intermediate and target compounds is reported. All the newly synthesized compounds were fully characterized using all the physico-chemical means needed. All the intermediates and the final esters and acids were tested against bacterial and fungal strains. The acids 25a and 25c proved to be very active against Gram positive and Gram negative bacteria with MIC 0.15-3 µg/mL. The structure-activity relationship of antibacterial thiadiazoloquinolones shows that compounds 25a and 25c are twice less potent than the corresponding cyclopropyl derivative 16. Therefore, the cyclopropyl moiety on N-9 seems to be the most suitable substituent.

3,4-Diaryl-isoxazoles and -imidazoles as potent dual inhibitors of p38alpha mitogen activated protein kinase and casein kinase 1delta.

In this study, we report on the discovery of isoxazole 1 as a potent dual inhibitor of p38alpha (IC(50) = 0.45 microM) and CK1delta (IC(50) = 0.23 microM). Because only a few effective small molecule inhibitors of CK1 have been described so far, we aimed to develop this structural class toward specific agents. Molecular modeling studies comparing p38alpha/CK1delta suggested an optimization strategy leading to design, synthesis, biological characterization, and SAR of highly potent compounds including 9 (IC(50) p38alpha = 0.006 microM; IC(50) CK1delta = 1.6 microM), 13 (IC(50) p38alpha = 2.52 microM; IC(50) CK1delta = 0.033 microM), 17 (IC(50) p38alpha = 0.019 microM; IC(50) CK1delta = 0.004 microM; IC(50) CK1epsilon = 0.073 microM), and 18 (CKP138) (IC(50) p38alpha = 0.041 microM; IC(50) CK1delta = 0.005 microM; IC(50) CK1epsilon = 0.447 microM) possessing differentiated specificity. Selected compounds were profiled over 76 kinases and evaluation of their cellular efficacy showed 18 (CKP138) to be a highly potent and dual-specific inhibitor of CK1delta and p38alpha.

Implications for selectivity of 3,4-diarylquinolinones as p38alphaMAP kinase inhibitors.

In this study we report on the specificity profiling of the MAP kinase inhibitors 1, 2, and 3 in a panel of 78 protein kinases including the MAPK isoforms p38(alpha,beta,gamma,delta), JNK1/2/3, and ERK1/2/8 showing 3-(4-fluorophenyl)-4-pyridin-4-ylquinolin-2(1H)-one (1) to be highly selective for p38alphaMAPK with an IC(50) of 1.8 microM. In contrast, besides p38alpha the isoxazoles 2 and 3 significantly inhibited JNK2/3 and further kinases beyond the MAPK family such as PKA, PKD, Lck, and CK1. By using sequence alignment and homology models of different members of the MAPK family the binding mode determining selectivity of 1 for the p38alpha isoform was investigated. For lead optimization of 1 a straightforward tandem-Buchwald-aldol synthetic approach toward the flexible decoration of the quinolin-2(1H)-one scaffold was employed. SAR for derivatives of 1 at the isolated p38alphaMAPK are presented.

From five- to six-membered rings: 3,4-diarylquinolinone as lead for novel p38MAP kinase inhibitors.

In this study we describe the design, synthesis, and biological evaluation of 3-(4-fluorophenyl)-4-pyridin-4-ylquinoline-2(1H)-one (5) as a new inhibitor of MAPK with a p38alphaMAPK IC50 of 1.8 muM. By keeping the common vicinal pyridine/4-F-phenyl pharmacophore, such as in prototypical imidazole 20 or isoxazole 13 but in 5 connected to the six-membered quinoline core, we were particularly interested in comparing biological activity, details of molecular geometry, and different binding modes of these compounds. Compounds 20 and 13 were active both in the p38alpha- and JNK3-assay, whereas 5 was selective for p38alpha, with no JNK3 inhibition. By comparing the X-ray structures of the compounds, we found a significantly larger distance between the pyridine and the 4-F-phenyl moiety in five-membered core structures relevant for ligand-protein interactions. Molecular modeling studies support the results based on differences in the ATP pockets of p38alpha and JNK3. Because most five-membered core based p38alpha inhibitors show also activity for JNK3, compound 5 is an interesting lead for selective p38alpha inhibitors.