Mechanism, Chemoselectivity, and Stereoselectivity of an NHC-Catalyzed Reaction of Aldehydes and Hydrazones: A DFT Study.

To elucidate the mechanism and origins of chemo- and enantioselectivities of the reaction between aliphatic aldehydes and hydrazones catalyzed by triazolium-derived NHC, density functional theory computations have been performed. According to our calculated results, the whole catalytic cycle for the formation of dihydropyridazinones proceeds via the initial nucleophilic addition of NHC to an aliphatic aldehyde, followed by the concerted intramolecular proton transfer and C-Cl bond cleavage. Subsequent deprotonation generates an enolate intermediate. The enolate intermediate then undergoes 1,4-addition to hydrazone to construct a new carbon-carbon bond. The following ring-closure would lead to a six-membered ring intermediate, which, upon the release of NHC, affords the final product dihydropyridazinone. The computation results reveal that intramolecular proton transfer is significantly promoted by the Brønsted acid DIPEA·H+. The carbon-carbon bond formation step could determine not only the chemoselectivity but also the stereoselectivity and lead to the S-isomer product. It was found that the stereoselectivity arises from a combination of weak interactions, including C-H···O, C-H···N, C-H···π, and LP···π. NHC could enhance the nucleophilicity of the aliphatic aldehyde and facilitate further reaction with hydrazone. This work could be beneficial for the development of new catalytic strategies in the future.

Systems-level analyses of protein-protein interaction network dysfunctions via epichaperomics identify cancer-specific mechanisms of stress adaptation.

Systems-level assessments of protein-protein interaction (PPI) network dysfunctions are currently out-of-reach because approaches enabling proteome-wide identification, analysis, and modulation of context-specific PPI changes in native (unengineered) cells and tissues are lacking. Herein, we take advantage of chemical binders of maladaptive scaffolding structures termed epichaperomes and develop an epichaperome-based 'omics platform, epichaperomics, to identify PPI alterations in disease. We provide multiple lines of evidence, at both biochemical and functional levels, demonstrating the importance of these probes to identify and study PPI network dysfunctions and provide mechanistically and therapeutically relevant proteome-wide insights. As proof-of-principle, we derive systems-level insight into PPI dysfunctions of cancer cells which enabled the discovery of a context-dependent mechanism by which cancer cells enhance the fitness of mitotic protein networks. Importantly, our systems levels analyses support the use of epichaperome chemical binders as therapeutic strategies aimed at normalizing PPI networks.

Copper Mediated Coupling of 2-(Piperazine)-pyrimidine Iodides with Aryl Thiols using Cu(I)Thiophene-2-carboxylate.

A copper-mediated synthesis of diaryl sulfides utilizing Cu(I)-thiophene-2-carboxylate (CuTC) is described. We demonstrate the use of CuTC as a soluble, non-basic catalyst in the coupling of aryl iodides and aryl thiols in the synthesis of synthetically advanced diaryl sulfides. This method allows for the successful coupling of challenging substrates including ortho-substituted and heteroaryl iodides and thiols. Additionally, most of the aryl iodide substrates used here contain the privileged piperazine scaffold bound to a pyrimidine, pyridine, or phenyl ring and thus this method allows for the elaboration of complex piperazine scaffolds into molecules of biological interest. The method described here enables the incorporation of late-stage structural diversity into diaryl sulfides containing the piperazine ring, thus enhancing the number and nature of derivatives available for SAR investigation.

Affinity purification probes of potential use to investigate the endogenous Hsp70 interactome in cancer.

Heat shock protein 70 (Hsp70) is a family of proteins with key roles in regulating malignancy. Cancer cells rely on Hsp70 to inhibit apoptosis, regulate senescence and autophagy, and maintain the stability of numerous onco-proteins. Despite these important biological functions in cancer, robust chemical tools that enable the analysis of the Hsp70-regulated proteome in a tumor-by-tumor manner are yet unavailable. Here we take advantage of a recently reported Hsp70 ligand to design and develop an affinity purification chemical toolset for potential use in the investigation of the endogenous Hsp70-interacting proteome in cancer. We demonstrate that these tools lock Hsp70 in complex with onco-client proteins and effectively isolate Hsp70 complexes for identification through biochemical techniques. Using these tools we provide proof-of-concept analyses that glimpse into the complex roles played by Hsp70 in maintaining a multitude of cell-specific malignancy-driving proteins.

Heat shock protein 70 inhibitors. 1. 2,5'-thiodipyrimidine and 5-(phenylthio)pyrimidine acrylamides as irreversible binders to an allosteric site on heat shock protein 70.

Heat shock protein 70 (Hsp70) is an important emerging cancer target whose inhibition may affect multiple cancer-associated signaling pathways and, moreover, result in significant cancer cell apoptosis. Despite considerable interest from both academia and pharmaceutical companies in the discovery and development of druglike Hsp70 inhibitors, little success has been reported so far. Here we describe structure-activity relationship studies in the first rationally designed Hsp70 inhibitor class that binds to a novel allosteric pocket located in the N-terminal domain of the protein. These 2,5'-thiodipyrimidine and 5-(phenylthio)pyrimidine acrylamides take advantage of an active cysteine embedded in the allosteric pocket to act as covalent protein modifiers upon binding. The study identifies derivatives 17a and 20a, which selectively bind to Hsp70 in cancer cells. Addition of high nanomolar to low micromolar concentrations of these inhibitors to cancer cells leads to a reduction in the steady-state levels of Hsp70-sheltered oncoproteins, an effect associated with inhibition of cancer cell growth and apoptosis. In summary, the described scaffolds represent a viable starting point for the development of druglike Hsp70 inhibitors as novel anticancer therapeutics.

Heat shock protein 70 inhibitors. 2. 2,5'-thiodipyrimidines, 5-(phenylthio)pyrimidines, 2-(pyridin-3-ylthio)pyrimidines, and 3-(phenylthio)pyridines as reversible binders to an allosteric site on heat shock protein 70.

The discovery and development of heat shock protein 70 (Hsp70) inhibitors is currently a hot topic in cancer. In the preceding paper in this issue ( 10.1021/jm401551n ), we have described structure-activity relationship studies in the first Hsp70 inhibitor class rationally designed to bind to a novel allosteric pocket located in the N-terminal domain of the protein. These ligands contained an acrylamide to take advantage of an active cysteine embedded in the allosteric pocket and acted as covalent protein modifiers upon binding. Here, we perform chemical modifications around the irreversible inhibitor scaffold to demonstrate that covalent modification is not a requirement for activity within this class of compounds. The study identifies derivative 27c, which mimics the biological effects of the irreversible inhibitors at comparable concentrations. Collectively, the back-to-back manuscripts describe the first pharmacophores that favorably and selectively interact with a never explored pocket in Hsp70 and provide a novel blueprint for a cancer-oriented development of Hsp70-directed ligands.

Identification of an allosteric pocket on human hsp70 reveals a mode of inhibition of this therapeutically important protein.

Hsp70s are important cancer chaperones that act upstream of Hsp90 and exhibit independent anti-apoptotic activities. To develop chemical tools for the study of human Hsp70, we developed a homology model that unveils a previously unknown allosteric site located in the nucleotide binding domain of Hsp70. Combining structure-based design and phenotypic testing, we discovered a previously unknown inhibitor of this site, YK5. In cancer cells, this compound is a potent and selective binder of the cytosolic but not the organellar human Hsp70s and has biological activity partly by interfering with the formation of active oncogenic Hsp70/Hsp90/client protein complexes. YK5 is a small molecule inhibitor rationally designed to interact with an allosteric pocket of Hsp70 and represents a previously unknown chemical tool to investigate cellular mechanisms associated with Hsp70.

Design of a flexible cell-based assay for the evaluation of heat shock protein 70 expression modulators.

Heat shock protein 70 (Hsp70) is a chaperone protein that helps protect against cellular stress, a function that may be co-opted to fight human diseases. In particular, the upregulation of Hsp70 can suppress the neurotoxicity of misfolded proteins, suggesting possible therapeutic strategies in neurodegenerative diseases. Alternatively, in cancer cells where high levels of Hsp70 inhibit both intrinsic and extrinsic apoptotic pathways, a reduction in Hsp70 levels may induce apoptosis. To evaluate and identify, in a single assay format, small molecules that induce or inhibit endogenous Hsp70, we have designed and optimized a microtiter assay that relies on whole-cell immunodetection of Hsp70. The assay utilizes a minimal number of neuronal or cancer cells, yet is sufficiently sensitive and reproducible to permit quantitative determinations. We further validated the assay using a panel of Hsp70 modulators. In conclusion, we have developed an assay that is fast, robust, and cost efficient. As such, it can be implemented in most research laboratories. The assay should greatly improve the speed at which novel Hsp70 inducers and inhibitors of expression can be identified and evaluated.

Microwave-assisted one step synthesis of 8-arylmethyl-9H-purin-6-amines.

Molecular chaperone heat shock protein 90 (Hsp90) is an important target in cancer and neurodegenerative diseases, and has rapidly become the focus of several drug discovery efforts. Among small molecule Hsp90 inhibitors with clinical applicability are derivatives of 8-arylmethyl-9H-purin-6-amine class. Here we report the use of microwave-assisted chemistry for the successful one-pot delivery of 8-arylmethyl-9H-purin-6-amines. We discuss the applicability as well as the limitations of this method towards the creation of a large chemical diversity in the 8-arylmethyl-9H-purin-6-amine series.

Design of a fluorescence polarization assay platform for the study of human Hsp70.

The 70kDa heat shock proteins (Hsp70) are molecular chaperones that assist in folding of newly synthesized polypeptides, refolding or denaturation of misfolded proteins, and translocation of proteins across biological membranes. In addition, Hsp70 play regulatory roles in signal transduction, cell cycle, and apoptosis. Here, we present a novel assay platform based on fluorescence polarization that is suitable for investigating the yet elusive molecular mechanics of human Hsp70 allosteric regulation.

Discovery and development of purine-scaffold Hsp90 inhibitors.

The heat-shock protein 90 (Hsp90), an important target in cancer and other diseases, has become recently the focus of several drug discovery and development efforts. The initially identified natural-product inhibitors of Hsp90, such as geldanamycin, played a major role in elucidating its biological function and in determining its clinical relevance. Upcoming synthetic inhibitors, such as the purine-scaffold class, furthered our understanding on Hsp90 in cancer and neurodegenerative diseases and delivered what are promised to be clinical candidates with favorable pharmacologic profiles. This review intends to inform the reader on efforts ranging from the discovery of purine-scaffold Hsp90 inhibitors to their clinical translation as well as on their use as chemical tools to dissect the roles of Hsp90 in pathogenic systems.

Selective compounds define Hsp90 as a major inhibitor of apoptosis in small-cell lung cancer.

The heat shock protein 90 (Hsp90) has a critical role in malignant transformation. Whereas its ability to maintain the functional conformations of mutant and aberrant oncoproteins is established, a transformation-specific regulation of the antiapoptotic phenotype by Hsp90 is poorly understood. By using selective compounds, we have discovered that small-cell lung carcinoma is a distinctive cellular system in which apoptosis is mainly regulated by Hsp90. Unlike the well-characterized antiapoptotic chaperone Hsp70, Hsp90 is not a general inhibitor of apoptosis, but it assumes this role in systems such as small-cell lung carcinoma, in which apoptosis is uniquely dependent on and effected through the intrinsic pathway, without involvement of caspase elements upstream of mitochondria or alternate pathways that are not apoptosome-channeled. These results provide important evidence for a transformation-specific interplay between chaperones in regulating apoptosis in malignant cells.

Structural and quantum chemical studies of 8-aryl-sulfanyl adenine class Hsp90 inhibitors.

Hsp90 chaperones play a critical role in modulating the activity of many cell signaling proteins and are an attractive target for anti-cancer therapeutics. We report here the structures of the water soluble 8-aryl-sulfanyl adenine class Hsp90 inhibitors, 1 (PU-H71) and 2 (PU-H64), in complex with the N-terminal domain of human Hsp90alpha. The conformation of 1 when bound to Hsp90 differs from previously reported 8-aryl adenine Hsp90 inhibitors including 3 (PU24FCl). While the binding mode for 3 places the 2'-halide of the 8-aryl group on top of the adenine ring, for 1 and 2, we show that the 2'-halide is rotated approximately 180 degrees away. This difference explains the opposing trends in Hsp90 inhibitory activity for the 2'-halo derivatives of the 3',4',5'-trimethoxy series where Cl > Br > I compared to the 4',5'-methylenedioxy series where I > Br > Cl. We also present quantum chemical calculations of 2 and its analogues that illuminate their basis for Hsp90 inhibition. The calculated conformation of 2 agreed well with the crystallographically observed conformations of 1 and 2. The predictive nature of the calculations has allowed the exploration of additional derivatives based on the 8-aryl adenine scaffold.

Synthesis of a red-shifted fluorescence polarization probe for Hsp90.

The synthesis of a red-shifted cy3B-GM ligand and its evaluation as a fluorescence polarization probe for Hsp90 is presented.

Towards supramolecular fixation of NOX gases: encapsulated reagents for nitrosation.

The use of simple calix[4]arenes for chemical conversion of NO2/N2O4 gases is demonstrated in solution and in the solid state. Upon reacting with these gases, calixarenes 1 encapsulate nitrosonium (NO+) cations within their cavities with the formation of stable calixarene-NO+ complexes 2. These complexes act as encapsulated nitrosating reagents; cavity effects control their reactivity and selectivity. Complexes 2 were effectively used for nitrosation of secondary amides 5, including chiral derivatives. Unique size-shape selectivity was observed, allowing for exclusive nitrosation of less crowded N-Me amides 5 a-e (up to 95 % yields). Bulkier N-Alk (Alk>Me) substrates 5 did not react due to the hindered approach to the encapsulated NO+ reagents. Robust, silica gel based calixarene material 3 was prepared, which reversibly traps NO2/N2O4 with the formation of NO+-storing silica gel 4. With material 4, similar size-shape selectivity was observed for nitrosation. The N-Me-N-nitroso derivatives 6 d,e were obtained with approximately 30 % yields, while bulkier amides were nitrosated with much lower yields (<8 %). Enantiomerically pure encapsulating reagent 2 d was tested for nitrosation of racemic amide 5 t, showing modest but reproducible stereoselectivity and approximately 15 % ee. Given high affinity to NO+ species, which can be generated by a number of NOX gases, these supramolecular reagents and materials may be useful for NOX entrapment and separation in the environment and biomedical areas.

Disproportionation reaction of NO2/N2O4 with a Ru(II) porphyrin.

A Ru(II) porphyrin rapidly reacts with NO2/N2O4 with the formation of a stable Ru(II) nitrosyl nitrato complex.

Sensing and fixation of NO2/N2O4 by calix[4]arenes.

An approach toward visual detection and chemical utilization of NO(2)/N(2)O(4) is proposed, which employs simple calix[4]arenes. Exposure of tetra-O-alkylated calix[4]arenes 1 and 2, possessing either a cone or a 1,3-alternate conformation, to NO(2)/N(2)O(4), both in chloroform solution and in the solid state, results in deeply colored calixarene-nitrosonium (NO(+)) complexes. In the presence of a Lewis acid, such as SnCl(4), stable calixarene-NO(+) complexes 7 and 8 were isolated in a quantitative yield and characterized by UV-vis, FTIR, high-resolution (1)H NMR spectroscopy and elemental analysis. NO(+) is found encapsulated within the calixarene cavity, and stable charge-transfer complexes result with K(ass) > 10(6) M(-1) (CDCl(3)). The NO(+) encapsulation was also demonstrated in titration experiments with calixarenes 1, 2, and 5 and commercially available NO(+)SbF(6)(-) salt in chloroform. The complexation process is reversible, and the complexes dissociate upon addition of water and alcohol, recovering the parent calixarenes. Attachment of functionalized calix[4]arenes to silica gel was demonstrated, which afforded a solid material 15 capable of visual detection and entrapment of NO(2)/N(2)O(4). Calixarene-NO(+) complexes can be utilized for the NO(+) transfer processes and nitrosation reactions. The NO(+) guest transfer between two calixarene containers 2 and 5 was achieved and studied by UV-vis and (1)H NMR spectroscopy. Chemical fixation of NO(2)/N(2)O(4) was demonstrated through their quantitative transformation into the calixarene-NO(+) complex and its use as a nitrosonium transfer agent in the synthesis of N-nitrosoamides. These results may lead toward novel nitrogen oxides storing materials.

Supramolecular fixation of NO2 with calix[4]arenes.

Reaction of NO2 with simple calix[4]arenes in chloroform in the presence of a Lewis acid rapidly results in intense coloration caused by the encapsulation of nitrosonium cation.