1,6-Naphthyridin-7(6H)-ones: synthesis and optical properties

Efficient synthesis of original 1,6-naphthyridin-7(6H)-ones and their optical properties are described. Their powerful fluorescence properties including dual fluorescence, solvatochromism, acidochromism, large Stokes shifts and high quantum yields, suitable for biological applications or as luminescent devices in materials science, are evidenced.

Iron Catalyzed Dearomatization of Pyridines into Annelated Azepine Derivatives in a One-Step, Three-Component Reaction

Commercially available Fe(TTP)Cl catalyzes three-component dearomative formal cycloaddition reactions between pyridines, diazo compounds, and coumalates. Diversely substituted annelated seven-membered N-heterocycles could be generated in less than 10 min in one step at room temperature. The reaction is compatible to gram scale. The extension to benzimidazoles in place of pyridines has been successfully demonstrated. The mechanism of this reaction has been carefully examined by computational studies that corroborate the observed regioselectivities.

Insights into the antiproliferative mechanism of (C^N)-chelated half-sandwich iridium complexes

Transition metal-based anticancer compounds, as an alternative to platinum derivatives, are raising scientific interest as they may present distinct although poorly understood mechanisms of action. We used a structure-activity relationship-based methodology to investigate the chemical and biological features of a series of ten (C^N)-chelated half-sandwich iridiumIII complexes of the general formula [IrCp*(phox)Cl], where (phox) is a 2-phenyloxazoline ligand forming a 5-membered metallacycle. This series of compounds undergoes a fast exchange of their chlorido ligand once solubilised in DMSO. They were cytotoxic to HeLa cells with IC50 values in the micromolar range and induced a rapid activation of caspase-3, an apoptosis marker. In vitro, the oxidative power of all the complexes towards NADH was highlighted but only the complexes bearing substituents on the oxazoline ring were able to produce H2O2 at the micromolar range. However, we demonstrated using a powerful HyPer protein redox sensor-based flow cytometry assay that most complexes rapidly raised intracellular levels of H2O2. Hence, this study shows that oxidative stress can partly explain the cytotoxicity of these complexes on the HeLa cell line and gives a first entry to their mechanism of action.

A Solvent-free, Catalyst-free Formal [3+3] Cycloaddition Dearomatization Strategy: Towards New Fluorophores for Biomolecules Labelling

A general, sustainable dearomatization reaction for nitrogen-containing heterocycles was developed. Under solvent free conditions and without catalyst, the biorenewable methyl coumalate (MC) reacted as an efficient C₃ partner to convert nine types of basic aromatic rings into their pyrido[1,2-a] fused derivatives in good to excellent yields. The fluorescence properties of some of the products were harnessed to conjugate fluorescent tags to bovine serum albumin (BSA) and immunoglobulin G.

The bio-based methyl coumalate involved Morita–Baylis–Hillman reaction

An efficient and sustainable method to prepare pharmaceutically important pyrone derivatives under very mild conditions, from bio-based methyl coumalate, is reported.

‘Heteroaromatic Rings of the Future’: Exploration of Unconquered Chemical Space

William Pitt and co-workers have created a virtual exploratory heterocyclic library ‘VEHICLe’ containing over 200 unconquered bicyclic heteroaromatic rings, synthetically feasible with potential medicinal interest. Since the publication of the 22 ‘heteroaromatic rings of the future’ by Pitt in 2009, 15 of them have been successfully synthesized as bicyclic or polycyclic forms and evaluated for applications in both biology and material science. This short review presents the critical synthesis associated with innovative synthetic methodologies of the synthetically conquered ring scaffolds from the list of 22 with a spotlight on the scientific contribution of this fascinating article for the expansion of the chemical diversity.

1 Introduction

2 Heteroaromatic Rings of the Future: The Synthetic challenge?

2.1 4-Pyrido[1,3]oxazin-4-one-P1

2.2 Pyrrolo[2,1-b][1,3]oxazin-4-one-P4

2.3 Furo[2,1-e]pyridazin-4(1H)-one-P5

2.4 Isoxazolo[3,4-c]pyridin-7-one-P6

2.5 5H,6H-[1,2]Thiazolo[5,4-c]pyridin-5-one-P7

2.6 4H,5H-Furo[3,2-b]pyridin-5-one-P8

2.7 1H,5H,6H-Pyrazolo[3,4-c]pyridin-5-one-P9

2.8 Thieno[3,4-c]pyridazine-P10

2.9 Pyrrolo[1,2-c][1,2,3]triazine-P11

2.10 Thieno[3,4-a]oxazole-P12

2.11 2,4-Dihydropyrrolo[3,2-c]pyrazole-P13

2.12 Pyrazolo[1,5-b]isoxazole-P14

2.13 Imidazo[1,5-c]pyrimidin-3(2H)-one-P16

2.14 Cyclopenta[b][1,4]oxazin-5(4H)-one-P17

2.15 2,3-Dihydro-2,6-naphthyridin-3-one-P18

3 Conclusion

Stable Carboxylate-Terminated Gold Surfaces Produced by Spontaneous Grafting of an Alkyltin Compound

Self-assembled monolayers formed by chemisorption of thiolated molecules on gold surfaces are widely applied for biosensing. Moreover, and due to the low stability of thiol-gold chemistry, contributions to the functionalisation of gold substrates with linkers that provide a more stable platform for the immobilisation of electroactive or biological molecules are highly appreciated. Herein, it is demonstrated that a carboxylated organotin compound can be successfully grafted onto gold substrates to form a highly stable organic layer with reactivity for subsequent binding to an aminated molecule. A battery of techniques were used to characterise the surface chemistry. The grafted layer was used to anchor aminoferrocene and subjected to both thermostability tests and long-term stability studies over a period of one year, demonstrating thermostability up to 90 °C and storage stability for at least 12 months at 4 °C protected from light. The stable surface tethering of molecules on gold substrates can be exploited in a plethora of applications, including molecular techniques, such as solid-phase amplification and solid-phase melting curve analysis, that require elevated temperature stability, as well as biosensors, which require long-term storage stability.

Electrochemical primer extension based on polyoxometalate electroactive labels for multiplexed detection of single nucleotide polymorphisms

Polyoxymetalates (POMs) ([SiW₁₁O₃₉{Sn(CH₂)₂CO)}]^4- and [P₂W₁₇O₆₁{Sn(CH₂)₂CO)}]^6-) were used to modify dideoxynucleotides (ddNTPs) through amide bond formation, and applied to the multiplexed detection of single nucleotide polymorphisms (SNPs) in an electrochemical primer extension reaction. Each gold electrode of an array was functionalised with a short single stranded thiolated DNA probe, specifically designed to extend with the POM-ddNTP at the SNP site to be interrogated. The system was applied to the simultaneous detection of 4 SNPs within a single stranded 103-mer model target generated using asymmetric PCR, highlighting the potential of POM-ddNTPs for targeted, multiplexed SNP detection. The four DNA bases were successfully labelled with both ([SiW₁₁O₃₉{Sn(CH₂)₂CO)}]^4- and [P₂W₁₇O₆₁{Sn(CH₂)₂CO)}]^6-), and [SiW₁₁O₃₉{Sn(CH₂)₂CO)}]^4- demonstrated to be the more suitable due to its single oxidation peak, which provides an unequivocal signal. The POM-ddNTP enzymatically incorporated to the DNA anchored to the surface was visualised by AFM using gold coated mica. The developed assay has been demonstrated to be highly reproducible, simple to carry out and with very low non-specific background signals. Future work will focus on applying the developed platform to the detection of SNPs associated with rifampicin resistance in real samples from patients suffering from tuberculosis.

PCR Incorporation of Polyoxometalate Modified Deoxynucleotide Triphosphates and Their Application in Molecular Electrochemical Sensing of Yersinia pestis

Redox-labeled nucleotides are of increasing interest for the fabrication of next generation molecular tools and should meet requirements of being thermally stable, sensitive, and compatible with polymerase-mediated incorporation while also being electrochemically discriminable. The synthesis and characterization of Keggin and Dawson polyoxometalate-deoxynucleotide (POM-dNTP) bioconjugates linked through 7-deaza-modified purines is described. The modified POM-dNTPs were used for polymerase-based amplification of a DNA sequence specific for Yersinia pestis and the amplified DNA detected using an electrochemical DNA sensor. This highlights the potential of polyoxometalates as thermally stable, sensitive and polymerase-compatible redox labels for exploitation in bioanalytical applications.

Preparation of Substituted 2H-Pyrans via a Cascade Reaction from Methyl Coumalate and Activated Methylene Nucleophiles

The reaction of methyl coumalate with a wide range of methylene active compounds, such as keto-esters or keto-sulfones and cyclic or acyclic diketones, afforded more than 30 2,3,5,6-tetrasubstituted 2H-pyrans. The reaction proceeds via a cascade reaction involving a Michael addition-6π-electrocyclic ring opening-proton transfer and 6π electrocyclization, in which a variety of functional groups were tolerated.

Electrochemical primer extension for the detection of single nucleotide polymorphisms in the cardiomyopathy associated MYH7 gene

We report the labelling of dideoxy nucleotides (ddNTPs) for use in electrochemical array based primer extension for the detection of single nucleotide polymorphisms (SNPs). The results confirm the extension of the immobilised primers for each of the four ddNTPs, representing a significant advance in achieving a cost-effective platform for screening of disease-specific SNPs.

Biofunctionalization of Polyoxometalates with DNA Primers, Their Use in the Polymerase Chain Reaction (PCR) and Electrochemical Detection of PCR Products

The bioconjugation of polyoxometalates (POMs), which are inorganic metal oxido clusters, to DNA strands to obtain functional labeled DNA primers and their potential use in electrochemical detection have been investigated. Activated monooxoacylated polyoxotungstates [SiW11 O39 {Sn(CH2 )2 CO}](8-) and [P2 W17 O61 {Sn(CH2 )2 CO}](6-) have been used to link to a 5'-NH2 terminated 21-mer DNA forward primer through amide coupling. The functionalized primer was characterized by using a battery of techniques, including electrophoresis, mass spectrometry, as well as IR and Raman spectroscopy. The functionality of the POM-labeled primers was demonstrated through hybridization with a surface-immobilized probe. Finally, the labeled primers were successfully used in the polymerase chain reaction (PCR) and the PCR products were characterized by using electrophoresis.

Intramolecular anion effect in polyoxometalate-based organocatalysts: reactivity enhancement and chirality transfer by a metal oxide-organic cation interaction

An α1 -Dawson polyanion bearing a lateral side chain with a 4-aminopyridine end group was synthesized. This organopolyoxometalate catalyzes the addition of indenyl allyl silanes to cinnamoyl fluorides. The polyanionic framework influences the organocatalyst activity and selectivity. A moderate but nonzero chirality transfer from the chiral inorganic framework to the organic substrate was observed.

Exploring the utility of organo-polyoxometalate hybrids to inhibit SOX transcription factors

Background

SOX transcription factors constitute an attractive target class for intervention with small molecules as they play a prominent role in the field of regenerative biomedicine and cancer biology. However, rationally engineering specific inhibitors that interfere with transcription factor DNA interfaces continues to be a monumental challenge in the field of transcription factor chemical biology. Polyoxometalates (POMs) are inorganic compounds that were previously shown to target the high-mobility group (HMG) of SOX proteins at nanomolar concentrations. In continuation of this work, we carried out an assessment of the selectivity of a panel of newly synthesized organo-polyoxometalate hybrids in targeting different transcription factor families to enable the usage of polyoxometalates as specific SOX transcription factor drugs.

Results

The residual DNA-binding activities of 15 different transcription factors were measured after treatment with a panel of diverse polyoxometalates. Polyoxometalates belonging to the Dawson structural class were found to be more potent inhibitors than the Keggin class. Further, organically modified Dawson polyoxometalates were found to be the most potent in inhibiting transcription factor DNA binding activity. The size of the polyoxometalates and its derivitization were found to be the key determinants of their potency.

Conclusion

Polyoxometalates are highly potent, nanomolar range inhibitors of the DNA binding activity of the Sox-HMG family. However, binding assays involving a limited subset of structurally diverse polyoxometalates revealed a low selectivity profile against different transcription factor families. Further progress in achieving selectivity and deciphering structure-activity relationship of POMs require the identification of POM binding sites on transcription factors using elaborate approaches like X-ray crystallography and multidimensional NMR. In summary, our report reaffirms that transcription factors are challenging molecular architectures and that future polyoxometalate chemistry must consider further modification strategies, to address the substantial challenges involved in achieving target selectivity.

Access to pyridyl-substituted 1,3,5-triazines from 4H-pyrido[1,3]oxazin-4-ones via a cyclocondensation process

Pyridyl-substituted 1,3,5-triazines were synthesized in good to excellent yields via an unprecedented one-step cyclocondensation of 4H-pyrido[1,3]oxazin-4-ones with amidines at room temperature or under microwave irradiations. The broad applicability was demonstrated by 33 examples with a variety of amidines and three different 4H-pyrido[1,3]oxazin-4-one chemical series. In addition, a one-pot process from 4H-pyrido[1,3]oxazin-4-one precursors (imide sodium salts) was developed and led to the desired triazines compounds, thus allowing a one-step economy in their global synthetic preparation. This approach provides rapid access to pyridyl (or pyridone)-substituted 1,3,5-triazines with high potential in various fields of application.

Addition of carbon nucleophiles to hemiaminals promoted by a Lewis acidic polyoxotungstate

Organic soluble TBA₅K[α₁Hf(H₂O)₄P₂W₁₇O₆₁] (POM/Hf) catalyzes the addition of pronucleophiles (silylenolethers, diketones, ketoesters, allylsilane) to unactivated hemiaminals.

Identification of polyoxometalates as nanomolar noncompetitive inhibitors of protein kinase CK2

Protein kinase CK2 is a multifunctional kinase of medical importance that is dysregulated in many cancers. In this study, polyoxometalates were identified as original CK2 inhibitors. [P2Mo18O62](6-) has the most potent activity. It inhibits the kinase in the nanomolar range by targeting key structural elements located outside the ATP- and peptide substrate-binding sites. Several polyoxometalate derivatives exhibit strong inhibitory efficiency, with IC50 values < or = 10 nM. Furthermore, these inorganic compounds show a striking specificity for CK2 when tested in a panel of 29 kinases. Therefore, polyoxometalates are effective CK2 inhibitors in terms of both efficiency and selectivity and represent nonclassical kinase inhibitors that interact with CK2 in a unique way. This binding mode may provide an exploitable mechanism for developing potent drugs with desirable properties, such as enhanced selectivity relative to ATP-mimetic inhibitors.

A General Strategy for Ligation of Organic and Biological Molecules to Dawson and Keggin Polyoxotungstates

The copper-catalyzed azide/alkyne cycloaddition (click chemistry) is used for the first time in polyoxometalate chemistry to graft any kind of organics (lipophilic, water-soluble, biologically relevant) to polyoxotungstates to generate hybrids. The method is not limited by solvent matching between the polyoxometallic platforms and the organic substrates.