Synthesis of 3,7-dihydroimidazo[1,2a]pyrazine-3-ones and their chemiluminescent properties

Divergent Synthesis of 1,2,3,4-Tetrasubstituted Cyclobutenes from a Common Scaffold: Enantioselective Desymmetrization by Dual-Catalyzed Photoredox Cross-Coupling

Four-membered carbocycles are important structural motifs found in several natural products and drugs. Amongst those, cyclobutenes are attractive intermediates because the residual olefin can be manipulated selectively into various saturated and unsaturated analogs. Few methods exist to access chiral tri- and tetra-C-substituted cyclobutenes and they are generally limited in terms of diversification. Herein, a divergent synthetic strategy was developed where a single optically enriched scaffold is diversified into a variety of derivatives with different substitution patterns. To this end, the enantioselective desymmetrization of prochiral 1,2-dibromocyclobutene imides was enabled by a dual Ir/Ni-catalyzed photoredox C(sp2 )-C(sp3 ) cross-coupling with an alkyltrifluoroborate salt to install a convertible carbon fragment in good yields and >90 % enantiomeric excess. Exceptional mono-coupling selectivity is observed and the resulting chiral bromocyclobutene serves as a common scaffold that can be transformed in a divergent manner into several valuable 1,2,3,4-tetra-C-substituted cyclobutane products while maintaining optical purity.

A New Method for Albuminuria Measurement Using a Specific Reaction between Albumin and the Luciferin of the Firefly Squid Watasenia scintillans

This study demonstrates that the luciferin of the firefly squid Watasenia scintillans, which generally reacts with Watasenia luciferase, reacted with human albumin to emit light in proportion to the albumin concentration. The luminescence showed a peak wavelength at 540 nm and was eliminated by heat or protease treatment. We used urine samples collected from patients with diabetes to quantify urinary albumin concentration, which is essential for the early diagnosis of diabetic nephropathy. Consequently, we were able to measure urinary albumin concentrations by precipitating urinary proteins with acetone before the reaction with luciferin. A correlation was found with the result of the immunoturbidimetric method; however, the Watasenia luciferin method tended to produce lower albumin concentrations. This may be because the Watasenia luciferin reacts with only intact albumin. Therefore, the quantification method using Watasenia luciferin is a new principle of urinary albumin measurement that differs from already established methods such as immunoturbidimetry and high-performance liquid chromatography.

Cardioluminescence in Transgenic Zebrafish Larvae: A Calcium Imaging Tool to Study Drug Effects and Pathological Modeling

Zebrafish embryos and larvae have emerged as an excellent model in cardiovascular research and are amenable to live imaging with genetically encoded biosensors to study cardiac cell behaviours, including calcium dynamics. To monitor calcium ion levels in three to five days post-fertilization larvae, we have used bioluminescence. We generated a transgenic line expressing GFP-aequorin in the heart, Tg(myl7:GA), and optimized a reconstitution protocol to boost aequorin luminescence. The analogue diacetylh-coelenterazine enhanced light output and signal-to-noise ratio. With this cardioluminescence model, we imaged the time-averaged calcium levels and beat-to-beat calcium oscillations continuously for hours. As a proof-of-concept of the transgenic line, changes in ventricular calcium levels were observed by Bay K8644, an L-type calcium channel activator and with the blocker nifedipine. The β-adrenergic blocker propranolol decreased calcium levels, heart rate, stroke volume, and cardiac output, suggesting that larvae have a basal adrenergic tone. Zebrafish larvae treated with terfenadine for 24 h have been proposed as a model of heart failure. Tg(myl7:GA) larvae treated with terfenadine showed bradycardia, 2:1 atrioventricular block, decreased time-averaged ventricular calcium levels but increased calcium transient amplitude, and reduced cardiac output. As alterations of calcium signalling are involved in the pathogenesis of heart failure and arrhythmia, the GFP-aequorin transgenic line provides a powerful platform for understanding calcium dynamics.

Single-molecule chemiluminescent photosensitizer for a self-activating and tumor-selective photodynamic therapy of cancer

While photodynamic therapy is known for significant advantages over conventional cancer therapies, its dependence on light has limited it to treating tumors on or just under the skin or on the outer lining of organs/cavities. Herein, we have developed a single-molecule photosensitizer capable of intracellular self-activation and with potential tumor-selectivity due to a chemiluminescent reaction involving only a cancer marker. Thus, the photosensitizer is directly chemiexcited to a triplet excited state capable of generating singlet oxygen, without requiring either a light source or any catalyst/co-factor. Cytotoxicity assays involving the photosensitizer show significant toxicity toward tumor cells, even better than reference drugs, while not inducing toxicity toward normal cells. This work provides a proof-of-concept for a novel type of photosensitizer that eliminates the current restrictions that photodynamic therapy presents regarding tumor size and localization.

Study of the Combination of Self-Activating Photodynamic Therapy and Chemotherapy for Cancer Treatment

Cancer is a very challenging disease to treat, both in terms of treatment efficiency and side-effects. To overcome these problems, there have been extensive studies regarding the possibility of improving treatment by employing combination therapy, and by exploring therapeutic modalities with reduced side-effects (such as photodynamic therapy (PDT)). Herein, this work has two aims: (i) to develop self-activating photosensitizers for use in light-free photodynamic therapy, which would eliminate light-related restrictions that this therapy currently possesses; (ii) to assess their co-treatment potential when combined with reference chemotherapeutic agents (Tamoxifen and Metformin). We synthesized three new photosensitizers capable of self-activation and singlet oxygen production via a chemiluminescent reaction involving only a cancer marker and without requiring a light source. Cytotoxicity assays demonstrated the cytotoxic activity of all photosensitizers for prostate and breast tumor cell lines. Analysis of co-treatment effects revealed significant improvements for breast cancer, producing better results for all combinations than just for the individual photosensitizers and even Tamoxifen. By its turn, co-treatment for prostate cancer only presented better results for one combination than for just the isolated photosensitizers and Metformin. Nevertheless, it should be noted that the cytotoxicity of the isolated photosensitizers in prostate tumor cells was already very appreciable.

Biothiol-Activatable Bioluminescent Coelenterazine Derivative for Molecular Imaging in Vitro and in Vivo

There is a high demand for sensitive biothiol probes targeting cysteine, glutathione, and homocysteine. These biothiols are known as playing essential roles to maintain homeostasis and work as indicators of many diseases. This work presents a bioluminescent probe (named AMCM) to detect biothiols in live mammalian cells and in vivo with a limit of detection of 0.11 μM for cysteine in solution and high selectivity for biothiols, making it suitable for real-time biothiol detection in biological systems. Upon application to live cells, AMCM showed low cytotoxicity and sensitively reported bioluminescence in response to changes of biothiol levels. Furthermore, a bioluminescence resonance energy transfer system consisting of AMCM combined with the near-infrared fluorescent protein iRFP713 was applied to in vivo imaging, with emitted tissue-permeable luminescence in living mice. In summary, this work demonstrates that AMCM is of high practical value for the detection of biothiols in living cells and for deep tissue imaging in living animals.

ATP-Independent Bioluminescent Reporter Variants To Improve in Vivo Imaging

Coelenterazine (CTZ)-utilizing marine luciferases and their derivatives have attracted significant attention because of their ATP-independency, fast enzymatic turnover, and high bioluminescence brightness. However, marine luciferases typically emit blue photons and their substrates, including CTZ and the recently developed diphenylterazine (DTZ), have poor water solubility, hindering their in vivo applications. Herein, we report a family of pyridyl CTZ and DTZ analogs that exhibit spectrally shifted emission and improved water solubility. Through directed evolution, we engineered a LumiLuc luciferase with broad substrate specificity. In the presence of corresponding pyridyl substrates (i.e., pyCTZ, 6pyDTZ, or 8pyDTZ), LumiLuc generates highly bright blue, teal, or yellow bioluminescence. We compared our LumiLuc-8pyDTZ pair with several benchmark reporters in a tumor xenograft mouse model. Our new pair, which does not need organic cosolvents for in vivo administration, surpasses other reporters by detecting early tumors. We further fused LumiLuc to a red fluorescent protein, resulting in a LumiScarlet reporter with further red-shifted emission and enhanced tissue penetration. LumiScarlet-8pyDTZ was comparable to Akaluc-AkaLumine, the brightest ATP-dependent luciferase-luciferin pair, for detecting cells in deep tissues of mice. In summary, we have engineered a new family of ATP-independent bioluminescent reporters, which will have broad applications because of their ATP-independency, excellent biocompatibility, and superior in vivo sensitivity.

New bioluminescent coelenterazine derivatives with various C-6 substitutions

A series of new coelenterazine analogs with varying substituents at the C-6 position of the imidazopyrazinone core have been designed and synthesized for the extension of bioluminescence substrates.

Site-selective Suzuki-Miyaura coupling of heteroaryl halides - understanding the trends for pharmaceutically important classes

Suzuki-Miyaura cross-coupling reactions of heteroaryl polyhalides with aryl boronates are surveyed. Drawing on data from literature sources as well as bespoke searches of Pfizer's global chemistry RKB and CAS Scifinder® databases, the factors that determine the site-selectivity of these reactions are discussed with a view to rationalising the trends found.

Synthetic Bioluminescent Coelenterazine Derivatives

The development of coelenterazine (CTZ) derivatives resulting in superior optical characteristics is an efficient method to extend the range of its possible applications. Here, we describe the synthesis of three C-6 substituted CTZ derivatives retaining the recognition by Renilla luciferase (RLuc) and its derivatives. The novel derivatives are useful as bright blue-shifted CTZ derivatives, which can be used as an alternative to hitherto reported compound DeepBlueC™.

Lighting up bioluminescence with coelenterazine: strategies and applications

Bioluminescence-based techniques, such as bioluminescence imaging, BRET and dual-luciferase reporter assay systems, have been widely used to examine a myriad of biological processes. Coelenterazine (CTZ), a luciferin or light-producing compound found in bioluminescent organisms, has sparked great curiosity and interest in searching for analogues with improved photochemical properties. This review summarizes the current development of coelenterazine analogues, their bioluminescence properties, and the rational design of caged coelenterazine towards biotargets, as well as their applications in bioassays. It should be emphasized that the design of caged luciferins can provide valuable insight into detailed molecular processes in organisms and will be a trend in the development of bioluminescent molecules.

Novel bioluminescent coelenterazine derivatives with imidazopyrazinone C-6 extended substitution for Renilla luciferase

Novel coelenterazine analogues displayed excellent bioluminescence properties in cellulo, thus becoming favourable molecules for bioluminescence techniques.

Recent advances in development of imidazo[1,2-a]pyrazines: synthesis, reactivity and their biological applications

The synthesis, reactivity and multifarious biological activities at the different positions of imidazo[1,2-a]pyrazines are concisely discussed in this review.

Access to 4-alkylaminopyridazine derivatives via nitrogen-assisted regioselective Pd-catalyzed reactions

3-Substituted, 6-substituted, and unsymmetrical 3,6-disubstituted 4-alkylaminopyridazines were prepared from a sequence of three chemo- and regioselective reactions combining amination and palladium-catalyzed cross-coupling reactions, such as reductive dehalogenation and Suzuki-Miyaura reactions. Extension of the methodology to Sonogashira reaction yielded a novel class of 3-substituted pyrrolopyridazines.

Molecular mechanism of Symplectoteuthis bioluminescence--part 4: chromophore exchange and oxidation of the cysteine residue

Symplectin is one of the few photoproteins, which forms covalent bonds with the dehydro-coelenterazine (DCL) at the binding sites and the active site. This binding takes place through the SH's of the cysteine residues via conjugate addition reaction. This photoprotein contains the chromophore molecules at the binding cites first, and then moves to the active cite Cys-390 for the luminescence. The current study focuses on these dynamic aspects of the chromophore using the natural photoprotein by analyzing the fluorescence changing of the DCL chromophores analogs with 8-(4'-methoxyphenyl)- or 8-(2'-naphthyl)-group and 2-(2',4'-difluorophenyl)-group. Exchanges of these chromophores were monitored the fluorescence at slightly acidic media and also from the luminescence function observed at the optimum pH 7.8. The non-fluorescent naphthyl analogs was even proven to make the covalent bond formation at pH 6.0 and evidently to obtain the corresponding luminescent product amide by liquid chromatographic detection from the spent solutions.

Interleukin-1β and transforming growth factor-β cooperate to induce neurosphere formation and increase tumorigenicity of adherent LN-229 glioma cells

INTRODUCTION

Glioma stem cells (GSCs) have the property of self-renewal and appear to be a driving force for the initiation and recurrence of gliomas. We recently found that the human tumorigenic LN-229 glioma cell line failed to form neurospheres in serum-free conditions and generated mostly small tumors in vivo, suggesting that either LN-229 GSCs are not active in these conditions or GSCs are absent in the LN-229 cell line.

METHODS

Using self-renewal assay, soft-agar colony assay, cell proliferation assay, invasion assay, real time PCR analysis, ELISA and in vivo tumorigenic assay, we investigated the effects of interleukin (IL)-1β and transforming growth factor (TGF)-β on the development of GSCs from LN-229 cells.

RESULTS

Here, we demonstrate that the combination of IL-1β and TGF-β can induce LN-229 cells to form neurospheres in serum-free medium. IL-1β/TGF-β-induced neurospheres display up-regulated expression of stemness factor genes (nestin, Bmi-1, Notch-2 and LIF), and increased invasiveness, drug resistance and tumor growth in vivo: hallmarks of GSCs. These results indicate that IL-1β and TGF-β cooperate to induce a GSC phenotype in the LN-229 cell line. Induction of nestin, LIF and Notch-2 by IL-1β/TGF-β can be reverted after cytokine withdrawal. Remarkably, however, up-regulated Bmi-1 levels remained unchanged after cytokine withdrawal; and the cytokine-withdrawn cells maintained strong clonogenicity, suggesting that Bmi-1 may play a crucial role in tumorigenesis.

CONCLUSIONS

Our finding indicates that glioma cells without self-renewal capability in standard conditions could also contribute to glioma malignancy when cytokines, such as IL-1β and TGF-β, are present in the tumor environment. Targeting GSC-promoting cytokines that are highly expressed in glioblastomas may contribute to the development of more effective glioma therapies.

Conformational stability, the spectroscopic (FT-IR and UV), first order hyperpolarizability, NBO analysis, HOMO and LUMO analysis of 6,8-diphenylimidazo[1,2-α]pyrazine molecule by ab initio HF and density functional methods

The conformational analysis of 6,8-diphenylimidazo[1,2-α]pyrazine molecule (abbreviated as 68DIP) was performed by using B3LYP/6-31G(d) level of theory to find the most stable form. Two staggered stable conformers were observed on the torsional potential energy surface. The equilibrium geometry, bonding features and vibrational frequencies of 68DIP have been investigated by using the DFT (B3LYP) and HF methods for the lowest energy conformer. The first order hyperpolarizability (β(total)) of this molecular system and related properties (β, μ, <α> and Δα) are calculated using HF/6-311++G(d,p) and B3LYP/6-311++G(d,p) methods based on the finite-field approach. Stability of the molecule arising from hyperconjugative interactions, charge delocalization and C-H⋯N intramolecular hydrogen-bond-like weak interaction has been analyzed using natural bond orbital (NBO) analysis by using B3LYP/6-311++G(d,p) method. The results show that electron density (ED) in the σ* and π* antibonding orbitals and second order delocalization energies E((2)) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. UV-vis spectrum of the compound was recorded and electronic properties, such as HOMO, LUMO energies, excitation energies and wavelength were performed by TD-DFT/B3LYP, CIS and TD-HF methods by using 6-311++G(d,p) basis set. Finally, the calculation results were applied to simulated infrared spectra of the title compound which show good agreement with observed spectra.

Ground state and excited state dipole moments of 6,8-diphenylimidazo[1,2-α]pyrazine determined from solvatochromic shifts of absorption and fluorescence spectra

Electronic absorption and dual fluorescence spectra of 6,8-diphenylimidazo[1,2-α]pyrazine (68DIP) was recorded in various solvents with different polarity at room temperature. The ground state (μg) and the excited state (μg) dipole moments of 68DIP were estimated from solvatochromic shifts of absorption and fluorescence spectra as a function of the dielectric constant (ɛ) and refractive index (n). The results show that the value of excited state dipole moment in SE: μeSE=2.8772 D and twisted intramolecular charge transfer (TICT) excited equilibrated state dipole moment value of μeLE=2.9744 D was found. The solvent dependent spectral shifts in absorption and fluorescence spectra were analyzed by the polarizability-polarity and Kamlet-Taft parameters.

Discovery of potent and selective inhibitors of ataxia telangiectasia mutated and Rad3 related (ATR) protein kinase as potential anticancer agents

DNA-damaging agents are among the most frequently used anticancer drugs. However, they provide only modest benefit in most cancers. This may be attributed to a genome maintenance network, the DNA damage response (DDR), that recognizes and repairs damaged DNA. ATR is a major regulator of the DDR and an attractive anticancer target. Herein, we describe the discovery of a series of aminopyrazines with potent and selective ATR inhibition. Compound 45 inhibits ATR with a K(i) of 6 nM, shows >600-fold selectivity over related kinases ATM or DNA-PK, and blocks ATR signaling in cells with an IC(50) of 0.42 μM. Using this compound, we show that ATR inhibition markedly enhances death induced by DNA-damaging agents in certain cancers but not normal cells. This differential response between cancer and normal cells highlights the great potential for ATR inhibition as a novel mechanism to dramatically increase the efficacy of many established drugs and ionizing radiation.

Regio- and chemoselective multiple functionalization of chloropyrazine derivatives. Application to the synthesis of coelenterazine

Successive regio- and chemoselective metalations of chloropyrazines using TMPMgCl x LiCl and TMPZnCl x LiCl furnish, after trapping with electrophiles, highly functionalized pyrazines in high yields. Application to a synthesis of coelenterazine, a bioluminescent natural product in jellyfish Aequorea victoria, in nine steps (9% overall yield) is reported.

Cobalt-Mediated [2+2+2] Cycloaddition versus CH and NH Activation of Pyridones and Pyrazinones with Alkynes: An Experimental Study

The reactivity of a range of pyridone and pyrazinone derivatives towards alkynes in the presence of cyclopentadienylcobaltbis(ethene) has been investigated. Depending on the nature of the substrates, [2+2+2]- or [2+2] cycloaddition, C-H, or N-H activation may occur. In the case of pyridones, the first three predominated with N-protected derivatives, whereas substrates containing N-H bonds followed an N-H activation pathway. The [2+2+2] cycloaddition of an N-butynylisoquinolone was applied successfully to the total synthesis of anhydrolycorinone. Pyrazinone substrates showed similar patterns of reactivity.

Luminescence of imidazo[1,2-a]pyrazin-3(7H)-one compounds

In this review I will discuss chemical principles of the luminescence of imidazo[1,2-a]pyrazin-3(7H)-one compounds described to date. The review is composed of two main parts, the first dealing with the bioluminescence of coelenterate luciferin "coelenterazine" and Cypridina luciferin in marine organisms and the second with the chemiluminescence of these luciferins and their analogues. In the second section, possible applications of chemiluminescence and enhanced chemiluminescence in the area of bioassay are also discussed.

Coelenterazine (marine bioluminescent substrate): a source of inspiration for the discovery of novel antioxidants

Coelenterazine and derivatives were initially considered in the scientific community for their (bio)luminescent properties. Now, another interest of such hetero-bicycles has been pointed out by the discovery of remarkable antioxidative properties, and an unique mode of action as a "cascade": the mother-compound (imidazolopyrazinone) is transformed by ROS into a daughter-compound (2-amino-pyrazine) also endowed with antioxidative properties. This review illustrates the therapeutic potential of synthetic imidazolopyrazinones (coelenterazine analogues): chemical reactivity assays with singulet oxygen, radical anion superoxide, peroxynitrite, and radicals formed during lipid and LDL peroxidation, cellular tests of protection against oxidative stress using keratinocyte, hepatocyte, neuronal and erythrocyte cells, and finally in vivo evaluation in a hamster model of ischemia-reperfusion, are fully described.