The environment-sensitive probe 2 with turn-on switch for Mcl-1 protein was developed herein. After careful evaluation, this small molecule fluorescent probe revealed a selective binding affinity with Mcl-1 protein with a Ki value of 2.6 μM and can be well applied to imaging Mcl-1 protein or detecting the cellular distribution of Mcl-1 protein inhibitors. Compared with other imaging approaches, such as the immunofluorescence and fluorescent protein-based techniques, this fluorescent method is rapid, convenient, and affordable, especially since a washing procedure is no longer needed. This environment-sensitive “off-on” design strategy may present a case in point for developing small-molecule fluorescent probe of Bcl-2 family proteins.

Hypoxia is a pathogenic characteristic of solid tumors owing to absent or abnormal vasculature in the tumor microenvironment and essential in tumor progression, angiogenesis, metastasis, invasion and resistance to immune system and therapy. In hypoxic environments, CYP450 enzymes are more efficient than in normoxia. Herein, based on the reductive capacity of CYP450 enzymes/NADPH system, we managed to cage aminoluciferin developing a reaction-based bioluminescent probe as well as an imaging method for the hypoxia detection. Exhibiting enhanced about 3-fold total flux in big (1.2 cm-diameter) tumors, Hypoxia BioLuminescent probe (HBL) can afford potential utility for in cellulo and in vivo hypoxia imaging in tumor model mice.

To enhance the efficiency of firefly luciferase/luciferin bioluminescence imaging, a series of N-cycloalkylaminoluciferins (cyaLucs) were developed by introducing lipophilic N-cycloalkylated substitutions. The experimental results demonstrate that these cyaLucs are effective substrates for native firefly luciferase (Fluc) and can produce elevated bioluminescent signals in vitro, in cellulo, and in vivo. It should be noted that, in animal studies, N-cyclobutylaminoluciferin (cybLuc) at 10 μM (0.1 mL), which is 0.01% of the standard dose of d-luciferin (dLuc) used in mouse imaging, can radiate 20-fold more bioluminescent light than d-luciferin (dLuc) or aminoluciferin (aLuc) at the same concentration. Longer in vivo emission imaging using cybLuc suggests that it can be used for long-time observation. Regarding the mechanism of cybLuc, our cocrystal structure data from firefly luciferase with oxidized cybLuc suggested that oxidized cybLuc fits into the same pocket as oxyluciferin. Most interestingly, our results demonstrate that the sensitivity of cybLuc in brain tumor imaging contributes to its extended application in deep tissues.

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. Some of them display excellent bioluminescence properties compared to DeepBlueC™ or native coelenterazine with both in vitro and in vivo biological evaluations, thus placing these derivatives among the most ideal substrates for Renilla bioluminescence applications.

The prodrug or caged-luciferin strategy affords an excellent platform for persistent bioluminescence imaging. In the current work, we designed and synthesized ten novel pro-substrates for Renilla luciferase by introducing ester protecting groups of different sizes into the carbonyl group of the free luciferin 1. Taking advantage of intracellular esterases, lipases, and nucleophilic substances, the ester protecting groups were hydrolyzed, resulting in the release of a free luciferin and a bioluminescence signal turn-on. Among the tested pro-substrates, the butyryloxymethyl luciferin 7 exhibited low cytotoxicity and a prolonged luminescence signal both in cellulo and in vivo. Therefore, the butyryloxymethyl luciferin 7 can act as a promising substrate for noninvasive extended imaging in diagnostic and therapeutic fields.

A series of probes with a turn-on switch for the p53–MDM2 protein–protein interaction were developed. After careful evaluation, these small molecule fluorescent probes exhibited high practical activity and selectivity in vitro and in cellulo. In particular probe 10, which had a Ki value of 0.03 μM, displayed much better binding affinity compared to the positive control Nutlin-3, which had a Ki value of 0.23 μM. These no-wash environment-sensitive turn-on fluorescent probes have been successfully applied to imaging p53–MDM2 interaction in the human lung cancer cell line A549 (wild-type p53) at the micromolar level. Therefore, these fluorescent probes are expected to be used in drug screening and cell staining in p53–MDM2 fields, as well as in pathological and physiological studies of the p53–MDM2 interaction.

Correction for ‘Environment-sensitive turn-on fluorescent probes for p53–MDM2 protein–protein interaction’ by Tingting Liu et al., MedChemCommun, 2017, DOI: 10.1039/c7md00287d.

Nitroreductase (NTR) is an endogenous reductase overexpressed in hypoxic tumors; however, its precise detection in living cells and animals remains a considerable challenge. Herein, we developed three reaction-based probes and a related bioluminescence assay for the real-time NTR detection. The high sensitivity and selectivity of probe 3, combined with its remarkable potential of bioluminescence imaging, affords a valuable approach for in vivo imaging of NTR in a tumor model mouse.

Considering that hydrogen sulfide (H2S) is an endogenous signaling molecule involved in numerous biological processes, a method for monitoring H2S as a powerful tool for investigating its complicated functions and mechanisms is urgently demanded. Herein, a bioluminescent turn-on probe was reported based on caged strategy for the detection of H2S in vitro and in vivo. This probe will help us understand the intricate contribution of H2S to a variety of physiological and pathological processes.

A novel environment-sensitive probe S2 with turn-on switch for Human Ether-a-go-go-Related Gene (hERG) potassium channel was developed herein. After careful evaluation, this fluorescent probe showed high binding affinity with hERG potassium channel with an IC50 value of 41.65 nM and can be well applied to hERG channel imaging or cellular distribution study for hERG channel blockers. Compared with other imaging techniques, such as immunofluorescence and fluorescent protein-based approaches, this method is convenient and affordable, especially since a washing procedure is not needed. Meanwhile, this environment-sensitive turn-on design strategy may provide a good example for the probe development for these targets that have no reactive or catalytic activity.

A novel bioluminescence probe for mercury(II) was obtained on the basis of the distinct deprotection reaction of dithioacetal to decanal, so as to display suitable sensitivity and selectivity toward mercury(II) over other ions with bacterial bioluminescence signal. These experimental results indicated such a probe was a novel promising method for mercury(II) bioluminescence imaging in environmental and life sciences ex vivo and in vivo.

Fluorescent ligands are gaining popularity as tools to aid GPCR research. Nonetheless, in vivo application of such tools is hampered due to their short excitation wavelengths in the visible range and lack of fluorogenic switch. Here we report the discovery of fluorescent ligands (3a–f) for α1-adrenergic receptors (α1-ARs) by conjugating the environment-sensitive fluorophore cyane 5 (Cy5) with the quinazoline pharmacophore. Among them, the conjugated compound 3a, with acylated piperazine and the shortest carbon chain spacer, exhibited potent binding and remarkable changes in fluorescence (10-fold) upon binding to α1-AR. Furthermore, it could be employed to selectively and specifically label α1-ARs with no washing procedures in single cells, prostate tissue slices, intact tumor xenografts and organs in living mice. Especially, the slice imaging results gave direct and visual evidence that there is a close relationship between α1-ARs and pathological prostate. It is anticipated that our fluorescent tools will find broad applications in the study of α1-AR pharmacology and physiology to aid development of novel therapeutics.

Two series of novel coelenterazine analogues (alkynes and triazoles) with imidazopyrazinone C-6 extended substitution have been designed and synthesized successfully for the extension of bioluminescent substrates. After extensive evaluation, some compounds display excellent bioluminescence properties compared with DeepBlueC in cellulo, thus becoming potential molecules for bioluminescence techniques.

High-throughput screening (HTS) of ligand library to find new active molecules for G protein-coupled receptors is still a major interest, as well as an actual challenge. Fluorescence polarization (FP) assay portrays an essential role in HTS; however, in many cases, it was restricted by the absence of FP probes, the narrow measurement window, and low signal-to-noise (S/N) ratio. Herein, based on the modification of our previous probe 1 (QFL), we discovered an FP probe 3 (QGGFL) for α1-adrenergic receptors (α1-ARs), which has satisfactory fluorescence intensity, specific binding ability to receptors, and suitable fluorescence properties that were compatible with the filters in the FP system. Meanwhile, an “ELISA-like” strategy was designed for FP-based HTS assay in which proteins were adhered into a solid phase to improve the measurement window and S/N ratio. With fluorescent antagonist QGGFL and the ELISA strategy, we succeeded in establishing the first competitive binding FP assay for α1-AR antagonists as the alternative of the radioligand binding assay.Keywords: ELISA; fluorescence polarization; fluorescent probe; GPCR; ligand screening; α1-Adrenergic receptors;

α1-Adrenoceptors (α1-ARs), including at least three subtypes, α1A, α1B and α1D, which play essential roles in G protein-coupled receptors (GPCRs), can convey multiple pivotal extracellular signals in varied tissues and organs. In this research, a series of napthalimide-based small-molecule fluorescent probes (1a–1f) for α1-ARs, including two parts, a pharmacophore (quinazoline and phenylpiperazine) for α1-AR recognition and a fluorophore (naphthalimide) for visualization, were designed and synthesized successfully. These compounds display excellent fluorescence property and high affinity to receptors, which were used successfully for in vitro visualization of α1-adrenoceptors.A series of napthalimide-based small-molecule fluorescent probes for α1-ARs were well designed and synthesized. These compounds display excellent fluorescence property and high affinity to receptors, which were used successfully for in vitro visualization of α1-adrenoceptors.

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.

The luciferase reporter gene assay system is broadly applied in various biomedical aspects, including signaling pathway dissection, transcriptional activity analysis, and genetic toxicity testing. It significantly improves the experimental accuracy and reduces the experimental error by the addition of an internal control. In the current research, we discovered some specific ions that could selectively inhibit firefly luciferase while having a negligible effect on renilla luciferase in vitro in the dual-reporter gene assay. We showed that these ionic compounds had a high potential of being utilized as quench-and-activate reagents in the dual-reporter assay. Furthermore, results from kinetic studies on ion-mediated quenching effects indicated that different ions have distinct inhibition modes. Our study is anticipated to guide a more affordable design of quench-and-activate reagents in biomedicine and pharmaceutical analysis.

Replacement of the methylene group at the C-8 position with an extended electronic conjugation is a new promising method to develop red-shifted coelenterazine derivatives. In this paper, we have described an oxygen-containing coelenterazine derivative with a significant red-shifted (63 nm) bioluminescence signal maximum relative to coelenterazine 400a (DeepBlueC™, 1). In cell imaging, the sulfur-containing coelenterazine derivative displayed a significantly (1.77 ± 0.09; P ≤ 0.01) higher luminescence signal compared to coelenterazine 400a and the oxygen-containing coelenterazine derivative exhibited a slightly (0.74 ± 0.08; P ≤ 0.05) lower luminescence signal. It is beneficial to understand further the underlying mechanisms of bioluminescence.The oxygen-containing coelenterazine derivative 2 exhibited a more significant red-shifted (63 nm) bioluminescence signal maximum relative to coelenterazine 400a (DeepBlueC™, 1). In cell imaging, the sulfur-containing coelenterazine derivative 3 displayed a significantly (1.77 ± 0.09; P ≤ 0.01) higher luminescence signal compared to 1 while the oxygen-containing coelenterazine derivative 2 exhibited a slightly (0.74 ± 0.08; P ≤ 0.05) lower luminescence signal.

Several novel fluorescent probes targeting α1-adrenergic receptors were well designed and synthesized by conjugating phenylpiperazine pharmacophore with coumarin and fluorescein fluorophores. These compounds showed suitable fluorescence property, high receptor affinity, and low cytotoxicity. Moreover, the cell imaging results displayed that these probes can be effective tools for the real-time detection of ligand-receptor interactions, as well as the visualization and location of α1-adrenergic receptors in living cells.

Two rapid bioluminescent probes for the detection of fluoride ion were developed on the basis of F–Si bond formation herein. It should be noted that probe 1 exhibited highly selective and sensitive detection toward fluoride ion over other anions and has been successfully applied in imaging fluoride ion in both living cells and animals.

The first small-molecule fluorogenic probe A1 for imaging the human Ether-a-go-go-Related Gene (hERG) potassium channel based on the photoinduced electron transfer (PET) off–on mechanism was described herein. After careful biological evaluation, this probe had the potential of detecting and imaging the hERG channel at the molecular and cellular level. Moreover, the competitive binding mechanism of this probe would presumably minimize the effects on the electrophysiological properties of the hERG channel. Therefore, this probe may serve as a powerful toolkit to the hERG-associated study.

Drug induced long QT syndrome is a high risk event in clinic, which mainly results from their high affinity to the Human Ether-a-go-go-Related Gene (hERG) potassium channel. Therefore, evaluation of the drug's inhibitory activity against the hERG potassium channel is a required step in drug discovery and development. In this study, we developed a series of novel conformation-mediated intramolecular photoinduced electron transfer fluorogenic probes for the hERG potassium channel. After careful evaluation, probes N4 and N6 showed good activity and may have a promising application in the cell-based hERG potassium channel inhibitory activity assay, as well as potential hERG-associated cardiotoxicity evaluation. Compared with other assay methods, such as patch clamp assay, radio-ligand competitive binding assay, fluorescence polarization and potential-sensitive fluorescent probes, this method is convenient and can also selectively measure the inhibitory activity in the native state of the hERG potassium channel. Meanwhile, these probes can also be used for hERG potassium channel imaging without complex washing steps.

As the most convenient and efficient bioluminescence system, the firefly luciferase/luciferin complex has been widely used in life science research and high-throughput screening (HTS). Nonetheless, the interpretation of firefly luciferase-based assay data is often complicated by the occurrence of “false positives,” in part because firefly luciferase (Fluc) is subject to direct inhibition by HTS compounds that might inadvertently act as inhibitors of its catalytic site. Here we report a series of 2-phenylnaphthalenes as Fluc inhibitors with suitable potency both in vitro and in vivo. Besides, our compound 5 showed significant systemic inhibition in transgenic mice. Enzymatic kinetics study reveals that compound 5 is competitive for substrate aminoluciferin and noncompetitive for the second substrate ATP. Furthermore, compound 5 exhibited good performance as a quenching agent in a dual-luciferase reporter assay. We anticipate that these Fluc inhibitors will contribute to the broader utilization of bioluminescence in life science research while circumventing or at least reducing the number of “false positives”.

α1-Adrenergic receptors (α1-ARs), as the essential members of G protein-coupled receptors (GPCRs), can mediate numerous physiological responses in the sympathetic nervous system. In the current research, a series of quinazoline-based small-molecule fluorescent probes to α1-ARs (1a–1e), including two parts, a pharmacophore for α1-AR recognition and a fluorophore for visualization, were well designed and synthesized. The biological evaluation results displayed that these probes held reasonable fluorescent properties, high affinity, accepted cell toxicity, and excellent subcellular localization imaging potential for α1-ARs.Keywords: cell imaging; fluorescent probes; quinazoline; subcellular localization; α1-Adrenergic receptors

Aminopeptidase N (APN) is an important drug target and biomarker for various tumors. The current work characterizes a novel APN-targeted fluorescent probe (Bes-Green, 2) that manifests comparable inhibitory activity with Bestatin. This probe has capacity of tightly binding to the APN for imaging endogenous APN in living human ovarian clear cell carcinoma cells (ES-2) and has potential application in biological study of cellular APN.In this article, a bestatin-based fluorescent probe has been well designed and synthesized for APN cellular imaging.

As the most studied bioluminescent system, firefly luciferase is widely applied in many aspects, such as developing small molecule probes, bioluminescent imaging, high-throughput screening, dual luciferase reporters, etc. Considering that a false positive phenomenon often emerges while researchers conduct high-throughput screening based on firefly luciferase, and that the triazole core is a “privileged” scaffold in drug design and development, we herein report a series of triazoles with potent inhibitory activity in vitro and in vivo, comparable to that of the well-known inhibitor resveratrol. More interesting, a kinetics study disclosed that these triazoles exhibited a brand new inhibition mode, mixed noncompetitive for the substrate aminoluciferin and noncompetitive for ATP. Henceforth, these compounds can notify researchers for possible “false positives”. Moreover, they will shed light on luciferase structure–function mechanistic exploration and help expand its application in various areas.

Naphthalene-bridged bis-triazole (NBT) complexes were prepared and characterized for investigation of their photophysical properties. Unlike our previously reported N-2-aryl triazoles, which gave strong emissions through the planar intramolecular charge transfer mechanism (coplanar conformation), this newly developed NBT adopted a noncoplanar conformation between triazole and naphthalene, achieving fluorescence through twisted intramolecular charge transfer.

The triazole–gold(I) complex catalyzed [3,3]-rearrangement of propargyl ester has been quantitatively investigated through in situ IR. First order dependence of the initial rates on [Au] and [propargyl ester] suggested that the turnover-limiting step is the associative ligand substitution. The activation enthalpy was also determined to be 7.8 kcal mol−1. TA–Au catalysts with different triazole derivatives were also tested, giving a linear free energy relationship with a ρ value of 0.74.

G-protein-coupled receptors (GPCRs), a superfamily of cell-surface receptors that are the targets of about 40% of prescription drugs on the market, can sense numerous critical extracellular signals. Recent breakthroughs in structural biology, especially in holo-form X-ray crystal structures, have contributed to our understanding of GPCR signaling. However, actions of GPCRs at the cellular and molecular level, interactions between GPCRs, and the role of protein dynamics in receptor activities still remain controversial. To overcome these dilemmas, fluorescent probes of GPCRs have been employed, which have advantages of in vivo safety and real-time monitoring. Various probes that depend on specific mechanisms and/or technologies have been used to study GPCRs. The present review focuses on surveying the design and applications of fluorescent probes for GPCRs that are derived from small molecules or using protein-labeling techniques, as well as discussing some design strategies for new probes.

To find an approach that can image the hydrolysis activity of aminopeptidase N (APN) both in vitro and in vivo, three bioluminescent probes have been well designed and synthesized herein. All of them can be recognized and hydrolyzed by APN to produce bioluminescence emission in the presence of firefly luciferase. To the best of our knowledge, they are the first bioluminescent probes for imaging APN in deep tissues and living animals.

Reactive oxygen species (ROS) often have significant roles in mediating redox modifications and other essential physiological processes, such as biological process regulation and signal transduction. Considering that H2O2 is a substantial member of ROS, detection and quantitation of H2O2 undertakes important but urgent responsibility. In this report, a bioluminescent probe for detecting H2O2 was well designed, synthesized, and evaluated. This probe was designed into three parts: a H2O2-sensitive aryl boronic acid, a bioluminescent aminoluciferin moiety, and a self-immolative linker. After extensive evaluation, this probe can selectively and sensitively react with H2O2 to release aminoluciferin. It should be pointed out that this probe is a potential bioluminescent sensor for H2O2 since it can provide a promising toolkit for real-time detection of the H2O2 level in vitro, in cellulo, and in vivo.

As the cardinal support of innumerable biological processes, biomacromolecules such as proteins, nucleic acids and polysaccharides are of importance to living systems. The key to understanding biological processes is to realize the role of these biomacromolecules in thte localization, distribution, conformation and interaction with other molecules. With the current development and adaptation of fluorescent technologies in biomedical and pharmaceutical fields, the fluorescence imaging (FLI) approach of using small-molecule fluorescent probes is becoming an up-to-the-minute method for the detection and monitoring of these imperative biomolecules in life sciences. However, conventional small-molecule fluorescent probes may provide undesirable results because of their intrinsic deficiencies such as low signal-to-noise ratio (SNR) and false-positive errors. Recently, small-molecule fluorescent probes with a photoinduced electron transfer (PET) “on/off” switch for biomacromolecules have been thoroughly considered. When recognized by the biomacromolecules, these probes turn on/off the PET switch and change the fluorescence intensity to present a high SNR result. It should be emphasized that these PET-based fluorescent probes could be advantageous for understanding the pathogenesis of various diseases caused by abnormal expression of biomacromolecules. The discussion of this successful strategy involved in this review will be a valuable guide for the further development of new PET-based small-molecule fluorescent probes for biomacromolecules.

Bioluminescent imaging (BLI) has been widely applicable in the imaging of process envisioned in life sciences. As the most conventional technique for BLI, the firefly luciferin–luciferase system is exceptionally functional in vitro and in vivo. The state-of-the-art strategy in such a system is to cage the luciferin, in which free luciferin is conjugated with distinctive functional groups, thus accommodating an impressive toolkit for exploring various biological processes, such as monitoring enzymes activity, detecting bioactive small molecules, evaluating the properties of molecular transporters, etc. This review article summarizes the rational design of caged luciferins towards diverse biotargets, as well as their applications in bioluminescent imaging. It should be emphasized that these caged luciferins can stretch out the applications of bioluminescence imaging and shed light upon understanding the pathogenesis of various diseases.

A novel fluorogenic probe for tert-butoxy radicals based on the hydrazino-naphthalimide system is reported. Interestingly, different regioisomers exhibited significantly different optical properties toward ROS, which suggested 4-hydrazinyl naphthalimide as a potential new platform for the in vitro and in cellulo detection of alkoxyl radicals.

Molecular docking, which is the indispensable emphasis in predicting binding conformations and energies of ligands to receptors, constructs the high-throughput virtual screening available. So far, increasingly numerous molecular docking programs have been released, and among them, AutoDock 4.2 is a widely used docking program with exceptional accuracy. It has heretofore been substantiated that the calculation of partial charge is very fundamental for the accurate conformation search and binding energy estimation. However, no systematic comparison of the significances of electrostatic potentials on docking accuracy of AutoDock 4.2 has been determined. In this paper, nine different charge-assigning methods, including AM1-BCC, Del-Re, formal, Gasteiger–Hückel, Gasteiger–Marsili, Hückel, Merck molecular force field (MMFF), and Pullman, as well as the ab initio Hartree–Fock charge, were sufficiently explored for their molecular docking performance by using AutoDock4.2. The results clearly demonstrated that the empirical Gasteiger–Hückel charge is the most applicable in virtual screening for large database; meanwhile, the semiempirical AM1-BCC charge is practicable in lead compound optimization as well as accurate virtual screening for small databases.

In the current paper, three activity-based colorimetric and ratiometric fluorescent probes based on a naphthalimide fluorophore were well designed and synthesized, which can be recognized and hydrolyzed by aminopeptidase N (APN) at both the enzymatic and cellular level by following the fluorescent emission wavelength change from blue to green light. As a result, these molecules were successfully identified as the first ratiometric fluorescent probes for APN cell imaging.

In the present paper, a new pH sensitive fluorescent probe based on a 4-acylated naphthalimide fluorophore was well designed and synthesized. It has a high specificity for lysosomes over other cell organelles. The intrinsic high signal to noise ratio in cell imaging, broad Stokes shift and practical fluorescence quantum yield of this probe will ensure its prominent position in the intracellular lysosome targeting and imaging toolbox.

This report discloses a series of naphthalimide-based bifunctional fluorescent probes for hydrogen peroxide and diols. As a result, these molecules not only demonstrated high turn-on fluorescent response and good selectivity towards hydrogen peroxide over other relevant reactive oxygen species, but also displayed different responses to diols. Therefore, these fluorescent probes could be served as sensitive, selective and practical chemosensors for both hydrogen peroxide and diols under physiological-like conditions.

G-protein coupled receptors (GPCRs) are recognized to constitute the largest family of membrane proteins. Due to the disproportion in the quantity of crystal structures and their amino acid sequences, homology modeling contributes a reasonable and feasible approach to GPCR theoretical coordinates. With the brand new crystal structures resolved recently, herein we deliberated how to designate them as templates to carry out homology modeling in four aspects: (1) various sequence alignment methods; (2) protein weight matrix; (3) different sets of multiple templates; (4) active and inactive state of templates. The accuracy of models was evaluated by comparing the similarity of stereo conformation and molecular docking results between models and the experimental structure of Meleagris gallopavo β1-adrenergic receptor (Mg_Adrb1) that we desired to develop as an example. Our results proposed that: (1) Cobalt and MAFFT, two algorithms of sequence alignment, were suitable for single- and multiple-template modeling, respectively; (2) Blosum30 is applicable to align sequences in the case of low sequence identity; (3) multiple-template modeling is not always better than single-template one; (4) the state of template is an influential factor in simulating the GPCR structures as well.

The current work describes the design and synthesis of the first ratiometric fluorescent probe, Ala-PABA-7HC, for the detection of aminopeptidase N (APN) at both the enzymatic and the cellular level. Upon addition of APN to the solution of Ala-PABA-7HC in PBS or culture medium, the maximum emission peak experienced a red shift from 390 nm to 450 nm, and the ratio of fluorescence intensity (I450/I390) (λex = 330 nm) significantly increased from 0.26 to 3.05 (R = 11.7-fold) in 15 min.

This study reports a benzothiazole-based fluorescent probe with simple structure for thiols. This probe exhibited high on/off signal ratios and good selectivity toward thiols over other analytes, and was successfully applied to the imaging of thiols in living cells.This Letter discloses a benzothiazole-based fluorescent probe for thiols, which exhibited high on/off signal ratios and good selectivity toward thiols over other analytes, and was successfully applied to the imaging of thiols in living cells.

In this letter, a high-throughput virtual screening was accomplished to identify potent inhibitors against AI-2 quorum sensing on the basis of Vibrio harveyi LuxPQ crystal structure. Seven compounds were found to inhibit AI-2 quorum sensing with IC50 values in the micromolar range, and presented low cytotoxicity or no cytotoxicity in V. harveyi.

This paper presents a series of first- and second-generation click-modified coumarin-based fluorescent probes for thiols. These molecules demonstrate high turn-on fluorescent response and good selectivity towards aromatic thiols over other relevant reactive sulfur species, reactive oxygen species and common nucleophiles. Moreover, probe 1a can detect thiols in the reduced rabbit plasma sample. Therefore, this approach provides a particularly impressive tool for detecting thiol in biological systems.

A series of novel nitric oxide-releasing tamibarotene derivatives were synthesized by coupling nitric oxide (NO) donors with tamibarotene via various spacers, and were evaluated for their antiproliferative activities against human leukemic HL-60, NB4 and K562 cell lines in vitro. The test results showed that three compounds (7g, 9a and 9e) exhibited more potent antileukemic activity than the control tamibarotene. Furthermore, the preliminary structure–activity analysis revealed that amino acids serving as spacers could bring about significantly improved biological activities of NO donor hybrids. These interesting results could provide new insights into the development of NO-based antileukemic agents.

In order to develop promising cyclin dependent kinase 1 inhibitors, homology modeling, docking and molecular dynamic simulation techniques were applied to get insight into the functional and structural properties of cyclin dependent kinase 1 (CDK1). Since there is no reported CDK1 crystal structural data, the three dimensional structure of CDK1 was constructed based on homology modeling. An extensive dynamic simulation was also performed on a Flavopiridol-CDK1 complex for probing the binding pattern of Flavopiridol in the active site of CDK1. The binding modes of other inhibitors to CDK1 were also proposed by molecular docking. The structural requirement for developing more potent CDK1 inhibitors was obtained by the above-mentioned molecular simulations and pharmacophore modeling.

Computational chemistry is playing an increasingly important role in drug design and discovery, structural biology, and quantitative structure–activity relationship (QSAR) studies. For QSAR work, selecting an appropriate and accurate method to assign the electrostatic potentials of each atom in a molecule is a critical first step. So far several commonly used methods are available to assign charges. However, no systematic comparison of the effects of electrostatic potentials on QSAR quality has been made. In this study, twelve semi-empirical and empirical charge-assigning methods, AM1, AM1-BCC, CFF, Del-Re, Formal, Gasteiger, Gasteiger–Hückel, Hückel, MMFF, PRODRG, Pullman, and VC2003 charges, have been compared for their performances in CoMFA and CoMSIA modeling using several standard datasets. Some charge assignment models, such as Del-Re, PRODRG, and Pullman, are limited to specific atom and bond types, and, therefore, were excluded from this study. Among the remaining nine methods, the Gasteiger–Hückel charge, though commonly used, performed poorly in prediction accuracy. The AM1-BCC method was better than most charge-assigning methods based on prediction accuracy, though it was not successful in yielding overall higher cross-validation correlation coefficient (q2) values than others. The CFF charge model worked the best in prediction accuracy when q2 was used as the evaluation criterion. The results presented should help the selection of electrostatic potential models in CoMFA and CoMSIA studies.

Herein a water-soluble ‘click’ modified coumarin-based fluorescent probe for hydrogen peroxide is reported. This probe shows significant intensity increases (up to fivefold) in near-green fluorescence upon reaction with hydrogen peroxide, and good selectivity over other reactive oxygen species.A novel ‘click’ modified coumarin-based fluorescent probe for hydrogen peroxide is depicted.

Carbohydrates are considered as one of the most important classes of biomarkers for cell types, disease states, protein functions, and developmental states. Carbohydrate “binders” that can specifically recognize a carbohydrate biomarker can be used for developing novel types of site specific delivery methods and imaging agents. In this review, we present selected examples of important carbohydrate biomarkers and how they can be targeted for the development of therapeutic and diagnostic agents. Examples are arranged based on disease categories including (1) infectious diseases, (2) cancer, (3) inflammation and immune responses, (4) signal transduction, (5) stem cell transformation, (6) embryo development, and (7) cardiovascular diseases, though some issues cross therapeutic boundaries.

It is widely acknowledged that the H1 receptor antagonists have important therapeutic significance in the treatment of various allergic disorders, but little was known about the binding mode between the receptor and antagonists since the crystal structure of G-protein coupling receptors (GPCRs) were hard to obtain. In this paper, a theoretical three-dimensional model of human histamine H1 receptor (HHR1) was developed on the basis of recently reported high resolution structures of human A2A adenosine receptor, human β2-adrenoceptor and turkey β1-adrenoceptor. Furthermore, three representative H1 receptor antagonists were chosen for docking studies. Subsequently, a qualitative pharmacophore model was developed by Hiphop algorithm based on the docking conformations of these three antagonists. In this paper, active environment, certain key residues, and the corresponding pharmacophore features of H1 receptor were identified by such combinations of receptor-based and ligand-based approaches, which would give sufficient guidance for the rational design of novel antihistamine agents.

Bioluminescent imaging (BLI) has been widely applicable in the imaging of process envisioned in life sciences. As the most conventional technique for BLI, the firefly luciferin–luciferase system is exceptionally functional in vitro and in vivo. The state-of-the-art strategy in such a system is to cage the luciferin, in which free luciferin is conjugated with distinctive functional groups, thus accommodating an impressive toolkit for exploring various biological processes, such as monitoring enzymes activity, detecting bioactive small molecules, evaluating the properties of molecular transporters, etc. This review article summarizes the rational design of caged luciferins towards diverse biotargets, as well as their applications in bioluminescent imaging. It should be emphasized that these caged luciferins can stretch out the applications of bioluminescence imaging and shed light upon understanding the pathogenesis of various diseases.

A novel fluorogenic probe for tert-butoxy radicals based on the hydrazino-naphthalimide system is reported. Interestingly, different regioisomers exhibited significantly different optical properties toward ROS, which suggested 4-hydrazinyl naphthalimide as a potential new platform for the in vitro and in cellulo detection of alkoxyl radicals.

The first dual bioluminescent and chemiluminescent sensor for detecting highly toxic thiophenols has been developed. Such a probe was designed by using a coelenterazine analogue as the luminophore and dinitrophenyl ether as the recognition moiety. It should be noted that this probe displayed good sensitivity and selectivity toward thiophenols, and has been effectively applied for the quantitative detection of thiophenols in aqueous media and complex biological samples.

N-2-Aryl chelated 1,2,3-triazole-Ir(III) complexes with various substituents were prepared for the first time. These photoactive Ir(III) complexes were characterized by X-ray crystallography and their redox potentials were evaluated. This study revealed a new class of photocatalysts with tunable photoredox potentials.

The triazole–gold(I) complex catalyzed [3,3]-rearrangement of propargyl ester has been quantitatively investigated through in situ IR. First order dependence of the initial rates on [Au] and [propargyl ester] suggested that the turnover-limiting step is the associative ligand substitution. The activation enthalpy was also determined to be 7.8 kcal mol−1. TA–Au catalysts with different triazole derivatives were also tested, giving a linear free energy relationship with a ρ value of 0.74.

Two series of novel coelenterazine analogues (alkynes and triazoles) with imidazopyrazinone C-6 extended substitution have been designed and synthesized successfully for the extension of bioluminescent substrates. After extensive evaluation, some compounds display excellent bioluminescence properties compared with DeepBlueC in cellulo, thus becoming potential molecules for bioluminescence techniques.

In the current paper, three activity-based colorimetric and ratiometric fluorescent probes based on a naphthalimide fluorophore were well designed and synthesized, which can be recognized and hydrolyzed by aminopeptidase N (APN) at both the enzymatic and cellular level by following the fluorescent emission wavelength change from blue to green light. As a result, these molecules were successfully identified as the first ratiometric fluorescent probes for APN cell imaging.