Improvement of Fluorescence Characteristics of Coumarins: Syntheses and Fluorescence Properties of 6-Methoxycoumarin and Benzocoumarin Derivatives as Novel Fluorophores Emitting in the Longer Wavelength Region and Their Application to Analytical Reagents

Chemical constituents from Notopterygium incisum and their anti-neuroinflammatory activity

Phytochemical research on an extract of Notopterygium incisum yielded fifteen compounds (1-15), including four previously undescribed compounds (10-13). The structures of the unreported compounds were elucidated by spectroscopic and spectrometric data analysis such as 1D and 2D NMR, IR and HR-ESI-MS. Compounds 1-5 and 10-14 were isolated from N. incisum for the first time. 7S⁎,8R⁎-Phenethyl-(7-methoxy-8-isoeugenol)-ferulate (10), 7S⁎,8R⁎-p-hydroxyphenethyl-(7-methoxy-8-isoeugenol)-ferulate (11), 7S⁎,8R⁎-benzyl-(7-methoxy-8-isoeugenol)-ferulate (12) and p-hydroxyphenethyl-(4-benzoy-3-methoxy)-cinnamate (13) are the undescribed ferulic acid derivatives. Additionly, the anti-neuroinflammatory effects of compounds were evaluated in lipopolysaccharide (LPS)-induced BV2 cells. The pharmacological results showed that 6β,10β-epoxy-4α-hydroxy-guaiane (6), teuclatriol (7) and 7S⁎,8R⁎-p-hydroxyphenethyl-(7-methoxy-8-isoeugenol)-ferulate (11) inhibited the production and expression of nitric oxide (NO) in the LPS-induced BV2 cells in a concentration-dependent manner. Acorusnol (4), teucladiol (9), 7S⁎,8R⁎-benzyl-(7-methoxy-8-isoeugenol)-ferulate (12) and p-hydroxyphenethyl-(4-benzoy-3-methoxy)-cinnamate (13) only inhibited the release of NO at concentration of 20 μM. Moreover, 7S⁎,8R⁎-p-hydroxyphenethyl-(7-methoxy-8-isoeugenol)-ferulate (11) reduced the level of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in LPS-stimulated BV2 cells. The results demonstrated 7S⁎,8R⁎-p-hydroxyphenethyl-(7-methoxy-8-isoeugenol)-ferulate (11) could be a potential anti-neuroinflammatory agent and is worthy of further study.

Theoretical investigation of substitution effect on the sixth and seventh positions of coumarin derivatives

The linear and non-linear optical properties of 6-donor and 7-donor substituted coumarins were compared using density functional theory (DFT) and time-dependent-DFT (TD-DFT). Charge transfer characteristics were investigated through natural bond order analysis, frontier molecular orbital, and molecular electrostatic potential plots. TD-DFT results suggested that the 6-donor substituted coumarins (PS1, PS3, and PS5) showed red-shifted absorption than the 7-donor substituted coumarins (PS2, PS4, and PS6). The chemical potential (μ) and electrophilicity index (ω) showed direct relation with the band gap and an inverse relation with chemical hardness (η) and hyperhardness (Γ). The global reactivity descriptors μ and ω showed direct and η and Γ showed an inverse correlation with first-order hyperpolarizability (β0) and second-order hyperpolarizability (γ). The β0 and γ for 7-donor substituted coumarin are higher than for 6-donor substituted coumarin.

Pd-Catalyzed Alkyne and Aryne Annulations: Synthesis and Photophysical Properties of π-Extended Coumarins

A Pd-catalyzed alkyne and aryne annulation strategy via C-H activation has been implemented for the synthesis of π-extended coumarins. This synthetic strategy provides a wide range of π-extended coumarins in moderate to good yields with good functional group compatibility. Photophysical properties of the synthesized π-extended coumarins have been evaluated, and some of them show interesting fluorescent properties. Three of the synthesized coumarins have been unambiguously established by a single-crystal XRD study.

The Electronic Effects of 3-Methoxycarbonylcoumarin Substituents on Spectral, Antioxidant, and Protein Binding Properties

Coumarin derivatives are a class of compounds with pronounced biological activities that depend primarily on the present substituents. Four 3-methoxycarbonylcoumarin derivatives with substituents of different electron-donating/electron-withdrawing abilities (Br, NO₂, OH, and OMe) were investigated structurally by NMR, IR, and UV-VIS spectroscopies and density functional theory methods. The appropriate level of theory (B3LYP-D3BJ/6-311++G(d,p) was selected after comparing similar compounds' experimental and theoretical structural parameters. The natural bond orbital and quantum theory of atoms in molecules were employed to investigate the intramolecular interactions governing stability. The electronic effects of substituents mostly affected the aromatic ring that the substituents are directly attached to. The antioxidant properties were investigated by electron paramagnetic resonance spectroscopy towards HO^•, and the percentages of reduction were between 13% (6-Br) and 23% (6-OMe). The protein binding properties towards transport proteins were assessed by spectrofluorimetry, molecular docking, and molecular dynamics (MD). The experimentally determined binding energies were well reproduced by molecular docking, showing that the spontaneity of ibuprofen binding was comparable to the investigated compounds. The flexibility of HSA in MD simulations depended on the substituents. These results proved the importance of electronic effects for the protein binding affinities and antioxidant properties of coumarin derivatives.

Designing Red-Shifted Molecular Emitters Based on the Annulated Locked GFP Chromophore Derivatives

Bioimaging techniques require development of a wide variety of fluorescent probes that absorb and emit red light. One way to shift absorption and emission of a chromophore to longer wavelengths is to modify its chemical structure by adding polycyclic aromatic hydrocarbon (PAH) fragments, thus increasing the conjugation length of a molecule while maintaining its rigidity. Here, we consider four novel classes of conformationally locked Green Fluorescent Protein (GFP) chromophore derivatives obtained by extending their aromatic systems in different directions. Using high-level ab initio quantum chemistry calculations, we show that the alteration of their electronic structure upon annulation may unexpectedly result in a drastic change of their fluorescent properties. A flip of optically bright and dark electronic states is most prominent in the symmetric fluorene-based derivative. The presence of a completely dark lowest-lying excited state is supported by the experimentally measured extremely low fluorescence quantum yield of the newly synthesized compound. Importantly, one of the asymmetric modes of annulation provides a very promising strategy for developing red-shifted molecular emitters with an absorption wavelength of ∼600 nm, having no significant impact on the character of the bright S-S1 transition.

The visible-light-induced acylation/cyclization of alkynoates with acyl oximes for the construction of 3-acylcoumarins

A nitrogen-centered radical-mediated carbon-carbon bond cleavage strategy is described to synthesize functionalized 3-acylcoumarins. The strategy is enabled by the visible-light-induced acylation/cyclization of alkynoates with various acyl oxime compounds in acetonitrile. The difunctionalization of carbon-carbon triple bonds precedes the generation of iminyl radicals, which is followed by the formation of acyl radicals. The acyl radicals then attack the carbon-carbon triple bonds, followed by 5-exo-trig cyclization and 1,2-ester migration. This strategy has wide substrate adaptability and good substituent tolerance.

Synthesis, cytotoxicity and in silico study of some novel benzocoumarin-chalcone-bearing aryl ester derivatives and benzocoumarin-derived arylamide analogs

The development of new prostate cancer protein receptor cytochrome P450 17A1 inhibitors offers the possibility of generating structures of increased potency. To this end, the chalcone analogs 7 and 8 were prepared from treatment of methyl 3-oxo-3H-benzocoumarin-2-carboxylate (4) with aryl aldehydes. Treatment of 7 and 8 with three anti-inflammatory drugs, flurbiprofen, ketoprofen and ibuprofen, in the presence of POCl3/DMAP gave the ester analogs 9–12. Analogously, treatment of ethyl 3-oxo-3H-benzocoumarin-2-carboxylate (15), prepared previously from 2-hydroxy-1-naphthaldehyde (13) and dimethylmalonate (14), with various arylamines: 4-bromoaniline, 2-amino-6-methylpyridine, amino-antipyrine and 2-amino-5-nitrothiazole, in the presence of potassium tert-butoxide gave the benzocoumarine-3-arylamide analogs. The in vitro cytotoxic activities of 9–12 and 16–19 were evaluated against human prostate cancer cell lines (PC-3) and normal human liver epithelia (WRL-68) by MTT assay. Compounds 10 and 17 were the most active cytotoxic agents among the series against PC-3 cells with IC50 values of 71.35 and 78.25 μg mL–1 with SI values of 3.0 and 4.2, respectively (calculated from the cytotoxicity effects of 10 and 17 on the normal human liver epithelia [WRL-68]). Furthermore, compounds 11 and 12 were tested against breast cancer (HER2 cell lines), prostate cancer (DU-135 cell lines) and MCF-7 but were inactive. Molecular docking studies between the protein receptor CYPP450 17A1 and compounds 10 and 17 revealed that these compounds primarily form hydrophobic interactions with the receptor.

7-Alkoxy-appended coumarin derivatives: synthesis, photo-physical properties, aggregation behaviours and current-voltage (I-V) characteristic studies on thin films

In this study, we designed and synthesised a series of coumarin derivatives appended with a long alkoxy chain on the seventh position of the coumarin-3-carboxylate/carboxylic acid core to make thin film materials. Synthesised compounds were characterized by their UV and fluorescence spectra in solutions as well as their films prepared by both LB and spin-coated methods. The surface morphology and electrical behaviour of thin films were judged by AFM, SEM and I-V characteristic mapping respectively. Isotherm, UV-Vis absorption and fluorescence spectroscopic investigations revealed the formation of aggregates on thin films. The result of SEM and AFM images provides the information about the length and height of aggregates on the thin films of coumarin derivatives. From I-V characteristics, it was found that at room temperature, the spin-coated films of coumarin derivatives containing an ester functional group exhibited a threshold switching behaviour, whereas derivatives containing the carboxylic acid functional group showed both threshold and bipolar switching behaviours. We also noticed that the I-V characteristic features of synthesized materials depended on the length of the alkyl chain of individual series.

A coumarin embedded highly sensitive nitric oxide fluorescent sensor: kinetic assay and bio-imaging applications

Fluorescence spectroscopy is a significant bio-analytical technique for specific detection of nitric oxide (NO) and for broadcasting the in vitro and in vivo biological activities of this gasotransmitter. Herein, a benzo-coumarin embedded smart molecular probe (BCM) is employed for NO sensing through detailed fluorescence studies in purely aqueous medium. All the spectroscopic analysis and literature reports clearly validate the mechanistic insight of this sensing strategy i.e., the initial formation of 1,2,3,4-oxatriazole on treatment of the probe with NO which finally converted to its carboxylic acid derivative. This oxatriazole formation results in a drastic enhancement in fluoroscence intensity due to the photoinduced electron transfer (PET) effect. The kinetic investigation unveils the second and first-order dependency on [NO] and [BCM] respectively. The very low detection limit (16 nM), high fluorescence enhancement (123 fold) in aqueous medium and good formation constant (Kf = (4.33 ± 0.48) × 104 M-1) along with pH invariability, non-cytotoxicity, biocompatibility and cell permeability make this probe a very effective one for tracking NO intracellularly.

Interaction of amphiphilic coumarin with DPPC/DPPS lipid bilayer: effects of concentration and alkyl tail length

In this work, interactions between amphiphilic amino methyl coumarin and dipalmitoyl-sn-glycero-3-phosphocholine/dipalmitoyl-sn-glycero-3-phosphoserine (DPPC/DPPS) lipid bilayer were investigated. A combination of experimental techniques (zeta potential, fluorescence spectroscopy, and differential scanning calorimetry) along with molecular dynamics simulations was employed to examine the influence of alkyl tail length and concentration of the amphiphilic coumarin on the lipid bilayer. Alkyl tails comprising 5(C₅), 9(C₉), and 12(C₁₂) carbon atoms were conjugated to amino methyl coumarin via a single-step process. The binding and insertion mechanisms of the amphiphilic coumarins were studied in increasing concentrations for short-tailed (C₅) and long-tailed (C₁₂) coumarins. The simulation results show that C₅ coumarin molecules penetrate the lipid bilayer, but owing to the short alkyl tail, they interact primarily with the lipid head groups resulting in lipid bilayer thinning; however, at high concentrations, the C₅ coumarins undergo continuous insertion-ejection from the outer leaflet of the lipid bilayer. In contrast, C₁₂ coumarins interact favorably with the hydrophobic lipid tails and lack the ejection-reinsertion behavior. Instead, the C₁₂ coumarin molecules undergo flip-flops between the outer and inner leaflets of the lipid bilayer. At high concentrations, the high-frequency flip-flops lead to lipid destabilization, causing the lipid bilayer to rupture. The simulation results are in excellent agreement with the toxicity of amphiphilic coumarin activity in cancer cells. The efficacy of amphiphilic coumarins in liposomal lipid bilayers demonstrates the promise of these molecules as a tool in the treatment of cancer.

Coumarin as a structural component of substrates and probes for serine and cysteine proteases

Coumarins represent well-established structures to introduce fluorescence into tool compounds for biochemical investigations. They are valued for their small size, chemical stability and accessibility as well as their tunable photochemical properties. As components of fluorophore/quencher pairs or FRET donor/acceptor pairs, coumarins have frequently been applied in substrate mapping approaches for serine and cysteine proteases. This review also focuses on the incorporation of coumarins into the side chain of amino acids and the exploitation of the resulting fluorescent amino acids for the positional profiling of protease substrates. The protease-inhibiting properties of certain coumarin derivatives and the utilization of coumarin moieties to assemble activity-based probes for serine and cysteine proteases are discussed as well.

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Coumarins represent well-established structures to introduce fluorescence into tool compounds for biochemical investigations.

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They are valued for their small size, chemical stability and accessibility as well as their tunable photochemical properties.

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Coumarins are components of fluorophore/quencher pairs or FRET donor/acceptor pairs in substrate mapping of proteases.

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Coumarins have been incorporated into amino acids side chains to be used for the positional profiling of protease substrates.

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Coumarins have protease-inhibiting properties and are used for activity-based probes for serine and cysteine proteases.

Traditional Chinese Medicine of Angelicae Pubescentis Radix: A Review of Phytochemistry, Pharmacology and Pharmacokinetics

Angelicae Pubescentis Radix (APR) is a widely used antirheumatic Chinese medicinal herb known as "Duhuo" in China. It has the effects of dispelling wind and removing dampness, diffusing impediment, and relieving pain, and is mainly indicated for rheumatic arthritis with pain in the lower back and knees, and headache. To the best of our knowledge, an attempt is made to provide an up-to-date review on these aspects based on published materials, including ancient and modern books; Master's and doctoral theses; monographs on medicinal plants; the pharmacopoeia of different countries, websites for publication of patent and electronic databases, such as SCI finder, PubMed, Web of Science, ACS, Science Direct, Wiley, Springer, Taylor, CNKI, and Google Scholar. APR, which has a good clinical effect, has been used for traditional Chinese medicine more than 2000 years. Since 1957, a variety of chemical constituents have been reported from the medicinal plants of this herb, mostly coumarins and volatile oil. In the past 30 years, numerous studies have shown that the extracts and compounds isolated from APR showed effective analgesic and anti-inflammatory actions, also showing well effects on central nervous system, effects on cardiovascular system and deworming activity. In addition, we also present and discuss the botany, traditional medicinal use, pharmacokinetics, toxicity, quality control, future trends and prospects of APR. All this information suggest that future research of APR should be supplemented in the area of pharmacology and toxicology to provide further insight on the clinical use and quality control.

One-Pot Synthesis of 4-Carboalkoxy-Substituted Benzo[h]coumarins from α- and β-Naphthols and Their Excited-State Properties

One-pot synthesis has been developed for 4-carboethoxybenzo[h]coumarins starting from α-/β-naphthols. Accordingly, diverse 4-carboethoxybenzocoumarins can be synthesized in moderate-to-excellent (31-75%) isolated yields. The synthesis involves initial oxidation of naphthols to the intermediary 1,2-naphthoquinones with 2-iodoxybenzoic acid followed by a cascade of reactions, namely, Wittig olefination, Michael addition, β-elimination, and cyclization. Furthermore, we have comprehensively investigated the excited-state properties of differently substituted 4-carboalkoxybenzo[h]coumarins. It is shown that they exhibit low to high fluorescence quantum yields (1-36%) and excited-state lifetimes (ca. 1-7 ns) depending on the substitution pattern and solvent employed.

Notopterygium incisum extract and associated secondary metabolites inhibit apple fruit fungal pathogens

In the search for antifungal lead compounds from natural resources, Notopterygium incisum, a medicine plant only distributed in China, showed antifungal potential against apple fruit pathogens. Based on the bioassay-guided isolation, chromatography fraction 6 of the ethyl acetate partition exhibited significant in vitro and in vivo antifungal activities against apple fruit pathogens. Furthermore, nine antifungal secondary metabolites, including five linear furocoumarins (1-5), two phenylethyl esters (6-7), one falcarindiol (8), and one sesquiterpenoid (9), were isolated and elucidated from fraction 6. Compound 5 is a new metabolite, and 9 isolated from the genus Notopterygium for the first time. The purified compounds (1-9) were firstly reported to exhibit antifungal activities against apple fruit pathogens of Colletotrichum gloeosporioides and Botryosphaeria dothidea with the MIC values ranging from 8 to 250 mg L^-1, especially 8 of 16 and 8 mg L^-1, respectively. Moreover, 8 could inhibit the spore germination and new sporulation of B. dothidea, as well as enhance the membrane permeabilization of B. dothidea spores. This was the first investigation for the antifungal components against apple fruit pathogens from Notopterygium incisum, which has great potential to be developed into bio-fungicides.

Dye Tool Box for a Fluorescence Enhancement Immunoassay

Immunochemical analytical methods are very successful in clinical diagnostics and are nowadays also emerging in the control of food as well as monitoring of environmental issues. Among the different immunoassays, luminescence based formats are characterized by their outstanding sensitivity making this format especially attractive for future applications. The need for multiparameter detection capabilities calls for a tool box of dye labels in order to transduce the biochemical reaction into an optically detectable signal. Here, in a multiparameter approach each analyte may be detected by a different dye with a unique emission color (covering the blue to red spectral range) or a unique luminescence decay kinetics. In the case of a competitive immunoassay format for each of the different dye labels an individual antibody would be needed. In the present paper a slightly modified approach is presented using a 7-aminocoumarin unit as the basic antigen against which highly specific antibodies were generated. Leaving the epitope region in the dyes unchanged but introducing a side group in positon 3 of the coumarin system allowed us to tune the optical properties of the coumarin dyes without the necessity of new antibody generation. Upon modification of the parent coumarin unit the full spectral range from blue to deep red was accessed. In the manuscript the photophysical characterization of the coumarin derivatives and their corresponding immunocomplexes with two highly specific antibodies is presented. The coumarin dyes and their immunocomplexes were characterized by steady-state and time-resolved absorption as well as emission spectroscopy. Moreover, fluorescence depolarization measurements were carried out to complement the data stressing the different binding modes of the two antibodies. The binding modes were evaluated using the photophysics of 7-aminocoumarins and how it was affected in the respective immunocomplexes, namely, the formation of the intramolecular charge transfer (ICT) as well as the twisted intramolecular charge transfer (TICT). In contrast to other antibody-dye pairs reported a distinct fluorescence enhancement upon formation of the antibody-dye complex up to a factor of 50 was found. Because of the easy emission color tuning by tailoring the coumarin substitution for the antigen binding in nonrelevant position 3 of the parent molecule, a dye tool box is on hand which can be used in the construction of competitive multiparameter fluorescence enhancement immunoassays (FenIA).

Visible-light-promoted radical acylation/cyclization of alkynoates with aldehydes for the synthesis of 3-acylcoumarins

A new, efficient, and atom-economic visible-light-promoted radical acylation/cyclization of alkynoates with aldehydes was developed for the synthesis of 3-acylcoumarins.

BINOL derivatives with aggression-induced emission

A new series of BINOL derivatives were synthesized which could be turned from ACQ to AIE fluorophores by changing the electron withdrawing group.

Benzo[g]coumarin-Based Fluorescent Probes for Bioimaging Applications

Benzo[g]coumarins, which consist of coumarins fused with other aromatic units in the linear shape, have recently emerged as an interesting fluorophore in the bioimaging research. The pi-extended skeleton with the presence of electron-donating and electron-withdrawing substituents from the parent coumarins changes the basic photophysical parameters such as absorption and fluorescence emission significantly. Most of the benzo[g]coumarin analogues show red/far-red fluorescence emission with high two-photon absorbing property that can be applicable for the two-photon microscopy (TPM) imaging. In this review, we summarized the recently developed benzo[g]coumarin analogues including photophysical properties, synthesis, and applications for molecular probes that can sense biologically important species such as metal ions, cell organs, reactive species, and disease biomarkers.

A review of the ethnopharmacology, phytochemistry and pharmacology of Notopterygium incisum

ETHNOPHARMACOLOGICAL RELEVANCE

Notopterygium incisum Ting ex H.T. Chang, known in Chinese as 'Qianghuo' is a traditional Chinese medicinal herb with the rhizome and roots associated with meridians of the kidney and urinary bladder. It is pungent, bitter and warm in nature. It has been used over the years to disperse cold, prevent painful obstructions from wind, damp and warm pain. It has also been used with other herbs to treat wind-cold exterior syndrome and wind-cold-damp bi-syndromes and has been known to grow well in regions of high altitude such as Gansu, Tibet etc.

THE AIM OF THE REVIEW

This systematic review focuses on the ethnopharmacological uses of this herb, including recent advances on the phytochemical and pharmacological study of N. incisum. Recent analytical methods developed for the quantitative and qualitative determination of constituents in this herb have also been reviewed. Additionally, future trends and prospects in the study of this herb have been proposed.

MATERIALS AND METHOD

Various literature and electronic databases such as Pubmed, Science Direct, Springer, Wiley etc were searched and data obtained. Other online academic libraries such as Google Scholar and ethnopharmacological literature were searched systematically for more information on the herb.

RESULTS

This review focuses on the ethnopharmacological uses of N. incisum and also the various chemical constituents present in the herb and their various therapeutic effects such as analgesic, anti-inflammatory, anti-cancer and antioxidants effects. Analytical methods developed for the quantitative and qualitative determination of various compounds in this herb were further reviewed.

CONCLUSION

In this paper, we have reviewed various researches conducted on N. incisum especially in areas of its ethnopharmacological use, phytochemicals, pharmacology and developed analytical methods. This herb has been used over the years in treating headache, rheumatoid arthritis, cold, diaphoretic etc, prompting many types of research into identifying which compounds are responsible for these activities and their mechanism of action. More research is needed in the area of pharmacokinetics and toxicology to give further information on the clinical use and control the quality of the herb.

A new facile way for the preparation of 3-formylcoumarins

3-Formylcoumarins 2 are formed as single products in high yields upon reduction of 3-cyanocoumarins 1 with Raney nickel in formic acid. The starting materials 1 are easily accessible by Knoevenagel condensation of commercially available salicylaldehydes.

Fluorescein-Based Chromogenic and Ratiometric Fluorescence Probe for Highly Selective Detection of Cysteine and Its Application in Bioimaging

A dual mode fluorescent probe, which is based on an integration of fluorescein and coumarin fluorophores, was developed for the discrimination of Cys from Hcy and GSH. This probe (2) shows the advantage of quick reaction (5 min) with Cys, resulting in a strong fluorescence turn-on response when excited at 450 nm. Notably, it also demonstrates the ratiometric fluorescence property while excited by a shorter wavelength (332 nm). All of results suggest probe 2 has a high selectivity toward Cys even in the presence of other amino acids, cations and anions. The detection limit of Cys was calculated as 0.084 μM, which was much lower than the intracellular concentration. ¹H NMR, MS and DFT calculation were used to reveal the detection mechanism further. Finally, this low cytotoxic probe was successfully applied in bioimaging within HepG2 cells.

Simultaneous Determination of Bergapten, Imperatorin, Notopterol, and Isoimperatorin in Rat Plasma by High Performance Liquid Chromatography with Fluorescence Detection and Its Application to Pharmacokinetic and Excretion Study after Oral Administration of Notopterygium incisum Extract

A specific, sensitive, and reliable high performance liquid chromatography with fluorescence detection (HPLC-FLD) was first optimized and then used in the simultaneous quantification of bergapten, imperatorin, notopterol, and isoimperatorin in rat plasma using osthole as the internal standard. Liquid-liquid extraction with ethyl acetate was employed in treating the rat plasma samples obtained. Separation was carried out with a Hedera™ ODS column (4.6 × 250 mm, 5 μm) by gradient elution at a temperature of 40°C. Excitation and emission of the fluorescence detector were set to 300 and 490 nm, respectively. The lower limits of quantification for bergapten, imperatorin, notopterol, and isoimperatorin in rat plasma were 4, 40, 4, and 2 ng mL⁻¹, respectively. The intraday and interday precision and accuracy for the four coumarins were within acceptable criteria. The recovery of the method was satisfactory with a range of 80.3–114%. The validated method was successfully used for the simultaneous determination of the four coumarins in Notopterygium incisum extracts and also for the pharmacokinetic and excretion study of bergapten, imperatorin, notopterol, and isoimperatorin in rats.

6-Methyl-2-oxo-N-(quinolin-6-yl)-2H-chromene-3-carboxamide: crystal structure and Hirshfeld surface analysis

The title coumarin derivative, C20H14N2O3, displays intra-molecular N-H⋯O and weak C-H⋯O hydrogen bonds, which probably contribute to the approximate planarity of the mol-ecule [dihedral angle between the coumarin and quinoline ring systems = 6.08 (6)°]. The supra-molecular structures feature C-H⋯O hydrogen bonds and π-π inter-actions, as confirmed by Hirshfeld surface analyses.

Crystal structures of three 6-substituted coumarin-3-carboxamide derivatives

Three coumarin derivatives, viz. 6-methyl-N-(3-methyl-phen-yl)-2-oxo-2H-chromene-3-carboxamide, C18H15NO3 (1), N-(3-meth-oxy-phen-yl)-6-methyl-2-oxo-2H-chromene-3-carboxamide, C18H15NO4 (2), and 6-meth-oxy-N-(3-meth-oxy-phen-yl)-2-oxo-2H-chromene-3-carboxamide, C18H15NO5 (3), were synthesized and structurally characterized. The mol-ecules display intra-molecular N-H⋯O and weak C-H⋯O hydrogen bonds, which probably contribute to the approximate planarity of the mol-ecules. The supra-molecular structures feature C-H⋯O hydrogen bonds and π-π inter-actions, as confirmed by Hirshfeld surface analyses.

Dipolar Dyes with a Pyrrolo[2,3-b]quinoxaline Skeleton Containing a Cyano Group and a Bridged Tertiary Amino Group: Synthesis, Solvatofluorochromism, and Bioimaging

Two strongly polarized dipolar chromophores possessing a cyclic tertiary amino group at one terminus of the molecule and a CN group at the opposite terminus were designed and synthesized. Their rigid skeleton contains the rarely studied pyrrolo[2,3-b]quinoxaline ring system. The photophysical properties of these regioisomeric dyes were different owing to differing π conjugation between the CN group and the electron-donor moiety. These dipolar molecules showed very intense emission, strong solvatofluorochromism, and sufficient two-photon brightness for bioimaging. One of these regioisomeric dyes, namely, 11-carbonitrile-2,3,4,5,6,7-hexahydro-1H-3a,8,13,13b-tetraazabenzo[b]cyclohepta[1,2,3-jk]fluorene, was successfully utilized in two-photon imaging of mouse organ tissues and showed distinct tissue morphology with high resolution.

Exploring coumarin potentialities: development of new enzymatic inhibitors based on the 6-methyl-3-carboxamidocoumarin scaffold

Novel 6-methyl-3-carboxamidocoumarins were synthesized by an effective three step synthetic strategy and screened towards MAO, AChE and BuChE enzymes.

Pentacyclic coumarin-based blue emitters – the case of bifunctional nucleophilic behavior of amidines

Esters of coumarin-3-carboxylic acids undergo addition to DBU and DBN leading to the formation of a 6-membered ring.

From π-expanded coumarins to π-expanded pentacenes

Dihydroxyanthraquinone can be transformed into head-to-tail bis-coumarins which undergo photo-dehydrogenative coupling leading to coronene derivatives.