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

Abstract

Fluorometric analysis is one of the most sensitive methods for detecting organic and/or inorganic compounds and therefore it has been widely used in many scientific fields with improving analytical instruments such as high-performance liquid chromatography (HPLC), capillary electrophoresis (CE), fluorescence confocal microscopy, etc. For these purposes, a great deal of effort has gone into the development of fluorescent reagents using various fluorophores, which can be utilized for derivatizing biologically active small molecules, labeling macromolecules such as proteins and DNAs, and probing ions such as biologically relevant metal cations and inorganic or organic anions. [1][2][3][4] In the development of such fluorescent reagents, it should first be ensured that the fluorophore used has a high fluorescence quantum yield because of the reliably high sensitivity in the detection. Fluorescein is one of the most widely used fluorophore for biological experiments, since it has a high fluorescence quantum yield of 0.90 or grater in aqueous solution and its excitation and emission wavelengths are in the visible region. Recently, Nagano and coworkers have succeeded in developing fluorescent reagents for the specific detection of nitric oxide (NO), [5][6][7][8] singlet oxygen ( 1 O 2 ), 9,10) and others 11,12) using fluorescein as the fluorophore. 4,4-Difluoro-4-bora-3a,4a-diazas-indacenes (BODIPYs) are also well-known fluorophores that have very sharp and narrow fluorescence bandwidths in addition to their high fluorescence quantum yield in aqueous solution. 4,13,14) Therefore they have been used as mother fluorophores for many analytical purposes. [15][16][17][18] However, the difference between the excitation and emission wavelengths of these derivatives are very small, less than approximately 30 nm for fluoresceins and 15 nm for BODIPYs, and it is necessary to correct their spectra from interferences such as Rayleigh or Raman scattering light.On the other hand, coumarin (2H-benzopyran-2-one), is also another interesting fluorophore, since its fluorescence changes drastically with substituents and their introduced positions. [19][20][21] In previous papers, we reported the fluorescence characteristics of methoxycoumarins and discussed the structural features of strongly fluorescing methoxycoumarins from the viewpoint of intramolecular charge transfer (ICT) between push-and pull-substituents in the ground and the excited states.22,23) Based on the above findings, we succeeded in developing novel fluorescent reagents with both high sensitivity and functions such as self-catalytic reactivity. [24][25][26] In the course of those studies, we suspected that most coumarin derivatives showed large Stokes shifts in their fluorescence spectra as compared with other fluorophores. These large Stokes shifts appear to be advantageous for escaping autofluorescence from biological molecules and reducing the self-absorption of chromophores. Further, if the emission bands of coumarins could be shifted to longer wavelengths with larg...

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

“…On the other hand, imperatorin, notopterol, and isoimperatorin exhibited a shorter half-life within 6 h; hence these compounds were eliminated faster in the blood when compared with bergapten. The half-life of imperatorin was 4.99 ± 3.02 h which was similar to that observed in a previous report [26]. The total drug exposure in rats in over 24 h, AUC 0–24 , is 1638 ± 2490, 10975 ± 11955, 101.6 ± 34.8, and 830.5 ± 762.4 ng mL −1  h for bergapten, imperatorin, notopterol, and isoimperatorin, respectively.…”

“…Coumarins are interesting fluorophores with their fluorescence changing drastically depending on the substituents added to the chemical structure and which positions they are introduced in [26]. In this study, we developed a relatively cheaper, specific, sensitive, and reliable HPLC-FLD method for the simultaneous determination of four coumarins in rat plasma and applied this method to the pharmacokinetic and excretion study of N. incisum after an oral administration of the extracts to rats.…”

π-Expanded coumarins: synthesis, optical properties and applications

“…3 This synthetic strategy is preferred for the formation of a specific type of benzocoumarins, as the regioselectivity of the ring formation depends on the position of the formyl and hydroxyl groups on the naphthalene ring of the starting o-hydroxynaphthaldehydes. 3 This synthetic strategy is preferred for the formation of a specific type of benzocoumarins, as the regioselectivity of the ring formation depends on the position of the formyl and hydroxyl groups on the naphthalene ring of the starting o-hydroxynaphthaldehydes.…”

Phosphorylated 3‐Heteroarylcoumarins and Their Use in Fluorescence Microscopy and Nanoscopy

“…offer fluorescent dyes and their conjugates with large Stokes shifts, but they do not publish their structures. [2,3] Large Stokes shifts in coumarins are provided by using intramolecular charge transfer (ICT) and excited state intramolecular proton transfer (ESIPT) mechanisms. Unavailable structures of the existing dyes also hamper the progress in basic research aimed at the creation of new fluorophores.…”