Fluorescence derivatization method for sensitive chromatographic determination of zidovudine based on the Huisgen reaction

Safirinium Fluorescent "Click" Molecular Probes: Synthesis, CuAAC Reactions, and Microscopic Imaging

Fluorescent labeling utilizing Cu(I)-catalyzed azide-alkyne cycloaddition reactions (CuAAC) is among the leading applications of the "click" chemistry strategy. Fluorescent probes for this approach can be constructed by linking an azide or alkyne group to a fluorophore, such as the recently developed Safirinium derivatives. These compounds are water-soluble, highly fluorescent heterocycles based on 1,2,4-triazolium, with significant potential for various labeling applications, although they have not yet been converted to azide or alkyne probes. Herein, we report the synthesis of Safirinium-based azide and alkyne functionalized molecular probes for "click" chemistry labeling. We also describe their CuAAC reactions with model compounds, including a lipid mimetic long-chain azide, an azido sugar derivative, and azidothymidine, as well as two model alkynes. We demonstrate that the Safirinium-based probes and their derivatives are chemically stable, suitable for fluorescent microscopy observations, and safe to use. Most of these probes show no toxic effects on CHO-K1 and NIH-3T3 cells.

Unique biomedical application of fluorescence derivatization based on palladium-catalyzed coupling reactions for HPLC analysis of pharmaceuticals and biomolecules

Palladium-catalyzed coupling reactions are versatile and powerful tools for the construction of carbon-carbon bonds in organic synthesis. Although these reactions have favorable features that proceed selectively in mild reaction conditions using aqueous organic solvents, no attention has been given to their application in the field of biomedical analysis. Therefore, we focused on these reactions and evaluated the scope and limitations of their analytical performance. In this review, we describe the pros and cons and future trends of fluorescence derivatization of pharmaceuticals and biomolecules based on palladium-catalyzed coupling reactions such as Suzuki-Miyaura coupling, Mizoroki-Heck coupling, and Sonogashira coupling reactions for HPLC analysis.

Design, synthesis, and anti-respiratory syncytial virus potential of novel 3-(1,2,3-triazol-1-yl)furoxazine-fused benzimidazole derivatives

Respiratory syncytial virus (RSV) is a major cause of serious lower respiratory tract infections in infants, children, and older persons. Currently, the only approved anti-viral chemotherapeutic drug for RSV treatment is ribavirin aerosol; however, its significant toxicity has led to restricted clinical use. In a previous study, we developed various benzimidazole derivatives against RSV. In this study, we synthesised 3-azide substituted furoxazine-fused benzimidazole derivatives by sulfonylation and azide substitution of the 3-hydroxyl group of the furoxazine-fused benzimidazole derivatives. Subsequently, a series of 3-(1,2,3-triazol-1-yl)-substituted furoxazine-fused benzimidazole derivatives were synthesised using the classical click reaction. Biological evaluations of the target compounds indicated that compound 4a-2 had higher activity against RSV (EC50 = 12.17 μM) and lower cytotoxicity (CC50 = 390.64 μM). Compound 4a-2 exerted anti-viral effects against the RSV Long strain by inhibiting apoptosis and the elevation of reactive oxygen species (ROS) and inflammatory factors caused by viral infection in vitro. Additionally, the clinical symptoms of the virus-infected mice were markedly relieved, and the viral load in the lung tissues was dramatically decreased. The biosafety profile of compound 4a-2 was also favourable, showing no detectable adverse effects on any of the major organs in vivo. These findings underscore the potential of compound 4a-2 as a valuable therapeutic option for combating RSV infections while also laying the foundation for further research and development in the field.

Novel fluorescence approach for trace quantification of levonorgestrel in breast milk based on click reaction with benzonitrofurazan azide (NBD-AZ)

Although the great importance of oral contraceptive agents in birth control, their existence in breast milk became a cause for concern, since infant exposure to these hormones is associated with many health problems. Consequentially, developing a sensitive bioanalytical method for monitoring their concentrations in breast milk is an urgent demand to examine the safety or the risk of these compounds on infants. Levonorgestrel is one of the most common contraceptive hormones under concern. Despite the high sensitivity of the fluorometric methods, detection of Levonorgestrel by them is confined because its structure does not exhibit any fluorescence. For the first time, we proposed a promising click fluorescent probe, 4-azido-7-nitrobenzoxadiazole to react with the alkyne group of Levonorgestrel, to give a highly fluorescent triazole derivative that exhibited strong signal at wavelength of 544 nm after excitation at 470 nm. Reaction parameters impacting the fluorescence were cautiously studied and optimized. The suggested approach has been successfully applied in Levonorgestrel estimation in breast milk samples with linearity of (0.4-80 ng.ml-1) and low detection limit of 0.12 ng.ml-1without interferences from any biological components and with mean % recovery of 97.84 ± 2.73. Accuracy, sensitivity, selectivity, simplicity, and low-cost makes this approach a convincing, promising, and appealing alternative over reported analytical methods for Levonorgestrel bioanalysis in different matrices.

Ligand assisted CuAAC labelling and RP-HPLC analysis of zidovudine and Retrovir using propargyl-Fmoc probe

The extensive application of zidovudine (ZDV) as a stand-alone anti-HIV drug and a component in antiviral combination therapies, has made its analysis important both in the pharmaceutical and environmental context. The azide group in ZDV structure makes it a ready-to-use substrate for copper-catalyzed azide-alkyne cycloaddition (CuAAC), which is an efficient method for "click chemistry" labeling. In this paper, we describe a ligand-assisted CuAAC procedure for the precolumn derivatization of ZDV. We used propargyl-Fmoc fluorescent label and trans-2-(4-((dimethylamino)methyl)-1H-1,2,3-triazol-1-yl)cyclohexan-1-ol (AMTC) as a copper-binding ligand. We tested the applicability of AMTC for precolumn derivatization and developed chromatographic analytical procedures for ZDV and its formulation (50 mg/5 ml oral solution, Retrovir™ syrup). Our research aimed to improve labeling efficiency with a Cu-chelating ligand, using an accessible and affordable fluorescent probe. We also developed a sustainable mechanochemical synthesis procedure for obtaining propargyl-Fmoc in a gram scale and thus boosted the accessibility of this probe. The advantages of the developed derivatization procedure are its simplicity and easy availability of the propargyl-Fmoc probe. Moreover, the high lipophilicity of the propargyl-Fmoc probe enables efficient separation of the analyte from polar matrix components. In addition, the derivatization procedure can be performed directly on a sample solution. We tested its usability for samples in environmental and biological matrices, including tap water, river water, urine, and human serum.

Development of a selective fluorescence derivatization strategy for thyroid hormones based on the Sonogashira coupling reaction

A new fluorescence derivatization technique for the determination of the thyroid hormones, 3,3',5-triiodo-L-thyronine (T₃, triiodothyronine) and 3,3',5,5'-tetraiodo-L-thyronine (T₄, L-thyroxine), in human serum was developed based on the Sonogashira coupling reaction. This derivatization reaction was recently utilized by our research group as a promising solution for the derivatization of ortho-substituted aryl halides that suffer from steric hindrance. T₃ and T₄ possess amino groups that could be derivatized by many reagents; however, these reagents are not useful in the case of biological analysis as they could non-selectively react with many biogenic amines and amino acids. Thus, herein we aimed at labeling the iodo-phenyl group of T₃ and T₄ as a selective fluorescence labeling approach suitable for biological analysis. The fluorescent alkyne, 2-(4-ethynylphenyl)-4,5-diphenyl-1H-imidazole (DIB-ET), can label the ortho-substituted aryl halides T₃ and T₄ in the presence of palladium and copper as catalysts, overcoming the steric hindrance of ortho-substitution. Furthermore, the application of the proposed method for the selective analysis of T₃ and T₄ in biological samples was successfully performed even in the presence of numerous biological components. The formed fluorescent derivatives produced from the reaction of DIB-ET and T₃ and T₄ could be determined by an HPLC system with fluorescence detection. The proposed method was successfully applied for the selective and sensitive determination of T₃ and T₄ in human serum with detection limits (S/N = 3) of 4.0 and 6.1 ng/mL and the recovery rate in the ranges of 84.3-92.1% and 81.3-84.9%, respectively. Therefore, the proposed method could be used as a new simple tool for the simultaneous determination of T₃ and T₄ in biological samples.

Click Isotope Mass Probe for Highly Selective Determination of Trace Steroid Hormones in Food Samples

Matrix effects are a great challenge for the quantitative analysis of complex food samples by liquid chromatography-tandem mass spectrometry analysis (LC-MS/MS). Stable isotope labeling (SIL) has been widely used as an effective strategy to eliminate matrix effects. Herein, a copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click-reaction-based SIL method was proposed for a highly sensitive and selective determination of six synthetic steroid hormones in three different food samples (milk, yogurt, and eggs) by high-performance liquid chromatography (HPLC)-MS/MS. A pair of novel SIL agents, N-(2-azidyl ethyl) aniline (d₀-AEA) and d₅-N-(2-azidyl ethyl) aniline (d₅-AEA) were synthesized to label steroid hormones in the samples and standard solution, respectively. The reaction accomplishes in 30 min at 60 °C. The heavy labeled standards were used as internal standards (ISs), which experience the identical ionization processes with light labeled samples to minimize matrix effects. After derivatization, the ionization efficiencies of steroid hormones were greatly improved by 2-54-folds, and the matrix effects ranged from 88.6 to 99.8%. The established method achieved satisfactory detection limits (0.1-2.5 μg L^-1) and high recoveries (85-102%). These results demonstrated that the proposed method holds unique advantages for trace steroid hormones analysis in foodstuffs.

Click reaction triggered turn-on fluorescence strategy for highly sensitive and selective determination of steroid hormones in food samples

The copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction has becoming noticeable in the field of analytical chemistry. Mild reaction conditions, simple operation, high efficiency, and good regioselectivity make this classical click reaction a perfect strategy for chemical derivatization. Herein, we proposed a promising click fluorescent labeling method with high selectivity for the determination of five steroid hormones in food samples. The labeling strategy depends on the reaction between 3-Azido-7-hydroxycoumarin and the alkynyl group of steroid hormones, which shows a turn-on fluorescence response in the presence of copper (I). The formed fluorescent products were detected by HPLC-FLD. Under the optimized conditions, the proposed method presented excellent performance with good linearity (R² ≥ 0.9998) and low detection limit (1.8-7.3 μg L^-1). Further, satisfactory recoveries were obtained to be 82-107% in spiked meats with relative standard deviations (RSDs) ≤ 5.7%. Finally, the established method was successfully applied for the determination of steroid hormones in meat, indicating the potential prospect of the click reaction in chemical derivatization.

Analytical Methods for Determination of Antiviral Drugs in Different Matrices: Recent Advances and Trends

Viruses are the main pathogenic substances that cause severe diseases in humans and other living things. They are among the most common microorganisms, and consequently, antiviral drugs have emerged to prevent and treat viral infections. Antiviral drugs are an essential drug group considering their prescription and consumption rates for different diseases and indications. Therefore, it is crucial to develop accurate and precise analytical methods to detect antiviral drugs in various matrices. Chromatographic techniques are used frequently for the quantification purpose since they allow simultaneous determination of antivirals. Electrochemical methods have also gained importance since the analysis can be performed quickly without the need for pretreatment. Spectrophotometric and spectrofluorimetric methods are used because they are simple, inexpensive, and less time-consuming methods. The purpose of this review is to present an overview of the analysis of currently used antiviral drugs from 2010 to 2021. Since studies on antiviral drugs are numerous, selected publications were reviewed in this article. The analysis of antiviral drugs was divided into three main groups: chromatographic, spectrometric, and electrochemical methods which were applied to different matrices, including pharmaceutical, biological, and environmental samples.

The Utility of Sonogashira Coupling Reaction for the Derivatization of Aryl Halides with Fluorescent Alkyne

Aryl halides are a very important category of compounds that include many vital drugs and key industrial additives, such as clofibrate and bromobenzene, respectively. Due to their importance, our research group previously developed a novel fluorescence labeling approach for their analysis using a fluorescent aryl boronic acid as a reagent, based on the Suzuki coupling reaction. This coupling reaction was successfully applied for the determination of aryl halides in biological fluids; however, there was a limitation of low reactivity towards ortho-substituted aryl halides. In the present study, a novel fluorescence derivatization approach for aryl halides was developed using, 2-(4-ethynylphenyl)-4,5-diphenyl-1H-imidazole (DIB-ET) as a fluorescent alkyne reagent, based on the Sonogashira coupling reaction. DIB-ET reacted with aryl bromides in the presence of palladium and copper as catalysts, yielding fluorescent derivatives that could be subsequently determined by an HPLC system with fluorescence detection. The detection limits (S/N = 3) for aryl bromides were in the range of 14 - 23 nM, which is 3.5 - 18-times more sensitive than our previously developed approach, Suzuki coupling derivatization. Moreover, in contrast to the previous technique, the reactivity of DIB-ET to ortho-substituted aryl bromides was almost equivalent to that of the para-substituted aryl bromides. Hence, by using this newly developed approach we could label the aryl halides with more sensitivity and reactivity. Finally, the proposed method was successfully applied for the selective determination of aryl bromides in human serum with good recovery (84.6 - 107%), which proves the ability of the developed method to determine occupational exposure to aryl halides.