A simple and highly selective fluorescent sensor for palladium based on benzofuran-2-boronic acid

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.

Regioselective Transition Metal-Free Catalytic Ring Opening of 2H-Azirines by Phenols and Naphthols; One-Pot Access to Benzo- and Naphthofurans

Benzofuran and naphthofuran derivatives are synthesized from readily available phenols and naphthols. Regioselective ring openings of 2H-azirine followed by in situ aromatization using a catalytic amount of Brønsted acid have established the novelty of the methodology. The involvement of a series of 2H-azirines with a variety of phenols, 1-naphthols, and 2-naphthols showed the generality of the protocol. In-depth density functional theory calculations revealed the reaction mechanism with the energies of the intermediates and transition states of a model reaction. An alternate pathway of the mechanism has also been proposed with computer modeling.

A colorimetric and fluorescent signaling probe for assaying Pd2+ in practical samples

We developed an optical signaling probe to detect Pd2+ ions in Pd-containing catalyst and drug candidate. The Pd2+ signaling probe (Res-DT) was readily prepared by reacting the versatile fluorochrome resorufin with phenyl chlorodithioformate. In a phosphate-buffered saline solution (pH 7.4) containing sodium dodecyl sulfate (SDS) as a signal-boosting surfactant, Res-DT exhibited a pronounced colorimetric response with a chromogenic yellow to magenta shift, leading to a substantial increase in the fluorescence intensity. The Pd2+ signaling performance of Res-DT was attributed to the Pd2+-promoted hydrolysis of the dithioate moiety. The probe displayed high selectivity toward Pd2+ ions and remained unaffected by commonly encountered coexisting components. Moreover, the detection limit of Res-DT for Pd2+ ions was 10 nM, and the signaling was achieved within 7 min. Furthermore, to demonstrate the real-world applicability of Res-DT, a Pd2+ assay was performed in Pd-containing catalyst and drug candidate using an office scanner as an easily accessible measurement device. Our results highlight the prospects of Res-DT as a tool to detect Pd2+ ions in various practical samples, with potential applications in catalysis, medicine, and environmental science.

Simple Fluorescence Assay for Triethylamine Based on the Palladium Catalytic Dimerization of Benzofuran-2-boronic Acid

Although benzofuran-2-boronic acid hardly emits fluorescence, it can be rapidly converted to a highly fluorescent benzofuran dimer after mixing with a palladium catalyst and amine. We found that a fluorescence enhancement accompanying dimerization was quantitatively promoted upon increasing the concentration of amine. In the present study, we developed a simple fluorescence assay for amines based on the promotive effect. As the result of a fluorescence measurement of the reaction mixture of 19 kinds of typical amines, it was found that tertiary amines including triethylamine (TEA) provided a significant fluorescence enhancement. Finally, the fluorogenic reaction could be applied to develop a high-throughput fluorescent microplate assay for TEA with the limit of detection (blank + 3SD) of 0.091 μM.

A selective and highly sensitive high performance liquid chromatography with fluorescence derivatization approach based on Sonogashira coupling reaction for determination of ethinyl estradiol in river water samples

A selective and highly sensitive high performance liquid chromatography (HPLC) with fluorescence derivatization method was developed for determination of ethinyl estradiol (EE); one of endocrine-disrupting compounds (EDCs). The fluorescence derivatization procedure was based on Sonogashira coupling reaction using 4-(4, 5-diphenyl-1H-imidazole-2-yl) iodobenzene (DIB-I), a fluorescence labeling reagent, to derivatize EE in presence of copper and palladium ions. The formed fluorescent product was separated on Cosmosil 5C₁₈ MS-II by an isocratic elution with a mobile phase composed of acetonitrile: 5.0 mM Tris-HNO₃ buffer, pH 7.4 (60:40, v/v %). The detection wavelengths were set at 310 and 400 nm as excitation and emission wavelengths, respectively. Various parameters affecting derivatization reaction were optimized. Further, the proposed method was validated and a good linearity with low detection limit (S/N=3) 7.4 ng L^-1 was obtained in water sample after a simple solid-phase disk extraction (C₁₈ SPE disk) method. The proposed method was successfully applied for detection of EE in river water samples in order to monitor EE concentration and to distinguish its effect on the ecosystem and human health.

A highly selective and sensitive boronic acid-based sensor for detecting Pd2+ ion under mild conditions

Herein, a boronic acid-based sensor was reported selectively to recognize Pd²⁺ ion. The fluorescence intensity increased 36-fold after sensor binding with 2.47 × 10^-5 M of Pd²⁺ ion. It was carried out in the 99% aqueous solution for binding tests, indicating sensor having good water solubility. In addition, it is discernible that Pd²⁺ ion turned on the blue fluorescence of sensor under a UV-lamp (365 nm), while other ions (Ag⁺, Al³⁺, Ba²⁺, Ca²⁺, Cr²⁺, Cd²⁺, Co²⁺, Cs²⁺, Cu²⁺, Fe²⁺, Fe³⁺, K⁺, Li⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺ and Zn²⁺) did not show the similar change. Furthermore, sensor has a low limit of detection (38 nM) and high selectivity, which exhibits the potential for the development of Pd²⁺ recognition in practical environments.

A Near-infrared Fluorescent Probe of Dicyanoisophorone Derivatives for Selective Detection and Fluorescence Cellular Imaging of Palladium

Palladium (Pd) has been acknowledged to be a rare inner transition metal, which plays a pivotal role in many fields. This article focuses on developing a safe and effective near-infrared fluorescent probe, MW-PD, which would make a great contribution to the detection of palladium residue in drugs, especially trace residues. The fluorescent probe was rationally designed by combining the dicyanoisophorone fluorophore with an allyloxycarbonyl group. Based on the Tsuji-Trost reaction, the probe exhibited high selectivity and sensitivity toward Pd (0) over other common metal ions with a low detection limit (8.0 nM). Moreover, MW-PD showed biocompatibility and was successfully applied to imaging Pd (0) in Hela cells.

An umbelliferone-derivated fluorescent sensor for selective detection of palladium(II) from palladium(0) in living cells

Palladium (Pd) has drawn worldwide attentions because its connections to industry, chemistry, biological material and public health. Quantitative and selective detection tools for Pd and its ion forms are in urgent necessity. Here an umbelliferone derivative Umb-Pd2 was provided as a small, steady, safe and selective sensor for detecting Pd(II). It indicated advantages including sensitive (LOD 1.1 nM), wide pH tolerance (5.0-10.0), applicable linear range (0-1.8 equivalent) and low toxicity. The most attractive point was its explicit selectivity towards Pd(II) from Pd(0) in both independent and coexistence systems. This distinguishing ability was further utilized in imaging in living cells, raising this work as a rare and important example among all the published papers on palladium sensing. Thus, Umb-Pd2 supplied a potential approach for further improvement and applications in both daily chemistry and public health.

Natural source, bioactivity and synthesis of benzofuran derivatives

Benzofuran compounds are a class of compounds that are ubiquitous in nature. Numerous studies have shown that most benzofuran compounds have strong biological activities such as anti-tumor, antibacterial, anti-oxidative, and anti-viral activities. Owing to these biological activities and potential applications in many aspects, benzofuran compounds have attracted more and more attention of chemical and pharmaceutical researchers worldwide, making these substances potential natural drug lead compounds. For example, the recently discovered novel macrocyclic benzofuran compound has anti-hepatitis C virus activity and is expected to be an effective therapeutic drug for hepatitis C disease; novel scaffold compounds of benzothiophene and benzofuran have been developed and utilized as anticancer agents. Novel methods for constructing benzofuran rings have been discovered in recent years. A complex benzofuran derivative is constructed by a unique free radical cyclization cascade, which is an excellent method for the synthesis of a series of difficult-to-prepare polycyclic benzofuran compounds. Another benzofuran ring constructed by proton quantum tunneling has not only fewer side reactions, but also high yield, which is conducive to the construction of complex benzofuran ring systems. This review summarizes the recent studies on the various aspects of benzofuran derivatives including their important natural product sources, biological activities and drug prospects, and chemical synthesis, as well as the relationship between the bioactivities and structures.