High-Shear Enhancement of Biginelli Reactions in Macromolecular Viscous Media

Chemical reactions and transformations in non-traditional vessels have gained significant interest in recent years. Flow chemistry, with its advantages in mixing, mass transfer, scalability, and automation, is a driving force behind this paradigm shift. In particular, the Vortex Fluidic Device (VFD) has emerged as a versatile tool across various applications, from organic synthesis to materials science. In this study, the role of the VFD in performing the Biginelli reaction, a multicomponent reaction widely used in pharmaceutical and polymer science, for a post-polymerization modification is explored. By conducting the Biginelli reaction in the VFD, rapid product formation with low catalyst loading and without the need for high temperatures is achieved. However, the critical need to understand and know solution viscosity, especially within the context of modifying macromolecules is highlighted.

Coumarin-imidazopyridine hybrids and their first-in-class ZnII metal complexes as potent dual entry and replication inhibitors of Zika viral infection

In this study, we synthesized and characterized a series of coumarin-imidazopyridine hybrid ligands (HL1-HL4) and their corresponding Zn(II) complexes (C1-C4). The ligands were synthesized via a two-step process in 56-90 % yields. The resulting ligands, were utilized to form Zn(II) complexes, characterized by conductivity measurements, HRMS, IR, 1H NMR spectroscopy and X-ray diffractions. Biological evaluations revealed that these compounds exhibited potent antiviral activity against Zika virus (ZIKV), with EC50 values ranging from 0.55 to 4.8 µM and SI of up to 1490. Notably, the complexes (the first-in-class Zn(II) anti-ZIKV complexes) generally displayed enhanced activity compared to their respective ligands, with some compounds outperforming the reference antiviral, ribavirin. The Time of Addition assay suggested that while some compounds interfere with both viral entry (with a virucidal component) and replication phases, other only acted in replication phases. These results together with molecular modeling studies on ZIKV Envelope protein and ZIKV NS2B-NS3 offered insights for their mode of actions and further optimizations.

Functional chromophores synthesized via multicomponent Reactions: A review on their use as cell-imaging probes

This review aims to provide a comprehensive overview of recent advancements and applications of fluorescence imaging probes synthesized via MCRs (multicomponent reactions). These probes, also known as functional chromophores, belong to a currently investigated class of fluorophores that are presently being successfully applied in bioimaging experiments, especially in various living cell lineages. We describe some of the MCRs that have been employed in the synthesis of these probes and explore their applications in biological imaging, with an emphasis on cellular imaging. The review also discusses the challenges and future perspectives in the field, particularly considering the potential impact of MCR-based fluorescence imaging probes on advancing this field of research in the coming years. Considering that this area of research is relatively new and nearly a decade has passed since the first publication, this review also provides a historical perspective on this class of fluorophores, highlighting the pioneering works published between 2011 and 2016.

Multicomponent synthesis of chromophores – The one-pot approach to functional π-systems

Multicomponent reactions, conducted in a domino, sequential or consecutive fashion, have not only considerably enhanced synthetic efficiency as one-pot methodology, but they have also become an enabling tool for interdisciplinary research. The highly diversity-oriented nature of the synthetic concept allows accessing huge structural and functional space. Already some decades ago this has been recognized for life sciences, in particular, lead finding and exploration in pharma and agricultural chemistry. The quest for novel functional materials has also opened the field for diversity-oriented syntheses of functional π-systems, i.e. dyes for photonic and electronic applications based on their electronic properties. This review summarizes recent developments in MCR syntheses of functional chromophores highlighting syntheses following either the framework forming scaffold approach by establishing connectivity between chromophores or the chromogenic chromophore approach by de novo formation of chromophore of interest. Both approaches warrant rapid access to molecular functional π-systems, i.e. chromophores, fluorophores, and electrophores for various applications.

Cytotoxicity evaluation and DNA interaction of RuII-bipy complexes containing coumarin-based ligands

Although there are various treatment options for cancer, this disease still has caused an increasing number of deaths, demanding more efficient, selective and less harmful drugs. Several classes of ruthenium compounds have been investigated as metallodrugs for cancer, mainly after the entry of imidazolH [trans-RuCl4-(DMSO-S)(imidazole)] (NAMI-A) and indazolH [trans-RuCl4-(Indazol)2] (KP1019) in clinical trials. In this sense, RuII complexes with general formula [Ru(L1-3)(bipy)2]PF6 (1-3) (L1 = ethyl 3-(6-methyl-2-oxo-2H-chromen-3-yl)-3-oxopropanoate, L2 = ethyl 3-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)-3-oxopropanoate, L3 = ethyl 3-(8-methoxy-2-oxo-2H-chromen-3-yl)-3-oxopropanoate and bipy = bipyridine) have been synthesized. The crystal structure of 2 revealed that the RuII atom lies on a distorted octahedral geometry with the deprotonated ligand (L2-) coordinated through β-ketoester group oxygen atoms. In vitro cytotoxic activity of the compounds was evaluated against 4T1 (murine mammary carcinoma) and B16-F10 (murine metastatic melanoma) tumor cells, and the non-tumor cell line BHK-21 (baby hamster kidney). Coordination with RuII resulted in expressive enhancement of cytotoxic activity. The precursors were inactive below 100 μM and the final RuII complexes (1-3) showed IC50 ranging from 2.0 to 12.8 μM; 2 being the most potent compound. DNA interaction studies revealed a greater capacity of the complexes to interact with DNA than the ligands, where, 2 exhibited the highest Kb constant of 2.2 × 104 M-1. Fluorescence investigation demonstrated that 1-3 are capable of quenching the fluorescence emission of the EtdBr-DNA complex up to 40%. Molecular docking showed that the interaction of 1-3 between the DNA base pairs from the coumarin portion was with scores of 67.28, 68.62 and 64.88, respectively, and 75.45 for ellipticine, suggesting an intercalative mode of binding. Our findings show that the RuII complexes are eligible for continuing to be investigated as potential antitumor compounds.

Polarized Helical Coumarins: [1,5] Sigmatropic Rearrangement and Excited-State Intramolecular Proton Transfer

The tandem process of phenol addition to a cyclic α,β-unsaturated ester followed by intramolecular transesterification and [1,5] sigmatropic rearrangement affords a series of helical coumarins based upon a previously unknown 3-amino-7-hydroxybenzo[3,4]cyclohepta[1,2-c]chromen-6-one core. These novel polarized coumarins, possessing a β-ketoester moiety, have been employed to synthesize more rigid and helical coumarin–pyrazolones, which display green fluorescence. The enhanced emission of coumarin–pyrazolones in polar solvents depends on the nature of the S₁ state. The coumarin–pyrazolones are predicted to have two vertical states close in energy: a weakly absorbing S₁ (¹LE) followed by a bright S₂ state (¹CT). In polar solvents, the ¹CT can be stabilized below the ¹LE and may become the fluorescent state. Solvatochromism of the fluorescence spectra confirms this theoretical prediction. The presence of an N—H···O=C intramolecular hydrogen bond in these coumarin–pyrazolone hybrids facilitates excited-state intramolecular proton transfer (ESIPT). This process leads to a barrierless conical intersection with the ground electronic state and opens a radiationless deactivation channel effectively competing with fluorescence. Solvent stabilization of the CT state increases the barrier for ESIPT and decreases the efficiency of the nonradiative channel. This results in the observed correlation between solvatochromism and an increase of fluorescence intensity in polar solvents.

Reaction-based chemosensor as dual-channel indicator for visualizing and bioimaging of exogenous hypochlorite concentrations in living cells, Pseudomonas aeruginosa, and zebrafish

Tracking and quantifying hypochlorite (ClO^-) in biological systems and environments remain challenging tasks, and many efforts have been made to improve ClO^- recognition performance by modifying the sensor structure. In this study, a pre-designed coumarin/furanohydrazide-based sensor (CMFH) with the coumarin moiety as the building block (fluorogen) was rationally prepared as a ratiometric and colorimetric chemosensor for ClO^- recognition. As expected, CMFH demonstrated excellent sensitivity and selectivity for ClO^- detection. The fluorescence signal ratio (F₄₆₆/F₅₅₆) showed strong ClO^- dependency, and the sensor exhibited ultrafast detection (within 60 s) and a low detection limit of 563 nM. Due to its low cytotoxicity and good tissue permeability, CMFH was demonstrated as a dual-channel sensor for ClO^- bioimaging and visualization in cells, zebrafish, and even bacteria. Furthermore, CMFH-loaded paper strips were successfully applied to the colorimetric and fluorescent visualization of ClO^-. The results demonstrate that CMFH has potential application value for tracking ClO^- in various biosystems and environments.

4-Aminocoumarin derivatives: synthesis and applications

4-Aminocoumarins represent an important class of a versatile scaffold in organic synthesis and have been consistently used as a building block in organic chemistry for the synthesis of different heterocyclic compounds.

Hybrid 3,4-dihydropyrimidin-2-(thi)ones as dual-functional bioactive molecules: fluorescent probes and cytotoxic agents to cancer cells

A series of new hybrid fluorescent Biginelli compounds, including a Monastrol derivative, were designed and synthesized with good yields.

Efficient Rapid Access to Biginelli for the Multicomponent Synthesis of 1,2,3,4-Tetrahydropyrimidines in Room-Temperature Diisopropyl Ethyl Ammonium Acetate

The diisopropyl ethyl ammonium acetate (DIPEAc)-promoted Biginelli protocol has been developed for the first time by a successive one-pot three-component reaction of aldehydes, ethylcyanoacetate/ethyl acetoacetate, and thiourea/urea to afford pharmacologically promising 1,2,3,4-tetrahydropyrimidines in high yields at room temperature. The key benefits of the present scheme are the capability to allow a variability of functional groups, short reaction times, easy workup, high yields, recyclability of the catalyst, and solvent-free conditions, thus providing economic and environmental advantages. In addition, a series of 4-oxo-6-aryl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carbonitriles analogues were synthesized and selected for their in vitro antifungal and antibacterial activities.

Bioactive Phenolic Components from the Twigs of Atalantia buxifolia

Five new compounds named buxifoximes A-C (1-3), buxifobenzoate (4), and 7- O-(7'-peroxygeranyl) coumarin (5), together with 25 known compounds, were identified from the twigs of Atalantia buxifolia. Compounds 1-3 are unique secondary metabolites with the aldoxime functionality. The structures of the isolates were determined on the basis of spectroscopic data analyses, and the structure of 1 was confirmed by an X-ray single-crystallographic analysis. With respect to bioactivity, antidengue virus, anti-inflammatory, and cytotoxic activities of all purified compounds were tested and evaluated. Compound 1 showed a significant anti-inflammatory effect by inhibiting superoxide anion generation with an IC₅₀ value of 4.8 ± 0.7 μM. Among the acridone alkaloids, 5-hydroxy- N-methylseverifoline (23) exhibited antidengue activity (IC₅₀ = 5.3 ± 0.4 μM), and atalaphyllinine (20) demonstrated cytotoxicity (IC₅₀ = 6.5 ± 0.0 μM) against the human liver cancer cell line, HepG2.

Lophine and pyrimidine based photoactive molecular hybrids. Synthesis, photophysics, BSA interaction and DFT study

New photoactive molecular hybrids containing both lophine and pyrimidine moieties as optical sensors.

New visible light excitable donor-acceptor 7-hydroxy-coumarins as blue fluorescent probes for selective staining of vacuoles in yeasts and L. donovani

In order to address the existing limitations of the commercially available fluorescent probe CMAC (7-amino-4-chloromethylcoumarin), a new series of highly fluorescent donor-acceptor 7-hydroxy-coumarin derivatives was prepared and these derivatives were used as vacuole specific fluorescent probes for live cell imaging of unicellular parasitic protozoa L. donovani promastigotes and yeast cells S. pombe and S. cerevisiae. The synthesized 7-hydroxy-coumarins exhibited interesting photophysical properties and have advantages such as excitation in the visible region, good water solubility, photo-stability, good quantum yield and low cytotoxicity.

Synthesis and photophysical study of new fluorescent proton transfer dihydropyrimidinone hybrids as potential candidates for molecular probes

New photoactive hybrid dihydropyrimidinones were achieved by the Biginelli multicomponent reaction.

MoO2Cl2 catalyzed efficient synthesis of functionalized 3,4-dihydropyrimidin-2(1H)-ones/thiones and polyhydroquinolines: recyclability, fluorescence and biological studies

MoO₂Cl₂ catalyzed Biginelli, Hantzsch reactions exploring spectroscopic and biological properties of novel compounds.

‘Naked-eye’ colorimetric/fluorimetric detection of F− ions by biologically active 3-((1H-indol-3-yl)methyl)-4-hydroxy-2H-chromen-2-one derivatives

An improved synthetic protocol has been developed to construct highly functionalized heterologous alkyl and benzyl indolyl-coumarin derivatives using a rapid, catalyst-free and solvent-free one-pot three-component reaction of indole, aldehyde and 4-hydroxy-coumarin.

Microwave-assisted synthesis and photophysical studies of novel fluorescent N-acylhydrazone and semicarbazone-7-OH-coumarin dyes

Emissive 7-OH-coumarins were synthesized by a microwave-assisted protocol and spectral changes were induced after conformational changes in low polarity media.