An overview on synthetic strategies to coumarins

Direct Oxidative Cyclization of 3-Arylpropionic Acids to 3,4-Dihydrocoumarins: Reinvestigation of the Reaction Mechanism

Instigated by olfactory analysis of odorant molecules, the constitutions of 3,4-dihydrocoumarins prepared by PIFA-based oxidative cyclizations of 3-arylpropionic acids were revised by means of 2D NMR and X-ray analysis. Supported by computational analysis, the migratory mechanism of intermediate spirolactonic cations has been amended: 1,2-alkyl shifts instead of 1,2-carboxylic shifts were selectively obtained.

Recent Advances in Biologically Active Coumarins from Marine Sources: Synthesis and Evaluation

Coumarin and its derivatives have significantly attracted the attention of medicinal chemists and chemical biologists due to their huge range of biological, and in particular, pharmacological properties. Interesting families of coumarins have been found from marine sources, which has accelerated the drug discovery process by inspiring innovation or even by the identification of analogues with remarkable biological properties. The purpose of this review is to showcase the most interesting marine-derived coumarins from a medicinal chemistry point of view, as well as the novel and useful synthetic routes described to date to achieve these chemical structures. The references that compose this overview were collected from PubMed, Mendeley and SciFinder.

Synthesis and Antiproliferative Effect of Halogenated Coumarin Derivatives

A series of 6- and 6,8-halocoumarin derivatives have been investigated as potential antiproliferative compounds against a panel of tumor and normal cell lines. Cytotoxic effects were determined by the MTT method. To investigate the potential molecular mechanism involved in the cytotoxic effect, apoptosis assay, cell cycle analysis, reactive oxygen species (ROS), and reduced glutathione analysis were performed. Among the screened compounds, coumarins 6,8-dibromo-2-oxo-2H-chromene-3-carbonitrile 2h and 6,8-diiodo-2-oxo-2H-chromene-3-carbonitrile 2k exhibited the most antiproliferative effect in thyroid cancer-derived cells TPC-1. The apoptosis assay showed that both 2h and 2k induced apoptosis in TPC-1 thyroid cancer cells. According to these experiments, both coumarins induced a slight increase in TPC-1 cells in the G2/M phase and a decrease in the S phase. A significant increase in ROS levels was observed in TPC-1 treated with diiodocoumarin 2k, while the dibromocoumarin 2h induced a decrease in ROS in a dose and time-dependent manner.

Photoinduced radical cascade cyclization of acetylenic acid esters with oxime esters to access cyanalkylated coumarins

A photoinduced radical cascade cyclization of acetylenic acid esters with oxime esters is described, providing cyanalkylated coumarins in superior yields under mild conditions. Radical capture and luminescence quenching experiments showed that this transformation was accomplished via a radical addition/5-exo spirocyclization/1,2-ester migration process.

An Efficient and Versatile Deep Eutectic Solvent-Mediated Green Method for the Synthesis of Functionalized Coumarins

Herein, we report a green and efficient synthetic route for the construction of diverse functionalized coumarins in good-to-excellent yields (60-98%) via the Pechmann condensation. The optimized synthetic route involves a biodegradable, reusable, and inexpensive deep eutectic solvent (DES) of choline chloride and l-(+)-tartaric acid in a ratio of 1:2 at 110 °C. Interestingly, phloroglucinol and ethyl acetoacetate, upon reaction, furnished the functionalized coumarin (20) in 98% yield within 10 min. On the other front, the same DES at relatively lower reaction temperature (90 °C) was found to provide the bis-coumarins in decent yields (81-97%) within 20-45 min. Moreover, this particular method was found to be quite effective for large-scale coumarin synthesis without noteworthy reduction in the yields of the desired products. Noticeably, in this versatile approach, the DES plays a dual role as solvent as well as catalyst, and it was effectively recycled and reused four times with no significant drop-down in the yield of the product.

Coumarins Synthesis and Transformation via C–H Bond Activation—A Review

For several decades, coumarins have attracted considerable attention due to the fact of their application in diverse fields such as medical science and biomedical research as well as several industrial branches. Recently, many compounds containing the coumarin moiety have been intensively studied, mainly due to the fact of their biological activities such as antitumor, antioxidative, anti-HIV, vasorelaxant, antimicrobial, and anticancer. They are also widely used as fluorescent dyes and probes because of their great structural flexibility and large fluorescent quantum yields. For this reason, numerous attempts have been made to develop new and more practical methods for the synthesis of these compounds. This review aims at providing a comprehensive overview of coumarin synthesis methods by direct C–H bond activation in order to demonstrate the current state-of-the-art methods as well as the current limitations.

Copper-Catalyzed Synthesis of Coumarins. A Mini-Review

Coumarin (2H-chromen-2-one) derivatives have important uses in medicinal and synthetic chemistry, for example, as fluorescent probes. These properties have prompted chemists to develop efficient synthetic methods to synthesize the coumarin core and/or to functionalize it. In this context, many metal-catalyzed syntheses of coumarins have been introduced; among them, copper-catalyzed reactions appear to be very promising owing to the non-toxicity and cheapness of copper complexes. In this mini-review, the results in this field are summarized. We hope to stimulate other applications of these complexes in the preparation of coumarin derivatives.

Natural products from Brazilian biodiversity identified as potential inhibitors of PknA and PknB of M. tuberculosis using molecular modeling tools

Mycobacterium tuberculosis was discovered in 1882 by Robert Koch but, since its discovery, the tuberculosis (TB) epidemic has endured, being one of the top 10 causes of death worldwide. Drug-resistant TB continues to be a public health threat and bioactive compounds with a new mode of action (MoA) are needed to overcome this. Since natural products are described as important sources for the development of new drugs, the objective of this work was to identify potential ligands from Brazilian natural products (NPs) for M. tuberculosis targets using molecular modeling tools. Using chemogenomics we identified the Serine/Threonine Protein Kinase PknB as a putative target for 13 NPs from a database from Brazilian biodiversity (NuBBE). Literature data supported further investigation of NuBBE105, NuBBE598, NuBBE936, NuBBE964, NuBBE1045, and NuBBE1180 by molecular docking and dynamics. Key interactions were observed with PknB and simulations confirmed stability and favorable binding energies. Considering structural similarity with PknB, we further explored binding of the NPs to PknA, critical for M. tuberculosis survival, and all of them resembled important interactions with the enzyme, showing stable and favorable binding energies, whilst van der Waals interactions seem to play a key role for binding to PknA and PknB. NuBBE936 and NuBBE1180 have already had their antimycobacterial activity reported and our results can provide a basis for their MoA. Finally, the other NPs which have not been tested against M. tuberculosis deserve further investigation, aiming at the discovery of antimycobacterial drug candidates with innovative MoA.

Synthetic Routes to Coumarin(Benzopyrone)-Fused Five-Membered Aromatic Heterocycles Built on the α-Pyrone Moiety. Part 1: Five-Membered Aromatic Rings with One Heteroatom

This review gives an up-to-date overview of the different ways (routes) to the synthesis of coumarin (benzopyrone)-fused, five-membered aromatic heterocycles with one heteroatom, built on the pyrone moiety. Covering 1966 to 2020.

Analysis of Fluorescence Quenching of Coumarin Derivative under Steady State and Transient State Methods

Nature has gifted us many organic molecules which have remarkable influence in our daily life. Amongst many organic molecules, heterocyclic organic molecules have gained potential applications in the advanced field of biomedicine, pharmaceutical, electronics and many more. In the present work fluorescence quenching of biologically active fluorescent probe 8EMOHCC by aniline in different solvents have been studied at room temperature. To understand the molecular behaviour in different media, solvents of different refractive index and dielectric constant have been used. Spectroscopic measurement techniques such as UV/Vis spectroscopy and time related single photon counting are employed to characterise the molecule at room temperature. The fluorescence quenching study shows linear dependence of SV-plot in solvents of different dielectric constants. It reveals that quenching reactions are dynamic in nature. Various parameters of quenching have been determined and identified the type of quenching involved in the quenching reaction. Further, k_q is found to be greater than [Formula: see text] in ACN, methanol, propanol and dioxane. Activation energy of quenching (E_a) is found to be greater than energy of diffusion (E_d) in ACN, methanol, propanol, THF solvents and E_d > E_a in dioxane, indicating that quenching reaction is not solely controlled by material diffusion but also activation process.

Gold(I)-Catalyzed Intramolecular Hydroarylation of Phenol-Derived Propiolates and Certain Related Ethers as a Route to Selectively Functionalized Coumarins and 2H-Chromenes

Methods are reported for the efficient assembly of a series of phenol-derived propiolates, including the parent system 56, and their Au(I)-catalyzed cyclization (intramolecular hydroarylation) to give the corresponding coumarins (e.g., 1). Simple syntheses of natural products such as ayapin (144) and scoparone (145) have been realized by such means, and the first of these subject to single-crystal X-ray analysis. A related process is described for the conversion of propargyl ethers such as 156 into the isomeric 2H-chromene precocene I (159), a naturally occurring inhibitor of juvenile hormone biosynthesis.

Visible-light-induced tandem radical addition/cyclization of 2-alkenylphenols and CBr4 for the synthesis of 4-arylcoumarins

A visible-light-induced photoredox-catalyzed tandem radical addition/cyclization of 2-alkenylphenols and CBr4 is developed, providing efficient and practical access to various 4-arylcoumarins in a one-pot fashion.

Bumpy Roads Lead to Beautiful Places: The Twists and Turns in Developing a New Class of PN-Heterocycles

The Haley and Johnson labs at the University of Oregon have been collaborating since 2006, combining skillsets in synthetic organic, physical organic, and supramolecular chemistries. This joint project has produced many examples of host molecules that bind anionic guests and give chemical, photophysical, and/or electrical responses. Many of these receptors utilize two-armed arylethynyl backbones that have a variety of hydrogen- or halogen-bonding functional groups appended. However, in attempts to produce a bisamide-containing host using a peptide-coupling protocol with P(OPh)3 present, we isolated something unexpected – a heterocycle containing neighboring P and N atoms. This ‘failed’ reaction turned into a surprisingly robust synthesis of phosphaquinolinones, an unusual class of PN-heterocycles. This Account article tells the rollercoaster story of these heterocycles in our lab. It will highlight our key works to this field, including a suite of fundamental studies of both the original PN-naphthalene moiety, as well as a variety of structural modifications to the arene backbone. It will also discuss the major step forward the project took when we developed a phosphaquinolinone-containing receptor molecule capable of binding HSO4 – selectively, reversibly, and with recyclability. With these findings, the project has gone from hospice care to making a full, robust recovery.

1 Introduction

2 Initial Discovery

3 Setbacks Breathe New Life

4 A New Dynamic Duo Develops Dozens of Derivatives

5 Physicochemical Characterization

5.1 Fluorescence

5.2 Molecular Structures

5.3 Solution Dimerization Studies

6 Applying What We Have Learned

6.1 Development of Supramolecular Host

6.2 Use of PN Moiety as an Impressive Fluorophore

7 Conclusions and Outlook

An Overview of Coumarin as a Versatile and Readily Accessible Scaffold with Broad-Ranging Biological Activities

Privileged structures have been widely used as an effective template for the research and discovery of high value chemicals. Coumarin is a simple scaffold widespread in Nature and it can be found in a considerable number of plants as well as in some fungi and bacteria. In the last years, these natural compounds have been gaining an increasing attention from the scientific community for their wide range of biological activities, mainly due to their ability to interact with diverse enzymes and receptors in living organisms. In addition, coumarin nucleus has proved to be easily synthetized and decorated, giving the possibility of designing new coumarin-based compounds and investigating their potential in the treatment of various diseases. The versatility of coumarin scaffold finds applications not only in medicinal chemistry but also in the agrochemical field as well as in the cosmetic and fragrances industry. This review is intended to be a critical overview on coumarins, comprehensive of natural sources, metabolites, biological evaluations and synthetic approaches.

Crystal structure of a new polymorph of 3-acetyl-8-meth-oxy-2H-chromen-2-one

A new polymorphic form of 3-acetyl-8-meth­oxy-2H-chromen-2-one is described and compared with the previously reported polymorph. In the crystal, hydrogen bonds, π–π inter­actions and anti­parallel C=O⋯C=O inter­actions give rise to a helical supra­molecular architecture

A new polymorphic form of the title compound, C₁₂H₁₀O₄, is described in the ortho­rhom­bic space group Pbca and Z = 8, as compared to polymorph I, which crystallizes in the monoclinic space group C2/c and Z = 8 [Li et al. (2012). Chin. J. Struct. Chem.31, 1003–1007.]. In polymorph II, the coumarin ring system is almost planar (r.m.s. deviation = 0.00129 Å). In the crystal, mol­ecules are connected by Csp³—H⋯O and C_ar—H⋯O hydrogen bonds, forming mol­ecular sheets linked into zigzag shaped layers along the b-axis direction. The three-dimensional lattice is assembled through stacking of the zigzag layers by π–π inter­actions with a centroid-to-centroid distance of 3.600 (9) Å and anti­parallel C=O⋯C=O inter­actions with a distance of 3.1986 (17) Å, which give rise to a helical supra­molecular architecture.

Coumarin-Based Small-Molecule Fluorescent Chemosensors

Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

Synthesis, photophysical properties, and self-dimerization studies of 2-λ5-phosphaquinolin-2-ones

Rationally designed phosphaquinolinone derivatives containing electron-donating and/or -withdrawing groups are reported, with dimerization constants up to 525 M⁻¹.