Rapid, Efficient, and Green Synthesis of Coumarin Derivatives via Knoevenagel Condensation and Investigating Their Biological Effects

Gaafar AR, Gurusamy R, Akbar I. Synthesis of anthraquinone-connected coumarin derivatives via grindstone method and their evaluation of antibacterial, antioxidant, tyrosinase inhibitory activities with molecular docking, and DFT calculation studies

Anthraquinones and coumarins have excellent pharmacological activities and are an important class of natural plant metabolites with various biological activities. In this study, anthraquinone-9,10-dione and coumarin derivatives were combined to develop a novel anthraquinone-connected coumarin-derivative sequence. The synthesised novel anthraquinone-connected coumarin derivatives (1a-t) were screened for in vitro antibacterial, antioxidant, and tyrosinase inhibitory activities. The antibacterial activities of the synthesised compounds (1a-t) were tested against both gram-positive and gram-negative bacteria. Specifically, compound 1t was more active against E. aerogenes than ciprofloxacin. With regard to antioxidant activity, compound 1o (50.68 % at 100 μg/mL) was highly active compared to the other compounds, whereas it was less active than the standard BHT (76.74 % at 100 μg/mL). In terms of compound 1r (9.31 ± 0.45 μg/mL) was highly active against tyrosinase inhibitory activity compared with kojic acid (10.42 ± 0.98 μg/mL). In the molecular docking study, compound 1r had a higher docking score (-8.8 kcal mol-1) than kojic acid (-1.7 kcal mol-1). DFT calculations were performed to determine the energy gap of highly active compound 1r (ΔE = 0.11) and weakly active compound 1a (ΔE = 0.12). In this study, we found that every molecule displayed significant antibacterial, antioxidant, and tyrosinase inhibitory properties. Based on these reports, compounds 1r and 1t may act as multi-target agents.

From Conventional to Sustainable Catalytic Approaches for Heterocycles Synthesis

Synthesis of heterocyclic compounds is fundamental for all the research area in chemistry, from drug synthesis to material science. In this framework, catalysed synthetic methods are of great interest to effective reach such important building blocks. In this review, we will report on some selected examples from the last five years, of the major improvement in the field, focusing on the most important conventional catalytic systems, such as transition metals, organocatalysts, to more sustainable ones such as photocatalysts, iodine-catalysed reaction, electrochemical reactions and green innovative methods.

Green Synthesis of Electrophilic Alkenes Using a Magnesium Catalyst under Aqueous Conditions and Mechanistic Insights by Density Functional Theory

A green approach for the synthesis of electrophilic alkenes has been developed via Knoevenagel condensation between active methylene compounds and carbonyl compounds using Mg powder under aqueous conditions. In this strategy, Mg(OH)2 acts as a catalyst, which was generated in situ by the reaction between metallic Mg (20 mol %) and water. Mg was found to be an efficient, nontoxic, and inexpensive metal catalyst system for producing a range of electrophilic alkenes in excellent yields (≤98%). A gram-scale synthesis of electrophilic alkenes has been developed, and Mg metal was recovered and recycled up to three times without an appreciable loss of catalytic activity. A catalytic cycle was proposed, and the reaction mechanism was investigated using density functional theory. The key steps are enolization of ethyl cyanoacetate, C-C bond formation, and then regeneration of the catalyst via metathesis with H2O. The overall reaction occurs easily with a maximum ΔG°⧧ value of 7.9 kcal/mol for the rate-determining C-C bond formation step. Our protocol has several advantages and can be further extended to one-pot sequential Knoevenagel condensation and Michael addition, and one-pot sequential Knoevenagel condensation and chemoselective reduction can be used for the synthesis of valuable precursors of pharmaceutical products under green and aqueous conditions.

Temperature-Controlled Chemoselective Synthesis of Multisubstituted 4-Alkynyl/trans 4-Alkenyl Coumarins

A temperature-controlled facile synthesis of multisubstituted 4-alkynyl/trans 4-alkenyl coumarins with a metal salt cascade approach is reported. H₂O serves both as a nucleophile and hydrogen source. The presence of metal salt facilitates the reduction of alkyne. The present protocol bypasses the structural shortcomings of the existing Sonogashira and Heck coupling reactions. In addition, the obtained 2,3-disubstituted coumarins are readily transformed into 2,3-disubstituted dihydrocoumarins, which serve as important building blocks in organic transformations.

A phenothiazine coumarin based ratiometric fluorescent probe for real-time detection of lysosomal hypochlorite in living cell and zebra fish

Hypochlorite (ClO^-), a type of reactive oxygen species (ROS), plays an essential role in complex biological systems. Real-time detection of the content and distribution of ClO^- in cells or subcellular organelle is critically essential. In this paper, a lysosomal-targeted fluorescent probe, Cou-Lyso, was constructed for real-time detection of ClO^- in a ratiometric manner, achieving high sensitivity with a low detection limit (0.58 μM). Upon reaction with ClO^-, this probe was subjected to a significant fluorescence change from red emission (λ_maxem = 610 nm) to green emission (λ_maxem = 535 nm) with the ratio of I_{535 nm}/I_{610 nm} displaying a 76-fold enhancement from 0.04 to 3.03. The confocal imaging experiments for Cou-Lyso showed that this probe could detect ClO^- in living cell and zebra fish. This probe has been successfully applied to stain lysosome and image lysosomal ClO^- based on co-localization imaging experiments.

Pharmacological report of recently designed multifunctional coumarin and coumarin-heterocycle derivatives

Coumarin is a naturally available molecule and has been identified as a potent pharmacophore due to its pharmacological activity. Because of this, coumarin has been exploited synthetically to prepare a wide range of derivatives. In fact, most coumarin derivatives have been found to be less toxic, which is the most essential property for a drug molecule. Such molecules are being prepared for therapeutic use as broad-spectrum pharmacological agents. Microbial diseases including viral diseases have become very common and are responsible for many deaths worldwide. In particular, microbial drug resistance is a problem that needs to be tackled in an effective manner. Also, for Alzheimer's disease, which affects most elderly persons, no efficient chemotherapy exists. In addition, although diabetes, a metabolic syndrome, can be treated with many drugs, there is no complete cure. Thus, more potent antidiabetic agents are required for the management of diabetes. Likewise, for the treatment of a wide range of ailments caused by microbes, genetic factors, or lifestyle-related factors, an efficient drug regimen is needed. In view of this, coumarin derivatives are designed and evaluated. Here, coumarin derivatives that have been reported recently are compiled, classified and evaluated critically. This study briefly takes the structure-activity relationship into consideration and suggests the next suitable step. With a focus on the most potent molecules, the pharmacological activity of the evaluated molecules is described.

Probing the interaction between 7-geranyloxycoumarin and bovine serum albumin: Spectroscopic analyzing and molecular docking study

7-Geranyloxycoumarin (auraptene; AUR), as a potent phytochemical, is the naturally abundant prenyloxycoumarin found in many genera of the Rutaceae family. As the interaction with serum albumins may play a crucial role in identifying their pharmacological properties, we investigated AUR binding profile with bovine serum albumin (BSA) by experimental and computational methods. Binding constant, binding site, mode of binding, and the BSA structural change upon AUR addition, were studied. UV-vis spectroscopy results and fluorescence quenching analysis proposed that AUR can form the ground state complex with BSA. Meantime, thermodynamic parameters (negative ΔH and ΔS values) revealed that hydrogen bonds and van der Waals interactions play major role, as intermolecular forces, in the AUR-BSA complex formation. Synchronous fluorescence spectra and circular dichroism (CD) data showed that the secondary structure of BSA did not change significantly in the presence of AUR. Moreover, molecular docking results showed that AUR binds to the subdomain IIIB of BSA.