PhI(OAc) 2 mediated an efficient Knoevenagel reaction and their synthetic application for coumarin derivatives

Recent Developments in Coumarin Derivatives as Neuroprotective Agents

BACKGROUND

Neurodegenerative diseases are among the diseases that cause the foremost burden on the health system of the world. The diseases are multifaceted and difficult to treat because of their complex pathophysiology, which includes protein aggregation, neurotransmitter breakdown, metal dysregulation, oxidative stress, neuroinflammation, excitotoxicity, etc. None of the currently available therapies has been found to be significant in producing desired responses without any major side effects; besides, they only give symptomatic relief otherwise indicated off-episode relief. Targeting various pathways, namely choline esterase, monoamine oxidase B, cannabinoid system, metal chelation, β-secretase, oxidative stress, etc., may lead to neurodegeneration. By substituting various functional moieties over the coumarin nucleus, researchers are trying to produce safer and more effective neuroprotective agents.

OBJECTIVES

This study aimed to review the current literature to produce compounds with lower side effects using coumarin as a pharmacophore.

METHODS

In this review, we have attempted to compile various synthetic strategies that have been used to produce coumarin and various substitutional strategies used to produce neuroprotective agents from the coumarin pharmacophore. Moreover, structure-activity relationships of substituting coumarin scaffold at various positions, which could be instrumental in designing new compounds, were also discussed.

RESULTS

The literature review suggested that coumarins and their derivatives can act as neuroprotective agents following various mechanisms.

CONCLUSION

Various studies have demonstrated the neuroprotective activity of coumarin due to an oxaheterocyclic loop, which allows binding with a broad array of proteins, thus motivating researchers to explore its potential as a lead against various neurodegenerative diseases.

Synergistic Effect of Cerium in Dual Photoinduced Ligand-to-Metal Charge Transfer and Lewis Acid Catalysis: Diastereoselective Alkylation of Coumarins

We report the dual role of cerium to promote the photoinduced ligand-to-metal charge transfer (LMCT) process for the generation of the alkyl radical and subsequent Lewis acid catalysis to construct stereodefined C-C bonds. This paradigm utilized ubiquitous carboxylic acids as alkyl radical surrogates and offers excellent diastereoselectivity for the formation of C-4 alkylated coumarins in good to excellent yield. UV-vis spectroscopy studies in combination with in situ Fourier transform infrared spectroscopy are consistent with the proposed mechanism, supporting the participation of the Ce^IV-carboxylate complex in photoinduced LMCT and its subsequent homolysis to generate the alkyl radial through the exclusion of CO₂. Finally, the oxophilicity of cerium enables a two-point complexation with the in situ generated enolate intermediate and facilitates the diastereoselective protonation to form the desired product. Furthermore, this mild and atom-economical catalytic manifolds allow the late-stage modification of pharmaceuticals.

Recent Advances in the Synthesis of Coumarin Derivatives from Different Starting Materials

The study of coumarin dates back to 1820 when coumarin was first extracted from tonka bean by Vogel. Compounds containing coumarin backbone are a very important group of compounds due to their usage in pharmacy and medicine. Properties and biological activities of coumarin derivatives have a significant role in the development of new drugs. Therefore, many different methods and techniques are developed in order to synthesize coumarin derivatives. Coumarin derivatives could be obtained from different starting materials with various methods but with big differences in yield. This review summarized various methods, techniques and reaction conditions for synthesis of coumarins from different compounds such as aldehydes, phenols, ketones and carboxylic acids.

The first report of the synthesis of organo-functionalized triethoxysilanes via a Knoevenagel condensation approach

The present work involves the design of a new synthetic pathway for the preparation of organo-functionalized triethoxysilanes (OTES) via Knoevenagel condensation.

Covalently anchored tertiary amine functionalized ionic liquid on silica coated nano-Fe3O4 as a novel, efficient and magnetically recoverable catalyst for the unsymmetrical Hantzsch reaction and Knoevenagel condensation

A novel MNP-supported basic IL catalyst was prepared and used as a magnetically recoverable catalyst for Hantzsch and Knoevenagel condensation.