Current Organic Chemistry - Volume 23, Issue 24, 2019

Bicyclic compounds derived from pyrazine and aromatic five-membered heterocycles including thiophene, furan and pyrrole show various biological and pharmacological properties, such as anti-inflammatory, antiviral, antitumor, antioxidant, antimycobacterial, and cytostatic activities. In many cases, it has been demonstrated that there are more potent cytostatic and cytotoxic agents against human tumor cell lines, leukemia, colon cancer, central nervous system cancer, melanoma, ovarian cancer, prostate cancer and breast cancer. They are also useful precursors for the large scale preparation of inorganicorganic hybrid solar cells, suitable acceptors for the synthesis of low-band gap polymers. They use ligands for serotoninergic 5-HT7 receptor and are effective in neurogical and psychiatric diseases, antimalarial, neuroleptic and cardiovascular. The absence of any useful review concerning the chemistry and synthesis of the above-mentioned heterocyles encouraged us to underscore the recent advances in chemistry and synthetic approaches leading to the preparation of thienopyrazines, pyrrolopyrazines and furopyrazines since 1990.

Keeping in view the ever growing demand and application of the organic small molecules based sensitive and selective fluorescence detection strategies for the trace metallic ions in the ecosystem, fluids and inside intracellular media, the present literature survey was focused on the recent development on the organic skeleton based fluorescence sensor for the zinc ion as Zn2+ is the second most abundant transition metal after iron in human body. The prominent organic based skeletons introduced during the past three years for zinc detection including azine, ((Z)-N´-(quinolin-2-ylmethylene)furan-2- carbohydrazide), nicotinohydrazide, hydrazone, phenolic cage, 4-methyl-2,6-bis[(E)-(2- (4-phenylthiazol-2-yl)hydrazono)methyl]phenol, bipyridine, N-(quinoline-8-yl)pyridine-2- carboxamide, anthracene, Schiff base, salen, helicene, Carbon Quantum Dots (CDs) functionalized with Calix[4]arene, coumarin, diaminomaleonitrile, peptide, hydroxypyrazole, salicylhydrazide were discussed in detail with particular focus on ligand-zinc complexation mechanism, UV-visible and fluorescence investigation, spectral variation, isosbestic emergence, limit of detection, ligand-zinc binding stoichiometry, association/binding constant and applications for intracellular tracing of metallic contamination via confocal fluorescence microscopic studies. Among the several discussed optical probes, rhodamine and fluorescein based material offer appreciable sensitivity, exhibiting drawback of pH sensitivity. Probes based on these ligands triggered “turn-on” signal even in the absence of metals upon fluctuation in pH e.g., acidic in former case and basic in the latter case. Hydroxypyrazole-based ligands also showed detection signal variation by switching the pH of the solution. Schiff base and bipyridyl scaffold were found to possess good ligation toward the several transition metals. Azole, oxazole, thiazole, thiadiazole, hydrazine carboxamide and hydrazine carbothiomide are the bioactive molecules exhibiting good cell viability and probes designed by using these central nucleus might be better to invest for intracellular imaging. Symmetrical heterocyclic cage like probe showed better chelation toward several transition metals and it is a good choice for the design and development of sensor for simultaneous detection of several transition metals.

Pyrano- and dipyranocoumarins are classes of naturally occurring organic compounds with very interesting biological activities. This review focuses on the synthetic strategies for the synthesis of pyranocoumarins and dipyranocoumarins and the biological properties of those compounds. The synthesis involves the formation of the pyran ring, at first, from a coumarin or the formation of pyranone moiety from an existing pyran. Pyranocoumarins and dipyranocoumarins present anti-HIV, anti-cancer, neuroprotective, antidiabetic, antibacterial, antifungal, anti-inflammatory activities. Especially khellactones and calanolides are usually potent and selective in anti-HIV activity. Decursin and decursinol derivatives are effective as anticancer, neuroprotective, antidiabetic, antibacterial, and antifungal agents.

Coumarins (2H-chromen-2-ones) are heterocyclic compounds of wide scientific interest due to their important biological and pharmaceutical properties such as antitumor, antioxidant, anti-inflammatory and antimicrobial activities as well as enzymatic inhibitors related to neurodegenerative diseases. Due to their structural variability, this compound class has been attracting considerable interest in the natural products and synthetic organic chemistry areas. Coumarins and their derivatives have been prepared by a variety of methods, including Perkin, Wittig and Reformatsky reactions, Pechmann and Knoevenagel condensations, and Claisen rearrangement, among others. In the present review we report the different synthetic methods used in the preparation of coumarin derivatives exploited in the last ten years (from 2008 to 2018), regarding the research demand for new structural scaffolds.

The present study provides an overview of the chemistry and biological importance of the cationic chalcophene derivatives (furans, thiophenes and selenophenes). The summarized literature survey includes synthetic methods, reactivity and biological activities of aryl/hetarylchalcophenes that have been reported mainly from 2001 to 2019 focusing on monochalcophenes. A discussion demonstrating the proposed mechanisms of some interesting synthetic routes and linking structure features to biological activities is presented. These classes of compounds including cationic chalcophenes possess antiproliferative, antimicrobial and antiprotozoal activities. This review highlights recent advances for arylchalcophene derivatives and may contribute to the design and structure optimization of new chalcophene derivatives in the future.