Current Organic Synthesis - Volume 21, Issue 6, 2024

> Background: Porphyrins are highly conjugated heterocyclic compounds and are found as the backbone of many natural products such as heme and chlorophyll. To improve its biological and optical properties, the functionalization of porphyrin at its β- and meso-position has gained importance in recent years. Objective: The purpose of this review is to describe the Pictet-Spengler method for the incorporation of nitrogenous and biologically important heterocyclic scaffolds such as pyrrolo-/indolo[1,2- a]quinoxaline, pyrrolo[1,2-a]pyrazine, and quinoline at the β- and meso-positions of the porphyrins to increase π-conjugation and improve their biological, optical, and electrochemical properties. Conclusion: This review provides a comprehensive overview of the synthesis of N-heterocyclic extended porphyrins and metalloporphyrins via a modified Pictet-Spengler approach. The synthesized porphyrins were found to be highly conjugated and exhibited improved photophysical properties compared to their parent analogues. Moreover, the review article provided a brief overview of the Pictet-Spengler procedure, including product yields, reaction conditions, photophysical properties of the synthesized products, and potential applications in a variety of fields.

The thiazole derivatives as important members of heterocyclic compounds have attracted much synthetic interest due to their different biological properties. In recent years, studies on the synthesis of morpholine compounds have increased because of the properties of this core. In particular, the hybrid structures in which the thiazole ring is linked to morpholine nuclei in one molecular frame have gained popularity. The presented review is an attempt to summarize a huge volume of data on morpholinothiazoles being a widely studied class of these molecules used in modern organic and medicinal chemistry. The manuscript covers the approaches to the synthesis of the morpholinothiazoles derivatives. The synthetic strategies of the target compounds depend on one-pot or multistage reactions or the transformation of other related heterocycles. Additionally, we covered the biological activities and other applications of certain morpholinothiazoles. The information on these compounds made special consideration of medicinal chemists to yield a combinatorial library and carry out thorough efforts in the search of morpholinothiazoles.

Transition metals catalyzed C-H bond activation reactions have appeared as an emerging field to introduce different functional groups in the inactivated saturated and unsaturated C-H bonds. C-S and C-Se bond constructions in aromatic scaffolds are very interesting due to the important applications of organochalcogen reagents in pharmaceutical chemistry and the material world. The introduction of sulphur or selenium moiety to an inert C-H functionality of an arene under transition metal catalysis has become one of the prime challenges and targets in recent years. In this perspective, various transition metals such as Cu, Ni, Co, Pd, Rh, Ru etc. have been extensively studied. Aromatic arenes owning bearing suitable directing groups appeared as the most promising coupling partners to selectively synthesize differently substituted aryl sulfones and aryl sulfides/selenides. The synthetic strategies were highly convenient owing to the regioselectivity of products, broad substrate scope, mild reaction conditions and excellent functional group tolerance. The current review article comprehensively summarizes the extent of C-S/Se bond formation via transition metal-catalyzed C-H bond activation with the assistance of directing groups to govern the site selectivity.

>Background: Three imine derivatives (1, 2 & 3) have been prepared via condensation reaction of phenyl hydrazine, 2-hydrazino pyridine and 4-methoxy aniline with 4-formyl pyridine. Materials and Methods: Electron impact mass spectrometry (EIMS), proton nuclear magnetic resonance (1H-NMR), ultra violet- visible (UV-Vis) and fourier transform infrared (FTIR) spectroscopy have been utilized for the characterization. The chemosensing properties of [4((2-phenyl hydrazono)methyl) pyridine] (1), [2-(2-(pyridin-4-ylmethylene)hydrazinyl) pyridine] (2) & [4-methoxy-N-yl methylene) aniline] (3) imino bases are explored for the first time in aqueous media. The photophysical properties of chemosensors (1, 2 and 3) were examined by various cations (Na⁺, NH⁴⁺, Ba⁺², Ni⁺², Ca⁺², Hg⁺², Cu⁺², Mg⁺², Mn⁺² and Pd⁺²). Results and Discussion: The chemosensor (1) has shown very selective binding capability with copper ions at low concentration (20 μM) without influence of any other mentioned ions. The maximum complexation was noted with Cu⁺² and 1 at pH (7-7.5). The stoichiometry binding ratio between chemosensor (1) and Cu⁺² was determined by Job’s plot and it is found to be (1:2). Conclusion: Current study explores the use of these Schiff bases for the first time as heterocyclic chemosensors. DPPH radical scavenging, urease enzyme inhibition activities along with molecular docking simulation and density functional theory (DFT) analysis of compounds 1, 2 and 3 were also explored.

>Background: The emergence of drug-resistant bacteria and multidrug-resistant diseases, both of which are associated with high mortality, has posed a serious global health issue. Thiazoles and coumarins were reported as antimicrobial agents. Objective: This research paper aims to describe the synthesis of some novel thiazole derivatives bearing a coumarin residue as antibacterial agents. Methods: The thiazole - coumarin hybrids were synthesized starting from the condensation of 3- acetyl coumarin (1) hydrazine carbothioamide (2) or thisemicarbazide then reacting the resulting products with different p-substituted phenacyl bromides (4a-e), hydrazonoyl chlorides (8a-e), and (11). In vitro antibacterial activity was studied in this work. In addition, molecular docking studies for the new compounds have also been carried out to investigate the binding mode of actions against the target DNA gyrase B. Results: Some of the newly synthesized compounds such as compounds 10b, 7, and 6b showed pronounced activities against Gram (+ve) and Gram (-ve) bacteria compared to a reference antibacterial agent. Compounds 10b, 7, and 6b exhibited the best binding affinity against the target. Conclusion: We could obtain a series of precious hitherto unknown thiazole derivatives with varied antibacterial activities from cheap laboratory-available starting material following rather simple environmentally friendly techniques avoiding the use of hazardous or heavy metal-containing catalysts.