Current Organic Synthesis - Volume 20, Issue 5, 2023

The approach of utilizing protecting groups (PGs) in organic chemistry has led to the successful syntheses of an array of useful organic compounds. This strategy has also addressed some of the complexities associated with many organic reactions. These PGs find useful applications in simple and complex reactions that involve the synthesis of large organic compounds such as peptides, and oligosaccharides. The fundamental role of PGs is to prevent undesired reactions that could hinder the progress or completion of such reactions. Ideal PGs must be utilized in this regard to achieve the desired objectives. This review describes the diverse protecting groups found in the literatures, the functional moieties for the protection, deprotection strategies, and their relevant applications in organic synthesis.

Benzazoles (Bz) and derivatives are interesting molecules in medicinal chemistry. Several of these compounds display diverse biological activities; some are still used in clinical applications. In this way, synthetic chemists are interested in developing new procedures to access compounds with the guanidine moiety as 2-aminobenzimidazole (2ABI), Astemizole (antihistaminic), Albendazole (anthelmintic) and Carbendazim (fungicide). The guanidine group, considered a super base bonded to a benzoxazole ring, results in the 2-guanidinobenzazoles (2GBZs), which could modify the biological activity of these heterocycles. On these bases, we prepared this review article, which covers chemical aspects of 2-guanidinobenzoazoles as potential therapeutic agents and summarizes the current knowledge on the mechanism of pharmacological activities such as cytotoxic, inhibition of cell proliferation via angiogenesis and apoptosis. Specifically, it highlights the most recent results of synthetic approaches to 2GBZs with variety of modifications and functionalization with aromatic, carbohydrate, and amino-acid moieties as illustrated on 28 schemes and is concluded with 141 references. Additionally, the format of this interesting review is exclusively designed on specifically classified category of chemical reactions with primary precursors such as o-substituted anilines and 2-aminobenzazoles (2ABZs). This will constitute the important goals and novelty of this paper to facilitate synthetic chemists in the investigation about development of new pharmacophores.

Background: Molecules bearing an active methylene bridge are one of the most fruitful and remarkable precursors that have been incorporated into the synthetic strategy of an assortment of bioactive compounds. Objective: The reactive methylene derivatives have been endowed with multiple reactions, which target biological and medicinal applications and result from their structural diversity and discrete reactivity. Methods: The present report endeavors to synthesize, characterize, and in-vitro evaluate several novel propanoic acids, coumarin, and pyrazole derivatives as antimicrobial and antiproliferative agents. The in-silico molecular docking, physicochemical, pharmacokinetic/ADMET, bioactivity, and drug-likeness predictions were conducted for all the synthesized compounds. Results: The highest docking score is -9.9 and -8.3 kcal/mol, respectively, for compound 9 (azocoumarin) and 13 (acrylic acid derivative) with the target proteins E. coli topoisomerase II, DNA gyrase subunit B and PI3K p110α domain, respectively. Moreover, this study predicts the synthesized molecules that may inhibit the novel COVID-19, obtained through virtual screenings only, where compounds 9, 13, 14, 17, and 19 came to the limelight with good docking scores i.e., more than -8 Kcal/mol. Safety profiling of the most potent compound 9 was utilized against normal cell lines and the hemolytic effect on RBCs. Conclusion: The in-silico ADMET studies of the synthesized compounds revealed moderate to good -likeness, high gastro intestinal (GI) absorption, and inhibiting the Cytochrome CYP2C19 and CYP2C9 and all the derivatives possess non-cancerous nature. The in-vitro screening demonstrated that several of the novel molecules are promising drug candidates. The density functional theory (DFT) theoretical calculations were performed to calculate the energy levels of the FMOs and their energy gaps, dipolemoment, andmolecular electrostatic potential. Such parameters, along with the physicochemical parameters, could be a good tool to confirm biological activity.

Background: Quinoline and its derivatives have been shown to display a wide spectrum of biological properties, especially anticancer activity. Particularly, diverse potent anticancer drugs are based on the 4-phenoxyquinoline skeleton, acting as small-molecules VEGR2 and/or c-Met kinase inhibitors. However, the design of new drugs based on these quinoline derivatives remains a challenge. Up till now, all approaches to 4-phenoxyquinoline skeleton construction do not obey any green chemistry principles. Aims and Objectives: Developing a new, and efficient protocol for the synthesis of potentially bioactive 4-phenoxyquinoline derivatives and benzazole-quinoline-quinoline hybrids from commercially available 4,7-dichloroquinoline and phenol derivatives using microwave energy (MW) in the presence of 1-methyl 3-butylimidazolium hexafluorophosphate. Methods: Neweco-efficient protocol for valuable 7-chloro-4-phenoxyquinolines and their hybrids, which is based on SNAr reaction of 4,7-dichloroquinoline with respective simple phenols and hydroxyaryl- benzazoles under MWenergy in green reaction media, is studied for the first time. Results: We found that among various solvents tested, the ionic liquid 1-methyl 3-butylimidazolium hexafluorophosphate ([bmim][PF6]) favored the SNAr reaction affording phenoxyquinolines in excellent yields (72-82%) in 10 min. The developed protocol allowed to obtain quickly in good yields (48-60%) new diverse benzazole-quinoline hybrids, which are expected to be pharmacologically active. According to the calculated bioactivity scores, new hybrids are potential kinase inhibitors that could be useful in anticancer drug research. Conclusion: We developed for the first time a new green, efficient method to prepare potentially bioactive functionalized 7-chloro-4-phenoxyquinolines and benzazole-quinoline molecules. Good to excellent yields of the quinoline products, use of MW irradiation in ([bmim] [PF6] as a green solvent, and short times of reactions are some of the main advantages of this new protocol.

Objective: This study aimed at developing new methodologies for 1,3-dipolar cycloaddition. Methods: A new series of tricyclic derivatives (13a-d) were synthesized via 1, 3-dipolar cycloaddition of nitrones (8a-c) and (9a-c) using intramolecular cyclisation at the reflux of toluene and radical intramolecular cyclisation in the presence of tributyltin hydride and AIBN as an initiator in benzene, which are two techniques to prepare cycloadducts (11a-d), followed by cleavage of the N-O bond performed using Sml in THF. Results: The structures of these new tricyclic derivatives have been confirmed by Mass, 1H-NMR (1d, 2d), 13C-NMR, and IR spectral data. Conclusion: In summary, we have investigated the possibility of synthesizing some new and straightforward methods to access an A-C-D tricyclic skeleton of morphinans from symmetrical arylcyclohexadienes.

Background: 1,2,3-Triazole-tetrazoles have received substantial attention because of their unique bioisosteric properties and an extraordinarily broad spectrum of biological activity, making them interesting for the drug design, and synthesis of a delightful class of widely investigated heterocyclic compounds. To address major health concerns, it is consequently important to devote ongoing effort to the identification and development of New Chemical Entities (NCEs) as possible anticancer medicines. Methods: We began our initial investigation of the reaction between 5-(azidomethyl)-1H-pyrrolo[ 2,3-b]pyridine and 1-phenyl substituted-5-(prop-2-yn-1-ylthio)-1 H-tetrazole under click chemistry to give the corresponding triazole precursors and screened for their cytotoxicity reported by variations in therapeutic actions of the parent molecule. All of the prepared scaffolds were characterized by proton, carbon resonance spectroscopy, IR, and mass spectral techniques. Results:When tested for in vitro antitumor activity the prepared compounds 7e, 7h had a significant anticancer activity against human adenocarcinoma Hs766T cell line with IC50 = 5.33, 4.92 μg/mL and Hs460 cell line with IC50 = 4.82, 6.15 μg/mL respectively. Final scaffolds 7f, 7h, and 7j acquire the highest potential drug binding scores ΔG = -10.42, -8.80, -9.37 Kcal/, with amino acids residues Ala A:11 (2.195 A° ), Asp A:119 (1.991 A° ), Thr A:58 (1.890 A°), Lys A:16 (1.253 A°), Asp A:38 (2.013 A°), Lys A:117 (2.046 A°) respectively and process Lipinski’s rule of five as good agents for oral bioavailability. Conclusion: The molecular framework for the synthesis of novel Aza indole 1,2,3-triazole scaffolds coupled to tetrazole core was discovered in our study and evaluated for their anticancer activity.