Copper(II) catalyzed aromatization of tetrahydrocarbazole: An unprecedented protocol and its utility towards the synthesis of carbazole alkaloids

Tetrahydrocarbazoles incorporating 5-arylidene-4-thiazolinones as potential antileukemia and antilymphoma targeting tyrosine kinase and tubulin polymerase enzymes: Design, synthesis, structural, biological and molecular docking studies

Finding effective and selective anticancer agents is a top medical priority due to high clinical treatment demand. However, current anticancer agents have serious side effects and resistance development remains a big concern. This creates an urgent need for new multitarget drugs that could solve these problems. Tetrahydrocarbazoles and 5-arylidene-4-thiazolinones have always attracted researchers for their multifaced anticancer activities and the possibility to be easily derivatized. Thereby, herein we report the combination of the two scaffolds to provide compounds 9a-j and 10a-j that were fully characterized and their tautomeric form was confirmed by crystal structure. 9a-j and 10a-j wereassessedfor invitro antiproliferative activityusing SRB assay against a panel of seven human cancer cell lines with doxorubicin as the standard. The results revealed that the cell lines derived from leukemia (Jurkat) and lymphoma (U937) are the most sensitive. Compounds 9d, 10e, 10g, and 10f revealed the highest potency (IC50 = 3.11-11.89 μM) with much lower effects on normal lymphocytes cell line (IC50 > 50 µM). The results show that modifications at 6th position of the THC and the nature of the substituent at the arylidene moiety affect the activity. To exploit the mode of action, 9d, 10e, 10f, and 10g were evaluated as VEGFR-2 and EGFR inhibitors. 10e is the most potent (IC50 0.26 and 0.14 μM) against both enzymes. It also induced G0-G1-phase cell cycle arrest and apoptosis. While 10g exhibited higher potency (IC50 9.95 μM) than vincristine (IC50 15.63 μM) against tubulin. A molecular docking study was carried out to understand the interactions between 10e, 10g and their targets. This study reveals 10e and 10g as possible candidates for developing multitarget anticancer agents against leukemia and lymphoma.

Phenalenyl-Based Photocatalyst for Bioinspired Oxidative Dehydrogenation of N-Heterocycles and Benzyl Alcohols

The environmental benefits of molecular oxygen as the oxidizing agent in oxidation reactions that synthesize fine chemicals cannot be overstated. Increased interest in developing robust photocatalysts is stimulated by the fact that the current photocatalytic transformation boom has made previously inaccessible synthetic approaches possible. Motivated by enzymatic catalysis, employing a reusable phenalenyl-based photocatalyst, we have successfully developed oxidative dehydrogenation utilizing molecular oxygen as a greener oxidant. Under photoinduced oxidative dehydrogenation conditions, different types of saturated N-heterocycles and alcohols were successfully dehydrogenated. The versatility of this bioinspired protocol is demonstrated by the fact that a wide variety of N-heteroaromatics, such as quinoline, carbazole, quinoxaline, acridine, and indole derivatives, as well as aldehydes and ketones, were successfully synthesized. Detailed mechanistic studies validate the proposed mechanism. Fluorescence lifetime and CV experiments revealed the crucial role of water on the efficiency of the reaction. The present protocol also provides chemoselectivity and scalability, leading to superior results and allowing for the functionalization of bioactive molecules at a late stage in a sustainable manner.

Trends in carbazole synthesis - an update (2013-2023)

The interest of scientists in the carbazole core has risen steadily over the last 30 years, particularly over the last decade given its presence in several active pharmaceutical ingredients, functional materials and a wide range of biologically active natural products. The continuous development of more efficient, more (regio-)selective and "greener" methodologies to access the carbazole core is thus imperative. This review compares and evaluates synthetic strategies towards the carbazole core that have been reported since 2013, with a focus on their applicability towards the total synthesis of carbazole-containing natural products.

Anodic Dehydrogenative Aromatization of Tetrahydrocarbazoles Leading to Carbazoles

Anodic oxidation-promoted aromatization of 1,2,3,4-tetrahydrocarbazoles was achieved. Nitrogen-protected tetrahydrocarbazoles could be converted to the corresponding carbazoles with the use of bromide as a mediator. LiBr, an inexpensive bromide source, allowed for efficient transformation in the presence of AcOH.

Electrochemical Annulation of Indole-Tethered Alkynes Enabling Synthesis of Exocyclic Alkenyl Tetrahydrocarbazoles

An electrochemical sulfonylation-triggered cyclization reaction of indole-tethered terminal alkynes with sulfinates as sulfonyl sources has been developed, which affords exocyclic alkenyl tetrahydrocarbazoles in good chemical yields. This reaction features convenient operation and tolerates a wide scope of substrates with a variety of electronically and sterically diverse substituents. Furthermore, high E-stereoselectivity is observed for this reaction, which provides an efficient method for the preparation of functionalized tetrahydrocarbazole derivatives.

The Synthesis of 2,2-BIS(1-INDOL-3-YL)Acenaphthylene-1(2)-Ones Using Nanocatalysis: Fluorescent Sensing for Cu2+ Ions

2,2-bis(1H-indol-3-yl)acenaphthylene-1(2H)-ones were synthesised by the reaction of acenaphthenequinone and 2 equivalents of indole using Fe3O4@SiO2@Si-Pr-NH-CH2CH2NH2 as the basic magnetic nanocatalyst, assembled under greener and sustainable conditions in high purity and yields. Furthermore, the photoluminescence properties of 2,2-bis(2-methyl-1H-indol-3-yl)acenaphthylene-1(2H)-one were exploited for the sensing of copper ions in the mixed solvent systems comprising H2O and CH3CN in excitation wavelength at 410 nm with a detection limit of 9.5 ∙ 10–6 M.

In Situ Grignard Metalation Method for the Synthesis of Hauser Bases

The in situ Grignard Metalation Method (iGMM) is a straightforward one-pot procedure to quickly produce multigram amounts of Hauser bases R2 N-MgBr which are valuable and vastly used metalation reagents and novel electrolytes for magnesium batteries. During addition of bromoethane to a suspension of Mg metal and secondary amine at room temperature in an ethereal solvent, a smooth reaction yields R2 N-MgBr under evolution of ethane within a few hours. A Schlenk equilibrium is operative, interconverting the Hauser bases into their solvated homoleptic congeners Mg(NR2 )2 and MgBr2 depending on the solvent. Scope and preconditions are studied, and side reactions limiting the yield have been investigated. DOSY NMR experiments and X-ray crystal structures of characteristic examples clarify aggregation in solution and the solid state.

Recent advances in the synthesis of N-heteroarenes via catalytic dehydrogenation of N-heterocycles

Bio-active molecules having N-heteroarene core are widely used for numerous medicinal applications and as lifesaving drugs. In this direction, dehydrogenation of partially saturated aromatic N-heterocycles shows utmost importance for the synthesis of heterocycles. This feature article highlights the recent advances, from 2009 to April 2021, on the dehydrogenation of N-heteroaromatics. Notable features considering the development of newer catalysis for dehydrogenations are: (i) approaches based on precious metal catalysis, (ii) newer strategies and catalyst development technology using non-precious metal-catalysts for N-heterocycles having one or more heteroatoms, (iii) Synthesis of five or six-membered N-heterocycles using photocatalysis, electrocatalytic, and organo-catalytic approaches using different homogeneous and heterogeneous conditions' (iv) metal free (base and acid-promoted) dehydrogenation along with I₂, N-hydroxyphthalimide (NHPI) and bio catalyzed miscellaneous examples have also been discussed, (v) mechanistic studies for various dehydrogenation reactions and (vi) synthetic applications of various bio-active molecules including post-drug derivatization are discussed.

Exploiting an intramolecular Diels-Alder cyclization/dehydro-aromatization sequence for the total syntheses of ellipticines and calothrixin B

The tetracyclic and pentacyclic skeletons of pyrido and quinolinocarbazole alkaloids have been synthesized via a unified strategy. The prominent key step involved a Diels-Alder intramolecular cyclization/dehydro-aromatization sequence. From these carbazole-lactam cores, linear syntheses have been developed for ellipticines and calothrixin B.

A phenanthrene[9,10-d]imidazole-phenol-based fluorescent probe combining ESIPT and AIE for the “turn-on” detection of Cu2+ with green-emission and improved Stokes’ shift, and its application

The “turn-on” probe PIA(OH)-Py responds to Cu2+ in living cells and can determine the concentration of Cu2+ in blood samples.

Construction of Unusual Indole-Based Heterocycles from Tetrahydro-1H-pyridazino[3,4-b]indoles

Herein, we report the successful syntheses of scarcely represented indole-based heterocycles which have a structural connection with biologically active natural-like molecules. The selective oxidation of indoline nucleus to indole, hydrolysis of ester and carbamoyl residues followed by decarboxylation with concomitant aromatization of the pyridazine ring starting from tetrahydro-1H-pyridazino[3,4-b]indole derivatives lead to fused indole-pyridazine compounds. On the other hand, non-fused indole-pyrazol-5-one scaffolds are easily prepared by subjecting the same C2,C3-fused indoline tetrahydropyridazines to treatment with trifluoroacetic acid (TFA). These methods feature mild conditions, easy operation, high yields in most cases avoiding the chromatographic purification, and broad substrate scope. Interestingly, the formation of indole linked pyrazol-5-one system serves as a good example of the application of the umpolung strategy in the synthesis of C3-alkylated indoles.