The first synthesis of clausenamine-A and cytotoxic activities of three biscarbazole analogues against cancer cells

Syntheses of Carbazoles by Photosensitized Electrocyclization of Triarylamines. Effect of Inductive Electron-Withdrawing Groups on the Photocyclization

The acetone-sensitized [6π]-electrocyclization of unsubstituted, mono-, and disubstituted triarylamines (TAAs: substituents H, CH₃, CH₃O, Cl, CnF₂n+1; n=1, 3, 4, 6, 8, 10) under 310 nm light led to the formation of endo- and exo-carbazoles in high yields; particularly, TAAs substituted with inductive electron-withdrawing groups (Cl, CnF2n+1) exhibit remarkable endo-selectivity towards cyclization. For TAAs substituted with both inductive electron- withdrawing and donating groups, the photocyclization towards endo carbazoles is dictated by the presence of the electron-withdrawing groups. Chemical yields (%), quantum yields of conversion (φR), apparent cyclization rate constants (kcyc), and Hammett plots correlations are illustrated for all substituted TAAs in acetone. Photophysical studies reveal that TAAs substituted with resonance electron-withdrawing groups (OAc, NO2, CHO) do not undergo electrocyclization in acetone at 310 nm due to formation of charge-transfer states that vastly deactivate the triplet reactive manifold, paralleling the behavior observed in MeCN as solvent. Absorption and emission spectra, Stokes shifts, and singlet excited state energies are illustrated for substituted TAAs and carbazoles. In-silico studies support the high stereoselectivity observed for the preferred endo- photosensitized [6π]-electrocyclization of Cl- and perfluoroalkyl-substituted TAAs.

Preparation of Carbazoles Involving 6π-Electrocyclization, Photoredox-, Electrochemical-, and Thermal Cyclization Reactions: Mechanistic Insights

Carbazole is a heterocyclic motif that can be found in a diverse array of natural and unnatural products displaying a wide range of biological and physiological properties. Furthermore, this heterocycle is part of electronic materials like photoconducting polymers and organic optoelectronic materials owing to its excellent photophysical characteristics. Consequently, the development of synthetic strategies for carbazole scaffolds holds potential significance in biological and material fields. In this regard, a variety of preparation methods has been developed to exploit their efficient and distinct formation of new C-C and C-heteroatom bonds under mild conditions and enabling broad substrate diversity and functional group tolerance. Therefore, this review focuses on the synthesis of a set of carbazole derivatives describing a variety of methodologies that involve direct irradiation, photosensitization, photoredox, electrochemical and thermal cyclization reactions.

Update on novel synthetic approaches towards the construction of carbazole nuclei: a review

The carbazole scaffold is a significant entity in organic compounds due to its variety of biological and synthetic applications. Traditionally, carbazole skeletons have been synthesized either via the Grabe-Ullman method, Clemo-Perkin method or Tauber method. With the passage of time, these methods have been modified and explored to accomplish the synthesis of target compounds. These methods include hydroarylations, C-H activations, annulations and cyclization reactions mediated by a variety of catalysts to construct carbazole-based compounds. This brief review article intends to provide recent updates on important methodological developments reported for the synthesis of carbazole nuclei covering 2019-2023.

Dimeric Drugs

This review intends to summarize the structures of an extensive number of symmetrical-dimeric drugs, having two monomers linked via a bridging entity while emphasizing the large versatility of biologically active substances reported to possess dimeric structures. The largest number of classes of these compounds consist of anticancer agents, antibiotics/antimicrobials, and anti-AIDS drugs. Other symmetrical-dimeric drugs include antidiabetics, antidepressants, analgesics, anti-inflammatories, drugs for the treatment of Alzheimer's disease, anticholesterolemics, estrogenics, antioxidants, enzyme inhibitors, anti-Parkisonians, laxatives, antiallergy compounds, cannabinoids, etc. Most of the articles reviewed do not compare the activity/potency of the dimers to that of their corresponding monomers. Only in limited cases, various suggestions have been made to justify unexpected higher activity of the dimers vs. the corresponding monomers. These suggestions include statistical effects, the presence of dimeric receptors, binding of a dimer to two receptors simultaneously, and others. It is virtually impossible to predict which dimers will be preferable to their respective monomers, or which linking bridges will lead to the most active compounds. It is expected that the extensive number of articles summarized, and the large variety of substances mentioned, which display various biological activities, should be of interest to many academic and industrial medicinal chemists.

A concise Friedländer/Buchwald–Hartwig approach to the total synthesis of quindoline, a bioactive natural indoloquinoline alkaloid, and toward the unnatural 10-methylquindoline

Friedländer and Buchwald–Hartwig reactions were used to achieve an efficient total synthesis of quindoline and a new synthesis of the unnatural 10-methylquindoline. DFT calculations were employed to explain the outcome of a failed key transformation.

Anticancer carbazole alkaloids and coumarins from Clausena plants: A review

Pharmaceutical research has focused on the discovery and development of anticancer drugs. Clinical application of chemotherapy drugs is limited due to their severe side effects. In this regard, new naturally occurring anticancer drugs have gained increasing attention because of their potential effectiveness and safety. Fruits and vegetables are promising sources of anticancer remedy. Clausena (family Rutaceae) is a genus of flowering plants and includes several kinds of edible fruits and vegetables. Phytochemical and pharmacological studies show that carbazole alkaloids and coumarins from Clausena plants exhibit anticancer activity. This review summarizes research progresses made in the anticancer properties of plants belonging to Clausena; in particular, compounds with direct cytotoxicity, cell cycle arrest, apoptosis induction, and immune potentiation effects are discussed. This review reveals the potential use of plants from Clausena in preventing and treating cancer and provides a basis for development of relevant therapeutic agents.

Efficient and simple synthesis of 6-aryl-1,4-dimethyl-9H-carbazoles

A synthetic method for the preparation of 6-aryl-1,4-dimethyl-9H-carbazoles involving a palladium catalyzed coupling reaction of 1,4-dimethyl-9H-carbazole-6-boronic acids and (hetero)aryl halides is described.

Biarylic biscarbazole alkaloids: occurrence, stereochemistry, synthesis, and bioactivity

The structurally and pharmacologically intriguing but stereochemically initially disregarded small class of biarylic biscarbazole alkaloids is presented, starting with an introduction of the different structural patterns found in nature. For the construction of the biaryl bond, mainly biomimetic oxidative coupling reactions were used, as shown for the natural products bismurrayaquinone-A, bis-2-hydroxy-3-methylcarbazole, clausenamine-A, and murrastifoline-F. For most of these compounds, a resolution of the respective atropo-enantiomers succeeded either directly, by high-performance liquid chromatography by HPLC on a chiral phase, or via atropo-diastereomers, after derivatization with a chiral auxiliary. The absolute configurations of the pure enantiomers were assigned by comparison of experimental (CD) spectra with those quantum chemi-cally calculated, or, for atropo-diastereomeric derivatives, by means of ROESY investigations and X-ray crystallography. Ullmann-type coupling conditions were also found to be feasible for the construction of the 2,2'-biscarbazole core, necessitating a completely regioselective 2-bromination protocol. The first atroposelective synthesis of such a basic target structure was achieved by application of the "lactone methodology," giving rise to an atropisomeric ratio of 85 : 15. Some of the biscarbazole alkaloids and their derivatives were found to have interesting bioactivities, and for the first time, the natural atropo-enantiomeric ratio in the plants was determined for one of these compounds, murrastifoline-F.