Baylis–Hillman Reaction of 1-Formyl-β-carboline: One-Step Synthesis of the Canthin-6-one Framework by an Unprecedented Cascade Cyclization Reaction

Morita–Baylis–Hillman reaction of 3-formyl-9H-pyrido[3,4-b]indoles and fluorescence studies of the products

β-Carboline is a privileged class of the alkaloid family and is associated with a broad spectrum of biological properties. 3-Formyl-9H-pyrido[3,4-b]indole is a such potent precursor belonging to this family which can be tailored for installing diversity at various positions of β-carboline to generate unique molecular hybrids of biological importance. The present work is a step towards this and assimilates the results related to the exploration of 3-formyl-9H-β-carbolines for the synthesis of β-carboline C-3 substituted MBH adducts followed by evaluation of their fluorescent characteristic. The effect of contact time, solvent system, concentration and substituents was also studied during investigation of fluorescence properties of these derivatives.

In(OTf)3 assisted synthesis of β-carboline C-3 tethered imidazo[1,2-a]azine derivatives

Synthesis of β-carboline based natural products and synthetic derivatives is one of the frontier areas of research owing to their medicinal properties.

Natural product inspired design and synthesis of β-carboline and γ-lactone based molecular hybrids

β-Carboline and γ-lactone moieties have been selected by nature as privileged scaffolds and display a wide range of pharmacological properties. Following nature, we envisaged the preparation of new β-carboline and γ-lactone based molecular hybrids incorporating both the pharmacophores. In this regard, a water-assisted In-mediated environmentally benign and easy to execute single-step tandem Barbier type allylation-lactonisation process has been devised in order to afford the targeted molecular architectures. It is anticipated that aqueous medium plays the key role in allylation as well as in the subsequent lactonisation process for the diastereo-selective synthesis of these conjugates. It is believed that water drives the reaction pathway through dual activation, it increases the electrophilic character of formyl and ester functionalities and simultaneously enhances the nucleophilic potential of the hydroxyl group to facilitate the in situ intramolecular condensation. Importantly, during this synthetic strategy no column chromatographic purification was required at any stage.

Synthesis of S-(-)-5,6-Dihydrocanthin-4-ones via a Triple Cooperative Catalysis-Mediated Domino Reaction

An enantioselective synthesis of S-(-)-5,6-dihydrocanthin-4-ones via a triple cooperative catalysis-mediated domino reaction having a broad substrate scope is reported. The reaction between substituted 1-formyl-9H-β-carbolines and terminal alkynes in the presence of catalytic amounts of Jorgensen-Hayashi catalyst, copper iodide, and Hunig base proceeded via a multicascade route, affording the title compounds in good yields and excellent ees with interesting mechanistic features. These compounds were assessed for in vitro antiplasmodial activity against P. falciparum strains. Additionally, 5,6-dihydrocanthin-4-ones are demonstrated to be a versatile precursor to different fused β-carboline derivatives via simple synthetic transformations.

Fruitful Decades for Canthin-6-ones from 1952 to 2015: Biosynthesis, Chemistry, and Biological Activities

In this review, more than 60 natural canthin-6-one alkaloids and their structures are considered. The biosynthesis, efficient and classic synthetic approaches, and biological activities of canthin-6-one alkaloids, from 1952 to 2015, are discussed. From an analysis of their structural properties and an investigation of the literature, possible future trends for canthin-6-one alkaloids are proposed. The information reported will be helpful in future research on canthin-6-one alkaloids.

Metal-free 1,3-dipolar cycloaddition approach towards the regioselective synthesis of β-carboline and isoxazole based molecular hybrids

Nature has nourished β-carboline and isoxazole derivatives as privileged scaffolds and consequently they are ubiquitously found in alkaloids isolated from various sources.

In(OTf)3 catalysed an expeditious synthesis of β-carboline–imidazo[1,2-a]pyridine and imidazo[1,2-a]pyrazine conjugates

β-Carboline containing alkaloids are ubiquitously present in Nature, while an imidazo[1,2-a]pyridine nucleus is incorporated in various synthetic commercial drugs and biologically previliged moieties.

When Indolizine Meets Quinoline: Diversity-Oriented Synthesis of New Polyheterocycles and Their Optical Properties

Fluorescence-based technologies play a pivotal role in various biomedical applications. Here we report an efficient route to a new class of fluorophores, indolizino[3,2-c]quinolines, via the oxidative Pictet-Spengler cyclization strategy. The condensation of several 2-methylpyridines with 2-bromo-2'-nitroacetophenone allowed for the rapid assembly of indolizines with a 2-nitrophenyl group at the C2 position. The subsequent reduction of the nitro group under mild conditions followed by oxidative Pictet-Spengler cyclization with various aryl aldehydes in the presence of a catalytic amount of FeCl3 furnished the indolizino[3,2-c]quinolines in good overall yields. We also examined the photophysical properties of this new series of polyheterocyclic compounds. Several indolizino[3,2-c]quinolines were found to have unique and desirable optical properties, suggesting that these compounds may be suitable for use as prospective fluorescent probes in aqueous systems.

Synthesis of β-Carboline-Based N-Heterocyclic Carbenes and Their Antiproliferative and Antimetastatic Activities against Human Breast Cancer Cells

A series of novel β-carboline-based N-heterocyclic carbenes was prepared via Mannich reaction between methyl 1-(dimethoxymethyl)-9H-pyrido[3,4-b]indole-3-carboxylate, formaldehyde, and primary amines. All compounds were evaluated for their antiproliferative activity using human breast cancer and lung cancer cell lines. Three compounds, 3c, 3j, and 3h, were discovered to display IC50 less than 10 μM against human breast cancer MDA-MB-231 cells at 24 h of treatment. Pharmacologically these compounds lead to G2/M phase cell cycle arrest and induction of cellular apoptosis by triggering intrinsic apoptotic pathway through depolarization of mitochondrial membrane potential and activation of caspases. At lower concentrations, these compounds also showed antimigratory and antiinvasive effects against highly metastatic human breast cancer MDA-MB-231 cells via aberration of MAP-kinase signaling and by the inhibition of matrix metalloproteinases. However, these analogues lack in vivo effect in mouse model which may be attributed to their strong affinity to HSA that was investigated spectroscopically with compound 3h.

Novel β-carboline–quinazolinone hybrid as an inhibitor of Leishmania donovani trypanothione reductase: Synthesis, molecular docking and bioevaluation

Novel β-carboline–quinazolinone hybrids are able to inhibit Leishmania donovani TR (LdTR). Molecular docking studies to investigate possible binding sites were performed.

Synthesis of novel β-carboline based chalcones with high cytotoxic activity against breast cancer cells

A series of novel β-carboline based chalcones was synthesized and evaluated for their cytotoxic activity against a panel of human cancer cell lines. Among them we found that two of the compounds 7c and 7d, showed marked anti-proliferative activity in a panel of solid tumor cell lines with highest effect in breast cancer. The compounds 7c and 7d showed an IC50 of 2.25 and 3.29 μM, respectively against human breast cancer MCF-7 cell line. Further, the compound 7c markedly induced DNA fragmentation and apoptosis in breast cancer cells.

An efficient combinatorial synthesis of allocolchicine analogues via a triple cascade reaction and their evaluation as inhibitors of insulin aggregation

A controlled cascade: A divergent, diastereoselective and efficient one-pot synthesis of allocolchicinoids via a cascade Suzuki-Michael addition-Carbocyclization sequence is described. The utility of the compounds as possible inhibitors of insulin aggregation is also presented.

Progress in the synthesis of canthine alkaloids and ring-truncated congeners

The canthines represent a fairly large subclass of β-carboline alkaloids, with the first members described 75 years ago. Over the last 60 years, many members of the parent compound, canthin-6-one (1), have been isolated from various plant sources, principally the Rutaceae and Simaroubaceae families, and recently from fungi. Structures isolated from these sources have been the subject of total synthesis, which continues to the present day. This review gives a broad overview of synthetic approaches to canthines over a 30-year period from 1982 to 2012 and summarizes recent reports on the synthesis of less well known ring-truncated congeners. These include C-ring-truncated ("ABD", 2) and A-ring-truncated ("BCD", 3) ring systems, which are providing new scaffolds for potentially useful therapeutic applications.

Design and synthesis of Pictet-Spengler condensation products that exhibit oncogenic-RAS synthetic lethality and induce non-apoptotic cell death

A series of Pictet-Spengler condensation derivatives (tetrahydro-β-carbolines) was designed, synthesized and evaluated for lethality against a panel of seven cancer cell lines. Seven compounds (2a, 13, 20, 21, 27, 29 and 34) showed lethality in at least five cell lines. Among these, compound 27 showed a unique selectivity towards oncogenic-RAS expressing BJ-TERT/LT/ST/RAS(V12) tumor cells, compared to non-transformed BJ-TERT cells. Further investigation revealed that 27 induces cell death without activation of caspases. This represents a useful new probe of non-apoptotic cell death and oncogenic-RAS synthetic lethality.

Three-step synthesis of Ethyl Canthinone-1-carboxylates from ethyl 4-bromo-6-methoxy-1,5-naphthyridine-3-carboxylate via a Pd-catalyzed Suzuki-Miyaura coupling and a Cu-catalyzed amidation reaction [corrected]

Ethyl canthin-6-one-1-carboxylate (1b) and nine analogues 1c-k were prepared from readily prepared ethyl 4-bromo-6-methoxy-1,5-naphthyridine-3-carboxylate (2b) via a three-step non-classical approach that focused on construction of the central pyrrole (ring B) using Pd-catalyzed Suzuki-Miyaura coupling followed by Cu-catalyzed C-N coupling. Furthermore, treatment of the ethyl canthinone-1-carboxylate 1b with NaOH in DCM/MeOH (9:1) gave the canthin-6-one-1-carboxylic acid (6) in high yield. All compounds are fully characterized.

Aplidiopsamine A, an antiplasmodial alkaloid from the temperate Australian ascidian, Aplidiopsis confluata

A polyaromatic alkaloid, aplidiopsamine A was isolated from the temperate Australian ascidian, Aplidiopsis confluata, and its structure was determined from interpretation of mass, 1D and 2D NMR spectra. Aplidiopsamine A is the first alkaloid to possess the tricyclic aromatic substructure 3H-pyrrolo[2,3-c]quinoline conjugated to an adenine. Aplidiopsamine A exhibited significant inhibition of growth of chloroquine resistant and sensitive strains of the malaria parasite, Plasmodium falciparum, and minimal toxicity toward human cells.

Two-step total syntheses of canthin-6-one alkaloids: new one-pot sequential Pd-catalyzed Suzuki-Miyaura coupling and Cu-catalyzed amidation reaction

Canthin-6-one (1) and nine analogues including the naturally occurring 9-methoxycanthin-6-one (2) and amaroridine (3) are prepared rapidly and in high yields via a convergent "non-classical" strategy that focuses on construction of the central ring B. The strategy relies on concomitant Pd-catalyzed Suzuki-Miyaura C-C coupling followed by a Cu-catalyzed C-N coupling that can be achieved either stepwise or in a new one-pot protocol starting from the appropriate 8-bromo-1,5-naphthyridine.