Rapid access to α-carbolines via a one-pot tandem reaction of α,β-unsaturated ketones with 2-nitrophenylacetonitrile and the anti-proliferative activities of the products

Novel access to α-carbolines with biological applications

In recent years, the 9H-pyrido[2,3-b]indole nuclei, also named α-carboline which is found in many organic compounds such as natural products, pharmaceuticals, and materials, have intensively stimulated the research of new synthetic pathways. After a brief report published in 2015 describing novel accesses and biological applications of α-carbolines, this update reports between 2015 and 2023 on the emergence of original syntheses to this heterocyclic nucleus. Examples representing these processes are described and the biological activities of α-carbolines are mentioned when they have been prepared for therapeutic purposes.

Comprehensive review of α-carboline alkaloids: Natural products, updated synthesis, and biological activities

α-carboline (9H-pyrido[2,3-b]indole), contains a pyridine ring fused with an indole backbone, is a promising scaffold for medicinal chemistry. In recent decades, accumulating evidence shows that α-carboline natural products and their derivatives possess diverse bioactivities. However, hitherto, there is no comprehensive review to systematically summarize this important class of alkaloids. In this perspective, this paper represents the first review to provide a comprehensive description of α-carbolines including natural products, updated literature of synthesis, and their diverse biological activities. Their biological activities including antitumor, anti-microbial, anti-Alzheimer’s disease, anti-atherosclerosis, and antioxidant activities were hilighted. And the targets and the main structure activity relationships (SARs) will be presented. Finally, challenges and future directions of this class of compounds will be discussed. This review will be helpful in understanding and encouraging further exploration for this group of alkaloids.

Discovery of novel α-carboline derivatives as glycogen synthase kinase-3β inhibitors for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a chronic and progressive neurodegenerative disease, characterized by irreversible cognitive impairment, memory loss, and behavioral disturbances, ultimately resulting in death. The critical roles of glycogen synthase kinase-3β (GSK-3β) in tau pathology have also received considerable attention. Based on molecular docking studies, a series of novel α-carboline derivatives were designed, synthesized, and evaluated as GSK-3β inhibitors for their various biological activities. Among them, compound ZCH-9 showed the most potent inhibitory activity against GSK-3β, with an IC₅₀ value of 1.71 ± 0.09 µM. The cytotoxicity assay showed that ZCH-9 had low cytotoxicity toward the cell lines SH-SY5Y, HepG2, and HL-7702. Moreover, Western blot analysis indicated that ZCH-9 effectively inhibited hyperphosphorylation of the tau protein in okadaic acid-treated SH-SY5Y cells. The binding mode between ZCH-9 and GSK-3β was analyzed and further clarified throughout the molecular dynamics simulations. In general, these results suggested that the α-carboline-based small-molecule compounds could serve as potential candidates targeting GSK-3β for the treatment of AD.

Benzannulation strategies for the synthesis of carbazoles, indolocarbazoles, benzocarbazoles, and carbolines

This review presents a critical and authoritative analysis of several exciting benzannulation approaches developed in the past decade for the construction of carbazoles, indolocarbazoles, benzocarbazoles, and carbolines.

Regioselective synthesis of substituted thiazoles via cascade reactions from 3-chlorochromones and thioamides

An efficient and regioselective strategy to synthesize substituted thiazoles via a cascade reaction in an environmentally benign medium was developed.

One Pot and Metal-Free Approach to 3-(2-Hydroxybenzoyl)-1-aza-anthraquinones

Herein, a direct strategy to synthesize 3-(2-hydroxybenzoyl)-1-aza-anthraquinones with excellent efficiency, mild conditions, and benign functional group compatibility was reported. A variety of 3-formylchromone compounds were employed as compatible substrates and this protocol gave the 3-(2-hydroxybenzoyl)-1-aza-anthraquinone derivatives in good to excellent yields without inert gas and expensive transition metal catalysts. Some compounds displayed good anti-proliferative activities.

Convenient Synthesis of 6,7,12,13-Tetrahydro-5H-Cyclohepta[2,1-b:3,4-b']diindole Derivatives Mediated by Hypervalent Iodine (III) Reagent

Bisindolyl alkaloids represent a large family of natural and synthetic products that display various biological activities. Among the bisindole compounds, 6,7,12,13-tetrahydro-5H-cyclohepta[2,1-b:3,4-b']diindoles have received little attention. Only two methods have been developed for the construction of the 6,7,12,13-tetrahydro-5H-cyclohepta[2,1-b:3,4-b']diindole scaffold thus far, including the classical Fischer indole synthesis conducted by reacting indole-fused cycloheptanone and hydrazines, and the condensation reaction to build the seven-membered ring. Here, we report for the first time a new route to synthesize 6,7,12,13-tetrahydro-5H-cyclohepta[2,1-b:3,4-b']diindoles through intramolecular oxidative coupling of 1,3-di(1H-indol-3-yl)propanes in the presence of PIFA, DDQ and TMSCl with moderate to excellent yields.

Regioselective switching approach for the synthesis of α and δ carboline derivatives

A metal-free protocol for accessing both α and δ-carboline derivatives, starting from a common indolylchalcone oxime ester precursor is reported.

Dual targeting of microtubule and topoisomerase II by α-carboline derivative YCH337 for tumor proliferation and growth inhibition

Both microtubule and topoisomerase II (Top2) are important anticancer targets and their respective inhibitors are widely used in combination for cancer therapy. However, some combinations could be mutually antagonistic and drug resistance further limits their therapeutic efficacy. Here we report YCH337, a novel α-carboline derivative that targets both microtubule and Top2, eliciting tumor proliferation and growth inhibition and overcoming drug resistance. YCH337 inhibited microtubule polymerization by binding to the colchicine site and subsequently led to mitotic arrest. It also suppressed Top2 and caused DNA double-strand breaks. It disrupted microtubule more potently than Top2. YCH337 induced reversible mitotic arrest at low concentrations but persistent DNA damage. YCH337 caused intrinsic and extrinsic apoptosis and decreased MCL-1, cIAP1 and XIAP proteins. In this aspect, YCH337 behaved differently from the combination of vincristine and etoposide. YCH337 inhibited proliferation of tumor cells with an averaged IC₅₀ of 0.3 μM. It significantly suppressed the growth of HT-29 xenografts in nude mice too. Importantly, YCH337 nearly equally killed different-mechanism-mediated resistant tumor cells and corresponding parent cells. Together with the novelty of its chemical structure, YCH337 could serve as a promising lead for drug development and a prototype for a dual microtubule/Top2 targeting strategy for cancer therapy.

One-pot transition-metal-free cascade synthesis of thieno[2,3-c]coumarins from chromones

A one-pot transition-metal-free, base-mediated synthesis of a novel series of functionalized thieno[2,3-c]coumarins has been developed through a cascade reaction from chromones.

Synthesis of Functionalized Chromeno[2,3-b]pyrrol-4(1H)-ones by Silver-Catalyzed Cascade Reactions of Chromones/Thiochromones and Isocyanoacetates

A novel and convenient approach to the synthesis of chromeno[2,3-b]pyrrol-4(1H)-ones has been developed. Furthermore, the method involves a facile silver-catalyzed cascade cyclization reaction including an intramolecular C-O bond formation. The silver salt acts as a key promoter.

Efficient Pd-catalyzed domino synthesis of 1-phenyl-1H-indol-2-amine and 5-amino-indolo[1,2-a]quinazoline derivatives

An efficient and practical one-pot domino synthesis of 1-phenyl-1H-indol-2-amine and 5-amino-indolo[1,2-a]quinazoline derivatives from readily available 2-(2-bromophenyl)acetonitriles was developed. The overall protocol involves a Buchwald-Hartwig type coupling and a base-promoted intramolecular nucleophilic reaction. The reaction scope, advantages and limitations are discussed.

Efficient synthesis of α- and δ-carbolines by sequential Pd-catalyzed site-selective C–C and twofold C–N coupling reactions

Two concise and efficient approaches were developed for the synthesis of α- and δ-carboline derivatives.

Synthesis of substituted pyrroles using a silver-catalysed reaction between isocyanoacetates/benzyl isocyanides and chromones

A novel synthetic strategy to construct substituted-pyrroles has been developed through silver-catalysed cycloadditions of isocyanides with chromones.