A copper-catalyzed reaction of 3-diazoindolin-2-imines with 2-(phenylamino)ethanols: convenient access to spiro[indoline-3,2′-oxazolidin]-2-imines

3-Diazoindolin-2-imines reacted with chiral 2-(phenylamino)ethanols under copper catalysis to furnish chiral spiro[indoline-3,2′-oxazolidin]-2-imines in good yields with excellent diastereoselectivity.

A novel approach to 5H-pyrazino[2,3-b]indolesviaannulation of 3-diazoindolin-2-imines with 2H-azirines or 5-alkoxyisoxazoles under Rh(ii) catalysis

The first example of rhodium carbenoid-mediated intermolecular annulation of cyclic diazo compounds with azirines and alkoxyisoxazoles is presented.

Facile synthesis of pyrroloindoles via a rhodium(ii)-catalyzed annulation of 3-benzylidene-indolin-2-ones and α-imino carbenes

A novel carbenoid strategy to construct pyrrole-fused indole alkaloids.

Ring-Fused Cyclic Aminals from Tetrahydro-β-carboline-Based Dipeptide Compounds

An acid- and oxidant-promoted intramolecular cyclization of a tetrahydro-β-carboline-based dipeptide has been developed to prepare new indole-fused aminoacetals. This approach involves N-acyliminium formation from readily available precursors and cyclization under mild reaction conditions. The diastereoselectivity in the formation of the products is influenced by the specific substituents of the starting reagents, which has been rationalized analyzing the energy profile of the related reactions and the relative stability of the proposed structures based on DFT computational methods.

Indole diterpenoid natural products as the inspiration for new synthetic methods and strategies

Indole terpenoids comprise a large class of natural products with diverse structural topologies and a broad range of biological activities. Accordingly, indole terpenoids have and continue to serve as attractive targets for chemical synthesis. Many synthetic efforts over the past few years have focused on a subclass of this family, the indole diterpenoids. This minireview showcases the role indole diterpenoids have played in inspiring the recent development of clever synthetic strategies, and new chemical reactions.

Recent progress in organocatalytic asymmetric total syntheses of complex indole alkaloids

Indole and its structural analogues have been frequently found in numerous alkaloids, pharmaceutical products and related materials. The enantioselective construction of these structures allows efficient total synthesis of optically pure indole alkaloids, and hence has received worldwide interest. In the past decade, asymmetric organocatalysis has been recognized as one of the most powerful strategies to create chiral molecules with high levels of stereoselectivity. In particular, organocatalytic asymmetric cascade reactions often occur with multiple bond-breaking and forming events simultaneously or sequentially, leading to the appearance of various straightforward approaches to access core structures for asymmetric total synthesis. This review will summarize recent applications of asymmetric organocatalysis in the enantioselective synthesis of indole alkaloids.

E/Z isomerization, solvatachromism and aggregation-induced emission enhancement of donor–acceptor type oligo(p-phenylene vinylene)s

A donor–acceptor molecule, PICNDSB, with cyclopenta[b]indole as the donor and (1,4-phenylene)bis(3-phenylacrylonitrile) as the acceptor, is designed and synthesized. PICNDSB shows typical aggregation-induced emission characteristics. The photoluminescence quantum yield of PICNDSB in dilute THF was only 0.7% and reaches 51.4% in the solid state. Compared with its analogue CzCNDSB, PICNDSB possesses stronger intramolecular charge transfer properties, as revealed from CV measurements, theoretical calculations, and their fluorescence behaviors. Correspondingly, the relatively more efficient electron-donating terminal group of cyclopenta[b]indole endows the molecule with a much higher two-photon absorption cross section of 1286 GM compared to CzCNDSB (357 GM).

Synthesis of functionalised azepanes and piperidines from bicyclic halogenated aminocyclopropane derivatives

Reductive amination of aldehydes or ketones with suitable dihalogenated bicyclic aminocyclopropanes gives functionalised ring-expanded products in a single step.

Design, selective alkylation and X-ray crystal structure determination of dihydro-indolyl-1,2,4-triazole-3-thione and its 3-benzylsulfanyl analogue as potent anticancer agents

Three sets of substituted indolyl-triazoles were synthesized by the alkylation of 1,2-dihydro-5-(1H-indol-2-yl)-1,2,4-triazole-3-thione with different alkyl halides. The use of pyridine restricted the alkylation to sulfur. Whereas, upon using K₂CO₃, the alkylation exceeded sulfur to one of the remaining triazole nitrogens. The assignment of which nitrogen is alkylated besides sulfur is made for the first time using X-ray analysis of single crystals and 2D NMR which indicated that S-, 2-N-isomers will be preferably formed over the S-, 1-N-isomers. The antiproliferative activity on HEPG-2 and MCF-7 cancer cell lines was tested. The results showed that compound 2a is the most active with an IC50 3.58 μg/mL and 4.53 μg/mL for HEPG-2 and MCF-7 respectively and compound 7 is the least active with an IC₅₀ > 100 μg/mL compared to the standard drug doxorubicin (IC₅₀ 4.0 μg/mL). The interaction of the synthesized compounds with tyrosine kinases, namely, Akt, PI3, and EGFR was also studied using molecular docking simulation to predict their mode of action which will drive future work directions.

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.

Highly enantioselective Pd-catalyzed indole allylic alkylation using binaphthyl-based phosphoramidite-thioether ligands

A new type of phosphoramidite-thioether ligand has been developed for Pd-catalysed asymmetric C-3 allylic alkylation of indoles with excellent yields and enantioselectivities.

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.

Chiral N-1-adamantyl-N-trans-cinnamylaniline type ligands: synthesis and application to palladium-catalyzed asymmetric allylic alkylation of indoles

Chiral P/olefin ligands with C–N bond axial chirality were synthesized and utilized for palladium-catalyzed asymmetric allylic alkylation of indoles.

Diversity Oriented Synthesis of Indoloazepinobenzimidazole and Benzimidazotriazolobenzodiazepine from N(1)-Alkyne-1,2-diamines

A one-pot protocol for the diversity oriented synthesis of two N-polyheterocycles indoloazepinobenzimidazole and benzimidazotriazolobenzodiazepine from a common N(1)-alkyne-1,2-diamine building block is described. The approach involves sequential formation of benzimidazole through cyclocondensation and oxidation, which is followed by the formation of either an azepine ring (through alkyne activation and 6-endo-dig cyclization, 1,2-migration with ring expansion, and re-aromatization), or diazepine and triazole rings through 1,3-dipolar cycloaddition.

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.

Metabolomics-Driven Discovery of a Prenylated Isatin Antibiotic Produced by Streptomyces Species MBT28

Actinomycetes are a major source of antimicrobials, anticancer compounds, and other medically important products, and their genomes harbor extensive biosynthetic potential. Major challenges in the screening of these microorganisms are to activate the expression of cryptic biosynthetic gene clusters and the development of technologies for efficient dereplication of known molecules. Here we report the identification of a previously unidentified isatin-type antibiotic produced by Streptomyces sp. MBT28, following a strategy based on NMR-based metabolomics combined with the introduction of streptomycin resistance in the producer strain. NMR-guided isolation by tracking the target proton signal resulted in the characterization of 7-prenylisatin (1) with antimicrobial activity against Bacillus subtilis. The metabolite-guided genome mining of Streptomyces sp. MBT28 combined with proteomics identified a gene cluster with an indole prenyltransferase that catalyzes the conversion of tryptophan into 7-prenylisatin. This study underlines the applicability of NMR-based metabolomics in facilitating the discovery of novel antibiotics.