Marine indole alkaloids containing an 1-(indol-3-yl)ethane-1,2-diamine fragment (Review)

Boron Trifluoride Etherate Promoted Regioselective 3-Acylation of Indoles with Anhydrides

An efficient, high-yielding and scalable procedure for the regioselective 3-acylation of indoles with anhydrides promoted by boron trifluoride etherate under mild conditions was reported. This novel protocol provided a simple way to prepare 3-(benzofuran-2-yl) indole in three steps.

Recent Advances on Marine Alkaloids from Sponges

Alkaloids from marine secondary metabolites have received extensive attention from pharmacists in recent years. Miscellaneous alkaloids derived from marine sponges possessed various pharmacological activities including cytotoxicity, antimicrobial, antioxidant, and so on. Herein, we summarized 149 marine alkaloids from sponges based on their structures and bioactivities reported from 2015 to 2020 and analyzed the production environment of marine sponges with rich alkaloids. Moreover, we discussed biosynthesis routes of pyrrole and guanidine alkaloids from marine sponges Agelas and Monanchora. This article will be beneficial for future research on drugs from marine natural products.

1-Benzyl-2-(thien-2-yl)-4,5-dihydro-1H-imidazole

Imidazolines are a valuable class of organic compounds, namely ligands of imidazoline receptors, chiral ligands for metal catalysis, synthetic intermediates. The title compound has been prepared through a modified procedure, employing N-benzylethylenediamine and thiophene-2-carbaldehyde under the action of N-bromosuccinimide (NBS) in dichloromethane (DCM) in a good 78% yield.

Synthesis and Cytotoxic Activity of Novel Mono- and Bis-Indole Derivatives: Analogues of Marine Alkaloid Nortopsentin

BACKGROUND

The oceans cover more than 70% of the earth's surface, which represents over 95% of the biosphere. Therefore, oceans provide a wealth of marine invertebrates, especially sponges, ascidians, bryozoans and molluscs that produce structurally unique bioactive metabolites such as alkaloids. The bioactive scaffolds of marine alkaloids exhibit cytotoxic activities against human cancer cell lines.

OBJECTIVE

To prepare analogues of the marine alkaloid nortopsentin [having 2,4-bis(3'- indolyl)imidazole scaffold] as cytotoxic agents via structural modification of the core imidazole ring and one of the side indole rings.

METHODS

Four series of nortopsentin analogues were synthesized in which the imidazole ring was replaced by pyrazole, pyrido[2,3-d]pyrimidinone and pyridine rings. Furthermore, one of the side indole rings was replaced by substituted phenyl moiety. The target compounds were tested for their in vitro cytotoxic activity against HCT-116 cell-line and the most potent compound was subjected to further investigation on its effect on HCT-116 cell cycle progression.

RESULTS

The cytotoxic screening of the synthesized compounds revealed that bis-indolylpyridinedicarbonitriles 8a-d exhibited the most potent cytotoxic activity with IC₅₀=2.6-8.8 μM. Compound 8c was further tested by flow cytometry analysis to explore its effect on HCT-116 cell cycle progression that, in turn, indicated its anti-proliferative effect.

CONCLUSION

Marine-derived bis-indole alkaloids (nortopsentins) have emerged as a new class of indole-based antitumor agents. The design of new analogues involved several modifications in order to obtain more selective and potent cytotoxic agents. Indole derivatives bearing a pyridine core displayed more potent cytotoxic activity than those containing pyrido[2,3-d]pyrimidin-4(1H)-one moiety.

Insilico analysis of marine indole alkaloids for design of adenosine A2A receptor antagonist

Neurological disease is the disease associated with most of geriatric population in the world. The diseases like Alzheimer's disease and Parkinson's disease are associated with the change in the life style in current era. Treatment of these diseases normally focused on the agents which can able to manipulate the neurotransmitter release, so it is associated with severe side effects. Adenosine receptors are the upcoming targets for the inflammatory as well as neurological diseases as agents like istradefylline are in the clinical use. Marine natural products are the rich source of the valuable drug like substances, number marine alkaloids are known for their ability to pass blood brain barrier (BBB) which is major hurdle in the neurological drug discovery. Here, we report the virtual screening of some marine alkaloids for adenosine 2 receptor binding potential. Results indicated topsentin C, 6'-debromohamacanthin, 6-hydroxydiscodermindole and discodermindole are having excellent binding affinity towards the adenosine 2A receptor than other selected alkaloids.Communicated by Ramaswamy H. Sarma.

Marine Alkaloid 2,2-Bis(6-bromo-3-indolyl) Ethylamine and Its Synthetic Derivatives Inhibit Microbial Biofilms Formation and Disaggregate Developed Biofilms

The antimicrobial activity of the marine bisindole alkaloid 2,2-bis(6-bromo-3-indolyl) ethylamine (1) and related synthetic analogues (compounds 2–8) against target microorganisms was investigated by Minimum Inhibitory Concentration (MIC) determination. Compound 1 showed the greatest antimicrobial activity with the lowest MIC (8 mg/L) against Escherichia coli, Staphylococcus aureus, and Klebsiella pneumoniae, while the derivatives exhibited higher MICs values (from 16 to 128 mg/L). Compounds 1, 3, 4, and 8, the most active ones, were then tested against E. coli, S. aureus, K. pneumoniae, and Candida albicans during biofilms formation as well as on 24 h developed biofilms. The natural alkaloid 1 inhibited the biofilm formation of all the tested microorganisms up to 82.2% and disaggregated biofilms of E. coli, S. aureus, K. pneumoniae, and C. albicans after 30 min of contact, as assessed by viable plate count and crystal violet (CV) staining (optical density at 570 nm). Synthetic derivatives 3, 4, and 8 displayed anti-biofilm activity toward individual bacterial populations. This study highlights the potential of marine bisindole alkaloid 1 as anti-biofilm agent and shows, through a preliminary structure activity relationship (SAR), the importance of halogens and ethylamine side chain for the antimicrobial and antibiofilm activities of this bisindole series.

Synthesis of Indoles via Electron-Catalyzed Intramolecular C-N Bond Formation

A new protocol for the preparation of N-substituted indole-3-carboxylates has been developed. The key C-N bond formation occurs under transition-metal-free conditions employing a t-BuOK/DMF system without special initiators or additives. Across a number of substrates, indoles were afforded in yields higher or comparable to those obtained under transition-metal-catalyzed conditions. While demonstrating high functional group tolerance, new conditions are particularly attractive for manufacturing halogenated indoles that cannot be made in a pure form using other metal-based catalytic methods.

Dragmacidins G and H, Bisindole Alkaloids Tethered by a Guanidino Ethylthiopyrazine Moiety, from a Lipastrotethya sp. Marine Sponge

LCMS analysis of the extract and a cytotoxicity assay of the HPLC fractions generated from a small-scale extract of a Lipastrotethya sp. marine sponge demonstrated the presence of bisindole alkaloids that were associated with the cytotoxic activity. Two bisindole alkaloids tethered by a guanidino ethylthiopyrazine moiety, dragmacidins G (1) and H (2), were isolated, and their structures were assigned by analysis of the MS and NMR data. They showed moderate cytotoxic activity against HeLa cells.

Marine natural products

This review covers the literature published in 2013 for marine natural products (MNPs), with 982 citations (644 for the period January to December 2013) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1163 for 2013), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Concise synthesis of didebromohamacanthin A and demethylaplysinopsine: addition of ethylenediamine and guanidine derivatives to the pyrrole-amino acid diketopiperazines in oxidative conditions

Oxidative nucleophilic addition of ethylenediamine and guanidine derivatives to pyrrole-amino acid diketopiperazines was shown to provide substituted 5,6-dihydro-2(1H)-piperazinones, quinoxalinones, and 2-aminoimidazolones. On the basis of this methodology, a concise approach to natural products didebromohamacanthin A and demethylaplysinopsine has been demonstrated.