Reaction of 3/2-formylindoles with TOSMIC: formation of indolyloxazoles and stable indolyl primary enamines

Natural and synthetic 5-(3'-indolyl)oxazoles: Biological activity, chemical synthesis and advanced molecules

5-(3'-Indolyl)oxazole moiety is a privileged heterocyclic scaffold, embedded in many biologically interesting natural products and potential therapeutic agents. Compounds containing this scaffold, whether from natural sources or synthesized, have demonstrated a wide array of biological activities. This has piqued the interest of synthetic chemists, leading to a large number of reported synthetic approaches to 5-(3'-indolyl)oxazole scaffold in recent years. In this review, we comprehensively overviewed the different biological activities and chemical synthetic methods for the 5-(3'-indolyl)oxazole scaffold reported in the literatures from 1963 to 2024. The focus of this study is to highlight the significance of 5-(3'-indolyl)oxazole derivatives as the lead compounds for the lead discovery of anticancer, pesticidal, antimicrobial, antiviral, antioxidant and anti-inflammatory agents, to summarize the synthetic methods for the 5-(3'-indolyl)oxazole scaffold. In addition, the reported mechanism of action of 5-(3'-indolyl)oxazoles and advanced molecules studied in animal models are also reviewed. Furthermore, this review offers perspectives on how 5-(3'-indolyl)oxazole scaffold as a privileged structure might be exploited in the future.

Sequential annulation and isomerisation reaction of 3-acylmethylidene oxindoles with Huisgen zwitterions and synthesis of 5-(3-oxindolyl)oxazoles

Herein, we report a facile synthesis of 5-(3-oxindolyl)oxazole derivatives via a sequential annulation and isomerisation reaction of 3-acylmethylidene oxindoles with in situ generated Huisgen zwitterions (HZs) from PPh3 and azodicarboxylates. This reaction exhibits good functional group tolerance with 30 examples of structurally diverse products prepared with moderate to good efficiencies (up to 88% yield), thus providing a generally applicable route to the biologically important 5-(3-indolyl)oxazole structural motifs. Key to the success of this sequential one-pot strategy is the utilization of DBU as a base to promote the isomerisation process of the corresponding intermediate annulation products.

Streptonaphthyridine A, a new naphthyridine analogue with antiproliferative activity against human glioma cells from mariana trench-associated actinomycete Streptomyces sp. SY2111

A new naphthyridine analogue, named streptonaphthyridine A (1), together with eight previously reported compounds (2-9), were isolated from a Mariana Trench sediment-associated actinomycete Streptomyces sp. SY2111. Planar structure of streptonaphthyridine A was established by analyses of its HRESIMS data and extensive NMR spectra and its absolute configuration was determined by a combination of single crystal X-ray diffraction analysis and optical rotation calculations. Streptonaphthyridine A (1) had antiproliferative activity against human glioma U87MG and U251 cells with IC₅₀ values of 7.9 ± 1.3 and 13.4 ± 2.7 µM, respectively, and the known compound monomethylsulochrin (7) showed more potent activity with IC₅₀ values of 0.6 ± 0.1 µM for U87MG cells and 0.1 ± 0.0 µM for U251 cells.

Recent Advances in the Synthesis of Oxazole-Based Molecules via van Leusen Oxazole Synthesis

Oxazole compounds, including one nitrogen atom and one oxygen atom in a five-membered heterocyclic ring, are present in various biological activities. Due to binding with a widespread spectrum of receptors and enzymes easily in biological systems through various non-covalent interactions, oxazole-based molecules are becoming a kind of significant heterocyclic nucleus, which have received attention from researchers globally, leading them to synthesize diverse oxazole derivatives. The van Leusen reaction, based on tosylmethylisocyanides (TosMICs), is one of the most appropriate strategies to prepare oxazole-based medicinal compounds. In this review, we summarize the recent advances of the synthesis of oxazole-containing molecules utilizing the van Leusen oxazole synthesis from 1972, aiming to look for potential oxazole-based medicinal compounds, which are valuable information for drug discovery and synthesis.

An efficient synthesis and antifungal evaluation of natural product streptochlorin and its analogues

Streptochlorin, a small indole alkaloid isolated from marine Streptomyces sp., exhibits a wide range of potent biological activities. An efficient and economic synthetic protocol for streptochlorin has been developed and validated, 4 steps from indole in a total yield of 45%, and further applied for the synthesis of its analogues. Biological testing showed that most of the target compounds exhibited potential antifungal activity in the primary assays, especially compounds 6, 7 and 9c were the most active ones, representing effective activity against the phytopathogenic fungi screened in preliminary test and might be explored for the study of mode of action in the future.

Facile One-Pot Green Synthesis of Some New Annulated Polyfunctionalised 2-Amino-4H-Pyrans

The reaction of cyclic CH-acids such as 5,5-dimethyl-1,3-cyclohexanedione, 1,3-cyclohexanedione, 4-hydroxy-6-methyl-2 H-pyran-2-one, or 4-hydroxycumarin with dialkyl acetylene dicarboxylates in the presence of tosylmethyl isocyanide (TosMIC) in polyethylene glycol (PEG-300) leads to new annulated highly functionalised 2-amino-4 H-pyrans at room temperature in good yields.

A Van Leusen deprotection-cyclization strategy as a fast entry into two imidazoquinoxaline families

A concise synthesis of two pharmacologically relevant classes of molecules possessing the imidazoquinoxaline core is reported. The protocol involves use of 1,2-phenylenediamines and glyoxylic acid derivatives, namely ethyl glyoxylate or benzylglyoxamide, along with tosylmethylisocyanides in a microwave-assisted Van Leusen three-component condensation. Subsequent unmasking (Boc removal) of an internal amino-nucleophile promotes deprotection and cyclization that take place either spontaneously in a one-pot fashion to give 8 or upon acidic treatment under microwave irradiation after isolation of the imidazole intermediate to give 11. Of note, a tricyclic framework is hence assembled by means of a rapid and straightforward method with a high bond-forming efficiency.

Synthesis and biological evaluation of achiral indole-substituted titanocene dichloride derivatives

Six new titanocene compounds have been isolated and characterised. These compounds were synthesised from their fulvene precursors using Super Hydride (LiBEt₃H) followed by transmetallation with titanium tetrachloride to yield the corresponding titanocene dichloride derivatives. These complexes are bis-[((1-methyl-3-diethylaminomethyl)indol-2-yl)methylcyclopentadienyl] titanium (IV) dichloride (5a), bis-[((5-methoxy-1-methyl,3-diethylaminomethyl)indol-2-yl)methylcyclopentadienyl] titanium (IV) dichloride (5b), bis-[((1-methyl,3-diethylaminomethyl)indol-4-yl)methylcyclopentadienyl] titanium (IV) dichloride (5c), bis-[((5-bromo-1-methyl)indol-3-yl)methylcyclopentadienyl] titanium (IV) dichloride (5d), bis-[((5-chloro-1-methyl)indol-3-yl)methylcyclopentadienyl] titanium (IV) dichloride (5e), and bis-[((5-fluoro-1-methyl)indol-3-yl)methylcyclopentadienyl] titanium (IV) dichloride (5f). All six titanocenes 5a–5f were tested for their cytotoxicity through MTT-based in vitro tests on CAKI-1 cell lines using DMSO and Soluphor P as solubilising agents in order to determine their IC₅₀ values. Titanocenes 5a–5f were found to have IC₅₀ values of 10 (±2), 21 (±3), 29 (±4), 140 (±6), and 450 (±10) μM when tested using DMSO.

Synthesis and fungicidal activity of novel pimprinine analogues

A simple and efficient synthetic protocol for 5-(3-indolyl)-oxazoles has been developed and further used to synthesize a series of novel analogues of natural product pimprinine. All new compounds were identified by (1)H NMR, high resolution mass spectrometry, and the structures of 10 and 18o were further confirmed by X-ray crystallographic diffraction analysis. Bioassay conducted at Syngenta showed that several of the synthesized compounds exhibited fungicidal activity. Compounds 10, 17, 18 h, 18o, 19 h, 19i and 19 l all showed effective control of three out of the seven tested phytopathogenic fungi at the highest rate screened. Compounds 17 and 19 h in particular showed activity against the four pathogens screened in artificial media; Pythium dissimile, Alternaria solani, Botryotinia fuckeliana and Gibberella zeae.