Cage-Monoterpenoid Quinoline Alkaloids with Neurite Growth Promoting Effects from the Fruits of Melodinus yunnanensis

Natural 3,4-Dihydro-2(1H)-quinolinones - part III: biological activities

Natural products have played a crucial role in drug discovery, but their development is hindered by challenges such as inadequate availability and complex synthesis methods. However, both natural and synthetic compounds that have the core structure of 3,4-dihydro-2(1H)-quinolinone, also known as 2-oxo-1,2,3,4-tetrahydroquinoline (2O-THQ), display a diverse array of effects in both central and peripheral tissues, with some showing therapeutic potential in treating various disorders. Despite the significance of this family of compounds, the current literature lacks comprehensive coverage of their biological functions. This article aims to address this gap by extensively reviewing the biological activities of 2O-THQ alkaloids from diverse organisms and exploring their potential to serve as a source of innovative bioactive natural products.

Copper-catalyzed dehydrogenative cyclization/alkenylation towards dihydroquinolinones

An efficient copper-catalyzed one-pot sequential synthesis of alkenylated quinolinyl dihydroquinolinones is reported, utilizing ketones, 1,3-cyclohexanediones, and benzyl alcohols via dehydrogenative cyclization, followed by alkenylation. This highly straightforward method provides a mild and environmentally friendly approach, and scalable reactions are carried out without generating side products. Furthermore, a plausible reaction mechanism is proposed based on control-experiment studies and reaction monitoring via1H NMR analysis. In addition, the photophysical behavior of the synthesized products showed various responses in the absorption and emission spectra. Upon further examination, compound 4F was found to have acidochromic properties, leading to noticeable colour changes.

Casuattimines A-N, fourteen new Lycopodium alkaloids from Lycopodiastrum casuarinoides with Cav3.1 channel inhibitory activity

Two new dimeric Lycopodium alkaloids, casuattimines A and B (1 and 2), along with twelve previously undescribed Lycopodium alkaloids, casuattimines C-N (3-14), and eight known Lycopodium alkaloids, were isolated from Lycopodiastrum casuarinoides. Casuattimines A and B (1 and 2) are the first two ether-linked Lycopodium alkaloid dimers. Casuattimines C and D (3 and 4) are unique Lycopodium alkaloids characterized by a long fatty acid chain. Structural elucidation was achieved through HRESIMS, NMR, and electronic circular dichroism (ECD) calculations. In addition, the absolute configurations of compounds 7, 13, and 14 were determined by single crystal X-ray diffraction. Compounds 1, 2, and 4 demonstrated notable Cav3.1 channel inhibitory activities presenting IC50 values of 10.75 ± 1.02 μM, 9.33 ± 0.79 μM, and 7.14 ± 0.86 μM, respectively. The dynamics of compound 4 against the Cav3.1 channel and preliminary structure-activity relationships of these active Lycopodium alkaloids were also discussed.

Neurotrophic Natural Products

Neurotrophins (NGF, BDNF, NT3, NT4) can decrease cell death, induce differentiation, as well as sustain the structure and function of neurons, which make them promising therapeutic agents for the treatment of neurodegenerative disorders. However, neurotrophins have not been very effective in clinical trials mostly because they cannot pass through the blood-brain barrier owing to being high-molecular-weight proteins. Thus, neurotrophin-mimic small molecules, which stimulate the synthesis of endogenous neurotrophins or enhance neurotrophic actions, may serve as promising alternatives to neurotrophins. Small-molecular-weight natural products, which have been used in dietary functional foods or in traditional medicines over the course of human history, have a great potential for the development of new therapeutic agents against neurodegenerative diseases such as Alzheimer's disease. In this contribution, a variety of natural products possessing neurotrophic properties such as neurogenesis, neurite outgrowth promotion (neuritogenesis), and neuroprotection are described, and a focus is made on the chemistry and biology of several neurotrophic natural products.

Diverse aspidosperma-type alkaloids from the leaves of Tabernaemontana bovina with anti-hepatoma activity

Seventeen undescribed Aspidosperma-type alkaloids (ASPs), along with nine known ones were isolated from the leaves of Tabernaemontana bovina. Taberbovermines A and B were assigned to tabersonine-type with a contracted A- and E-ring, respectively. Taberbovermine C was attributed to tabersonine without D ring. These structures of the ASPs were established on the basis of comprehensive spectroscopic data, electronic circular dichroism calculations and X-ray diffraction. The summaries of structure-activity relationship of tabersonine class were discussed based on hepatoma cells screening.

Structure elucidation of an aspidofractinine-type monoterpene indole alkaloid from Melodinus reticulatus

The structure and complete NMR assignments of aspidoreticulofractine, an aspidofractinine N-oxide, are reported. Its structure was elucidated based on a combination of spectroscopic techniques including 1D and 2D NMR, high-resolution mass spectrometry, and electronic circular dichroism.

Monoterpenoid indole alkaloid adducts and dimers from Melodinus fusiformis

Eight unprecedented monoterpenoid indole alkaloid (MIA) adducts and dimers, melofusinines A-H (1-8), and three undescribed melodinus-type MIA monomers, melofusinines I-K (9-11), together with six putative biogenetic precursors were isolated from the twigs and leaves of Melodinus fusiformis Champ. ex Benth. Compounds 1 and 2 are unusual hybrid indole alkaloids incorporating an aspidospermatan-type MIA with a monoterpenoid alkaloid unit via C-C coupling. Compounds 3-8 feature the first MIA dimers constructed through an aspidospermatan-type monomer and a rearranged melodinus-type monomer with two different types of couplings. Their structures were elucidated by spectroscopic data, single crystal X-ray diffraction, and calculated electric circular dichroism spectra analysis. In addition, dimers 5 and 8 showed significant neuroprotection effects on MPP ⁺-injured primary cortical neurons.

Visible-Light-Induced 1,7-Enyne Dicyclization: Synthesis of Ester-Substituted Benzo[j]phenanthridines

A novel alkoxycarbonyl-radical-triggered cascade cyclization of 1,7-enynes, with alkyloxalyl chlorides as the ester units, for the synthesis of benzo[j]phenanthridines is described. The reaction conditions exhibit excellent compatibility with a broad range of alkoxycarbonyl radical sources and realize the installation of an ester group in the polycyclic compound. This radical cascade cyclization reaction features excellent functional group tolerance, mild reaction conditions, and good to excellent yields.

A review on natural products with cage-like structure

Natural products with diverse structures and significant biological activities are essential sources of drug lead compounds, and play an important role in the research and development of innovative drugs. Cage-like compounds have various structures and are widely distributed in nature, especially caged xanthones isolated from Garcinia genus, paeoniflorin and its derivatives isolated from Paeonia lactiflora Pall, tetrodotoxin (TTX) and its derivatives, and so on. In recent years, the development and utilization of cage-like compounds have been a research hotspot in chemistry, biology and other fields due to their special structures and remarkable biological activities. In this review, we mainly summarized the cage-like compounds with various structures found and isolated from natural drugs since 1956, summarized its broad biological activities, and introduced the progress in the biosynthesis of some compounds, so as to provide a reference for the discovery of more novel compounds, and the development and application of innovative drugs.

Biology of quinoline and quinazoline alkaloids

Quinoline and quinazoline alkaloids, two important classes of N-based heterocyclic compounds, have attracted scientific and popular interest worldwide since the 19th century. More than 600 compounds have been isolated from nature to date. To build on our two prior reviews, we reexamined the promising molecules described in previous reports and provided updated literature on novel quinoline and quinazoline alkaloids isolated over the past 5 years. This chapter reviews and discusses 205 molecules with a broad range of bioactivities, including antiparasitic and insecticidal, antibacterial and antifungal, cardioprotective, antiviral, anti-inflammatory, and other effects. This survey should provide new clues or possibilities for the discovery of new and better drugs from the original naturally occurring quinoline and quinazoline alkaloids.

Synthesis of Dihydroquinolinone Derivatives via the Cascade Reaction of o-Silylaryl Triflates with Pyrazolidinones

Presented herein is a novel synthesis of dihydroquinolinone derivatives through an unprecedented cascade reaction of o-silylaryl triflates with pyrazolidinones. Mechanistically, the formation of the title products is believed to involve a cascade procedure including in situ formation of aryne and its addition with pyrazolidinone followed by N-N bond cleavage and intramolecular C-C bond formation/annulation. Compared with literature methods for the synthesis of dihydroquinolinones, this protocol has advantages such as multistep transformations accomplished in one pot, broad substrate scope, mild reaction conditions, and good tolerance of diverse functional groups. In addition, the products thus obtained demonstrated significant in vitro antiproliferative activity in selected human cancer cell lines.

Classifying natural products from plants, fungi or bacteria using the COCONUT database and machine learning

Natural products (NPs) represent one of the most important resources for discovering new drugs. Here we asked whether NP origin can be assigned from their molecular structure in a subset of 60,171 NPs in the recently reported Collection of Open Natural Products (COCONUT) database assigned to plants, fungi, or bacteria. Visualizing this subset in an interactive tree-map (TMAP) calculated using MAP4 (MinHashed atom pair fingerprint) clustered NPs according to their assigned origin ( https://tm.gdb.tools/map4/coconut_tmap/ ), and a support vector machine (SVM) trained with MAP4 correctly assigned the origin for 94% of plant, 89% of fungal, and 89% of bacterial NPs in this subset. An online tool based on an SVM trained with the entire subset correctly assigned the origin of further NPs with similar performance ( https://np-svm-map4.gdb.tools/ ). Origin information might be useful when searching for biosynthetic genes of NPs isolated from plants but produced by endophytic microorganisms.

Monoterpenoid indole alkaloids with potential neuroprotective activities from the stems and leaves of Melodinus cochinchinensis

A chemical study on the stems and leaves of Melodinus cochinchinensis resulted in the isolation and identification of a new monoterpenoid indole alkaloid, melodicochine A (1), together with seven known monoterpenoid indole alkaloids (2-8). The chemical structure of 1 was elucidated on the basis of extensive spectral data analyses and the known compounds were identified by comparing their experimental spectral data with the reported data in the literature. All isolated indole alkaloids were evaluated for their neuroprotective effects against 6-hydroxydopamine induced cell death in human neuroblastoma SH-SY5Y cells in vitro. Monoterpenoid indole alkaloids 1-8 exhibited notable neuroprotective effects with EC₅₀ values in range of 0.72 ± 0.06 to 17.89 ± 0.16 μM.

Diastereoselective construction of cage-like and bridged azaheterocycles through dearomative maximization of the reactive sites of azaarenes

A highly diastereoselective multicomponent dearomative multifunctionalization of N-alkyl activated azaarenes with 1,5-diazapentadienium salts has been developed to access structurally rigid and synthetically challenging cage-like and bridged azaheterocycles.

Hot off the Press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as longisglucinol A from Hypericum longistylum.