Copper-mediated C-O/C-N Bond Formation: A Facile Synthesis of 3-Amidocoumarin, 3-amidoazacoumarin and N-Aeroylindole Derivatives

Three different heterocyclic systems, 3-amidocoumarins 1, 3-amidoazacoumarins 11, and N-benzoylindol-2-carboxamides 12 were synthesized based on the strikingly different selectivity of copper-mediated C-O/C-N bond formation from azlactones under conventional heating conditions. The results demonstrated that the stereochemistry of the double bond dictated the outcome of the products. The microwave irradiation played an important role in the isomerization of the trisubstituted olefin leading to the formation of 3-amidocoumarins 1 and 3-amidoazacoumarins 11. Compounds 1h, 1i, and 1l showed promising to good cytotoxic activity against a panel of cancer cell lines including HepG2 (hepatoblastoma) and MOLT-3 (T-lymphoblast acute lymphoblastic leukemia).

An Expeditious Modular Hybrid Strategy for the Diversity-Oriented Synthesis of Lamellarins/Azalamellarins with Anticancer Cytotoxicity

A modular hybrid strategy has been developed for the diversity-oriented synthesis of lamellarins/azalamellarins. The common pentacyclic pyrrolodihydroisoquinoline lactone/lactam core was formed via the Michael addition/ring closure (Mi-RC) and the copper(I) thiophene-2-carboxylate (CuTC)-catalyzed C-O/C-N Ullmann coupling. Subsequent direct functionalization at C1, DDQ-mediated C5═C6 oxidation, and global deprotection of all benzyl-type O- and N-protecting groups furnished the desired lamellarins/azalamellarins. The late-stage functionalization at C1 provided a handle to accommodate a wider scope of functional groups as they need to tolerate only the DDQ oxidation and global deprotection. Moreover, with the C1-H pyrrole as the late-stage common intermediate, it was also possible to divergently exploit not only its nucleophilic nature to react with some electrophilic species but also some transition-metal-catalyzed cross-coupling reactions (via the intermediacy of the C1-iodopyrrole) to incorporate diversity at this position. Overall, this strategy simplifies the preparation of lamellarins/azalamellarins; including the Mi-RC, these C1-structurally diverse analogues could be prepared efficiently in 6-7 steps from the easily accessed 1-acetoxymethyldihydroisoquinoline and β-nitrocinnamate. Some selected azalamellarins were evaluated for their inhibitory effect against HeLa cervical cancer cells. An acute induction of intrinsic apoptosis was detected and may lead to growth suppression of or cytotoxicity against cancer cells.

Roles of autophagy in relation to mitochondrial stress responses of HeLa cells to lamellarin cytotoxicity

As a promising class of bioactive marine pyrrole alkaloids, lamellarins reportedly act on multiple targets to suppress the vitality of various cancer cell lines. Nevertheless, an in-depth understanding of the molecular mechanisms governing their cytotoxicity is still in demand. Here we report that while activating intrinsic apoptosis, up to 5 μM of lamellarins and their lactam-containing analogs, azalamellarins, also induced mitochondrial stress responses and autophagy in HeLa cervical cancer cells. Detailed characterization of the mitochondria in the treated cells revealed shifted abundance of the two optic atrophy protein 1 (Opa1) isoforms, disturbed morphology, and dissipated membrane potential, leading to PTEN-induced kinase-1 (PINK1) and microtubule-associated protein 1 light chain 3-II (LC3-II) accumulation as a molecular signature of mitophagy. Furthermore, an acute treatment with lamellarins also modulated cellular autophagy flux as evidenced by elevated LC3-II levels, LC3 puncta formation, and p62 degradation. Surprisingly, clustered regularly interspaced short palindromic repeats (CRISPR)-based suppression of autophagy transiently affected the number of apoptotic cells induced by these compounds. Our findings illustrate the potential of these alkaloids for further development into prospective anti-cancer agents.

Marine Pyrrole Alkaloids

Nitrogen heterocycles are essential parts of the chemical machinery of life and often reveal intriguing structures. They are not only widespread in terrestrial habitats but can also frequently be found as natural products in the marine environment. This review highlights the important class of marine pyrrole alkaloids, well-known for their diverse biological activities. A broad overview of the marine pyrrole alkaloids with a focus on their isolation, biological activities, chemical synthesis, and derivatization covering the decade from 2010 to 2020 is provided. With relevant structural subclasses categorized, this review shall provide a clear and timely synopsis of this area.

Synthesis and evaluation of azalamellarin N and its A-ring-modified analogues as non-covalent inhibitors of the EGFR T790M/L858R mutant

Azalamellarin N, a synthetic lactam congener of the marine natural product lamellarin N, and its A-ring-modified analogues were synthesized and evaluated as potent and non-covalent inhibitors of the drug-resistant epidermal growth factor receptor T790M/L858R mutant. An in vitro tyrosine kinase assay indicated that the inhibitory activities of the synthetic azalamellarin analogues were higher than those of the corresponding lamellarins. The azalamellarin analogue bearing two 3-(dimethylamino)propoxy groups at C20- and C21-positions exhibited the highest activity and selectivity against the mutant kinase [IC₅₀ (T790M/L858R) = 1.7 nM; IC₅₀ (WT) = 4.6 nM]. The inhibitory activity was attributed to the hydrogen bonding interaction between the lactam NH group of the B-ring and carbonyl group of a methionine residue.

Concise synthesis and in vitro anticancer activity of benzo[g][1]benzopyrano[4,3-b]indol-6(13H)-ones (BBPIs), topoisomerase I inhibitors based on the marine alkaloid lamellarin

Benzo[g][1]benzopyrano[4,3-b]indol-6(13H)-ones (BBPIs) are potent anticancer compounds having unique BBPIs ring system designed on the basis of the marine natural product lamellarin D. In this study, we describe an alternative synthesis of a 2-demethoxy series of BBPIs, employing van Leusen pyrrole synthesis and an intramolecular Heck reaction as the key reactions. Cytotoxicity of the derivatives against several cancer and normal cell lines is reported.

Lamellarin alkaloids: Isolation, synthesis, and biological activity

Lamellarins are marine alkaloids containing fused 14-phenyl-6H-[1]benzopyrano[4',3':4,5]pyrrolo[2,1-a]isoquinoline or non-fused 3,4-diarylpyrrole-2-carboxylate ring systems. To date, more than 50 lamellarins have been isolated from a variety of marine organisms, such as mollusks, tunicates, and sponges. Many of them, especially fused type I lamellarins, exhibit impressive biological activity, such as potent cytotoxicity, topoisomerase I inhibition, protein kinases inhibition, and anti-HIV-1 activity. Due to their useful biological activity and limited availability from natural sources, a number of synthetic methods have been developed. In this chapter, we present an updated and comprehensive review on lamellarin alkaloids summarizing their isolation, synthesis, and biological activity.

Synthesis of Functionalized Indolines and Dihydrobenzofurans by Iron and Copper Catalyzed Aryl C-N and C-O Bond Formation

A simple and effective one-pot, two-step intramolecular aryl C-N and C-O bond forming process for the preparation of a wide range of benzo-fused heterocyclic scaffolds using iron and copper catalysis is described. Activated aryl rings were subjected to a highly regioselective, iron(III) triflimide-catalyzed iodination, followed by a copper(I)-catalyzed intramolecular N- or O-arylation step leading to indolines, dihydrobenzofurans, and six-membered analogues. The general applicability and functional group tolerance of this method were exemplified by the total synthesis of the neolignan natural product, (+)-obtusafuran. DFT calculations using Fukui functions were also performed, providing a molecular orbital rationale for the highly regioselective arene iodination process.

Catalyst-free [3 + 2] cyclization of imines and Morita–Baylis–Hillman carbonates: a general route to tetrahydropyrrolo[2,1-a]isoquinolines and dihydropyrrolo[2,1-a]isoquinolines

A mild and efficient catalyst-free [3 + 2] cyclization of isoquinoline imines and Morita–Baylis–Hillman carbonates has been developed.

Catalytic Enantioselective Synthesis of N-C Axially Chiral Phenanthridin-6-one Derivatives

N-C axially chiral phenanthridin-6-one derivatives bearing various ortho-substituted phenyl groups on the nitrogen atom were enantioselectively prepared through (R)-DTBM-SEGPHOS-Pd(OAc)2-catalyzed intramolecular Buchwald-Hartwig amination. The enantioselectivity strongly depended on solvents, bases, and reaction temperature as well as on the bulkiness of ortho-substituents.

Anticancer properties of lamellarins

In 1985 the first lamellarins were isolated from a small oceanic sea snail. Today, more than 50 lamellarins have been inventoried and numerous derivatives synthesized and tested as antiviral or anticancer agents. The lead compound in the family is lamellarin D, characterized as a potent inhibitor of both nuclear and mitochondrial topoisomerase I but also capable of directly interfering with mitochondria to trigger cancer cell death. The pharmacology and chemistry of lamellarins are discussed here and the mechanistic portrait of lamellarin D is detailed. Lamellarins frequently serve as a starting point in the design of anticancer compounds. Extensive efforts have been devoted to create novel structures as well as to improve synthetic methods, leading to lamellarins and related pyrrole-derived marine alkaloids.

Lycophlegmariols A-D: cytotoxic serratene triterpenoids from the club moss Lycopodium phlegmaria L

Lycopodium serratene triterpenoids, along with an abietane-type diterpene were isolated from the methanol extract of club moss Lycopodium phlegmaria L. The structures of these hitherto unknown lycopodium terpenoids were elucidated on the basis of spectroscopic analysis. Pentacyclic triterpenoids, 21β-hydroxy-serrat-14-en-3α-ol (1) and 21β-hydroxy-serrat-14-en-3α-yl acetate (2) were isolated together with four serratene triterpeneoids established as 21β,29-dihydroxyserrat-14-en-3α-yl dihydrocaffeate (lycophlegmariol A, 5), 21β,24,29-trihydroxyserrat-14-en-3β-yl dihydrocaffeate (lycophlegmariol B, 6), 21α,24-dihydroxyserrat-14-en-3β-yl 4-hydroxycinnamate (lycophlegmariol C, 7), and 14β,21α,29-trihydroxyserratan-3β-yl dihydrocaffeate (lycophlegmariol D, 8) as well as a known lycophlegmarin (9). An abietane-type diterpene, 8,11,13-abietatriene-3β,12-dihydroxy-7-one (margocilin, 10), was isolated for the first time from a Lycopodium plant. Lycophlegmariol B (6), D (8) and compound 1 showed inhibitory effects against MOLT-3 acute lymphoblastic leukemia (T-lymphoblast) with IC(50) of 14.7, 3.0 and 2.9 μM, respectively.

Synthesis of chromeno[3,4-b]indoles as Lamellarin D analogues: a novel DYRK1A inhibitor class

A library of substituted chromeno[3,4-b]indoles was developed as Lamellarin isosters. Synthesis was achieved from indoles after a four-step pathway sequence involving C-3 iodination, a Suzuki cross-coupling reaction, and a one pot deprotection/lactonisation step. Twenty final compounds were tested in order to determine their activity against topoisomerase I and kinases, the two major biological activities of Lamellarins. One newly synthesized derivative exhibited a strong topoisomerase activity comparable to reference compounds such as campthotecin and Lamellarin with only a weak kinase inhibition. Two other lead compounds were identified as new nanomolar DYRK1A inhibitors and several other drugs affected the kinases in the sub-micromolar range. These results will enable us to use the chromeno[3,4-b]indole as a pharmacophore to develop potent treatments for neurological or oncological disorders in which DYRK1A is fully involved.

Synthesis and topoisomerase I inhibitory activity of a novel diazaindeno[2,1-b]phenanthrene analogue of Lamellarin D

A novel 5-oxa-6a,8-diazaindeno[2,1-b]phenanthren-7-one scaffold was designed and synthesized as an active analogue of the cytotoxic marine alkaloid Lamellarin D. The design was based on molecular modeling of the site of interaction of Lamellarin D with DNA-topoisomerase I cleavable complex, whereas the synthesis capitalized on a simple Friedel-Crafts cyclization of indole to a β-carbolinone nucleus. The product exhibited topoisomerase I poisoning activity and submicromolar cytotoxicity on human non-small cell lung cancer H460 cell line.

Progress on lamellarins

The latest developments towards the synthesis of lamellarins, their structure–activity relationship and advances in the mechanism of action are described.