Domino Reaction for the Synthesis of Polysubstituted Pyrroles and Lamellarin R

Investigating the antiviral therapeutic potentialities of marine polycyclic lamellarin pyrrole alkaloids as promising inhibitors for SARS-CoV-2 and Zika main proteases (Mpro)

The new coronavirus variant (SARS-CoV-2) and Zika virus are two world-wide health pandemics. Along history, natural products-based drugs have always crucially recognized as a main source of valuable medications. Considering the SARS-CoV-2 and Zika main proteases (Mpro) as the re-production key element of the viral cycle and its main target, herein we report an intensive computer-aided virtual screening for a focused list of 39 marine lamellarins pyrrole alkaloids, against SARS-CoV-2 and Zika main proteases (Mpro) using a set of combined modern computational methodologies including molecular docking (MDock), molecule dynamic simulations (MDS) and structure-activity relationships (SARs) as well. Indeed, the molecular docking studies had revealed four promising marine alkaloids including [lamellarin H (14)/K (17)] and [lamellarin S (26)/Z (39)], according to their notable ligand-protein energy scores and relevant binding affinities with the SARS-CoV-2 and Zika (Mpro) pocket residues, respectively. Consequentially, these four chemical hits were further examined thermodynamically though investigating their MD simulations at 100 ns, where they showed prominent stability within the accommodated (Mpro) pockets. Moreover, in-deep SARs studies suggested the crucial roles of the rigid fused polycyclic ring system, particularly aromatic A- and F- rings, position of the phenolic -OH and δ-lactone functionalities as essential structural and pharmacophoric features. Finally, these four promising lamellarins alkaloids were investigated for their in-silico ADME using the SWISS ADME platform, where they displayed appropriated drug-likeness properties. Such motivating outcomes are greatly recommending further in vitro/vivo examinations regarding those lamellarins pyrrole alkaloids (LPAs).Communicated by Ramaswamy H. Sarma.

Progress on synthesis and structure-activity relationships of lamellarins over the past decade

Lamellarins are polyaromatic alkaloids isolated from marine organisms, including mollusks, tunicates, and sponges. Currently, over 60 structurally distinct natural lamellarins have been reported, and most of them exhibit promising biological activities, such as topoisomerase inhibition, mitochondrial function inhibition, multidrug resistance reversing, and anti-HIV activity. There has also been a significant progress on the synthetic study of lamellarins which has been regularly updated by numerous medicinal chemists as well. This review provides a detailed summary of the synthesis, pharmacology, and structural modification of lamellarins over the past decades.

Arynes as synthetic linchpins towards the construction of diversely functionalized natural product skeletons

Arynes are a privileged class of reactive intermediates in synthetic organic chemistry, and their unusual reactivities have been the subject of engrossing research interest. Recently, there are many reports on novel aryne-based synthetic innovations as a linchpin approach to accomplish the total synthesis of structurally diverse natural products or their derivatives in a racemic and enantiopure fashion. This review provides an overview of the literature on synthetic strategies, employing arynes as crucial intermediates to construct architecturally intriguing bioactive natural products/derivatives in a period of 2019 to 2022. This study highlights the need to investigate the effective synthesis and search for new biological uses of highly functionalized natural product skeletons.

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.

Three-Component, Diastereoselective [6 + 3] Annulation of Tropone, Imino Esters, and Arynes

A transition-metal-free, three-component, and diastereoselective [6 + 3] annulation reaction employing tropone, imino esters, and arynes allowing the synthesis of bridged azabicyclo[4.3.1]decadienes is demonstrated. The key nitrogen ylides for the [6 + 3] annulation were generated by the addition of imino esters to the arynes followed by a proton transfer. The nitrogen ylides undergo a regioselective addition to tropone to furnish the desired products in moderate to good yields with good functional group tolerance under mild conditions.

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.

Mild and Efficient Copper-Catalyzed Synthesis of Trisubstituted Pyrroles

A sustainable and time economic approach has been developed for the synthesis of polysubstituted pyrroles using copper iodide as a catalyst. The reaction proceeded through imine formation followed by cyclization with alkyne-Cu intermediate, which was supported by control experiments studies. The newly formed substituted pyrroles were obtained in excellent yields with high regioselectivity under mild conditions.

Efficient reduction of nitro compounds and domino preparation of 1-substituted-1H-1,2,3,4-tetrazoles by Pd(ii)-polysalophen coated magnetite NPs as a robust versatile nanocomposite

A new, versatile, and green methodology has been developed for the efficient NaBH4-reduction of nitroarenes as well as the domino/reduction MCR preparation of 1-substituted-1H-1,2,3,4-tetrazoles using Pd(ii)-polysalophen coated magnetite NPs as an efficient heterogeneous magnetically recyclable nanocatalyst. Polysalophen was firstly prepared based on a triazine framework with a high degree of polymerization, then coordinated to Pd ions and, finally, the resulting hybrid was immobilized on magnetite NPs. The catalyst was characterized by various instrumental and analytical methods, including GPC, DLS, N2 adsorption-desorption, TGA, VSM, TEM, HRTEM, EDX, XPS, XRD, and ICP analyses. The catalyst possesses dual-functionality including the reduction of nitroarenes and the construction of tetrazole rings all in one step via a domino protocol. High to excellent yields were obtained for both nitro reduction and the direct preparation of 1-substituted-1H-1,2,3,4-tetrazoles from nitro compounds. Insight into the mechanism was conducted by XPS in situ as well as DLS in situ along with several control experiments. Recyclability of the catalyst was studied for 6 consecutive runs along with metal leaching measurements in each cycle.

Green synthesis of fluorescent Schiff bases: chemo-photophysical characterization, X-ray structures, and their bioimaging

Two Schiff bases have been prepared by mechano- and ultrasound-assisted synthesis and their structures were elucidated by X-ray diffraction. One of them showed good fluorescent cell staining in vitro and low cytotoxicity.

Synthesis of lamellarin R, lukianol A, lamellarin O and their analogues

Three lamellarin alkaloids type III (lamellarin R, lukianol A and lamellarin O) were synthesized using the Barton–Zard reaction as a key step to construct the central pyrrole core. Some of their corresponding 4-benzoyl and 5-phenyl substituted pyrrole analogues were also prepared via an initial three-component reaction of glycine methyl ester, benzaldehyde, and chalcone to generate the pyrrolidine scaffold, and followed by DDQ oxidation and N-alkylation.

Several lamellarin alkaloids type III and analogues were synthesized using Barton–Zard and three-component reactions to construct the central pyrrole core.