Total synthesis of thiaplakortone a: derivatives as metabolically stable leads for the treatment of malaria

Synthesis and Antimalarial Evaluation of Halogenated Analogues of Thiaplakortone A

The incorporation of bromine, iodine or fluorine into the tricyclic core structure of thiaplakortone A (1), a potent antimalarial marine natural product, is reported. Although yields were low, it was possible to synthesise a small nine-membered library using the previously synthesised Boc-protected thiaplakortone A (2) as a scaffold for late-stage functionalisation. The new thiaplakortone A analogues (3-11) were generated using N-bromosuccinimide, N-iodosuccinimide or a Diversinate™ reagent. The chemical structures of all new analogues were fully characterised by 1D/2D NMR, UV, IR and MS data analyses. All compounds were evaluated for their antimalarial activity against Plasmodium falciparum 3D7 (drug-sensitive) and Dd2 (drug-resistant) strains. Incorporation of halogens at positions 2 and 7 of the thiaplakortone A scaffold was shown to reduce antimalarial activity compared to the natural product. Of the new compounds, the mono-brominated analogue (compound 5) displayed the best antimalarial activity with IC₅₀ values of 0.559 and 0.058 μM against P. falciparum 3D7 and Dd2, respectively, with minimal toxicity against a human cell line (HEK293) observed at 80 μM. Of note, the majority of the halogenated compounds showed greater efficacy against the P. falciparum drug-resistant strain.

Thiaplakortone B attenuates RANKL-induced NF-κB and MAPK signaling and dampens OVX-induced bone loss in mice

Osteoclasts play an important role in maintaining the relative stability of bone mass. Abnormal number and function of osteoclasts are closely related to osteoporosis and osteolytic diseases. Thiaplakortone B (TPB), a natural compound derived from the Great Barrier Reef sponge Plakortis lita, has been reported to inhibit the growth of the malaria parasite, Plasmodium falciparum, but its effect on osteoclastogenesis has not been previously investigated. In our study, we found that TPB suppresses the receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL)-induced osteoclast formation and resorption activity by tartrate-resistant acid phosphatase (TRAcP) staining, immunofluorescence staining of F-actin belts and hydroxyapatite resorption assay. Furthermore, using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting analysis, we discovered that TPB inhibits osteoclast-specific genes and proteins expression. Mechanistically, TPB blocks multiple upstream pathways including calcium oscillation, NF-κB, mitogen-activated protein kinase (MAPK) and nuclear factor of activated T cells 1(NFATc1) signaling pathways. In vivo, TPB could dampen bone loss in an ovariectomy (OVX) mouse model by micro-CT assessment and histological staining. Therefore, TPB may serve as a potential therapeutic candidate for the treatment of osteoporosis and osteolysis.

Marine alkaloids as bioactive agents against protozoal neglected tropical diseases and malaria

Covering: 2000 up to 2021Natural products are an important resource in drug discovery, directly or indirectly delivering numerous small molecules for potential development as human medicines. Among the many classes of natural products, alkaloids have a rich history of therapeutic applications. The extensive chemodiversity of alkaloids found in the marine environment has attracted considerable attention for such uses, while the scarcity of these natural materials has stimulated efforts towards their total synthesis. This review focuses on the biological activity of marine alkaloids (covering 2000 to up to 2021) towards Neglected Tropical Diseases (NTDs) caused by protozoan parasites, and malaria. Chemotherapy represents the only form of treatment for Chagas disease, human African trypanosomiasis, leishmaniasis and malaria, but there is currently a restricted arsenal of drugs, which often elicit severe adverse effects, show variable efficacy or resistance, or are costly. Natural product scaffolds have re-emerged as a focus of academic drug discovery programmes, offering a different resource to discover new chemical entities with new modes of action. In this review, the potential of a range of marine alkaloids is analyzed, accompanied by coverage of synthetic efforts that enable further studies of key antiprotozoal natural product scaffolds.

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 in vitro antileishmanial efficacy of novel benzothiadiazine-1,1-dioxide derivatives

Leishmaniasis is a major vector-borne parasitic disease that affects thousands of people in tropical and subtropical developing countries. In 2019 alone, it killed 26,000-65,000 individuals. Leishmaniasis is curable, yet its eradication and elimination are hampered by major hurdles, such as the availability of only a handful of clinical toxic drugs and the emergence of pathogenic resistance against them. This underscores the imperative need for new and effective antileishmanial drugs. In search for such agents, we synthesized and evaluated the in vitro antileishmanial potential of a small library of benzothiadiazine derivatives by assessing their activity against the promastigotes of three strains of Leishmania and toxicity in healthy cells. The derivatives were found to have no toxicity to the mammalian cells and were, in general, active against all parasites. The benzothiadiazine derivative 1e, 3-methyl-2-[3-(trifluoromethyl)benzyl]-2H-benzo[e][1,2,4]thiadiazine 1,1-dioxide, was found to be the most active (IC₅₀ , 0.2 μM) against Leishmania major, responsible for the most prevalent disease form, cutaneous leishmaniasis. Conversely, benzothiadiazine 2c, 2-(4-bromobenzyl)-3-phenyl-2H-benzo[e][1,2,4]thiadiazine 1,1-dioxide, was the most potent (IC₅₀ , 6.5 μM) against Leishmania donovani, a causative strain of the lethal visceral leishmaniasis. Both compounds stand as antipromastigote hits for further lead investigation into their potential to act as new antileishmanial agents.

The wavelength-regulated stereodivergent synthesis of (Z)- and (E)-1,4-enediones from phosphonium ylides

The wavelength-regulated, photoredox-catalyzed stereodivergent synthesis of (Z)- and (E)-1,4-enediones from phosphonium ylides is reported.

Recent progress in the total synthesis of pyrrole-containing natural products (2011–2020)

This review discusses total syntheses of pyrrole-containing natural products over the last ten years, highlighting recent advances in the chemistry of pyrroles in the context of their innate reactivity, and their preparation in complex settings.

Bromotryptamine and Imidazole Alkaloids with Anti-inflammatory Activity from the Bryozoan Flustra foliacea

Chemical investigation of the marine bryozoan Flustra foliacea collected in Iceland resulted in isolation of 13 new bromotryptamine alkaloids, flustramines Q-W (1-7) and flustraminols C-H (8-13), and two new imidazole alkaloids, flustrimidazoles A and B (14 and 15), together with 12 previously described compounds (16-27). Their structures were established by detailed spectroscopic analysis using 1D and 2D NMR and HRESIMS. Structure 2 was verified by calculations of the 13C and 1H NMR chemical shifts using density functional theory. The relative and absolute configurations of the new compounds were elucidated on the basis of coupling constant analysis, NOESY, [α]D, and ECD spectroscopic data, in addition to chemical derivatization. The compounds were tested for in vitro anti-inflammatory activity using a dendritic cell model. Eight compounds (1, 3, 5, 13, 16, 18, 26, and 27) decreased dendritic cell secretion of the pro-inflammatory cytokine IL-12p40, and two compounds (4 and 14) increased secretion of the anti-inflammatory cytokine IL-10. Deformylflustrabromine B (27) showed the most potent anti-inflammatory effect (IC50 2.9 μM). These results demonstrate that F. foliacea from Iceland expresses a broad range of brominated alkaloids, many without structural precedents. The potent anti-inflammatory activity in vitro of metabolite 27 warrants further investigations into its potential as a lead for inflammation-related diseases.

Increasing the Strength and Production of Artemisinin and Its Derivatives

Artemisinin is a natural sesquiterpene lactone obtained from the Artemisia annua herb. It is widely used for the treatment of malaria. In this article, we have reviewed the role of artemisinin in controlling malaria, spread of resistance to artemisinin and the different methods used for its large scale production. The highest amount of artemisinin gene expression in tobacco leaf chloroplast leads to the production of 0.8 mg/g of the dry weight of the plant. This will revolutionize the treatment and control of malaria in third world countries. Furthermore, the generations of novel derivatives of artemisinin- and trioxane ring structure-inspired compounds are important for the treatment of malaria caused by resistant plasmodial species. Synthetic endoperoxide-like artefenomel and its derivatives are crucial for the control of malaria and such synthetic compounds should be further explored.

Synthesis of an unusual quinazoline alkaloid: theoretical and experimental investigations of its structural, electronic, molecular and biological properties

An unusual quinazoline alkaloid (1) was obtained when 2-aminobenzaldehyde was refluxed with pyrrolidine in ethanol for 12 h. The synthesized compound was characterized using spectral data analysis augmented with X-ray and literature precedent. Single crystal analysis depicted four conformations differing slightly in bond angles and bond lengths. Compound 1 crystallizes in a triclinic crystal system with a P1̄ space group having two molecules within the unit cell. The experimentally obtained parameters were compared to those obtained theoretically, which depicted a good agreement. Using the DFT/B3LYP/6-31G (d,p) level of theory, HOMO–LUMO energy gap, molecular electrostatic potential (MEP), vibrational (IR) and NMR analyses were carried out. The HOMO–LUMO energy gap allowed the calculation of chemical hardness, chemical inertness, electronegativity and the electrophilicity index of the molecule, which depicted its potential kinetic stability and reactivity. Prediction of activity spectra of the target compound revealed that compound 1 possesses notable antineoplastic activity with P_a = 0.884. The molecule was therefore evaluated against various cancerous cell lines in an in vitro SRB assay which depicted that compound 1 possesses the highest growth inhibition activity against THP-1 cell lines with an IC₅₀ of 7 μM.

A comparative overview of theoretical and experimental studies concerning the electronic, structural and biological domains of the synthesized unusual quinazoline alkaloid is presented.

Bioactive Thiazine and Benzothiazine Derivatives: Green Synthesis Methods and Their Medicinal Importance

Thiazines are a group of heterocyclic organic compounds that are still largely unexplored for their pharmacological activities. There are different available methods for the synthesis of thiazine derivatives in the literature. In this review, we discuss available methods of thiazine preparation through green synthesis methods. Beside their synthesis, many thiazine derivatives are biologically active and play an important role in the treatment of various diseases and show promising results of varying degrees, where they act as antibacterial, antifungal, antitumor, antimalarial, antineoplastic, antiviral, anti-inflammatory, analgesic and anticancer agents and thus they represent an interesting class of heterocyclic medicinal compounds worthy of further exploration.

Marine natural products

This review covers the literature published in 2014 for marine natural products (MNPs), with 1116 citations (753 for the period January to December 2014) 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 (1378 in 456 papers for 2014), 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.

Synthesis and Antiplasmodial Evaluation of Analogues Based on the Tricyclic Core of Thiaplakortones A-D

Six regioisomers associated with the tricyclic core of thiaplakortones A-D have been synthesized. Reaction of 1H-indole-4,7-dione and 1-tosyl-1H-indole-4,7-dione with 2-aminoethanesulfinic acid afforded a regioisomeric series, which was subsequently deprotected and oxidized to yield the tricyclic core scaffolds present in the thiaplakortones. All compounds were fully characterized using NMR and MS data. A single crystal X-ray structure was obtained on one of the N-tosyl derivatives. All compounds were screened for in vitro antiplasmodial activity against chloroquine-sensitive (3D7) and multidrug-resistant (Dd2) Plasmodium falciparum parasite lines. Several analogues displayed potent inhibition of P. falciparum growth (IC50 < 500 nM) but only moderate selectivity for P. falciparum versus human neonatal foreskin fibroblast cells.

Synthesis and antimalarial evaluation of amide and urea derivatives based on the thiaplakortone A natural product scaffold

A series of amide and urea analogues based on the thiaplakortone A natural product scaffold were synthesised and screened forin vitroantimalarial activity.

C–H functionalization of terminal alkynes towards stereospecific synthesis of (E) or (Z) 2-methylthio-1,4-ene-diones

An efficient metal free self-sorting tandem protocol for stereospecific synthesis of (E) or (Z) 2-methylthio-1,4-ene-diones has been developed.

NMR fingerprints of the drug-like natural-product space identify iotrochotazine A: a chemical probe to study Parkinson's disease

The NMR spectrum of a mixture of small molecules is a fingerprint of all of its components. Herein, we present an NMR fingerprint method that takes advantage of the fact that fractions contain simplified NMR profiles, with minimal signal overlap, to allow the identification of unique spectral patterns. The approach is exemplified in the identification of a novel natural product, iotrochotazine A (1), sourced from an Australian marine sponge Iotrochota sp. Compound 1 was used as a chemical probe in a phenotypic assay panel based on human olfactory neurosphere-derived cells (hONS) from idiopathic Parkinson’s disease patients. Compound 1 at 1 μm was not cytotoxic but specifically affected the morphology and cellular distribution of lysosomes and early endosomes.