Brominated diterpenes with antibacterial activity from the red alga Sphaerococcus coronopifolius

Structure-dependent activity of plant natural products against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the major causes for nosocomial infections and has been classified as "high priority pathogen" by the World Health Organization. Its ability to develop resistances has been a challenge for the last decades and is still a threat to health care systems, as strains with resistances to the so-called drugs of last resort have been discovered. Therefore, new antibiotics are urgently needed. Natural products are an important source for the development of new drugs, thereby mostly serving as lead compounds for further modification. In this review, the data on plant natural products with reported anti-MRSA activity until the end of 2022 is discussed, highlighting the most effective drugs with respect to their inhibitory concentrations as well as with regard to eventual synergistic effects with existing antibiotics. In the latter sense, the class of alkaloids must be mentioned, exhibiting additive or synergistic effects by inhibiting bacterial efflux pumps. With regard to the antibiotic activity, phloroglucinol derivatives certainly belong to the most promising compounds, revealing several candidates with remarkable effects, e.g., lupulone, ivesinol, rhodomyrtone, aspidinol, or hyperforin. Also, the class of terpenoids yielded noteworthy compounds, such as the sesquiterpene lactones parthenolide and lactopicrin as well as acetophenone sesquiterpenes and sphaerodiene type diterpenoids, respectively. In addition, pronounced effects were observed for the macrolide neurymenolide A and three flavonol dicoumaroylrhamnosides.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Antifouling Activity of Halogenated Compounds Derived from the Red Alga Sphaerococcus coronopifolius: Potential for the Development of Environmentally Friendly Solutions

Nowadays, biofouling is responsible for enormous economic losses in the maritime sector, and its treatment with conventional antifouling paints is causing significant problems to the environment. Biomimetism and green chemistry approaches are very promising research strategies for the discovery of new antifouling compounds. This study focused on the red alga Sphaerococcus coronopifolius, which is known as a producer of bioactive secondary metabolites. Fifteen compounds, including bromosphaerol (1), were tested against key marine biofoulers (five marine bacteria and three microalgae) and two enzymes associated with the adhesion process in macroalgae and invertebrates. Each metabolite presented antifouling activity against at least one organism/enzyme. This investigation also revealed that two compounds, sphaerococcinol A (4) and 14R-hydroxy-13,14-dihydro-sphaerococcinol A (5), were the most potent compounds without toxicity towards oyster larvae used as non-target organisms. These compounds are of high potential as they are active towards key biofoulers and could be produced by a cultivable alga, a fact that is important from the green chemistry point of view.

Triphenyl-sesquineolignan analogues derived from Illicium simonsii Maxim exhibit potent antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) by disrupting bacterial membranes

Infections caused by clinical methicillin-resistant Staphylococcus aureus (MRSA) are a serious public problem. Triphenyl-sesquineolignans from Illicium genus possess antibacterial activity, but few researches have reported their antibacterial spectrums, structure-activity relationships (SARs) and antibacterial mechanism. In this study, three triphenyl-sesquineolignans, dunnianol (1), macranthol (2) and isodunnianol (3) were isolated from the stems and leaves of I. simonsii Maxim, and seven dunnianol derivatives were prepared through esterification, etherification and halogenation reactions. Among all triphenyl-sesquineolignan analogues, compound 6 showed the best antibacterial activity against four Gram-positive bacteria (MICs = 1-2 µg/mL) and ten clinical MRSA strains (MICs = 2-8 µg/mL), and also exhibited characteristics of killing MRSA more rapidly than tigecycline. Meanwhile, compound 6 did not only show a low probability of drug resistance development, but also exhibited relatively low hemolysis, and good stability in 50% plasma. Further mechanism studies revealed that 6 could kill bacterial strains by disrupting bacterial membranes. These results suggested that 6 may be developed into a new antibacterial candidate for combating MRSA infections.

Halogenated Diterpenes with In Vitro Antitumor Activity from the Red Alga Sphaerococcus coronopifolius

Eight new (1-8) structurally diverse diterpenes featuring five different carbocycles were isolated from the organic extracts of the red alga Sphaerococcus coronopifolius collected from the coastline of the Ionian Sea in Greece. The structures of the new natural products, seven of which were halogenated, and the relative configuration of their stereocenters were determined on the basis of comprehensive spectroscopic analyses, including NMR and HRMS data. Compounds 5 and 8 were found to possess in vitro antitumor activity against one murine and five human cancer cell lines with mean IC50 values 15 and 16 μM, respectively.

Antitumor and antimicrobial potential of bromoditerpenes isolated from the red alga, Sphaerococcus coronopifolius

Cancer and infectious diseases continue to be a major public health problem, and new drugs are necessary. As marine organisms are well known to provide a wide range of original compounds, the aim of this study was to investigate the bioactivity of the main constituents of the cosmopolitan red alga, Sphaerococcus coronopifolius. The structure of several bromoditerpenes was determined by extensive spectroscopic analysis and comparison with literature data. Five molecules were isolated and characterized which include a new brominated diterpene belonging to the rare dactylomelane family and named sphaerodactylomelol (1), along with four already known sphaerane bromoditerpenes (2-5). Antitumor activity was assessed by cytotoxicity and anti-proliferative assays on an in vitro model of human hepatocellular carcinoma (HepG-2 cells). Antimicrobial activity was evaluated against four pathogenic microorganisms: Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans. Compound 4 exhibited the highest antimicrobial activity against S. aureus (IC50 6.35 µM) and compound 5 the highest anti-proliferative activity on HepG-2 cells (IC50 42.9 µM). The new diterpene, sphaerodactylomelol (1), induced inhibition of cell proliferation (IC50 280 µM) and cytotoxicity (IC50 720 µM) on HepG-2 cells and showed antimicrobial activity against S. aureus (IC50 96.3 µM).

Peroxy natural products

This review covers the structures and biological activities of peroxy natural products from a wide variety of terrestrial fungi, higher plants, and marine organisms. Syntheses that confirm or revise structures or stereochemistries have also been included, and 406 references are cited.

Terpenes from the red alga Sphaerococcus coronopifolius inhibit the settlement of barnacles

In this study, we screened eight terpenes isolated from the organic extract of Sphaerococcus coronopifolius for their antifouling activity in order to find possible new sources of non-toxic or less toxic bioactive antifoulants. The anti-settlement activity (EC₅₀) and the degree of toxicity (LC₅₀) of S. coronopifolius metabolites was evaluated using larvae of the cirriped crustacean Amphibalanus (Balanus) amphitrite (cyprids and nauplii) as model organism. For five of eight tested metabolites EC₅₀ was lower than 5 mg/L. The most promising results were observed for bromosphaerol (3), which expressed an EC₅₀ value of 0.23 mg/L, in combination with low toxicity levels (LC₅₀ > 100 mg/L). The therapeutic ratio--an index used to estimate whether settlement inhibition is due to toxicity or other mechanisms--is also calculated and discussed.

Sphaeroane and neodolabellane diterpenes from the red alga Sphaerococcus coronopifolius

Investigation of minor metabolites in the extracts of the red alga Sphaerococcus coronopifolius collected from the rocky coasts of Corfu Island in the Ionian Sea yielded two new diterpene alcohols, sphaerollanes I, and II (1, 2) featuring neodolabellane skeletons, and the new sphaeroane diterpene alcohol 16-hydroxy-9S*-acetoxy-8-epi-isosphaerodiene-2 (3), along with two previously reported metabolites 4, 5. The structures of the new natural products, as well as their relative stereochemistry, were elucidated on the basis of extensive spectral analysis, including 2D-NMR experiments.