Chemical profiling (HPLC-NMR & HPLC-MS), isolation, and identification of bioactive meroditerpenoids from the southern Australian marine brown alga Sargassum paradoxum

Three new meroterpenoids from Sargassum macrocarpum and their inhibitory activity against amyloid β aggregation

Amyloid β (Aβ) is thought to be involved in the pathogenesis of Alzheimer's disease (AD). Aβ aggregation in the brain is considered the cause of AD. Therefore, inhibiting Aβ aggregation and degrading existing Aβ aggregates is a promising approach for the treatment and prevention of the disease. In searching for inhibitors of Aβ42 aggregation, we found that meroterpenoids isolated from Sargassum macrocarpum possess potent inhibitory activities. Therefore, we searched for active compounds from this brown alga and isolated 16 meroterpenoids, which contain three new compounds. The structures of these new compounds were elucidated using two-dimensional nuclear magnetic resonance techniques. Thioflavin-T assay and transmission electron microscopy were used to reveal the inhibitory activity of these compounds against Aβ42 aggregation. All the isolated meroterpenoids were found to be active, and compounds with a hydroquinone structure tended to have stronger activity than those with a quinone structure.

Structural diversity, biosynthesis, and health-promoting properties of brown algal meroditerpenoids

Marine algae that constitute hundreds of millions of tons of biomass are the oldest representatives of the plant kingdom. Recently, there has been growing interest in the utilization of algae as sustainable feedstocks for natural products with an economic value. Among these natural products are the meroditerpenoids, which are renowned for their protective effects against oxidative stress, inflammation, cancer, obesity, diabetes, and neurodegenerative disorders. Meroditerpenoids have a mixed biosynthetic origin and display a wide range of structural diversity. Their basic structure consists of a ring system bearing a diterpenoid side chain. Structural variations are observed in terms of the functional groups and saturation/cyclization of the diterpenoid side chain. This review classifies algal meroditerpenoids as plastoquinones, chromanols, chromenes, chromones, cyclic meroditerpenoids, nahocols, and isonahocols and examines their potential applications in functional foods and biopharmacology. Their lipid solubility, low molecular weight, and propensity to cross the blood-brain barrier places meroditerpenoids as potential drug candidates. There is growing interest in the study of algal meroterpenoids, and recent research has reported the structure of several new meroterpenoids and their biological activities. Further research is needed to extend the use of algal meroditerpenoids in preclinical trials. Understanding the mechanism of their biosynthesis will allow the development of de novo biosynthesis and biomimetic synthesis strategies for the industrial-scale production of meroditerpenoids and their synthetic derivatives to aid pharmaceutical research. This review is the first to summarize up-to-date information on all brown algae-derived meroditerpenoids.

Macrocarquinoids A-C, new meroterpenoids from Sargassum macrocarpum

The production and accumulation of advanced glycation end products (AGEs) have been implicated in diabetes and diabetic complication. This study was conducted as a search for an AGE inhibitor from brown alga, Sargassum macrocarpum. Separation and purification were performed using AGEs inhibitory activity as an index, yielding isolation of 11 meroterpenoids, of which 3 were new compounds: macrocarquinoids A (1), B (6), and C (9). Their structures were elucidated using NMR spectral analysis with 2D techniques. All tested compounds showed AGEs inhibitory activity. Particularly, macrocarquinoid C (9) possessed the strongest activity (IC50: 1.0 mM) of isolated compounds. This activity was stronger than that of aminoguanidine (positive control).

Bioremediation potential of Sargassum sp. biomass to tackle pollution in coastal ecosystems: Circular economy approach

During the past years, the ecological integrity and biodiversity of marine ecosystems have been highly threatened due to the controlled or uncontrolled release of high concentrations of pollutants generated through anthropogenic activities. The occurrence of environmentally related hazardous pollutants, such as toxic elements, and recalcitrant compounds in various environmental matrices has raised increasing concern. Different technologies have been developed for efficient removal and complete mitigation or degradation of these toxic elements from the aquatic environment. Among them, biosorption and bioaccumulation by renewable and biodegradable sources are of supreme interest and have not been reviewed much. For instance, the invasive seaweed Sargassum sp. has been spotted as a cost-effective natural material to capture targeted pollutants from the coastal ecosystem, which is currently becoming a pressing problem, around the globe, due to its unusual proliferation near tropical shores. This review is an effort to cover the left behind gap to present the multifunctional potentialities of Sargassum sp. biomass. Herein, salient information is given to highlight the potential of Sargassum sp. biomass for environmental decontamination with particular focus to coastal ecosystems. Bioremediation mechanisms, challenges of implementation and factors involved in adsorption and absorption of pollutants by seaweeds are also discussed in this review. Against this background, a circular economy perspective is given for the integrated use of the algal raw material. The up-taken pollutants can be recovered and reintegrated into the value chain of industrial processes, while residual biomass is refined to obtain added-value products as bioactive compounds with potential applications for biofuel, agriculture, cosmetics, nutraceutical, pharmaceutical industries among others, to make the most of renewable resources.

Natural Products of Marine Macroalgae from South Eastern Australia, with Emphasis on the Port Phillip Bay and Heads Regions of Victoria

Marine macroalgae occurring in the south eastern region of Victoria, Australia, consisting of Port Phillip Bay and the heads entering the bay, is the focus of this review. This area is home to approximately 200 different species of macroalgae, representing the three major phyla of the green algae (Chlorophyta), brown algae (Ochrophyta) and the red algae (Rhodophyta), respectively. Over almost 50 years, the species of macroalgae associated and occurring within this area have resulted in the identification of a number of different types of secondary metabolites including terpenoids, sterols/steroids, phenolic acids, phenols, lipids/polyenes, pheromones, xanthophylls and phloroglucinols. Many of these compounds have subsequently displayed a variety of bioactivities. A systematic description of the compound classes and their associated bioactivities from marine macroalgae found within this region is presented.

Pharmacological and natural products diversity of the brown algae genus Sargassum

Sargassum (F. Sargassaceae) is an important seaweed excessively distributed in tropical and subtropical regions.

Bioactive Prenyl- and Terpenyl-Quinones/Hydroquinones of Marine Origin †

The sea is a rich source of biological active compounds, among which terpenyl-quinones/hydroquinones constitute a family of secondary metabolites with diverse pharmacological properties. The chemical diversity and bioactivity of those isolated from marine organisms in the last 10 years are summarized in this review. Aspects related to synthetic approaches towards the preparation of improved bioactive analogues from inactive terpenoids are also outlined.

Secondary Metabolites and Biological Activity of Invasive Macroalgae of Southern Europe

In this review a brief description of the invasive phenomena associated with algae and its consequences on the ecosystem are presented. Three examples of invasive algae of Southern Europe, belonging to Rodophyta, Chlorophyta, and Phaeophyta, were selected, and a brief description of each genus is presented. A full description of their secondary metabolites and biological activity is given and a summary of the biological activity of extracts is also included. In Asparagopsis we encounter mainly halogenated compounds. From Caulerpa, several terpenoids and alkaloids were isolated, while in Sargassum, meroterpenoids prevail.

Absolute Configuration Determination of Retroflexanone Using the Advanced Mosher Method and Application of HPLC-NMR

The absolute configuration of retroflexanone (1) and a closely related phlorogluinol (2) was established using the advanced Mosher method and by application of HPLC-NMR. HPLC-NMR permitted a small scale Mosher method analysis to be carried out on these unstable phloroglucinols.

Natural 6-hydroxy-chromanols and -chromenols: structural diversity, biosynthetic pathways and health implications

We present the first comprehensive and systematic review on the structurally diverse toco-chromanols and -chromenols found in photosynthetic organisms, including marine organisms, and as metabolic intermediates in animals. The focus of this work is on the structural diversity of chromanols and chromenols that result from various side chain modifications. We describe more than 230 structures that derive from a 6-hydroxy-chromanol- and 6-hydroxy-chromenol core, respectively, and comprise di-, sesqui-, mono- and hemiterpenes. We assort the compounds into a structure-activity relationship with special emphasis on anti-inflammatory and anti-carcinogenic activities of the congeners. This review covers the literature published from 1970 to 2017.

Marine natural products

Covering: 2015. Previous review: Nat. Prod. Rep., 2016, 33, 382-431This review covers the literature published in 2015 for marine natural products (MNPs), with 1220 citations (792 for the period January to December 2015) 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 (1340 in 429 papers for 2015), 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.

HPLC-NMR and HPLC-MS investigation of antimicrobial constituents in Cystophora monilifera and Cystophora subfarcinata

The crude dichloromethane extracts of the marine brown algae Cystophora monilifera and Cystophora subfarcinata were subjected to phytochemical profiling. This enabled the structures of both new and known phloroglucinols to be dereplicated and proposed using HPLC-NMR and HPLC-MS. Subsequent isolation confirmed the presence of four new and eight previously reported compounds. Five of the isolated phloroglucinols displayed selective antimicrobial activity.

Phytochemical Investigation of the Constituents Derived from the Australian Plant Macropidia fuliginosa

A phytochemical study of the flowers and bulbs derived from the Australian plant Macropidia fuliginosa, involving hyphenated spectroscopic methodologies (HPLC-NMR and HPLC-MS), together with conventional isolation strategies, resulted in the identification of 16 constituents (1, 2, 4-17) representative of six different structural classes. Six new compounds (12-17) were identified from the bulbs of the plant. The isolated compounds were assessed for antimicrobial activity, and compound 8 was found to be more potent against P. aeruginosa than ampicillin.

Dereplication and chemotaxonomical studies of marine algae of the Ochrophyta and Rhodophyta phyla

Dereplication and chemotaxonomic studies of six marine algae of the Ochrophyta and one of the Rhodophyta phyla resulted in the detection of 22 separate compounds. All 16 secondary metabolites, including four new compounds (16–19), could be rapidly dereplicated using HPLC-NMR and HPLC-MS methodologies in conjunction with the MarinLit database. This study highlights the advantages of using NMR data (acquired via HPLC-NMR) for database searching and for the overall dereplication of natural products.