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Chemical investigation of the South-Pacific marine sponge Suberea clavata led to the isolation of eight new bromotyrosine metabolites named subereins 1–8 (2–9) along with twelve known co-isolated congeners. The detailed configuration determination of the first representative major compound of this family 11-epi-fistularin-3 (11R,17S) (1) is described. Their chemical characterization was achieved by HRMS and integrated 1D and 2D NMR (nuclear magnetic resonance) spectroscopic studies and extensive comparison with literature data. For the first time, a complete assignment of the absolute configurations for stereogenic centers C-11/17 of the known members (11R,17S) 11-epi-fistularin-3 (1) and 17-deoxyfistularin-3 (10) was determined by a combination of chemical modifications, Mosher’s technology, and ECD spectroscopy. Consequently, the absolute configurations of all our new isolated compounds 2–9 were determined by the combination of NMR, Mosher’s method, ECD comparison, and chemical modifications. Interestingly, compounds 2–7 were obtained by chemical transformation of the major compound 11-epi-fistularin-3 (1). Evaluation for acetylcholinesterase inhibition (AChE), DNA methyltransferase 1 (DNMT1) modulating activity and antifouling activities using marine bacterial strains are also presented.

Unraveling new environmentally friendly antifouling (AF) agents is one of the major quests currently facing marine biotechnology. Marine macroalgae represent a rich source of new compounds with promising biological properties, including AF activity, but most of the macroalgal compounds studied to date are terpenoids or polyphenolics. The aim of this work was to investigate the possible AF role played by a usually neglected class of marine natural products: glycolipids (monogalactosyldiacylglycerols – MGDG, digalactosyldiacylglycerols – DGDG and sulfoquinovosyldiacylglycerols – SQDG) isolated from the Phaeophyceae Sargassum vulgare collected along the coast of south-eastern Brazil. Among the 18 extracts, fractions and sub-fractions tested, 3 sub-fractions demonstrated particularly promising AF activity toward the growth inhibition of marine bacteria and microalgae: F3III117, F4II70a, and F4II70b. The main compounds present in these fractions were identified as MGDG, DGDG, and SQDG, respectively. These results highlight the potential of glycoglycerolipids from S. vulgare as new promising antifouling agents.

Microorganisms have the ability to settle on nearly all man-made surfaces in contact with seawater and subsequently to form biofilm. Biofilms control and removal is necessary in the sectors of maritime transport, energy... In this work, we present the development of new pure calcium, zinc or copper alginate, but also mixed Ca/Cu and Ca/Zn alginate hydrogels. These materials have been evaluated for their potential inhibition of adhesion of two key biofilm-forming microalgae Halamphora coffeaeformis and Cylindrotheca closterium). All the tested materials have presented high adhesion inhibition about 80%). Copper-base materials present a high toxicity against H. coffeaeformis. Pure zinc alginate is also toxic for this strain. However, the addition of calcium in zinc alginate leads to the toxicity reduction. The toxicity of these materials differs according to the strains. Consequently, mixed zinc/calcium alginate are efficient at inhibiting microalgal adhesion with a low level of cells toxicity. These alginate hydrogels are promising materials because they are efficient, cheap, easy to develop and eco-friendly.

This study aimed at the characterization of the antioxidant power of polyphenol extracts (PE) obtained from the algae Cystoseira foeniculacea (CYS) (Phaeophyta) and from the halophyte Halocnemum strobilaceum (HAL), growing in the solar saltworks of western Sicily (Italy), and at the evaluation of their anti-microfouling properties, in order to correlate these activities to defense strategies in extreme environmental conditions. The antioxidant properties were assessed in the PE based on the total antioxidant activity test and the reducing power test; the anti-microfouling properties of the two PE were evaluated by measuring the growth inhibition of marine fish and shellfish pathogen bacteria as well as marine surface fouling bacteria and microalgae exposed to the fractions. Similar polyphenol content (CYS 5.88 +/- 0.75 and HAL 6.03 +/- 0.25 mg gallic acid equivalents (GAE) g(-1) dried weight, DW) and similar reducing power percentage (93.91 +/- 4.34 and 90.03 +/- 6.19) were recorded for both species, even if they exhibited a different total antioxidant power (measured by the percentage of inhibition of the radical 2,2 diphenyl-1-picrylhydrazyl DPPH), with CYS (79.30) more active than HAL (59.90). Both PE showed anti-microfouling properties, being inhibitors of adhesion and growth of marine fish and shellfish pathogen bacteria (V. aestuarianus, V. carchariae, V. harveyi, P. elyakovii, H. aquamarina) and fouling bacteria (V. natriegens, V. proteolyticus, P. iirgensii, R. litoralis) with minimum inhibitory concentrations comparable to the commercial antifouling products used as a positive control (SEA-NINE 211N). Only CYS was a significant inhibitor of the microalgae strains tested, being able to reduce E. gayraliae and C. closterium growth (MIC 10 mu gmL(-1)) and the adhesion of all three strains tested (E. gayraliae, C. closterium and P. purpureum), suggesting its promise for use as an antifouling (AF) product.

The current study represents the first comprehensive investigation into the general antifouling activities of the natural drimane sesquiterpene polygodial. Previous studies have highlighted a high antifouling effect toward macrofoulers, such as ascidians, tubeworms, and mussels, but no reports about the general antifouling effect of polygodial have been communicated before. To probe the structural and chemical basis for antifouling activity, a library of 11 polygodial analogues was prepared by semisynthesis. The library was designed to yield derivatives with ranging polarities and the ability to engage in both covalent and noncovalent interactions, while still remaining within the drimane sesquiterpene scaffold. The prepared compounds were screened against 14 relevant marine micro- and macrofouling species. Several of the polygodial analogues displayed inhibitory activities at sub-microgram/mL concentrations. These antifouling effects were most pronounced against the macrofouling ascidian Ciona savignyi and the barnacle Balanus improvisus, with inhibitory activities observed for selected compounds comparable or superior to several commercial antifouling products. The inhibitory activity against the microfouling bacteria and microalgae was reversible and significantly less pronounced than for the macrofoulers. This study illustrates that the macro- and microfoulers are targeted by the compounds via different mechanisms.

The current study reports the first comprehensive evaluation of a class of allelopathic terrestrial natural products as antifoulants in a marine setting. To investigate the antifouling potential of the natural dihydrostilbene scaffold, a library of 22 synthetic dihydrostilbenes with varying substitution patterns, many of which occur naturally in terrestrial plants, were prepared and assessed for their antifouling capacity. The compounds were evaluated in an extensive screen against 16 fouling marine organisms. The dihydrostilbene scaffold was shown to possess powerful general antifouling effects against both marine microfoulers and macrofoulers with inhibitory activities at low concentrations. The species of microalgae examined displayed a particular sensitivity toward the evaluated compounds at low ng/mL concentrations. It was shown that several of the natural and synthetic compounds exerted their repelling activities via nontoxic and reversible mechanisms. The activities of the most active compounds such as 3,5-dimethoxybibenzyl (5), 3,4-dimethoxybibenzyl (9), and 3-hyolroxy-3',4,5'-trirnethoxybibenzyl (20) were comparable to the commercial antifouling booster biocide. Sea-nine, which was employed as a positive control. The investigation of terrestrial allelopathic natural products to counter marine fouling represents a novel strategy for the design of "green" antifouling technologies, and these compounds offer a potential alternative to traditional biocidal antifoulants.