Marine organisms exhibit some advantages as a renewable source of potential drugs, far beyond chemotherapics. Particularly, the number of marine natural products with antithrombotic activity has increased in the last few years, and reports show a wide diversity in scaffolds, beyond the polysaccharide framework. While there are several reviews highlighting the anticoagulant and antithrombotic activities of marine-derived sulfated polysaccharides, reports including other molecules are sparse. Therefore, the present paper provides an update of the recent progress in marine-derived sulfated polysaccharides and quotes other scaffolds that are being considered for investigation due to their antithrombotic effect.

Marine environment is rich in structurally unique molecules and can be an inspiring source of novel drugs. Currently, six marine-derived drugs are in the market with FDA approval and several more are in the clinical pipeline. Structurally diverse and complex secondary metabolites have been isolated from the marine world and these include sulfated steroids. Biological activities of nearly 150 marine sulfated steroids reported from 1978 to 2017 are compiled and described, namely antimicrobial, antitumor, cardiovascular and antifouling activities. Structure–activity relationship for each activity is discussed.

Marine biofouling represents a global economic and ecological challenge and few eco-friendly antifouling agents are available. The aim of this work was to establish the proof of concept that a recently synthesized nature-inspired compound (gallic acid persulfate, GAP) can act as an eco-friendly and effective antifoulant when immobilized in coatings through a non-release strategy, promoting a long-lasting antifouling effect. The synthesis of GAP was optimized to provide quantitative yields. GAP water solubility was assessed, showing values higher than 1000 mg/mL. GAP was found to be stable in sterilized natural seawater with a half-life (DT₅₀) of 7 months. GAP was immobilized into several commercial coatings, exhibiting high compatibility with different polymeric matrices. Leaching assays of polydimethylsiloxane and polyurethane-based marine coatings containing GAP confirmed that the chemical immobilization of GAP was successful, since releases up to fivefold lower than the conventional releasing systems of polyurethane-based marine coatings were observed. Furthermore, coatings containing immobilized GAP exhibited the most auspicious anti-settlement effect against Mytilus galloprovincialis larvae for the maximum exposure period (40 h) in laboratory trials. Overall, GAP promises to be an agent capable of improving the antifouling activity of several commercial marine coatings with desirable environmental properties.

The spike protein of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) relies on host cell surface glycans to facilitate interaction with the angiotensin-converting enzyme 2 (ACE-2) receptor. This interaction between ACE2 and the spike protein is a gateway for the virus to enter host cells and may be targeted by antiviral drugs to inhibit viral infection. Therefore, targeting the interaction between these two proteins is an interesting strategy to prevent SARS-CoV-2 infection. A library of glycan mimetics and derivatives was selected for a virtual screening performed against both ACE2 and spike proteins. Subsequently, in vitro assays were performed on eleven of the most promising in silico compounds to evaluate: (i) their efficacy in inhibiting cell infection by SARS-CoV-2 (using the Vero CCL-81 cell line as a model), (ii) their impact on ACE2 expression (in the Vero CCL-81 and MDA-MB-231 cell lines), and (iii) their cytotoxicity in a human lung cell line (A549). We identified five synthetic compounds with the potential to block SARS-CoV-2 infection, three of them without relevant toxicity in human lung cells. Xanthene 1 stood out as the most promising anti-SARS-CoV-2 agent, inhibiting viral infection and viral replication in Vero CCL-81 cells, without causing cytotoxicity to human lung cells.

Several biological activities from nearly 150 marine-derived sulfated steroids have been reported with both pharmacological (antimicrobial, antitumor, cardiovascular and/ or anti-inflammatory activities) and environmental (antifouling activity) applications [1]. Sulfation is used in Nature to avoid toxicity and therefore marine-inspired sulfated steroids could be an interesting strategy for drug discovery. The sulfated aminosterol squalamine, isolated from the internal organs of the dogfish shark, is in phase III of clinical trials as anti-angiogenic drug [2], which evidences the potential of sulfated steroids. Sulfation of small molecules using sulfur trioxide-amine complexes entails several advantages, such as persulfation, low degradation, and feasibility in the work-up [3]. Moreover, these complexes appear to be suitable for sulfation of alcohol groups present in steroids [4]. In this direction, sulfation of four sterols was achieved using triethylamine-sulfur trioxide adduct in dimethylacetamide under heating, with yields ranging from 3% to 93%. Purification involved insolubilization with diethyl ether followed by several methods to obtain the sulfated derivatives free of inorganic impurities, including dialysis and/ or chromatographic processes. Structure elucidation of these new compounds was established by infrared (IR), nuclear magnetic resonance (NMR) and high resolution mass spectrometry (HRMS). Biological activities will be further studied. Acknowledgements: This work was supported through national funds provided by FCT/MCTES - Foundation for Science and Technology from the Ministry of Science, Technology and Higher Education (PIDDAC) and European Regional Development Fund (ERDF) through the COMPETE Programa Operacional Factores de Competitividade (POFC) programme, under the projects PTDC/MAR-BIO/4694/2014 (reference POCI-01-0145-FEDER-016790; Project 3599–PPCDT), PTDC/AAGTEC/0739/2014 (reference POCI-01-0145-FEDER-016793; Project 9471-RIDTI) and POCI-01-0145-FEDER-028736 in the framework of the programme PT2020. Carvalhal F also acknowledges FCT for the grant PTDC/AAG- TEC/0739/2014-018. References: [1] Carvalhal, F., M. Correia-da-Silva, M.E. Sousa, M. Pinto, and A. Kijjoa, Journal of Molecular Endocrinology, 2018, 61(2) 211-231. [2] NCT02727881 (https://clinicaltrials.gov/ct2/show/NCT02727881, October 15, 2018) [3] Correia-da-Silva, M., E. Sousa, and M.M. Pinto, Medicinal Research Reviews, 2014, 34(2) 223-79. [4] Al-Horani, R.A., and U.R. Desai, Chemical Sulfation of Small Molecules - Advances and Challenges.Tetrahedron, 2010, 66(16), 2907-2918