Contents lists available at ScienceDirect Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv Overcoming environmental problems of biocides: Synthetic bile acid derivatives as a sustainable alternative Ana R. Neves a,b,1 , Joana R. Almeida a,1 , Francisca Carvalhal a,b , Amadeu Câmara b , Sandra Pereira a , Jorge Antunes a,c , Vitor Vasconcelos a,c , Madalena Pinto a,b , Elisabete R. Silva d,e , Emília Sousa a,b , Marta Correia-da-Silva a,b,* a CIIMAR/CIMAR - Interdisciplinary Centre of Marine and Environmental Research, University of Porto, Terminal de Cruzeiros do Porto de Leixões, Avenida General, Norton de Matos S/N, 4450-208, Matosinhos, Portugal b Laboratory of Organic and Pharmaceutical Chemistry, Department of Chemical Sciences, Faculty of Pharmacy, University of Porto, Rua Jorge Viterbo Ferreira, 228, 4050-313, Porto, Portugal c Department of Biology, Faculty of Sciences, University of Porto, Rua do Campo Alegre, 4069-007, Porto, Portugal d BioISI - Biosystems & Integrative Sciences Institute, Faculdade de Ciências, Universidade de Lisboa, Campo Grande C8 bdg, Lisboa, 1749-016 Portugal e CERENA - Centro de Recursos Naturais e Ambiente, Instituto Superior Técnico, University of Lisbon, Av. Rovisco Pais, 1, 1049-001, Lisboa, Portugal ARTICLE INFO Keywords: Bile acids Synthesis Antifouling activity Mussels Biofilm Marine coating ABSTRACT Marine biofouling represents a global economic and ecological challenge. Some marine organisms produce bioactive metabolites, such as steroids, that inhibit the settlement and growth of fouling organisms. The aim of this work was to explore bile acids as a new scaffold with antifouling (AF) activity by using chemical synthesis to produce a series of bile acid derivatives with optimized AF performance and understand their structure-activity relationships. Seven bile acid derivatives were successfully synthesized in moderate to high yields, and their structures were elucidated through spectroscopic methods. Their AF activities were tested against both macro- and microfouling communities. The most potent bile acid against the settlement of Mytilus galloprovincialis larvae was the methyl ester derivative of cholic acid (10), which showed an EC 50 of 3.7 μM and an LC 50 /EC 50 > 50 (LC 50 > 200 μM) in AF effectiveness vs toxicity studies. Two derivatives of deoxycholic acid (5 and 7) potently inhibited the growth of biofilm-forming marine bacteria with EC 50 values < 10 μM, and five bile acids (1, 5, and 7–9) potently inhibited the growth of diatoms, showing EC 50 values between 3 and 10 μM. Promising AF profiles were achieved with some of the synthesized bile acids by combining antimacrofouling and antimicrofouling activities. Initial studies on the incorporation of one of these promising bile acid derivatives in polymeric coatings, such as a marine paint, demonstrated the ability of these compounds to generate coatings with anti- macrofouling activity. 1. Introduction Marine biofouling is a complex biological process involving the accumulation of microorganisms, algae, and animals on a submerged surface (Simone Durr, 2010). When this process occurs on artificial marine surfaces, such as ship hulls, enormous economic and ecological problems can result (Gallardo et al., 2016; Demirel et al., 2017). The attachment of micro- and macroorganisms on the surface of ship hulls decreases speeds, which consequently increases fuel consumption (Schultz et al., 2011; Demirel et al., 2017), ultimately leading to in- creased air pollution and associated ecological problems. Additionally, marine biofouling promotes the spread of invasive aquatic species, which has well-recognized global effects through the food chains of aquatic environments (Gallardo et al., 2016) and has a negative influ- ence on global biodiversity (Bax et al., 2003). For a long time, marine biofouling treatments were based on bio- cides, namely, tributyltin (TBT) and copper (Yebra et al., 2004). However, the toxicities of these biocides against nonfouling marine organisms is now widely recognized (Katranitsas et al., 2003; Schiff et al., 2004; Micael et al., 2007; Zhang et al. 2011, 2013b; Yu et al., 2013; Zhang et al., 2016). After the banning of TBT in Europe in 2008, booster biocides were introduced in the market. Some of them, https://doi.org/10.1016/j.ecoenv.2019.109812 Received 27 July 2019; Received in revised form 10 October 2019; Accepted 12 October 2019 * Corresponding author. Laboratory of Organic and Pharmaceutical Chemistry, Department of Chemical Sciences, Faculty of Pharmacy, University of Porto, Rua Jorge Viterbo Ferreira, 228, Porto, 4050-313, Portugal. E-mail address: m_correiadasilva@ff.up.pt (M. Correia-da-Silva). 1 both authors contributed equally. Ecotoxicology and Environmental Safety 187 (2020) 109812 0147-6513/ © 2019 Elsevier Inc. All rights reserved. T