marine drugs Review Current Research on the Bioprospection of Linear Diterpenes from Bifurcaria bifurcata: From Extraction Methodologies to Possible Applications Adriana C.S. Pais 1, Jorge A. Saraiva 2,Sílvia M. Rocha 2, Armando J.D. Silvestre 1 and Sónia A.O. Santos 1,* 1 CICECO-Aveiro Institute of Materials, Chemistry Department, University of Aveiro, 3810-193 Aveiro, Portugal; [email protected] (A.C.S.P.); [email protected] (A.J.D.S.) 2 QOPNA/LAQV & REQUIMTE, Chemistry Department, University of Aveiro, 3810-193 Aveiro, Portugal; [email protected] (J.A.S.); [email protected] (S.M.R.) * Correspondence: [email protected]; Tel.: +351-234-370-711 Received: 23 August 2019; Accepted: 26 September 2019; Published: 28 September 2019 Abstract: Marine resources are considered as a very promising source of bioactive molecules, and macroalgae in particular have gained special attention, due to their structurally diverse composition. Particular interest has been devoted to the brown macroalga Bifurcaria bifurcata, due to their abundance in bioactive linear diterpenes. In this appraisal, a thorough review concerning the methodologies used in the extraction, fractionation, and identification of diterpenes from B. bifurcata is provided and discussed in detail. An exhaustive compilation of the mass spectra and nuclear magnetic resonance (NMR) data are also provided. The in vitro and in chemico assays already performed to assess different biological activities attributed to B. bifurcata diterpenes are also reviewed, emphasizing the use of isolated components, enriched fractions, or crude extracts. The associated major strengths and challenges for the exploitation of B. bifurcata diterpenes for high-value applications are critically discussed. Keywords: Bifurcaria bifurcata; linear diterpenes; extraction; identification; biological activities; macroalgae; high value applications 1. Introduction Marine resources have been seen as a promising source of added value molecules, an alternative of finite fossil resources, allowing for the boost of concepts such as biorefinery, circular economy, and blue economy [1–3]. In recent years, an increase in marine biotechnology investments has been observed around the world, with macroalgae being an object of particular interest, mainly due to their high productivity, wide diversity, and heterogeneous composition, notably with a high abundance of bioactive compounds [4]. In fact, besides the high content of polysaccharides, macroalgae have shown to be particularly rich in secondary metabolites with a wide range of biological activities, which can be exploited as functional ingredients, or in cosmetic and pharmaceutical formulations [4,5]. However, macroalgae metabolism, and consequently composition, is modulated by, among other factors, salinity, temperature, pressure, sunlight, geographic origin, and season of collection [6,7]. Macroalgae are ecologically and commercially important, being significant primary producers in oceanic aquatic foods chains [6]. These marine resources have been recognized to be a valuable source of polysaccharides, minerals, polyunsaturated fatty acids and vitamins, and, in some species, of phenolic compounds and terpenes [6,8,9]. Special attention has been devoted to brown macroalgae in particular, due to the presence of specific components, such as fucoidan, phlorotannins, or even fucoxanthin, for which promising Mar. Drugs 2019, 17, 556; doi:10.3390/md17100556 www.mdpi.com/journal/marinedrugs Mar. Drugs 2019, 17, 556 2 of 30 bioactivities have been described, namely antitumor, antioxidant, and antihypertensive activities, among others [10–12]. Notwithstanding, brown macroalgae have attracted an increasing attention due to the presence of other compounds, such as some linear diterpenes commonly found in the Sargassaceae family, and particularly in Bifurcaria bifurcata species [13]. Compared to their cyclic congeners, these are quite rare in nature.Mar. Drugs 2019 In, addition, 17, x FOR PEER a REVIEW widevariety of promising biological activities have been2 of attributed29 to these components. Although a detailed revision of the different linear diterpenes already identified in B. bifurcatabioactivitieshas been have previously been described, reported namely [ 14antitumor,], an overview antioxidant, of theand B.antihypertensive bifurcata diterpenes’ activities, properties among others [10–12]. together with information about how these components can be extracted and identified is needed Notwithstanding, brown macroalgae have attracted an increasing attention due to the presence in orderof toother boost compounds, their exploitation. such as some linear In this diterpenes vein, the commonly purpose found of in this the paperSargassaceae is to family, review and the different extractionparticularly and characterization in Bifurcaria bifurcata methodologies species [13]. Compared used to their extract cyclic and congeners, identify these linear are quite diterpenes rare from B. bifurcatain nature.as well In addition, as the currenta wide variety findings of promising on their biological biological activities properties. have been Theattributed major to challengesthese and strengthscomponents. for the exploitation Although a detailed of this revision fraction of oftheB. different bifurcata linearare diterpenes also discussed. already identified in B. bifurcata has been previously reported [14], an overview of the B. bifurcata diterpenes’ properties together with information about how these components can be extracted and identified is needed in 2. Bifurcaria bifurcata General Characteristics and Linear Diterpenes Chemical Families order to boost their exploitation. In this vein, the purpose of this paper is to review the different B.extraction bifurcata andis acharacterization brown macroalga, methodologies and dueused toto extract its morphology and identify linear it is diterpenes classified from as aB. cylindrical bifurcata as well as the current findings on their biological properties. The major challenges and species [15] and can be scientifically classified as follows [16]: strengths for the exploitation of this fraction of B. bifurcata are also discussed. Empire: Eukaryota • 2. Bifurcaria bifurcata General Characteristics and Linear Diterpenes Chemical Families Kingdom: Chromista • B. bifurcata is a brown macroalga, and due to its morphology it is classified as a cylindrical Phylum: Ochrophyta • species [15] and can be scientifically classified as follows [16]: Class:• PhaeophyceaeEmpire: Eukaryota • Subclass:• Kingdom: Fucophycidae Chromista • • Phylum: Ochrophyta Order: Fucales • • Class: Phaeophyceae Family:• Sargassaceae • Subclass: Fucophycidae Genus:• Order:Bifurcaria Fucales • • Family: Sargassaceae This• brownGenus: macroalgaBifurcaria lives in rock pools on the lower and middle tidal, needing shores for its settlement,This andbrown is macroalga distributed lives alongin rock thepools coast on the of lower the and Northern middle tidal, Atlantic, needing between shores for Morocco its and Northwesternsettlement, Ireland and is [17distributed]. About along 56% the of thecoast published of the Northern (and hereAtlantic, reviewed) between studiesMorocco concerningand the Northwestern Ireland [17]. About 56% of the published (and here reviewed) studies concerning the B. bifurcata linear diterpeneslinear diterpenes fraction fraction of of B. bifurcatause use samplessamples from from the the coast coast of France of France (Figure (Figure 1), which1), may which may be associatedbe associated with the with high the abundance high abundance of thisof this macroalga macroalga on that that area area [8,17–37]. [8,17– 37]. Figure 1. Distribution, in percentage, of the studies on B. bifurcata linear diterpenes and/or on related Figure 1. Distribution, in percentage, of the studies on B. bifurcata linear diterpenes and/or on related biological activities, according to the sampling location. The percentages presented in this graphic were biological activities, according to the sampling location. The percentages presented in this graphic determinedwere determined considering considering the number the number of samples of samples of each of each geographical geographical locationlocation in in all all published published studies here reviewed.studies here (Analyzing reviewed. (Analyzing Institute Institute for Scientific for Scientific Information Information (ISI) (ISI) Web Web of of Knowledge, Knowledge, keywords: Bifurcariakeywords: bifurcata, Bifurcariaditerpenes; bifurcata, timespan: diterpenes; 1980–2019).timespan: 1980–2019). Additionally,Additionally, all studies all studies reviewed reviewed herehere have have used used wild wild samples samples of B. bifurcata of B. bifurcata, with the, exception with the exception of the work of Santos et al. [38], in which B. bifurcata was collected from the Portuguese coast and of the work of Santos et al. [38], in which B. bifurcata was collected from the Portuguese coast and cultivated in a land-based aquaculture system for three weeks at constant controlled conditions. cultivated in a land-based aquaculture system for three weeks at constant controlled conditions. Mar. Drugs 2019, 17, 556 3 of 30 Concerning the different sampling locals as well as the exposure to different environmental factors, it is expected that this variety of B. bifurcata presents diverse compositions. Mar. Drugs 2019, 17, x FOR PEER REVIEW 3 of 29 Linear Diterpenes Families of B. bifurcata Concerning the different sampling locals as well as the exposure to different environmental