Characterization of substituted aryl meroterpenoids from red seaweed Hypnea musciformis as potential antioxidants Kajal Chakraborty ⇑ , Deepu Joseph, Minju Joy, Vamshi Krishna Raola Marine Biotechnology Division, Central Marine Fisheries Research Institute, Ernakulam North, P.B. No. 1603, Cochin, India article info Article history: Received 29 December 2015 Received in revised form 19 May 2016 Accepted 14 June 2016 Available online 15 June 2016 Keywords: Seaweed Hypnea musciformis Antioxidant activity Aryl meroterpenoids Nuclear magnetic resonance spectroscopy Structure-activity relationship abstract The ethyl acetate fraction of red seaweed Hypnea musciformis was purified to yield three substituted aryl meroterpenoids, namely, 2-(tetrahydro-5-(4-hydroxyphenyl)-4-pentylfuran-3-yl)-ethyl-4-hydroxy benzoate (1), 2-2-[(4-hydroxybenzoyl)-oxy]-ethyl-4-methoxy-4-2-[(4-methylpentyl)oxy]-3,4-dihydro-2 H-6-pyranylbutanoic acid (2) and 3-((5-butyl-3-methyl-5,6-dihydro-2H-pyran-2-yl)-methyl)-4-meth oxy-4-oxobutyl benzoate (3). The structures of these compounds, as well as their relative stereo- chemistries, were confirmed by exhaustive NMR spectroscopic data analyses. Compound 1 exhibited sim- ilar 2,2 0 -diphenylpicrylhydrazyl radical inhibiting and Fe 2+ ion chelating activities (IC 50 25.05 and 350.7 lM, respectively) as that of commercial antioxidant gallic acid (IC 50 32.3 and 646.6 lM, respec- tively), followed by 3 (IC 50 231.2 and 667.9 lM, respectively), and 2 (IC 50 322.4 and 5115.3 lM, respec- tively), in descending order of activities. Structure-activity relationship analysis revealed that the antioxidant activities of these compounds were directly proportional to the steric and hydrophobic parameters. The seaweed derived aryl meroterpenoids might serve as potential lead antioxidative mole- cules for use in pharmaceutical and food industries. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Marine resources, especially, seaweeds have drawn significant interest in recent years in the search for bioactive compounds, which showed great potential as anti-inflammatory, antimicrobial, antiviral and anti-tumor drugs (Souza et al., 2012; Chakraborty & Paulraj, 2010). Antioxidant compounds play an important role against these diseases, which explain their considerable commer- cial potential in pharmaceutical and food industries. Therefore, consumption and addition of antioxidant compounds in food materials protect the body, as well as food, against oxidative degra- dation of biomolecules. Due to concerns regarding the carcinogenic and adverse effects of commercially available synthetic antioxi- dants, the natural antioxidants were in greater demand in recent years (Yangthong, Towatana, & Phromkunthong, 2009). Seaweeds are photosynthetic organisms, and are exposed to a combination of stressful factors, namely, light and molecular oxy- gen, which are responsible for the formation of various oxidative agents and free radical species. Absence of oxidative damages in the structural components of these species, suggested the presence of bioactive metabolites with antioxidative defense systems in their cellular system (Escrig, Jiménez-Jiménez, Pulido, & Saura- Calixto, 2001). Therefore, these marine flora have been the favour- ite choice of natural chemical products to isolate potential antiox- idative lead molecules. Many researchers established that seaweeds are rich in compounds with free radical scavenging prop- erties (Wang, Zhang, Duan, & Li, 2009; Zubia et al., 2009), which can act against lipid oxidation in foods and oxidative stress in tar- get tissues. The majority of bioactive antioxidative compounds from seaweeds were identified as phylopheophylin in Eisenia bicy- clis (Cahyana, Shuto, & Kinoshita, 1992), phlorotannin metabolites from Sargassum kjellamanianum (Yan, Li, Zhou, & Fan, 1996) and fucoxanthin in Hijikia fusiformis (Yan, Chuda, Suzuki, & Nagata, 1999). In our previous study, we have demonstrated that the ethyl acetate (EtOAc) fraction derived from the aqueous methanol extract of red seaweed Hypnea musciformis has significantly higher antioxidant activity than n-hexane and dichloromethane (DCM) fractions (Chakraborty, Joseph, & Praveen, 2015). The preliminary antioxidant activity results for this seaweed obtained in our labo- ratory justifies the logistic need to pursue further research with regard to the antioxidative principles in the EtOAc fraction of the red seaweed H. musciformis. With this background, the current investigation was focused on isolation of the main antioxidant molecules from the EtOAc-soluble fraction of H. musciformis http://dx.doi.org/10.1016/j.foodchem.2016.06.039 0308-8146/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: kajal_cmfri@yahoo.com (K. Chakraborty). Food Chemistry 212 (2016) 778–788 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem