LAUSR

Nannochloropsis oculata is a unicellular small green alga belonging to the Eutigmatophyceae. It is found in both marine and freshwater. It plays an important role in the food chain and is commonly used as live feed [1, 2]. It is one of a few phytoplanktonic species available to grow on a large scale. To the best of our knowledge, most of the research on N. oculata have focused on the culturing conditions for lipid production [3–6] and its application as biodiesel [7–9]. The previous study showed that palmitic acid (C16:0), oleic acid (C18:1), and arachidic acid (C20:0) were dominant in N. oculata oil. To date, there is no paper on the isolation of other bioactive compounds from N. oculata. This is surprising due to the fact that many other microalgae genera are intensively screened with the aim of finding novel compounds that might lead to therapeutically useful agents [8–10]. This fact is the motivation of our research on the isolation and structural characterization of bioactive natural products from Nannochloropsis species. From our preliminary studies, N. oculata was selected since its ethyl acetate extract showed interesting antimicrobial activity against E. faecalis (MIC 128 μg/mL), S. aureus (MIC 256 μg/mL), B. cereus (MIC 256 μg/mL), and P. aeruginosa (MIC 256 μg/mL), and significant cytotoxic activity against MCF7, HepG2, SK-LU-1, and KB with IC50 values of 41.93 ± 4.51 to 65.08 ± 3.19 μg/mL. This is the first report on the chemical investigation and biological activity of N. oculata, which led to the isolation and identification, based on MS and NMR data and comparison with literature, of the compounds as (22E,24R)-ergosta-7,9,22-trien-3β-ol (1) [10], (22E,24R)-5α,8α-epidioxyergosta-6,22-dien-3β-ol (2) [11], (22E,24R)-ergosta7,22-dien-3β,5α,6β-triol (3) [12], phytol (4) [13], palmitic acid (5) [14], stearic acid (6) [14], and linoleic acid (7) [15]. Compounds 1–3 were tested for antimicrobial activity. Compound 1 shows remarkable activity against E. faecalis, S. aureus, and the yeast C. albicans with MIC values of 16, 64, and 128 μg/mL, respectively. Compound 3 is active against all of the tested microorganisms with MIC values of 128–256 μg/mL. Compound 2 shows no activity against any of the tested microorganisms. The cytotoxicity of isolated compounds 1–3 was tested against HepG2, MCF7, SK-LU-1, and KB cancer cell lines. Among these compounds, compound 1 was the most active against all of the tested cancer cell lines with IC50 values in the range of 22.17 ± 0.73 to 41.59 ± 1.68 μM. Compound 2 exhibits weak activity with IC50 values of 51.93 ± 2.51 to 65.08 ± 1.39 μM. Compound 3 shows no cytotoxicity against all of the tested cancer cell lines.