الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
The marine environment possesses unique biological and chemical characters that play a vital role in discovery of many drug leads. Marine organisms are rich in many active compounds that have valuable biological activities. Seagrasses are unique flowering plants that live submersed in shallow coastal seas. Limited studies are found on seagrass even though some valuable bioactive compounds were isolated from seagrasses. Thalassodendron ciliatum (Forssk.) Den Hartog is a seagrass belonging to the plant family Cymodoceaceae, with ubiquitous phytoconstituents and important pharmacological properties, including antioxidant, antiviral, and cytotoxic activities. In this work, a new ergosterol derivative, named thalassosterol 3, was isolated from the methanolic extract of T. ciliatum growing in the Red Sea, along with two known sterols, namely stigmasterol 1 and ergosterol 2 which are reported for the first time in T. ciliatum. The structure of the new compound was established based on 1D and 2D NMR spectroscopy and high-resolution mass spectrometry (HRMS). The new ergosterol derivative showed significant in vitro cytotoxic potential against the cervical cancer HeLa cell line and against the breast cancer MCF-7 cancer cell line, with IC50 values of 8.12 μM and 14.24 μM, respectively. Furthermore, molecular docking studies on the Ulva sp. exhibited diverse biological activities like anti-influenza virus, immune modulatory, anti-human metapneumovirus, antioxidant and antibacterial activities. Herein, we report the isolation of six ceramide compounds (10-15), four new ceramides along with two known ceramides. The isolated ceramides showed antiviral activity against COVID-19 virus via obstruction of viral binding to human host cells. Among them, compounds 13 and 14 were the most effective human angiotensin converting enzyme (hACE) – Spike protein complex inhibitor. Also, compound 13 showed inhibition of COVID-19 protease (Mpro) that is responsible for viral replication and transcription. Moreover, rapid identification of bioactive metabolites of methanolic crude extract of Ulva sp. were performed using liquid chromatography coupled to electrospray ionization high resolution mass spectroscopy (LC-ESI-HRMS). Some of these detected bioactive metabolites also possessed a promising antiviral activity as reported before in previous studies.