<jats:title>Abstract</jats:title> <jats:p>In the search for new bioactive compounds from extremophilic actinomycetes, a new marine actinomycete strain, <jats:italic>Nocardiopsis lucentensis</jats:italic> sp. ASMR2 has been isolated and taxonomically identified from marine plants collected in the Red Sea at Hurghada coasts. A large-scale fermentation of the strain on modified rice solid medium was performed, followed by work-up and purification of the obtained extract using a series of chromatographic purifications, delivering the novel butenolide system 3′-hydroxy-<jats:italic>N</jats:italic>-(2-oxo-2,5-dihydrofuran-4-yl)propionamide (<jats:bold>1a</jats:bold>) along with the naturally new 4-methoxy-2<jats:italic>H</jats:italic>-isoquinolin-1-one (<jats:bold>2</jats:bold>). Furthermore, eight known bioactive compounds are also reported, namely, indole-3-carboxylic acid, indole-3-acetic acid, indole-3-acetic acid methyl ester, furan-2,5-dimethanol, tyrosol, glycerol linoleate, cyclo-(Tyr, Pro), and adenosine. The chemical structures of the new compounds (<jats:bold>1a</jats:bold>, <jats:bold>2</jats:bold>) were confirmed by extensive one- and two-dimensional (1D and 2D) nuclear magnetic resonance (NMR) spectroscopy, electron ionization high resolution (EI-HR) mass spectrometry, and by comparison with literature data. The antimicrobial activity of the strain extract, as well as of compounds <jats:bold>1a</jats:bold> and <jats:bold>2</jats:bold>, were studied using a panel of pathogenic microorganisms. The <jats:italic>in vitro</jats:italic> cytotoxicity of the bacterial extract and compounds <jats:bold>1a</jats:bold> and <jats:bold>2</jats:bold> were studied against the human cervix carcinoma cell line (KB-3-1) and its multidrug-resistant subclone (KB-V1).