| Summary: | Two new pyrrolosesquiterpenes, glaciapyrroles D (<b>1</b>) and E (<b>2</b>) were discovered along with the previously reported glaciapyrrole A (<b>3</b>) from <i>Streptomyces</i> sp. GGS53 strain isolated from deep-sea sediment. This study elucidated the planar structures of <b>1</b> and <b>2</b> using nuclear magnetic resonance (NMR), mass spectrometry (MS), ultraviolet (UV), and infrared (IR) spectroscopic data. The absolute configurations of the glaciapyrroles were determined by Mosher’s method, circular dichroism spectroscopy, and X-ray crystallography. Under 366 nm UV irradiation, the glaciapyrroles were systematically converted to the corresponding photoglaciapyrroles (<b>4</b>–<b>6</b>) via photoisomerization, resulting in the diversification of the glaciapyrrole family compounds. The transformation of the glaciapyrrole <i>Z</i> to <i>E</i> isomers occurred in a 1:1 ratio, based on virtual validation of the photoisomerization of these olefinic compounds by <sup>1</sup>H-NMR spectroscopy and liquid chromatography/mass spectrometry (LC/MS) analysis. Finally, when encapsulated in poly(lactic-co-glycolic acid) nanoparticles, glaciapyrrole E and photoglaciapyrrole E displayed significant inhibitory activity against influenza A virus. This is the first report of antiviral effects from glaciapyrrole family compounds, whose biological functions have only been subjected to limited studies so far.
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