Magnificines A and B, Antimicrobial Marine Alkaloids Featuring a Tetrahydrooxazolo[3,2-a]azepine-2,5(<i>3H,6H</i>)-dione Backbone from the Red Sea Sponge <i>Negombata magnifica</i>

• Main Authors: Diaa T. A. Youssef, Hani Z. Asfour, Grégory Genta-Jouve, Lamiaa A. Shaala
• Format: Article
• Language: English
• Published: MDPI AG 2021-04-01
• Series: Marine Drugs
• Subjects: Red Sea sponge; <i>Negombata magnifica</i>; marine alkaloids; β-ionone; magnificines A and B; (±)-negombaionone
• Online Access: https://www.mdpi.com/1660-3397/19/4/214
• ISSN: 1660-3397

Investigation of the Red Sea sponge <i>Negombata magnifica</i> gave two novel alkaloids, magnificines A and B (<b>1</b> and <b>2</b>) and a new β-ionone derivative, (±)-negombaionone (<b>3</b>), together with the known latrunculin B (<b>4</b>) and 16-<i>epi</i>-latrunculin B (<b>5</b>). The analysis of the NMR and HRESIMS spectra supported the planar structures and the relative configurations of the compounds. The absolute configurations of magnificines A and B were determined by the analysis of the predicted and experimental ECD spectra. Magnificines A and B possess a previously unreported tetrahydrooxazolo[3,2-<i>a</i>]azepine-2,5(<i>3H,6H</i>)-dione backbone and represent the first natural compounds in this class. (±)-Negombaionone is the first β-ionone of a sponge origin. Compounds <b>1</b>-<b>3</b> displayed selective activity against <i>Escherichia coli</i> in a disk diffusion assay with inhibition zones up to 22 mm at a concentration of 50 µg/disc and with MIC values down to 8.0 µM. Latrunculin B and 16-<i>epi</i>-latrunculin B inhibited the growth of HeLa cells with IC₅₀ values down to 1.4 µM.