Antimicrobial Rubrolides from a South African Species of Synoicum Tunicate

The CH2Cl2–MeOH extract of a South African tunicate described as the new Synoicum globosum Parker-Nance sp. nov. (Ascidiacea, Aplousobranchia) was subjected to 1H NMR-guided fractionation. This resulted in the identification of new 3″-bromorubrolide F (1), 3′-bromorubrolide E (2), 3′-bromorubrolide F (3), and 3′,3″-dibromorubrolide E (4) and reisolation of known rubrolides E (5) and F (6), based on NMR spectroscopic and mass spectrometric data. Biological testing of both new and known members of this reported antimicrobial family of halogenated, aryl-substituted furanones indicated moderate antibacterial properties for 3′-bromorubrolide E (2), 3′,3″-dibromorubrolide E (4), and rubrolide F (6) against methicillin-resistant Staphylococcus aureus (MRSA) and S. epidermidis.