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 H-1 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.