LCMS analysis of an extract of the New Zealand tunicate <i>Synoicum kuranui</i> showed evidence for numerous new rubrolides. Following a mass spectrometry-guided isolation procedure, new hydrated rubrolides V and W (<b>5</b> and <b>6</b>), along with previously reported rubrolide G (<b>3</b>), were isolated and characterized using MS and NMR. The anti-bacterial and cell cytotoxic activity of the compounds were compared to the potent anti-MRSA compound rubrolide A; hydration across the C-5/C-6 bond was shown to abrogate antibacterial activity.