Purpuramine R, a New Bromotyrosine Isolated from Pseudoceratina cf. verrucosa Collected in the Kingdom of Tonga

Sponges in the verongiid genus <i>Pseudoceratina</i> Carter are well-known producers of bioactive secondary metabolites. Chemical screening of a Tongan <i>P.</i> cf. <i>verrucosa</i> Bergquist using NMR highlighted the presence of aromatic natural products. Subsequent extraction and purification of <i>P.</i> cf. <i>verrucosa</i> yielded a new bromotyrosine, purpuramine R (<b>1</b>), that exhibits moderate (MIC 16 µg/mL) antibacterial activity against Gram-positive <i>Staphylococcus aureus.</i> The <i>E</i>-geometry of the oxime was confirmed using a combination of NMR and computational approaches. Additionally, computational conformational analysis indicates that purpuramine R adopts a hairpin orientation, stabilized by intramolecular hydrogen and halogen bonds. Knowledge of this stabilized conformation can inform synthetic approaches to make analogues of the purpuramines for future SAR studies.