A Bastadin with Potent and Selective δ-Opioid Receptor Binding Affinity from the Australian Sponge Ianthella flabelliformis

Three new bastadins, bastadin 25 (1), 15-O-sulfonatobastadin 11 (2), and bastadin 26 (3), were isolated from a MeOH extract of the Australian marine sponge Ianthella flabelliformis. Their structures were determined by interpretation of 1D and 2D NMR spectra and mass spectrometry. Bastadin 26 (3) showed potent affinity for the guinea pig delta-opioid receptors with a K(i) value of 100 nM. The other two bastadins had a 100-fold lower affinity. The three compounds were also tested for their affinity to guinea pig mu- and kappa-opioid receptors and shown to have either no affinity or only very weak affinity toward both of these apioid receptors.