The re-investigation of the crude extract obtained from the sponge Aplysina caissara led to the isolation of five new dibromotyrosine derivatives, named agelocaissarines A1, A2, B1, B2 and caissarine C, along with the already known fistularin-3 and 11-hydroxyaerothionin. All compounds were identified by analysis of mono- and bidimensional NMR spectra, high resolution mass spectra, infrared and ultraviolet spectra. The relative stereochemistry of agelocaissarines could be established by analysis of ¹H NMR spectra and molecular modeling, while the absolute configuration of the spiroxazolidine moieties of fistularin-3, caissarine C and 11-hydroxyaerothionin was established by analysis of ¹H NMR and circular dichroism spectra. Fistularin-3 and 11-hydroxyaerothionin displayed moderate antibiotic activity against several pathogenic bacteria.
sponge; Aplysina caissara; dibromotyrosine; absolute configuration
