Structural and stereochemical studies on brominated meroterpenoids From the dictyoceratid sponge Cacospongia sp.
The structures of seven minor metabolites, (5)-(11), from the encrusting sponge Cacospongia sp. Were deduced by 1H, 13C and mass spectrometric data. Compounds (5)-(7) are hydroxy derivatives of the previously isolated tribromocacoxanthene (1); their relative stereochemistry was determined from 1H-1H coupling information. Compounds (8)-(11) represent an alternative cyclization mode of a cyclocymopol-related precursor (15) and possess a spiro-fused bicyclic ring system; the relative stereochemistry of (8)-(10) was deduced by 1H n.O.e. difference spectroscopy. The biological role of brominated meroterpenoids in Cacospongia sp. is discussed.