Two new sesterterpene tetronic acids, (8 Z,13 Z,18 S,20 Z )-strobilinin ( 1 ) and (7 E,12 Z,18 S,20 Z )-variabilin ( 3 ), together with the known compounds (7 E,12 E,18 S,20 Z )-variabilin ( 5 ), (7 E,13 Z,18 S,20 Z )-variabilin ( 7 ), and (7 Z,12 Z,20 Z )-variabilin ( 9 ), have been isolated from the sponge Ircinia oros as their 22- O -methyl derivatives 2, 4, 6, 8, and 10 . The structures of all compounds were determined by spectroscopic methods, mainly 1D and 2D NMR methodologies.
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Höller et al. (1997) studied this question.