Pursuing sesterterpene lactams in Australian Irciniidae sponges.

Chemical investigation of two Irciniidae sponges collected by hand (SCUBA) from Australian near shore waters, afforded six new examples of a rare class of sesterterpene lactam; ircinialactams B (1), G (2), H (5), and I (6), and 8-hydroxyircinialactams C (3) and G (4); together with the new biosynthetically related lactone, ircinialactone A (7). Also isolated were seven biosynthetically related known Irciniidae metabolites; ircinialactams A (8) and C (9), (7E,12E,20Z,18S)-variabilin (10), (7Z,12Z,20Z,18S)-variabilin (11), (7E,12Z,20Z,18S)-variabilin (12), (7Z,12E,20Z,18S)-variabilin (13) and irciniafuran A (14). The structure elucidation of 1-14 was achieved by detailed spectroscopic analysis, and consideration of a plausible biosynthetic relationship linking Irciniidae sesterterpene β-furans, lactams and lactones.