Parguerenes revisited: New brominated diterpenes from the southern Australian marine red alga Laurencia filiformis

Five new pargueranes, 15-bromoparguer-9(11)-ene-2,7,16,19-tetrol 2,7,16-triacetate (20), 15-bromoparguer-9(11)-ene-2,7,16-triol 2,7-diacetate (21), 15-bromoparguer-9(11)-ene-2,16-diol 2-acetate (22), 15-bromoparguer-9(11)-en-16-ol (23) and 15-bromoisoparguer-9(11)-en-16-ol (24), together with a plausible biosynthetic precursor, preparguerene (25), two known parguerenes, 15-bromoparguer-9(11)-ene-2,7,16,19-tetrol tetraacetate (4) and 15-bromoparguer-9(11)-ene-2,7,16-triol 2,16-diacetate (7), and the known algal metabolites (-)-aromadendrene (17), austradiol acetate (18) and austradiol diacetate (19), have been isolated from a collection of the southern Australian marine red alga Laurencia filiformis. The known synthetic parguerane 15-bromoparguer-9(11)-ene-2,7-16-triol triacetate (5) was also found for the first time as a natural product. In addition to securing the structures of new compounds by chemical correlation and detailed spectroscopic analysis, a plausible biosynthetic pathway has been proposed linking preparguerene, parguerene, isoparguerene and secoparguerene carbon skeletons.