(2 S ,3' S ,3a' R ,5' R ,7a' R )-5'-[( E )-5-(Furan-3-yl)-2-methyl-pent-1-en-1-yl]-3-hy-droxy-3',4,7'-trimethyl-1',2',3',3a',5',7a'-hexa-hydro-5 H -spiro-[furan-2,4'-inden]-5-one.

The title compound, ircinianin, C 25 H 32 O 4 , belongs to the sesterterpene tetronic acid compound family and was isolated from the marine sponge Ircinia wistarii . These chemical scaffolds are pharmacologically relevant, since they represent a new class of glycine receptor modulators. The furan ring makes a dihedral angle of 35.14 (12)° to the 4-hy-droxy-3-methyl-furan-2( 5H )-one ring. The crystal packing is characterized by inter-molecular O-H⋯O hydrogen bonds, which generate [010] chains.