Marilines A-C: Novel Phthalimidines from the Sponge-Derived Fungus Stachylidium sp.

A marine-derived fungus of the genus Stachylidium was isolated from the sponge Callyspongia cf. C. flammea. Chemical investigation of the bioactive fungal extract led to the isolation of the novel phthalimidine derivatives marilines A1 (1?a), A2 (1?b), B (2), and C (3). The absolute configurations of the enantiomeric compounds 1?a and 1?b were assigned by a combination of experimental circular dichroism (CD) investigations and quantum chemical CD calculations. The skeleton of marilines is most unusual, and its biosynthesis is suggested to require uncommon biochemical reactions in fungal secondary metabolism. Both enantiomers, marilines A1 (1?a) and A2 (1?b), inhibited human leukocyte elastase (HLE) with an IC50 value of 0.86 mu M.