Helicascolide C, a new lactone from an Indonesian marine algicolous fungus

From the agar-producing red alga Gracilaria sp., collected from the coast of South Sulawesi, Indonesia, an endophytic fungal strain KT32 was isolated. The fungus was then mass cultivated to produce external secondary metabolites. The ethyl acetate extracts of the culture broth exhibited antimicrobial activity against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Vibrio anguillarum and Aeromonas salmonicida.

The active compounds were determined using bioassay-guided fractionation. Separation by chromatography on silica gel column yielded an antimicrobially active fraction. Further purification of the compounds was done through semi-preparative HPLC. The new natural product helicascolide C was obtained as colorless crystals. Thin plates (5µm) were measured at 100 K with a Saturn92 CCD detector mounted on a Micromax007 rotating anode X-ray source (Rigaku). The collected data (0.85 Å resolution, space group P212121, a=5.718(8), b=9.789(10), c=20.33(10)) revealed a new chemical entity similar to known helicascolides. Previously the compounds helicascolides A and B were found from the marine fungus Helicascus kanaloanus [1]. The structure of the new compound reveals a keto group replacing an alcohol group. Additional characterization was done on the basis of NMR spectroscopic data and mass spectrometric analyses.

References: 1. Poch, G.K., Gloer, J.B. (1989)J. Nat. Prod. 52 (2):257–260.