Chemical constituents of the soft coral Sinularia gravis from the coast of Madagascar

Secondary metabolites obtained from marine organisms including animals, plants, and microorganisms are a rich source for new pharmacologically active compounds [1]. The sea waters of Madagascar, the fourth largest island in the world with nearly 5000 km of coastline, accommodates a wealth of marine organisms in its coastal region. To date, only few representatives of Madagascan soft corals have been investigated for their chemical constituents [2 – 4]. The present study aims at the investigation of the chemical constituents of the soft coral Sinularia gravis collected at the coast of Madagascar. Four new compounds, the spatane-type diterpenoid gravilin (1), the monoalkylmonoacylglycerol 2, the dihomoditerpenoid ketone 3, and isodecaryiol (4), along with the three known compounds (+)-(S)-geranyllinalool, (-)-(R)-nephthenol, and 11,12-epoxysarcophytol A have been isolated from S. gravis [5]. The isolated compounds were characterized using ¹H NMR and ¹³C NMR spectroscopy. In combination with COSY, NOESY, HMBC, and HSQC measurements, a complete structural elucidation was achieved. The structure of compound 4 including its absolute stereochemistry was confirmed by single crystal X-ray diffraction.

Acknowledgements: Marie Pascaline Rahelivao is grateful to the European Commission (Erasmus Mundus Programme), the Gesellschaft von Freunden und Förderern der TU Dresden (GFF TU Dresden), and the TUD Graduate Academy for their support by providing scholarships.

Keywords: Soft corals, Cembranoid, Spatane diterpenes, NMR spectroscopy, X-ray diffraction.

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