An NMR and ultra-high resolution mass investigation of secondary metabolites from a Red Sea sponge Ircinia sp. led to the isolation and characterisation of a new ketone. The structure has been assigned on the basis of detailed spectroscopic analysis (1H, 13C, DEPT, COSY, HMQC and HMBC NMR spectra) as 7-methyl-9-oxo-dec-7-eneoic acid (1). Ultra-high resolution FTMS was utilised to facilitate the formulation and structure assignment because there was a broad and undetectable carbon signal in the NMR spectra.
