Sulfated steroid – amino acid conjugate from the Irish marine sponge Polymastia boletiformis

Abstract

Polymastia boletiformis, a brightly coloured orange-yellow fistulose sponge is widespread on the coasts of Britain and Ireland. Previous studies on this genus have yielded a number of interesting polyenes [1] and steroids. [2]. In the course of our on-going investigations within the frame of Beaufort Marine Biosdiscovery Research Programme directed to the biological screening and isolation of bioactive metabolites from Irish marine organisms [3], we have evaluated the antifungal activity of a number of Irish marine sponges against the plant pathogen Cladosporium cucumerinum. The crude extract of P. boletiformis, collected from the west coast of Ireland, showed activity against C. cucumerinum at 1 mg/mL. Antifungal activity-guided fractionation of the aqueous methanol-soluble portion of the crude extract by RP18 Flash CC, Sephadex LH-20 gel chromatography and RP18 HPLC led to the isolation of a new, minor sulfated steroid – amino acid conjugate (1). The structure of the new natural product was elucidated on the basis of extensive spectral data analysis, including 1D and 2D NMR experiments (COSY, NOESY, HSQC, HMBC) and HRMS. The assessment of antifungal activity of this metabolite and the identification of the absolute stereochemistry of the chiral centers on the side chain of the molecule is currently underway.