Abstract
In our search for bioactive metabolites from marine organisms, we have investigated the polar fraction of the organic extract of the Red Sea sponge Theonella swinhoei. Successive chromatographic separations and final HPLC purification of the potent antifungal fraction afforded a new bicyclic glycopeptide, theonellamide G (1). The structure of the peptide was determined using extensive 1D and 2D NMR and high-resolution mass spectral determinations. The absolute configuration of theonellamide G was determined by chemical degradation and 2D NMR spectroscopy. Theonellamide G showed potent antifungal activity towards wild and amphotericin B-resistant strains of Candida albicans with IC50 of 4.49 and 2.0 μM, respectively. Additionally, it displayed cytotoxic activity against the human colon adenocarcinoma cell line (HCT-16) with IC50 of 6.0 μM. These findings provide further insight into the chemical diversity and biological activities of this class of compounds.
Highlights
The order Lithistida include the genera Theonella, Discodermia, Aciculites, Microscleroderma, and Callipelta
Lithistid sponges have been shown to yield a wide variety of bioactive marine natural products that include unique cyclic peptides and depsipeptides [1,2,3]
Our previous investigation on the Red Sea Theonella swinhoei led to the isolation of several macrolides including swinholide A, I and hurghadolide A [17]
Summary
The order Lithistida include the genera Theonella, Discodermia, Aciculites, Microscleroderma, and Callipelta. The genus Theonella is known to be a rich source of structurally diverse, biologically active peptides [1] including polytheonamides [4], cyclotheonamides [5], theonellapeptolides [6], theonellamides [7], theonegramides [8], keramamides [9], mozamides [3], mutoporins [10], microsclerodermins [11], cupolamide [12], oriamide [13], and cyclolithistide A [14]. Our previous investigation on the Red Sea Theonella swinhoei led to the isolation of several macrolides including swinholide A, I and hurghadolide A [17]. We describe the isolation, structure elucidation, and biological activity of a new bicyclic glycopeptide, theonellamide G (1). The Red Sea sample did not contain any of the previously reported theonellamides
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