Abstract
The chemical investigation of an Indonesian specimen of Theonella swinhoei afforded four aurantosides, one of which, aurantoside J (5), is a new compound. The structure of this metabolite, exhibiting the unprecedented N-α-glycosidic linkage between the pentose and the tetramate units, has been determined through detailed spectroscopic analysis. The four obtained aurantosides have been tested against five fungal strains (four Candida and one Fusarium) responsible of invasive infections in immuno-compromised patients. The non-cytotoxic aurantoside I (4) was the single compound to show an excellent potency against all the tested strains, thus providing valuable insights about the antifungal potential of this class of compounds and the structure-activity relationships.
Highlights
Aurantosides and rubrosides are orange-red pigments isolated from sponges of the generaTheonella, Homophymia and Siliquariaspongia, all belonging to the order Lithistida [1,2,3,4,5]
The structures of the known aurantosides G–I (2–4) were identified on the basis of the comparison of their spectral data with those reported in the literature [4]
It is worth noting that all the aurantosides isolated during this work showed the same length and constitution of the polyene side chain, while aurantosides with longer and/or dichlorinated polyene chain
Summary
Aurantosides and rubrosides are orange-red pigments isolated from sponges of the genera. Compared to non-ribosomial cyclic and linear peptides and to polyketide macrolides, the most widely investigated secondary metabolites from sponges of the Lithistida order, aurantosides have been largely overlooked, in terms of their biomedical potential The reasons for this observation can be mostly found in the difficulties associated to their isolation in the pure form and to their relative instability, which is obviously related to the presence of the polyene moiety. In the frame of our ongoing investigation of Indonesian invertebrates for bioactive secondary metabolites [6,7,8], we have recently analyzed a specimen of Theonella swinhoei (Theonellidae, Lithistida) and reported the isolation of dehydroconicasterol and of aurantoic acid (1) [9] This latter compound closely resembles the polyene moiety of aurantosides G–I [4], the biosynthetic relationship between aurantoic acid and aurantosides has not been established.
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