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Novel terpenoid metabolites from the marine sponge xestopongia vanilla

University of British Columbia

A chemical study of the marine petrosid sponge Xestospongia vanilla has led to the isolation of nine new isoprene derived secondary metabolites. Their proposed structures were elucidated by a combination of spectroscopic analysis and chemical degradation and interconversions. Xestodiol (94), a C₁₈ apocarotenoid, appears to be a degradation product of the abundant marine carotenoid fucoxanthin (103). The xestovanins (98-102) are triterpene glycosides; their isolation represents the second reported occurrence of this type of compound from sponges. Their triterpene carbon skeletons are unique, and are either monocyclic (secoxestovanane skeleton) or bicyclic (xestovanane skeleton). All the xestovanins contain the same disaccharide fragment composed of L-rhamnose alpha linked to the 4 position of D-fucose. The fucose residue is beta linked to the same position on the aglycone in all isolated xestovanins. Xestovanin D (102) contains an extra L-rhamnose residue attached to a different position on the aglycone. Xestovanin A (98) was found to be an inhibitor of fungal growth, while xestovanin C (101) inhibited the growth of bacteria. A series of three smaller apparently related terpenes was also isolated. Xestenone (95) and secoxestenone (97) both contained new C₁₉ carbon skeletons. Secoxestenone (97), a monocyclic compound, could be converted into the bicyclic xestenone (95) by an intramolecular aldol condensation. The C₂₀ xestolide (96), with a similar structure to both xestenone and secoxestenone, had an unique carbon skeleton that could not be derived readily from an unrearranged diterpene skeleton. It is suggested that these three smaller terpenes (95-97) are degraded triterpenes, derived from a secoxestovanane carbon skeleton. The secondary metabolite chemistry of the petrosid sponges is reviewed, and an overview of triterpenes of marine origin is presented.

Text

2010-10-18

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http://hdl.handle.net/2429/29253

Chemistry

University of British Columbia

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