New steroidal saponins from the sponge Erylus lendenfeldi

Our search for biologically active marine natural products has led to the isolation of two new steroidal saponins, eryloside K ( 2) and eryloside L ( 3) together with the known antitumor and antifungal glycoside eryloside A ( 1) from the organic extract of the sponge Erylus lendenfeldi (Geodiidae) collected in the Red Sea. The structures of the new compounds were elucidated on the basis of comprehensive spectral analyses (H-1, C-13, COSY, HMQC, HMBC and TOCSY NMR) as well as GC/MS analysis to infer the absolute stereochemistry of the sugar moieties. Eryloside K ( 2) is the 24,25-didehydro congener of 1, while eryloside L ( 3) features an unusual 8 alpha, 9 alpha-epoxy-4 alpha-methyl-8,9-secocholesta-7,9( 11), 14-triene skeleton which appears to be unprecedented in nature. Eryloside A ( 1) displayed antibacterial activity against Bacillus subtilis and Escherichia coli together with antifungal activity against Candida albicans.