New steroidal saponins from the sponge Erylus lendenfeldi

Abstract

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 ( 1 H, 13 C, 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 8,9-epoxy-4-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.