Feroxosides A-B, two norlanostane tetraglycosides from tbe Caribbean sponge Ectyoplasia ferox

Feroxosides A and B, have been isolated from the polar extract of the Carib bean sponge Ectyoplasia ferox. Their structures have been determined to be unusual C-4 nor-lanostane triterpenes glycosylated with a rhamnose containi ng tetrasaccharide chain, by interpretation of spectral data and chemical d egradation. Absolute stereochemistry at C-23 has been determined by applica tion of the modified Mosher method for secondary alcohols. Feroxosides A-B are moderately cytotoxic (IC50 19 mug/mL) against murine monocyte-macrophag e cell line. (C) 2001 Elsevier Science Ltd. All rights reserved.