Abstract: The subject invention concerns eryloside F, a novel disaccharide of the steroidal carboxylic acid penasterol. This compound can be isolated from an extract of the marine sponge Erylus formosus. The compound is a potent thrombin receptor antagonist and, furthermore, inhibits human platelet aggregation. Longer chain penasterol oligosaccharides were also isolated and characterized but these had weaker activity than eryloside F. The subject invention also concerns methods for inhibiting thrombin receptor activity and methods for inhibiting platelet aggregation through the administration of eryloside F, or a salt, derivative or analog thereof.

Abstract: The compound N-(.beta.-ketocaproyl)L-homoserine lactone is shown to be an autoinducer that enhances gene expression in a wide variety of microorganisms. Use can be made of this property for diagnostic purposes, e.g., when gene expression causes bioluminescence or antibiotic production, or to promote bacterial growth. The invention claims use for these purposes of the compound and analogs of formula (I) where n is 2 or 3, each of X and Y is O, S or NH, and R is optionally-substituted C1-C12 alkyl or acyl. Some of these are also claimed as new compounds.