Synthesis and identification of an endogenous sperm activating and attracting factor isolated from eggs of the ascidian Ciona intestinalis; an example of nanomolar-level structure elucidation of novel natural compound

A sperm-activating and attracting factor (SAAF) was isolated from the eggs of the ascidian Ciona intestinalis, and its structure was deduced with only approximately 4 μg of the specimen. Based upon the proposed structure, two epimers were synthesized from chenodeoxycholic acid in 16 steps. Comparison between synthetic and natural compounds led to the unambiguous structure determination of SAAF to be (3R,4R,7R,25S)-3,4,7,26-tetrahydroxycholestane-3,26-disulfate. The synthetic pure specimen was also utilized to confirm that both sperm-activation and attraction were elicited by a single compound.