Phrygiasterol, a cytotoxic cyclopropane-containing polyhydroxysteroid, and related compounds from the pacific starfish Hippasteria phrygiana

The new cyclopropane-containing steroid phrygiasterol (1) and steroid glycoside phrygioside B (2), along with previously known borealoside C (2a) and (20R,24S)-5alpha-cholesta-3beta,6alpha,8,15alpha,24-pentaol (3), have been isolated from the Pacific starfish Hippasteria phrygiana. On the basis of spectroscopic analyses, using 1D and 2D NMR techniques and some chemical transformations, the structures of 1 and 2 have been established as (20R,24R,25R)-24,26-cyclo-5alpha-cholesta-3beta,6alpha,8,15alpha,16beta,27-hexaol (1) and the sodium salt of (20R,24S)-24-O-(3-O-methyl-4-O-sulfate-beta-d-xylopyranosyl)-5alpha-cholesta-3beta,6alpha,8,15alpha,24-pentaol (2), respectively. Compound 1 inhibited the growth of Ehrlich carcinoma cells with an IC(50) of 50 microg/mL, whereas 2 induced apoptosis of the same cells (EC(50)=70 microg/mL) and inhibited Ca(2+) influx into mouse spleenocytes (EC(50)=20microg/mL).