Novel norsesterterpenes, which inhibit gastrulation of the starfish embryo, from the marine sponge Rhopaloeides sp.

Two new norsesterterpenes, rhopaloic acids B (2) and C (3), have been isola ted from the marine sponge Rhopaloeides sp. together with the known rhopalo ic acid A (1). Their structures have been elucidated by spectroscopic metho ds. Compounds 1, 2, and 3 potently inhibited gastrulation of the starfish ( Asterina pectinifera) embryo, whereas hydrogenation or esterification resul ted in toss of the inhibitory activity. Furthermore, methacrylic acid (9) d id not affect embryonic development. These results suggest that the a-exo-m ethylene carboxyl functionality attached to a tetrahydropyran ring is essen tial for the inhibitory activity of 1-3. (C) 1998 Elsevier Science Ltd. All rights reserved.