A bioactive cyclitol derivative (1) was isolated from the marine sponge Pet
rosia sp. The chemical structure of 1 was determined as (2S)-1-O-(2',3',4',
5'-tetrahydroxycyclopentyl)3-O-(10 "-methylhexadecyl)glycerol. Compound 1 i
nhibited DNA replication in vitro at the level of initiation.