Quintaquinone, a Merosesquiterpene from the Yellow Sponge Verongula cf. rigida Esper

A chemical investigation of the sponge Verongula cf. rigida led to the isolation of 13 merosesquiterpenes, among which quintaquinone (2), 5-epi-nakijiquinone L (3), and 3-farnesyl-2-hydroxy-5-methoxyquinone (4) were isolated and reported here for the first time. Particularly, compound 2 is the first member of merosesquiterpenes with a polyketide side chain substituted on C-19. All of the isolated compounds were examined for steroid 5a-reductase inhibitory activity. Cyclospongiaquinone 1 (5) showed a strong activity in the same range as that of standard finasteride.