Investigation of the role of diterpenes produced by marine pulmonates Trimusculus reticulatus and T-conica

The intertidal pulmonate limpet Trimusculus reticulatus, which is found in caves or crevices along the California coast, was previously reported to contain two novel diterpenoids, 6 beta-isovaleroxylabda-8,13-dien-7 alpha,15-diol (1) and 2 alpha,7 alpha-diacetoxy-6 beta-isovaleroxylabda-8,11-dien-15-ol (2). Dissection of the animals prior to extraction revealed that the diterpenoids were concentrated in the mantle, foot, and mucus, but not in the viscera. The presence of T. reticulatus or its mucus was toxic to veliger larvae of the sabellariid reef-building tube worm Phragmatopoma californica. The major diterpenoid 1 was responsible for the observed larvicidal activity. Protection against overgrowth by settling invertebrate larvae is important for the survival of this sessile filter-feeding pulmonate. A related pulmonate, T. conica, which was found in similar intertidal habitats in New Zealand, contained 6 beta-acetoxy-7 alpha-isovaleroxylabda-8,13-dien-15-oic acid (3) and 1 beta,7 beta,12 beta,18-tetraacetoxy- cholest-5-en-3 beta-ol (4). The diterpene 3 was also localized in the foot, mantle, and mucus of T. conica but was not larvicidal to P. californica.