Collisella limatula

The chemical defense of the intertidal limpet Collisella limatula collected from southern California has been identified to be a diketone—limatulone [15 7]( 115). A proposed biosynthesis of limatulone involves oxidation of two molecules of squalene to give keto aldehydes which then undergo aldol condensation to give 157. 

As already described in the first edition of this Comprehensive Series,42 the limpet Achmeia (Collisella) limatula produces a defensive metabolite, limatulone, both as the racemate (57 and its enantiomer) and as the meso-isomer 58.43 This example demonstrates that nature does not always produce enantiomerically pure compounds. 

The intertidal limpet Collisella limatula contains limatulone (914) which inhibits fish and crab predation (600b). Food pellets containing 914 at levels of 0.05% dry weight or more induced regurgitation in the intertidal fish Gibbonsia elegans, a known limped predator. The marine prosobranch mollusc, Lamellaria sp. furnished four aromatic metabolites, lamellarins A-D (915-918) (600 c). At concentrations of 19 pg/mL, 918 caused a 78% inhibition of cell division in the fertilized sea urchin egg assay while 917 caused 15% inhibition and 915 as well as 916 were inactive. 

Little work has been devoted to the class Gastropoda, from which only a few derivatives have been isolated. Limatu-lone is a bicydic triterpene of the squalenoid type produced by the limpet Collisella limatula for protection against predation by crabs and fish (Albizati, Pawhk, and Faulkner, 1985 Pawlik, Albizati, and Faulkner, 1986). Despite the presence of four asymmetric carbon atoms, limatulone is optically inactive and it was determined by total synthesis that natural limatulone contains both the meso derivative and the racemic mixture (Mori, Takikawa, and Kido, 1993). 

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