Siphonaria

Pulmonates are air-breathing molluscs that do not include many families and genera [68]. Siphonaria species from many distinct geographical areas possess a series of secondary metabolites with polypropionate skeletons characterized by the presence of ketal, pyrone and furanone moieties [47]. A rigorous biosynthetic experiment [69] proved that Siphonaria denticulata is able to... 

Biogenetic considerations [71], and a correlation of all polypropionates from pulmonate molluscs led to revision of the relative stereochemistry of pectinatone (20) and nor-pectinatone (21), metabolites of the pulmonate Siphonaria pectinata [72, 73] the point had already been questioned by Oppolzer s synthesis [74] and was definitively confirmed by two independent X-ray diffraction studies [71, 75] of pectinatone (20). 

Norte, M., Cataldo, F., and Gonzalez, A. G., Siphonarienedione and siphonarienolone, two new metabolites from Siphonaria grisea having a polypropionate skeleton, Tetrahedron Lett., 29, 2879, 1988. 

Manker, D. C., Garson, M. J., and Faulkner, D. J., De novo biosynthesis of polypropionate metabolites in the marine pulmonate Siphonaria denticulata, J. Chem. Soc. Chem. Commun., 1061, 1988. 

Garson, M. J., Jones, D. D., Small, C. J., Liang, J., and Clardy, J., Biosynthetic studies on polypropionates a stereochemical model for siphonarins A and B from the pulmonate limpet Siphonaria zelandica, Tetrahedron Lett., 35, 6921, 1994. 

Some shelled gastropods do produce chemical defenses, although this is far less common. One South African limpet, Siphonaria capensis, occurs at very high densities on rocky shores, apparently protected from predators by chemical feeding deterrents. These animals are rarely consumed relative to Patella granularis (a similar limpet that lacks defensive chemistry) and exude a repellent mucus onto the surface of their shell when attacked. Nonpolar extracts from Siphonaria confer resistance from predation to Patella when they are coated on its shell.20 Because the metabolites responsible for the chemical defense have not been fully isolated and characterized, it is still unclear whether the compounds that confer resistance to predation in Siphonaria are diet derived or synthesized de novo. 

McQuaid, C.D., Cretchley, R., and Rayner, J.L., Chemical defence of the intertidal pulmonate limpet Siphonaria capensis (Quoy Gaimard) against natural predators, J. Exp. Mar. Biol. Ecol, 237, 141, 1999. 

Active-Site Nucleophile of Bacillus circulans Xylanase Novel Metabolites of Siphonaria pectinata... 

The most prominent source of marine polypropionates are mollusks, in particular opisthobranchs (13). Among a variety of polypropionates, the simplest one is possibly siphonarienal (9) isolated from Siphonaria grisea, whereas such unusual pyrone-containing metabolites as siphonarin A (10) were isolated from S. zelandica. Marine polypropionates not only play defensive roles in mollusks, but also they show antimicrobial, anti vial, and cytotoxic activities. 

A chemical study of an acetone extract of the Mexican, maura (collected at Sayulita, Mexico) resulted in the isolation of two polypropionate metabolites, vallartanone A [ 15 5] and vallartanone B [156](114) which have structures quite different from other polypropionate metabolites of the genus Siphonaria. An unrelated polypropionate, maurenone [150] which was previously isolated from the Mexican 5. maura was also present along with vallartanone A and B. It appears that pulmonates of the genus Siphonaria synthesize similar metabolites derived fiom the condensation... 

In addition to siphonarin A [140], the fljian mollusk Siphonaria normalis has been reported to contain an unusual tricyclic ketal with a trioxaadamantane ring skeleton. The structure of muamvatin 2 [161] was determined by nmr spectroscopy (118). The possible roles of the polypropionate metabolites isolated from S honaria species could be associated with its trailfollowing habits along with defense against predators. 

Denticulatins A and B. The denticulatins A (250) and B (251) were isolated in 1983 from the marine mollusc Siphonaria denticulata and are highly oxygenated structures with seven contiguous stereocenters (Scheme 9-67). Three total syntheses of these molecules rely upon aldol reactions to assemble triketone 252. a key intermediate, forming either the Ciq-Ch or C9-C10 bond at a late stage. 

Snails of the genus Siphonaria live as lung-breathing mollusks in tidal zones of the oceans. They contain secondary metabolites biosynthetically formed by condensation of polypropionate units e.g.,D.A from S. den-ticulata, C23H40O5, Mr 396.57, oil, [aJu -30.7° and siphonarin A from S. zelandica and S. atra, C28H42O8, Mr 506.64, cryst., mp. 164-166 °C, [a]o +21.7°. 

Isol. from the mollusc Siphonaria zelandica. [a]r, —19 (CHCI3). 

Metab. of the mollusc Siphonaria maura. Oil. Related to Stegobiol, S-01220. 

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