Placobranchus ocellatus

When the sacoglossan Placobranchus ocellatus was immersed in seawater containing 14C sodium hydrogen carbonate, 14C label was incorporated into both 9,10-deoxytridachione (Structure 2.124) and the photorearrangement product photodeoxytridachione (Structure 2.125).242 In Elysia viridis, sodium [l-14C]propionate was incorporated into elysione (Structure 2.126), an ichthyotoxic metabolite found in the mollusc s mucus secretions.237 Attempts to repeat this propionate labeling experiment in Elysia timida and to test the putative role of acetate in the biosynthesis of 15-norphotodeoxytridachione (Structure 2.127) were unsuccessful.237 243 The metabolites shown in Structures 2.124, 2.125, 2.126, and 2.128, some of which were toxic, were present in the mucus secretion of Elysia timida, consistent with a defensive role.243 The hypothesis that these complex pyrones function as suncreens242 has been disputed.243... 

Ireland, C. M. and Scheuer, P. J., Photosynthetic marine mollusks in vivo 14C incorporation into metabolites of the sacoglossan Placobranchus ocellatus, Science, 205, 922, 1979. 

Placobranchus ocellatus contains both 9,10-deoxytridachione (124) and the photoproduct (125). This finding provides evidence supporting the relevance of a photochemical rearrangement in vivo. ... 

Isol. from Elysia timida and Placobranchus ocellatus. [aj ... 

Manzo, E., Ciavatta, M.L., Gavagnin, M., Mollo, E., Wahidulla, S., and Cimino, G. (2005b) New y-pyrone propionates from the Indian Ocean sacoglossan Placobranchus ocellatus. Tetrahedron Lett., 46, 465— 468. 

Schaefer, C. and Fu, G.C. (2005) Mining the tetraene manifold Total synthesis of complex pyrones from Placobranchus ocellatus. Angeiv. Chem. Int. Ed., 44, 4602-4606. 

The very rmusual bicydo[4.2.0]octane core of the polypropionates isolated from Placobranchus ocellatus and By-sia diomedea (Figure 23.29) is surmised to originate from an 8jt-6jt electrocyclic cascade (Cueto et al., 2005 Manzo et al, 2005a). The often simultaneous presence of 1,3-cyclohexadienic and bicyclohexenic derivatives results in a photorearrangement of the former into the latter, as has been demonstrated in vivo with Placobranchus ocellatus (Ireland and Scheuer, 1979) (Figure 23.30). 

Figure 23.30 Photorearrangement of 1,3-cyclohexadienes to bicyclohexenes by Placobranchus ocellatus.

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See also in sourсe #XX -- [ ]

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