Capnella imbricata Capnellene

Capnellane is the generic name applied to a group of sesquiterpene alcohols and the hydrocarbon isolated from the soft coral Capnella imbricata A < >-Capnellene (667), the presumed biosynthetic precursor of the capnellenols, was first synthesized in 1981 by Stevens and Paquette Their synthetic plan called for the construction of bicyclic ketone 668 and its appropriate annulation. The latter event was achieved by application of the Rupe rearrangement to 668, conjugate addition of a vinyl group to 669, ozonolysis, and cyclization (Scheme LXVIII). Hydrogenation and olefination completed the sequence. 

Laurencia, the diet of the marine molluscs. Examples of capnellane sesquiter-penoids isolated from the soft coral Capnella imbricata continue to emerge. The latest additions are the tetrol (674) and precapnelladiene (675). The latter is considered to be the bicyclic precursor of the tricyclic capnellane group, the simplest of which is A -capnellene (676). Closely related to the diene (675) is dactylol (677), which has been isolated both from the sea hare Aplysia dacty-lomela and from its dietary source, the red seaweed Laurentia poitei ... 

Curran and Chen have also applied the same single-step radical cyclization sequence to elaborate the marine metabolite ( )-capnel-lene (27) starting from the iodoenyne (26). It is interesting to note the similarity in design between this radical approach to capnellene and the strategy used by the author and his co-workers to the capnellenediol (28), which co-occurs with (27) in Capnella imbricata (Scheme 1). 

Carbon-carbon bond formation with acetylide anions is a valuable reaction used in the synthesis of numerous natural products. Two examples include capnellene, isolated from the soft coral The soft coral Capnella imbiicata Capnella imbricata, and niphatoxin B, isolated from a red sea sponge, as shown in Figure 11.6. 

Sheikh, Y.M., Djerassi, C., Braekman, J.C., Daloze, D., Kaisin, M., Tursch, B and Karlsson, R. (1977) A9(12)-Capnellene-3p,8p,10a,14-tetrol, a novel polyoxygenated sesquiterpene from the alcyonarian Capnella imbricata. Tetrahedron, 33, 2115-2117. 

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