Capnellanes from Capnella imbricata

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 ... 

A complete account of the experimental evidence leading to the structural elucidation of the first members (244a—d) of the capnellane group of sesquiterpenoids has been provided in a recent paper cf. Vol. 5, p. 70). These compounds (244a—d) are found in soft coral (Capnella imbricata) and it has been suggested that their biosynthesis involves cyclization of humulene followed by methyl migration from C-5 to C-4 [cf. (245)]. 

Sesquiterpenoids based on the capnellane framework (352) have previously been isolated from soft coral (Capnella imbricata) (cf. Vol. 5, p. 70 Vol. 7, p. 81). Two new compounds isolated from this source have been identified as... 

Kaisin, M., Sheikh, Y.M., Durham, LJ., Djerassi, C., Tursch, B., Daloze, D., Braekman, J.C., Losman, D., and Karlsson, R. (1974) Capnellane a new tricychc sesquiterpene skeleton from the soft coral Capnella imbricata. Tetrahedron Lett., 15,2239-2242. 

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