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... 

C15H24, Mr 204.36, oil, [a] -145° (CHCI3). The tricyclic sesquiterpene hydrocarbon C. (triquinane, deca-hydrocyclopenta[a]pentalene skeleton) is found in the soft coral Capnella imbricata. C. inhibits the growth of microorganisms and prevents the attachment of larvae to the coral. 

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). 

SPECTRAL data IR, PMR, Mass Spec organism Capnella imbricata (Coelenterata) REFERENCE 210... 

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. 

The capnellenols, e.g. (24) [cf. (10)], are a unique family of sesquiterpenes, found in the soft coral Capnella imbricata. They are related structurally to the hirsutane family of triquinane terpenes, e.g. (18), but with the three methyl groups distributed differently about the tricycle. A special feature of the capnellenols is the presence of an unusual Wj-allylic alcohol functionality associated with ring c. The 8-epimer of (24) has now been synthesized by a route (Scheme 3) in which this novel functionality is introduced by annulation to (23) via reductive cyclization of the keto-acetylene precursor (22), followed by treatment of the resulting allylic alcohol (23) with t-butyl hydroperoxide in the presence of catalytic selenium dioxide. ... 

Kaisin, M., J.C. Braekman, D. Daloze, and B. Tursch Novel Acetoxycapnellenes from the Alcyonacean Capnella imbricata. Tetrahedron 41, 1067 (1985). 

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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