SPONGIAN

Source Dendi illa rosea Mol. formula 20 30 4 Mol, wt. 334 Solvent CDCl, 

Source Dendrilta vosea Mol. formula 2l 32 Mol. wt. 348 Solvent CDC1  

Source Aplysilla roaea Barrois Mol. formula C24HggOg Mol. wt. 420 

Source Aplysilla rosea Barrois Mol. formula S4 36°7 Mol. wt. 436 Solvent CD2CI2 

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Miyamoto, T., Sakamoto, K., Arao, K, Komori, T., Higuchi, R., and Sasaki, T., Dorisenones, cytotoxic spongian diterpenoids, from the nudibranch Chromodoris obsoleta, Tetrahedron, 52, 8187, 1996. 

Keyzers RA, Northcote PT, Davies-Coleman MT. Spongian diterpenoids from marine sponges. Nat. Prod. Rep. 2006 23 321-334. 

Another dorid nudibranch, Doris verrucosa has been reported (70) to contain an analogue of methylthioadenosine [84] along with diterpenoic acid glycerides, verrucosin A [85] and verrucosin B [86]. The carbon skeleton of the vemicosins could be derived from isocopalane diterpenes which formerly were considered to be the biogenetic precursors of the tetracyclic spongiane diterpenes. 

Scheme 4-40 details an application of the triple 6-endo cyclization, triggered by the formation of an acyl radical by Pattenden to the synthesis of the marine sponge metabolite spongian-16-one [67]. 

Abad, A., Amo, M., Marin, M.L., and Zaragoza, R.J., Spongian pentacyclic diterpenes. Stereoselective synthesis of aplyroseol-1, aplyroseol-2 and deacetylaplyroseol-2, J. Chem. Soc., Perkin Trans. 1, 1861, 1993. 

Cu-Bisoxazoline-catalyzed asymmetric cyclopropanation of methyl 2-furoate with ethyl diazoacetate was a key step in the synthesis of the cw-fused 5-oxofuro[23-fc]furan core of spongiane diterpenoids <05OL5353>. An interesting example of rtiodium-catalyzed intramolecular addition of a diazoketone to furan affording a strained cyclobutenone, is illustrated below. Iodine-induced isomerization of the product provided the fused tricyclic dihydrofuran compound <05HCA33Q>. 

Goeller, F., Heinemann, C., Demuth, M., Investigations of Cascade Cyclizations of Terpenoid Polyalkenes via Radical Cations. A Biomimetic type Synthesis of ( ) 3 Hydroxy spongian 16 one, Synthesis 2001, 1114 1116. 

A number of oxacyclic natural products were synthesized via carbocycle-forming radical reaction of oxacyclic intermediates. An early example is the synthesis of (-)-dihydroagarofuran (170) by Biichi [109] (Scheme 58). The bridgehead chloride 168 obtained from the corresponding hydroxy ketone was amenable to radical cycliza-tion, and the tricyclic ether 169 was duly obtained. The aplysin synthesis [110] provides another example, and (—)-karahana ether (173) was synthesized via radical cyclization of the substrate 171 [111] (Scheme 59). Lactonic natural products (-1-)-eremantholide A [112], alliacolide [113], and (-)-anastrephin [114] were prepared via a variety of carbocycle-forming radical cyclization reactions. In the total synthesis of spongian-16-one (176) [115] (Scheme 60), the butenolide moiety in the substrate 174 served as the final radical acceptor for three consecutive 6-endo-. rig cyclizations. 

Applications included a related triple cyclization from lactone 74, which opened a route to spongian-16-one [37] and an approach to azasteroids involving an enamine double bond (75) as a final radical acceptor (Scheme 22) [38]. Moreover, spectacular tetracyclizations from acyclic 76 and 77 have also been accomplished to provide the corresponding aW-trans tetracyclic ketones [36], both of them consisting of ring D methyl epimers (Scheme 23). 

Latrunculin B was also present in extracts of C. hamiltoni collected from the reefs off southern Mozambique. The latter specimens of C. hamiltoni also yielded two spongiane diterpene lactones (150,151) [127]. No evidence of the hamiltonins was found in extracts of the Mozambique specimens of C. hamiltoni and possibly reflects geographical variation in the organisms that make up C. hamiltonf s diet in this region of the southern African coast. The structures of both spongiane diterpenes and the hamiltonins A -E were determined from spectroscopic data while the absolute stereochemistry at C-16 in 147 was established by comparison of its CD data with those of related compounds [127]. 

An alternative preparative method avoids the use of the Zn/Cu couple, using diethyl zinc instead. An example is taken from Abad s synthetic studies directed at spongiane.329 in this work, tricyclic alkene 416 was treated with diethylzinc and diiodomethane to give a 91% yield of 417. 

Isocopalane and its tetracyclic furan derivatives, referred to as spongianes, are found in various sponges such as Spongia officinalis, and in the naked snails eating these sponges. Such compounds include (+)-isocopalene-15,16-dial, the cyclohe-miacetal (-)-spongiane-15,16-diol, the lactone (+)-l ip-hydroxy-12-spongiene-16-... 

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