Briareum

Some time ago, we initiated a study of the coelenterate Briareum polvanthes to ascertain whether there was a chemotaxonomic basis for the species distinction between the Briareum found in Bermuda and the more common fl,. asbestinum found throughout the Caribbean. We have found a series of new diterpenes, 9-13, with the briaran skeleton (17.22.2T). It has been implied (24.2 5) that this class of compounds serves as a chemical defense against predation in the soft corals and sea pens which produce them, but this has not yet been demonstrated by bioassay. 

Fig. 3.5 Briareum asbestinum, a Caribbean gorgonian soft coral that produces numerous chlorinated diterpenes such as the briareins (513-519) and briantheins (520-524) (Photo W. Fenical)...

Fig. 3.6 Briareum stechei, a Western Pacific octocoral that produces the milolides (533-538) (Photo F. J. Schmitz)...

The stereochemistry of solenolide C (U) is also revised in this study (680). The new briviolides B (539) and C (540) were characterized from a Japanese collection of Briareum sp. (682). A study of octocorals from Pohnpei and Ant atoll in Micronesia led to the novel nui-inoalides A-D (541-544) (683). The absolute configuration of juncin E (W) was also established by these researchers. 

Harvell CD, Fenical W, Roussis V, Ruesink JL, Griggs CC, Greene CH (1993) Local and Geographic Variation in the Defensive Chemistry of a West Indian Gorgonian Coral (Briareum asbestinum). Mar Ecol Prog Ser 93 165... 

Rodriguez AD, Ramferz C, Cobar OM (1996) Briareins C-L, Ten New Briarane Diterpenoids from the Common Caribbean Gorgonian Briareum asbestinum. J Nat Prod 59 15... 

Stierle DB, Carte B, Faulkner DJ, Tagle B, Clardy J (1980) The Asbestinins, a Novel Class of Diterpenes from the Gorgonian Briareum asbestinum. J Am Chem Soc 102 5088... 

Selover SJ, Crews P, Tagle B, Clardy J (1981) New Diterpenes from the Common Caribbean Gorgonian Briareum asbestinum (Pallus). J Org Chem 46 964... 

Gonzalez N, Rodriguez J, Kerr RG, Jimenez C (2002) Cyclobutenbriarein A, the First Diterpene with a Tricyclo[8.4.0.0.3,6]tetradec-4-ene Ring System Isolated from the Gorgonian Briareum asbestinum. J Org. Chem 67 5117... 

Sheu J-H, Sung P-J, Cheng M-C, Liu H-Y, Fang L-S, Duh C-Y, Chiang MY (1998) Novel Cytotoxic Diterpenes, Excavatolides A-E, Isolated from the Formosan Gordonian Briareum excavation. J Nat Prod 61 602... 

Kwak JH, Schmitz FJ, Williams GC (2001) Milolides, New Briarane Diterpenoids from the Western Pacific Octocoral Briareum stechei. J Nat Prod 64 754... 

Iwagawa T, Babazono K, Okamura H, Nakatani M, Doe M, Morimoto Y, Shiro M, Takemura, K (2005) Briviolides, New Briarane Diterpenes from a Gorgonian Briareum sp. Heterocycles 65 2083... 

Harvell, C. D., Fenical, W., Roussis, V., Ruesink, J. L., Griggs, C. C., and Greene, C. H., Local and geographic variation in the defensive chemistry of a West Indian gorgonian coral (Briareum asbesti-num), Mar Ecol. Prog. Ser, 93, 165, 1993. 

Briareum asbestinum Larva Soft Corals Lecithotrophic star, amphipod Coral, fish 68, 72... 

Harvell, C.D., West, J.M., and Griggs, C., Chemical defense of embryos and larvae of a West Indian gorgonian coral, Briareum asbestinum, Invertebrate Reprod. Dev., 30, 239, 1996. 

The versatility of the enolone ester 27 is illustrated by a variety of synthetically useful addition reactions, e. g. with lithium alkyls, Grignard reagents and cyclopentadiene in a Diels-Alder type fashion (40, 48, 49), but, most notably, it could be utilized for straightforward syntheses of the marine natural products (-)-bissetone (28), a metabolite from the Gorgonian soft coral Briareum polyanthes (50), and (-)-palythazine (29), an unusual dipyranopyrazine isolated from the salt water invertebrate Palythoa tuberculosa (51). 

Next, the isolation and characterization of a series of briarane diterpenoids was reported from the Western Pacific octocoral Briareum stechi by Kwak et al.142 The general structural skeleton shared by a number of the 11 members of the series characterized by the authors is shown by 69. 

Again, soft corals and gorgonians are a rich source of diterpenoids of 19 structural classes, some of which are specific to them (35, 36). Besides tobacco plants, cembranoid diterpenes are limited to soft corals. Lophotoxin (126) isolated from sea whips of the genus Lophogorgia is a sodium channel inhibitor (3). Xenicin (127) from the soft coral Xenia elongata and briarein A (128) from the gorgonian Briareum asbestinum represent non-cembranolide diterpenes. Diterpenoids of these classes show antimicrobial, cytotoxic, and insecticidal activities. 

Heterocyclic natural products of gorgonian corals of genus Briareum exclusive of briarane-type diterpenoids 02H(57)1705. 

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