Xenicane diterpenes

There have been no natural products investigations of soft corals from the cool temperate west coast of southern Africa. Soft corals are common along the south-east coast of South Africa and as part of our ongoing search for bioactive metabolites from the marine invertebrate fauna of the Tsitsikamma Marine Reserve we isolated four bioactive xenicane diterpenes, the tsitsixenicins A - D (93 - 96) from the endemic soft coral Capnella thyrsoidea (Family Nephtheidae) [91]. The structures of 93 -96 were delineated from standard analysis of their NMR data and comparison of these data with those published for related compounds e.g. 9-deacetoxy-14,15-deepoxyxeniculin (diastereomic with 93) isolated from the Red Sea soft coral Xenia macrospiculata [92]. 

An unusual intraspecific variation in the structures of the diterpene metabolites produced by the soft coral Eleutherobia aurea (formerly Alcyonium aurea) has been observed from several collections of this species made from the Aliwal Shoal and Sodwana Bay regions [95]. The Sodwana Bay specimens yielded antheliatin (106), zahavins A and B (107,108) [96], sarcodictyin A (109) and eleuthosides A and B (110, 111) [95], In addition to 107, other xenicane diterpenes including 9-deacetoxy-14,15-deepoxyxeniculin (112), 7,8-epoxyzahavin A (113) and xeniolide C (114) were isolated from the Aliwal Shoal specimens of E. aurea [97]. Sarcodictyon A and 9-deacetoxy-14,15-deepoxyxeniculin were isolated previously from the stoloniferous octocoral Sarcodictyon roseum [98] and the soft coral Xenia obscuronata [99]. 

Standard analysis of spectroscopic data provided the structures of the xenicane diterpenes 107, 108 and 112 - 114 while the structure and stereochemistry of 106 were established via X-ray crystallography. The diacetoxypentose moiety in 110 and 111 was assigned as diacetoxyarabinose from 13C chemical shift data and coupling constant analysis. The total synthesis of 109 - 111 by Nicolaou et al. established that the ring junction stereochemistry for all three compounds was identical with that of eleutherobin (115) [100]. The structural similarity of these four compounds to the valdivones (101 - 105) is clearly evident. The total synthesis of 110 and 111 also confirmed the expected D-... 

GueUa, G., Ndiaye, L, Chiasera, G., and Pietra, F. (1993) Joahn, the first nitrogen-containing xenicane diterpene isolated from a brown seaweed collected off the Senegalese coast. J. Chem. Soc. Perkin Trans. 1.1545-1546. 

Iwagawa, T, Nakamura, K., Hirose, T., Okamura, H., and Nakatani, M. (2000b) New xenicane diterpenes isolated from the acetone extract of the soft coral Xenia Jlorida. J. Nat. Prod., 63, 468 72. 

Rudi, A., Ketzinel, S., Goldberg, I., Stein, Z., and Kashman, Y. (1995) Antheliatin and zahavins A and B, three new cytotoxic xenicane diterpenes from two soft corals./. Nat. Prod., 58,1581-1586. 

Brown algae of the family Dictyotaceae yielded diterpenes of the dolabellane, xenicane, crenulide as well as extended germacrane and hydroazulenoid types. Some of these compounds were identified as capable of demonstrating appreciable selectivity as antimalarial agents... 

Ohtani, I., Kusumi, T., Ishitsuka, M. O., and Kasikawa, H. 1989. Absolute configuration of marine diterpenes possessing a xenicane skeleton. An application of an advanced Mosher s method. Tetrahedron Lett. 30, 3147-3150... 

Figure 14.11 Diterpene carbon skeletons of the xenicane family (neither of the bracketed skeletons have known representatives in the brown...

Isolated from Dictyota divaricata harvested in the Indian Ocean, divarinone is a tricyclic diterpene whose original skeleton is closely related to that of xenicane (Trimurtulu, Kushlan, and Faulkner, 1992). No other similar diterpene seems to have been isolated. 

The Nobd Prize in Chemistry 1990. Professor E.J. Corey for his development of the theory and methodology of organic synthesis . http //www.marinespedes.org/index.php Worms, world Register of Marine Species. http //dcb-carot.unibe.ch/homepages /daniel /XENlintro.htm Xenicanes. Site dedicated to this particular family of diterpenes (xenicanes). 

Sarcoglane, a cytotoxic derivative isolated from Sarcoph-ytonglaucum (Alcyoniidae), may be another type of regular diterpene derived from xenicane. The tricyclic skeleton of cespitularane seems currently represented only in the genus Cespitularia (Xeniidae), particularly in the species C. hypotentaculata collected in Formosa. 

---