Ascidian

Certain vertebrates have an astonishing ability to accumulate vanadium in their blood. For example, the ascidian seaworm Phallusia mammilata has a blood concentration of V up to 1900 ppm, which represents more than a millionfold concentration with respect to the sea-water in which it lives. The related organism Ascidia nigra has an even more spectacular accumulation with concentrations up to 1.45% V (i.e. 14 500 ppm) in its blood cells, which also contain considerable concentrations of sulfuric acid (pH 0). One possibility that has been mooted is that the ascidia accumulates vanadate and polyvanadate ions in mistake for phosphate and polyphosphates (p. 528). 

Benzopentathiepins are stable solids. Varacin, a cytotoxic metabolite, was isolated from a marine ascidian.398 The parent benzopentathiepin exhibits infrared absorptions at 1620, 1570, 1235 and 1020 cm" 1.399 X-ray structure analyses of benzopentathiepin and 6-methylbenzopen-talhicpin show that the seven-membered ring in both compounds is nonplanar and that it adopts a chair conformation. The S-S bond lengths are in the range 204-206 pm.400... 

Fig. 10.S.3 Luminescence spectrum of the light emitted from freeze-dried, powdered specimens of the ascidian Clavelina miniata upon addition of water. The same luminescence spectrum was obtained when living specimens were stimulated. From Chiba et ai, 1998, with permission from John Wiley Sons Ltd.

Aoki, M., Hashimoto, K., and Watanabe, H. (1989). The intrinsic origin of bioluminescence in the ascidian. Clavelina minata. Biol. Bull. 176 57-62. 

Chiba, K., Hoshi, M., Isobe, M., and Hirose, E. (1998). Bioluminescence in the tunic of the colonial ascidian Clavelina miniata identification of luminous cells in vitro. J. Exp. Zool. 281 546-553. 

Hirose, E., Aoki, M., and Chiba, K. (1996). Fine structures of tunic cells and distribution of bacteria in the tunic of the luminescent ascidian Clavelina miniate. Zool. Sci. 13 519-523. 

Villa, L. Patricolo, E. Follicle cells of Styela plicata eggs (Ascidiacea), In Sawada, H. Yokosawa, H. Lambert, C. C. (Eds.), The Biology of Ascidians, Springer-Verlag, Tokyo, 2001. 

Takeuchi, K. et al., A genome-wide survey of genes for enzymes involved in pigment synthesis in an ascidian, Ciona intestinalis, Zool Scl, 22, 723, 2005. 

Holland, P. W. H. (1991). Cloning and evolutionary analysis of msh-like homeobox genes from mouse, zebrafish and ascidian. Gene 98 253-257. 

In an approach towards a total synthesis of the marine ascidian metabolite pero-phoramidine (6/1-96) [55], Weinreb and coworkers developed a domino Heck/car-bonylation process [56]. This allowed construction of the C,E,F-ring system of 6/1-96, together with the C-20 quaternary center and the introduction of a functionality at C-4 (Scheme 6/1.25). Thus, reaction of 6/1-97 in the presence of catalytic amounts of Pd(OAc)2 and P(oTol)3 under a CO atmosphere in DMA/MeOH led to 6/1-98 in 77% yield. 

Donia, M.S., Hathaway, B.J., Sudek, S. et al. (2006) Natural combinatorial peptide libraries in cyanobacterial symbionts of marine ascidians. Nature Chemical Biology, 2, 729. 

Two new polycyclic pyridoacridine alkaloids, arnoamine B, 289, and its demethylated analogue, arnoamine A, have been isolated from the ascidian Cystodytes sp. These new compounds are the first known examples of pyrroles fused to pyridoacridines, have antifungal properties, and are cytotoxic in several human tumor cell lines <1998JOC1657>. Both these compounds have been synthesized, starting from the hydrazone 290 with a Fischer indole synthesis (Scheme 73) <2000JOC5476>. 

The most well known and most widely used compounds mentioned in the chapter are the doubly protected monosaccharide derivatives (cf. Schemes 16-18 and 27-29), which serve as building blocks for the regio- and stereospecific synthesis of a host of more complex carbohydrates. A number of newly discovered alkaloids contain fused 5 6 6-triheterocyclic systems these compounds may come from not only traditional (plant) sources, for example, compounds 96, 292-294, 446, and 447, but also insects (compounds 531-533), marine animals of various kinds, for example, sponges (compounds 58 R = H or OH) and ascidians (compound 289), and amphibians (compound 535). Although the majority of these alkaloids are known to be toxic in sufficient quantity, any possible therapeutic applications have apparently not yet been disclosed. 

Little work has been reported on the biosynthesis of oxylipins in ascidians. One report describes the production of numerous oxidized AA metabolites by eggs... 

Hawkins, C.J., D.L. Parry, and C. Pierce. 1980. Chemistry of the blood of the ascidian Podoclavella moluc-censis. Biol. Bull. 159 669-680. 

The isolation from a marine ascidian and subsequent structure determination of polycitone A (105) (Fig. 6) was first reported [52] by Kashman and coworkers in 1994. In this paper, the penta-O-methyl derivative was reported to inhibit the growth of SV40 transformed fibroblast cells at a concentration of 10 jtg/mL. Loya, Hizi and Kashman published [53] an extensive account of the biological activity of polycitone A in 1999 in which case inhibition of retroviral reverse transcriptases and cellular DNA polymerases was described. The isolation from an ascidian and structure determination of polycitone B (106) (Fig. 4) was subsequently reported [54] by Kashman and coworkers in 2000. Obviously, the presence of extensive bromination in both polycitone A and B make this family of compounds unique among the 3,4-diarylpyrrole natural products. 

Steglich s group coupled A-methyl bromoindolylmaleimide 36 with 5-tributylstannyl-l-methyl-1//-imidazole to afford 37 and then converted 37 to didemnimide C (38), an alkaloid isolated from the Caribbean ascidian Didemnum conchyliatum [25]. 5-Tributylstannyl- 1-methyl-IH-imidazole, in turn, was prepared according to Undheim s direct metalation method from 1-methyl- l/Z-imidazole [26]. 

Figure 17.16 Model of the pathway for reduction and accumulation of vanadium in ascidian vanadocytes. (From Crans et al., 2004. Copyright (2004) American Chemical Society.)...

Tunicates (ascidians or sea-squirts) are invertebrate marine organisms, which can accumulate vanadium at concentrations approaching 350 mM (the concentration of vanadium in seawater is 10 8 M). This vanadium is taken up as V(V) from seawater (Figure 17.16), reduced to oxidation state III or IV and stored in a soluble form in the blood cells within acidic vacuoles at concentrations a million fold higher than in their external surroundings. 

CALCIUM-BASED BIOMINERALS CALCIUM CARBONATES IN ASCIDIANS AND MOLLUSCS... 

Ascidians (Tunicates) are a class of marine organisms (including sea squirts), which have a characteristic tough covering, called a tunic. The tunic is composed of cellulose and contains small calcium-containing spicules in a wide variety of shapes (Figure 19.8) ... 

Lesser MP, Stochaj WR (1990) Photoadaptation and protection against active forms of oxygen in the symbiotic prokaryote Prochloron sp. and its ascidian host. Appl Environ Microbiol 56 1530-1535... 

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