Ascidians discovered

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. 

The sea squirts or tunicates are fascinating marine creatures, their name being derived from the tunic made of cellulosic material that surrounds the body of the animal. In 1911, Henze discovered vanadium in the blood of Phallusia mammillata C.343 He later found the same with other ascidians (a class of tunicates). In vanadium-accumulating species, most vanadium is located in the vacuoles—vanadophores—of certain types of blood cells—the vanadocytes. The concentration in the vanadophore can be as high as 1M and this value must be compared with concentrations of the order of 2 x 10-8 M for vanadium in sea water.344 Kustin et al. have reviewed the work done to understand the efficient accumulation and the possible biological roles of the metal.345... 

Ascidians or tunicates (Phylum Chordata) belong to the class of Ascidiacea and are common marine animals whose body is enclosed in a jacket or tunic. The animals are attached to rocks and are either solitary or colonial. They continuously filter seawater to obtain minute organisms and particulate organics. As was originally discovered by Henze the animals concentrate vanadium from seawater to levels about 10 times that present in seawater (35 nM), a phenomenon that has attracted considerable interest. The transition metal is present... 

Tunicates (ascidians) are an excellent source of novel biologically active compounds of varied biosynthetic origin, particularly nitrogen-containing amino-acid-derived metabolites [146], The most important compounds discovered to date from tunicates may be the didemnins, potent cytotoxic and antiviral cyclic... 

Marine invertebrates have proved to be a rich source of biologically active prenylated heterocyclic natural products, with several prenylated quinones and chromenols having been discovered from ascidian species (sea squirts). Conicaquinones A and B (Figure 8) were isolated from the marine ascidian Aplidium conicum in 2003 (03EJO898), and are clearly related to the previously mentioned benzoquinone thiazine counterparts, the aplidinones (05EJ(35024). However, unlike the aplidinones, these... 

Remember that this species, which can be regarded as fixed, was discovered through the symbiotic relationship that it maintains with ascidians of the family Didemnidae, in particular Diplosoma similis and D. virens, Lissoclinum patella and I. voeltzkowi, Trididemnum cyclops and, more recentiy, the genus Polysyncraton (Duclaux, Lafargue, and Wahl, 1998). These relations have considerable importance insofar as the Didemnidae frequently contain antiviral and antitumor substances whose true origin is probably Prochloron. In our current state of knowledge, it has not yet been possible to cultivate in vitro-isolated... 

Currently, there has been no study of the secondary metabolites of Cephalochordata. Studies of Urochordata have been considerable but have focused on the class Ascidiacea (ascidians or sea squirts), which contain entire series of alkaloids, often with antiviral and anti-tumor properties. The ascidians share with sharks, which are primitive cartilaginous fish, the absence of liability to tumor development. In many species there is no epibio-sis, which often indicates the presence of cytotoxic and/or antibacterial substances, but antiviral substances were discovered among ascidians with epibionts (Eudistoma sp. and eudistomins (see below). 

Chichak, and Lown, 1999), and a recent study provides a comprehensive account of the possible structures, already known and still to be discovered (Skyler and Heathcock, 2002). The various pyridoacridines isolated from ascidians are shown in Figure 28.6, which shows that these alkaloids are mostly present in the families Polycitoridae (Cystodytes, Eudistoma) but have also been isolated from Didemnidae (Diplosoma, Leptoclinides, Lissoclinum, Trididemnum), Poly-dinidae (Aplidium) and Styehdae (Eusynstyella). 

Floresolide B (160), a recently discovered natural product isolated from an ascidian of genus ApJidiwm that exhibits cytotoxicity against KB tumor cells, contains an aromatic ring connected to a [10]-metacyclophane and a seven-membered ring lactone. The lactone bridge present in substrate 158 was installed prior to the... 

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