Cylindrospermopsin structure

Fig. 5.1 Common cyanobacterial hepatotoxins. (a) Generalized structure of microcystin, a cyclic heptapeptide. Note that X and Z are L-amino acids. For example, microcystin-LR possesses lysine and arginine residues at X and Z, respectively, (b) Cylindrospermopsin, a hepatotoxic alkaloid from Cylindrospermopsis raceborskii...

The novel structure of cylindrospermopsin, with a guanidine embedded in a tricyclic system, six chiral centers, and polar sulfate, uracil and guanidine functional groups, makes its synthesis challenging. Its potent toxicity makes the synthesis of cylindrospermopsin an important problem that has been the subject of intense interest.1,7 8... 

The spectral data of 24 are very similar to those of the right half of cylindrospermopsin (1), while those of 25 are quite different. For instance, the absorption of the side chain methine hydrogen H7 of 24 at 8 4.70 (d, 1, / = 4. 0 Hz) is identical to that of cylindrospermopsin and very different from that of 25 at 8 4.44 (d, 1, J = 6.8 Hz). Therefore, we concluded that 24 has the same stereochemistry as cylindrospermopsin. The spectral data for 25 was later used to support the structural assignment of 7-epicylindrospermopsin (2) in which the side chain hydrogen absorbs at 8 4.50 (d, 1, J = 6.6 Hz).5... 

FIGURE 39.1 Structures of microcystins (a), nodularin (b), and cylindrospermopsin (c). For abbreviations of amino acids see text. 

Figure 1 Structures of (A) microcystin-LR, (B) cylindrospermopsin, (C) anatoxin-a, (D) anatoxin-a(S), and (E) saxitoxin.

Cylindrospermopsin is an alkaloid consisting of a tricyclic guanidine coupled with hydrox3unethyluracil (Figure 31.2). It is a zwitterionic, highly water-soluble molecule (Ohtani et al., 1992). There are two known structural variants deoxycylindrospermopsin (Norris et al., 1999), which is relatively less toxic, and 7-epicyl-indrospermopsin (Banker et al., 2001), which is relatively... 

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