Diketopiperazines, polychlorinated

Eighteen polychlorinated diketopiperazines, the dysamides, have been isolated from the Micronesian sponge Dysidia chlorea. The presence of dichloromethyl and trichloromethyl groups is a rare structural feature in natural products. The structure of dysamide K (206) is shown as an example [164],... 

Reef provided 920-922, and the absolute configuration of the latter metabolite was established as shown (985). Dysidea fragilis from the South China Sea has yielded dysamide D (923) (986), and Dysidea chlorea from Micronesia afforded 12 new polychlorinated diketopiperazines, dysamides I-T (924—935) (987). In addition, this study (987) confirmed the structure of dysamide E (936) (988). Based on previous assignments the absolute configurations of 924—936 are believed to be those indicated. A Pacific Ocean collection of Dysidea sp. provided dysamide U (937), which is the first trichlorinated member of the diketopiperazine family to be identified (989). 

In their second 1998 report, Schmitz and co-workers97 reported the isolation and characterization of a series of 12 new polychlorinated diketopiperazines from the sponge Dysidae chlorea. The structure of one of these alkaloids, dysamide-I is shown (37). 

A thiazole nucleus or a diketopiperazine is associated with one or two trichloromefhyl groups, and munerous examples of such structures have been found in species of Dysidea. Most of these molecules contain 5,5,5-trichloro-N-mefhyl-leucine or 5,5-dichloro-N-methyl-leucine, which thus appear to be specific a-amino acids in the genus Dysidea, but are not present in peptides or depsipeptides. Figures 19.109 and 19.110 show some examples of these polychlorinated nitrogen derivatives. 

Figure 19.109 Examples of polychlorinated diketopiperazines isolated from Dysidea species.

---