Five- and Six-Membered Ring Alkaloids

For the most part, five-membered ring alkaloids tend to make one think of pyrrole- and imidazole-derived alkaloids. There are, however, also alkaloids that fall into this class that are, for example, derived from 1,2,4-thiadiazoles, for example, 19, the characterization of which is discussed Section 7.1.8. 

1 Characterization of Pyrrole Sulfoxides from Allium Subgenus melanocrommyum 

Al-Mourabit and coworkers [42] isolated and characterized four alkaloids from Pacific marine sponges Angelas, cf mauritania and Phakellia sp. 

HMBC data were acquired and utilized in the characterization of one of the four alkaloids, nagelamide T (12). As noted by the authors, the ... H- HMBC NMR experiments were performed in order to indicate the positions of the protons for both 2-aminoimidazole... moieties contained in the structure of nagelamide T. Details of the optimization of the HMBC experiment were not provided by the authors. 

13 Characterization of Benzosceptrin C A Bromopyrroie Aikaioid from the Sponge Agelas sp. 

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