MARINE ALKALOIDS .19. 3 NEW ALKALOIDS, SECURAMINES-E-G, FROM THE MARINE BRYOZOAN SECURIFLUSTRA-SECURIFRONS

Three new halogenated indole-imidazole alkaloids, securamines E (1), F (2), and G (3), have been isolated from the marine bryozoan Securiflu stra securifrons. Their structures were determined by NMR and mass spe ctrometry. The new alkaloids, 1-3, can all be related to the earlier r eported securamine C (4). Compound 1 has an additional bromine substit uent at the indole ring system compared to 4; 2 and 4 are diastereomer s differing in configuration at one of the four asymmetric carbon atom s; and 3 is a hydrogenated form of 4.