New Leukotriene B4 Receptor Antagonist: Leucettamine A and Related Imidazole Alkaloids from the Marine Sponge Leucetta microraphis

Three new imidazole alkaloids, leucettamines A [1] and B [2] and leucettamidine [3], have been isolated from the Palauan sponge Leucetta microraphis. Their structures were established on the basis of extensive spectral analyses. Leucettamine A showed potent leukotriene B 4 receptor binding activity (K i =1.3 μM), while leucettamine B was essentially inactive (K i =100 μM) and leucettamidine showed significant activity (K i =5.3 μM). With leucettamine A identified as a pure LTB 4 receptor antagonist, a new structure lead is presented to inflammation therapy