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

Abstract

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 B4 receptor binding activity (K(i) = 1.3 microM), while leucettamine B was essentially inactive (K(i) = 100 microM) and leucettamidine showed significant activity (K(i) = 5.3 microM). With leucettamine A identified as a pure LTB4 receptor antagonist, a new structure lead is presented to inflammation therapy.