Antiparasitic activity of bromotyrosine alkaloids and new analogues isolated from the Fijian marine Sponge Aplysinella rhax

Ten bromotyrosine alkaloids( 1 ‐ 10 ) were isolated and characterised from the marine sponge Aplysinella rhax ( de Laubenfels 1954) collected from the Fiji Islands, which included one new bromotyrosine analogue, psammaplin P ( 6 ) and two other analogues, psammaplins O ( 5 ) and 4‐bromo‐6‐carbomethoxy salicylic acid ( 7 ), which have not been previously reported from natural sources. HRESIMS, 1D and 2D NMR spectroscopic methods were used in the elucidation of the compounds. Bisaprasin, a biphenylic dimer of psammaplin A, showed moderate activity with IC 50 at 19+/‐ 5 and 29+/‐ 6 μM against Trypanzoma cruzi Tulahuen C4, and the lethal human malaria species Plasmodium falciparum clone 3D7, respectively, while psammaplins A ( 1 ) and D ( 4 ) exhibited low activity against both parasites. This is the first report of the antimalarial and antitrypanosomal activity of the psammaplin‐type compounds. Additionally, the biosynthesis hypotheses of the three natural products ( 5 , 6 and 7 ) were proposed.