With the aim of finding new natural product antimalarials, the novel indole alkaloids flinderole A-C were found to have selective antimalarial activities with IC(50) values between 0.15-1.42 microM. Flinderole A was isolated from the Australian plant Flindersia acuminata and flinderoles B and C from the Papua New Guinean plant F. amboinensis. Flinderoles A-C contain an unprecedented rearranged skeleton compared to their related isomers of the borreverine class of compounds.

A drug discovery program aimed at identifying new antimalarial leads from a prefractionated natural product library has resulted in the identification of a new bromotyrosine alkaloid, psammaplysin G (1), along with the previously isolated compound, psammaplysin F (2). When tested against two different strains of the parasite Plasmodium falciparum (Dd2 and 3D7), 2 displayed IC(50) values of 1.4 and 0.87 microM, respectively, while 1 showed 98% inhibition at 40 microM against the chloroquine-resistant (Dd2) strain of P. falciparum.

Bioassay-guided fractionation of a CH2Cl2/MeOH extract of the sponge Suberea clavata using the serine protease factor XIa to detect antithrombotic activity led to the isolation of the new marine natural products, clavatadines A and B. Clavatadines A and B inhibited factor XIa with IC50's of 1.3 and 27 microM, respectively. A crystal structure of protein-inhibitor (clavatadine A) complex was obtained and revealed interesting selective binding and irreversible inhibition of factor XIa. The cocrystal structure provides guidance for the design and synthesis of future factor XIa inhibitors as antithrombotic agents.