Clavatadine A, a natural product with selective recognition and irreversible inhibition of factor XIa

Bioassay-guided fractionation of a CH(2)Cl(2)/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 IC(50)'s of 1.3 and 27 mu M, 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.