Total synthesis of clavatadine A.

The first total synthesis of the potent and selective human blood coagulation factor XIa inhibitor clavatadine A (1) is described. Direct, early-stage guanidinylation enabled rapid, convergent access to an immediate clavatadine A precursor. Concomitant lactone hydrolysis and guanidine deprotection with aqueous acid cleanly provided clavatadine A (1) in only four steps (longest linear sequence, 41-43% overall yield).