Structurally novel thrombinreceptor (proteaseactivatedreceptor 1, PAR-1) antagonists based on the natural product himbacine are described. The prototypical PAR-1 antagonist 55 showed a Ki of 2.7 nM in the binding assay, making it the most potent PAR-1 antagonist reported. 55 was highly active in several functional assays, showed excellent oral bioavailability in rat and monkey models, and showed