Identification of the active metabolite of ticlopidine from rat in vitro metabolites

Ticlopidine is a well‐known anti‐platelet agent, but is not active by itself in vitro . We identified a metabolite with anti‐platelet activity, which was generated after incubation of 2‐oxo‐ticlopidine with phenobarbital‐induced rat liver homogenate in vitro . An active moiety (UR‐4501) was isolated by high‐performance liquid chromatography after large‐scale preparation of metabolites. The chemical structure of UR‐4501 was determined by a combination of liquid chromatography mass/mass spectrometry (LC/MS/MS) and nuclear magnetic resonance (NMR) analysis. UR‐4501 produced a concentration‐dependent inhibition (3–100 μ M ) of ADP (10 μ M )‐induced human platelet aggregation, whereas 2‐oxo‐ticlopidine (3–100 μ M ) did not elicit inhibitory responses. UR‐4501 (10–100 μ M ) strongly inhibited ADP‐ and collagen‐induced aggregation and slightly inhibited thrombin‐induced aggregation. The inhibition of rat washed platelet aggregation by UR‐4501 (100 μ M ) persisted, even after the platelets had been washed twice. These results suggest that UR‐4501 is the molecule responsible for the in vivo activities of ticlopidine.British Journal of Pharmacology (2004) 142 , 551–557. doi: 10.1038/sj.bjp.0705808