Discovery and development of the novel potent orally active thrombin inhibitor N-(9-hydroxy-9-fluorenecarboxy)prolyl trans-4-aminocyclohexylmethyl amide (L-372,460) : Coapplication of structure-based design and rapid multiple analogue synthesis on solid support

Early studies in these laboratories of peptidomimetic structures containing a basic P 1 moiety led to the highly potent and selective thrombin inhibitors 2 (K i = 5.0 nM) and 3 (K i = 0.1 nM). However, neither attains significant blood levels upon oral administration to rats and dogs. With the aim of improving pharmacokinetic properties via a more diverse database, we devised a resin-based route for the synthesis of analogues of these structures in which the P 3 residue is replaced with a range of lipophilic carboxylic amides. Assembly proceeds from the common P 2 -P 1 template 7 linked via an acid-labile carbamate to a polystyrene support. Application of the methodology in a repetitive fashion afforded several interesting analogues out of a collection of some 200 compounds. Among the most potent of the group, N-(9-hydroxy-9-fluorenecarboxy)-prolyl trans-4-aminocyclohexylmethyl amide (L-372,460 8, K i = 1.5 nM), in addition to being fully efficacious in a rat model of arterial thrombosis at an infusion rate of 10 μg/kg/min, exhibits oral bioavailability of 74% in dogs, and oral bioavailability of 39% in monkeys with a serum half-life of just under 4 h. On the basis of its favorable biological properties, inhibitor 8 has been subject to further evaluation as a possible treatment for thrombogenic disorders.