Non-peptide GPIIb IIIa inhibitors.: 20.: Centrally constrained thienothiophene α-sulfonamides are potent, long acting in vivo inhibitors of platelet aggregation

The synthesis and pharmacology of 4, a potent thienothiophene non-peptide fibrinogen receptor antagonist, are reported. Compound 4 inhibited the aggregation of human gel-filtered platelets with an IC50 of 8 nM and demonstrated an 8-fold improvement in affinity for isolated GPIIb/IIIa receptors over analogues possessing an isoindolinone backbone. Flow cytometry studies revealed that the binding of 4 to resting platelets is a diffusion-controlled process (k(on) = 3.3 x 10(6) M-1 s(-1)) and that 4 binds to dog and human platelets with comparable affinity (K-d = 0.04 and 0.07 nM, respectively). Ex vivo platelet aggregation in dogs was completely inhibited by an iv dose of 5 mg/kg, and an oral dose of 50-90 mg/kg followed by low daily doses of 10 mg/kg was sufficient to maintain similar to 80% inhibition of ex vivo platelet aggregation over several days. Inhibition of ADP-induced platelet aggregation in anesthetized dogs at 77 +/- 7% resulted in a moderate 2.5-fold increase in bleeding time, while complete inhibition (100%) resulted in an approximately 10-min bleeding time. Additional doses were required to increase the bleeding time to the maximum time allowed in the protocol (15 min), thus indicating a potentially useful and safe separation of efficacy and bleeding time.