Synthesis and in vitro activity of stereoisomers of a novel thromboxane receptor antagonist, (.+-.)-(5Z)-7-[(3-endo-[(phenylsulfonyl)amino]bicyclo[2.2.1]hept-2-exo-yl]heptenoic acid

Three stereoisomers of S-145 (1) with variations at the side-chain junctions were synthesized. Endo-cis isomer 10 and N-exo-trans isomer 18 were obtained via the common intermediate 5 having an endo-fused ring structure. Exo-cis isomer 28 was prepared via exo-fused azetidino compound 21. Inhibitory concentrations (IC50) of the sodium salts newly obtained for platelet aggregation were measured using washed rat platelets (WP) and human platelet-rich plasma (PRP). The IC50 values of these compounds for contraction of the rat aorta were also measured. Compound 1 of N-endo-trans structure and N-exo-trans isomer 18 exhibited more potent inhibitory activity than cis-isomers 10 and 28 against responses induced by TXA2-related substances for rat WP and rat thoracic aorta. However, these compounds exhibited almost comparable inhibitory activity for human PRP.