1 alpha,2 beta(5Z),3 beta(1E,3S),4 alpha,5 alpha,6 alpha]-7-[5,6-Epoxy-3- (3-cyclohexyl-3-hydroxy-3-methyl-1-propenyl)-7-oxabicyclo[2.2.1]-hept-2- yl]-5-heptenoic acid (31) and [1 alpha,2 beta(5Z),3 beta(1E,3S),4 alpha,5 alpha,6 alpha]-7-[5,6-epoxy-3-[3-hydroxy-5-(p-hydroxyphenyl)-1- pentenyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (37) were found to be selective TxA2 antagonists at the platelet and pulmonary thromboxane receptors. An efficient stereospecific synthesis of these compounds and a series of structural analogues is described. Compounds 31 and 37 both inhibited the bronchoconstriction induced by arachidonic acid in the anesthetized guinea pig.