Enantiomerically enriched disubstituted tetrahydrofurans, tetrahydrothiophenes, pyrrolidines and cyclopentanes are disclosed that reduce the chemotaxis and respiratory burst leading to the formation of damaging oxygen radicals of polymorphonuclear leukocytes during an inflammatory or immune response. The compounds exhibit this biological activity by acting as PAF receptor antagonists, by inhibiting the enzyme 5-lipoxygenase, or by exhibiting dual activity, i. e., by acting as both a PAF receptor antagonist and inhibitor of 5-lipoxygenase. It has been determined that 5-lipoxygenase activity, oral availability, and stability in vivo (for example, glucuronidation rate) can vary significantly among the optical isomers of the disclosed compounds.