Novel 7-thiaprostaglandin E1 derivatives and congeners were synthesized by a stepwise three-component coupling process, which involves the introduction of α-side chains (thiols) and β-side chains (organocopper reagents) into (R)-4-tert-butyldimethylsilyloxy-2-cyclopentenone. Several acid derivatives of 7-thiaprostaglandin E1 were also prepared either by enzymatic or by chemical methods. The stereochemistry of these products was assigned on the basis of the results with chiral protected cyclopentenones and chiral ω-side chains. Some of these 7-thiaprostaglandin E1 congeners were found to exhibit more potent platelet aggregation-inhibitory activity than PGE1. The structure-activity relationship of these congeners is discussed.