Ranunculin, a potent cytotoxic component of P. koreana, was synthesized by reacting (s)-(-)-5-(hydroxymethyl)-2(5H)-furanone with 2,3,4,6-tetra-O-acetyl-$alpha$-D-glucopyranosyl bromide and successive removal of the acetyl protecting group by 0.5 M HCl/MeOH. A new deacetylation process of the intermediate tetraacetylranunculin was deviced giving a yield of 83% of ranunculin. Protoanemonin, the cytotoxic structural moiety of ranunculin, was synthesized by dehydration of (s)-(-)-5-hydroxymethyl-2(5H)-furanone. Ranunculin showed a moderate cytototoxic activity against A-549 (ED$_{50}$=7.53 $mu extrm{g}$/$mell$), NIH3T (ED$_{50}$=13.6$mu extrm{g}$/$mell$), and SK-OV-3 (ED$_{50}$=17.5 $mu extrm{g}$/$mell$). Meanwhile, protoanemonin also exhibited moderate cytotoxicity against A-549 (ED$_{50}$=9.38 $mu extrm{g}$/$mell$), NIH3T (ED$_{50}$=13.8 $mu extrm{g}$/$mell$), and SK-OV-3 (ED$_{50}$=15.1 $mu extrm{g}$/$mell$). It was found that both of the synthetic products showed a potenter cytotoxicity against A-549.ainst A-549.