NSC255083 Poly[[4-[(5-fluoro-3,4-dihydro-2,4-dioxo-1(2H)-pyrimidinyl)carbonyl]tetrahydro-3-(methoxycarbonyl)-2H-pyran-2,6-diyl][2-[(5-fluoro-3,4-dihydro-2,4-dioxo-1(2H)-pyrimidinyl)carbonyl]-1-(methoxycarbonyl)-1,3-propanediyl]]