Ring-opening polymerization of ε-caprolactone initiated by the antitumor agent doxifluridine

A novel 5′-deoxy-5-fluorouridine–poly(ε-caprolactone) (5′-DFUR–PCL) polymer was synthesized from the antitumor agent doxifluridine (5′-DFUR) by the ring-opening polymerization of ε-caprolactone (ε-CL) using Sn(II) 2-ethylhexanoate (Sn(Oct)2) as the catalyst. The structure and molecular weight of these polymers were further elucidated by proton nuclear magnetic resonance and gel-permeation chromatography. The results revealed that the molecular weights of the 5′-DFUR–PCL polymers were close to the theoretical values calculated from the ε-CL to 5′-DFUR molar ratios and their recovery yields were as high as 90%. Two mechanisms of ε-CL polymerization initiated by Sn(Oct)2 were proposed involving either a single or two 5′-DFUR molecules. This study has provided an efficient method for the preparation of 5′-DFUR–PCL polymers. These novel 5′-DFUR–PCL polymers can be applied as drugs on carriers without the need for the coating or grafting processes associated with drugs in drug delivery and have great potential for cancer therapy.