Synthesis of PTX-Perfluorooctanol and PTX-Octanol Prodrugs

The preparation of the two prodrugs was according to the literature ¹⁶. In brief, dissolving dithiodiglycolic acid (4 mmol) with 6 mL of acetic anhydride in a flask. Remaining it stirs for 2 h with the protection of nitrogen atmosphere at 25 °C, then, methylbenzene (30 mL) was put into the reaction solution and evaporated under vacuum for several times. After that, 20 mL of anhydrous dichloromethane was immediately poured into the system to dissolve the crude product, and then DMAP (0.4 mmol) was dripped into the solution under stirring. Subsequently, perfluorooctanol or octanol (2 mmol) were added into the system. Remaining the solution stirs for 24 h at 25 °C, then, the silica gel column chromatography (cyclohexane/acetone = 20:1, 1% glacial acetic acid) was used to separate out the product (50% yield). After that, the product (1 mmol) obtained above was dissolved in a flask with dichloromethane and the solution of EDCI (2 mmol) and DMAP (1 mmol) was dripped into the system. Remaining the solution stirs for 2 h in ice bath under the protection of nitrogen, then, PTX (1 mmol) was added into the system and remained the system stirring for 24 h at 25 °C. Then, the crude product was purified using preparative liquid chromatography by utilizing acetonitrile/water (95:5) as the mobile phase (50% yield). NMR spectral analyses (400 MHz for ¹H) and mass spectrometry were used to certify the prodrug structure. The purity of the prodrugs was measured by high performance liquid chromatography (HPLC).