Fig. 3. (A) (i) Camptothecin 4, vinyl acetate, Na2CO3, [Ir(cod)Cl]2, 1,4-dioxane, 100 °C, 4 h. The reaction between tetrazine 1 and vinyl-O-camptothecin 3 gave >85% conversion (CH3OH/CH3CN/H2O) within 5 days as determined by HPLC. (B) Cell viability of PC3 cells after incubation with vinyl-O-camptothecin 3 (IC50 = 4.64 ± 1.13 μM) and camptothecin 4 (IC50 = 0.15 ± 0.06 μM) for 72 h at 37 °C; insert is non-linear fit used to determine IC50 values (MTT assay, n = 3).
