In an effort to improve the stability of labile lactone ring and water solubility of camptothecin, five novelspin-labeledcamptothecinderivatives were synthesized in quantitative yield by a simple modification of the carbodiimide method using the combination of scandium triflate (Sc(OTf)(3)) and 4-dimethylaminopyridine (DMAP), and the in vitro pharmacokinetic determination of the lactones of representative