A novel methodology for the synthesis of poly(ethylene glycol) (PEG) prodrugs of amino-containing compounds has been developed which is based on the trimethyl lock lactonization reaction. These PEG-modified double prodrugs are water soluble, and by selective modification of the specifier or trigger, plasma half-lives can be adjusted at will to result in a wide range of values. Facile syntheses of ester, carbonate, and carbamate functionalities were accomplished and combined with greater or lesser degrees of steric hindrance in the spacer group, or on the aromatic framework, to achieve predictable ranges of drug concentration in plasma. In vivo screening of PEG prodrugs was done using a M109 syngeneic solid mouse tumor model. One of the PEG-daunorubicin prodrugs, with a half-life of 2 h, was evaluated in an in vivo solid tumor panel and found to be more efficacious against ovarian tumors (SKOV3) than equivalent amounts of daunorubicin.