Design and mechanistic studies of low reduction potential specific anti-tumor agents

The synthesis and characterization of reductive alkylating agents based on the quinazoline, imidazo(4,5-g) quinazoline, pyrimido (4,5-g) quinazoline, and pyrimido (5,4-g) quinazoline ring systems were carried out in conjunction with the design of low reduction potential specific enzyme and DNA alkylating agents. Hydrolysis, product, and nucleophile trapping studies on the hydroquinone form of the above reductive alkylating agents indicated the presence of a steady state quinone methide species. On the other hand, the quinones from these systems were found to be stable in aqueous buffer.;Electrochemical studies revealed the influence of reduction potential on the reactivity and stability of the quinone methide intermediate. Thus, the quinone methide species from a low reduction potential quinone, such as the imidazo (4,5-g) quinazoline-4,9-dione, is relatively electron rich and hence is more adept at trapping electrophiles. The sole product from this type of quinone methide was the thermodynamically favored ketonized product. Unlike the quinone methide obtained from a low reduction potential quinone, the quinone methide species obtained from a high reduction potential quinone, such as the quinazoline-5,8-dione, is relatively electron deficient and is therefore more adept at trapping nucleophiles. Accordingly, in the presence of weak nucleophiles a mixture of quinone (ketonized product) and hydroquinone (nucleophile trapped product) was obtained, while in the presence of strong nucleophiles only the thermodynamically favored hydroquinone species was observed.;Enzymatic studies carried out with the quinazoline-5,8-dione ring system indicate it can irreversibly inhibit xanthine oxidase under anaerobic conditions. The proposed mechanism is described as follows: A two electron transfer to the quinone by reduced xanthine oxidase, followed by elimination of the leaving group from the newly formed hydroquinone affords the quinone methide species. Nucleophile trapping by the reactive intermediate then leads to irreversible alkylation of the enzyme. As expected, inactivation of the enzyme was not observed under aerobic conditions. These results suggest that purine-like reductive alkylating agent could selectively alkylate purine-utilizing enzymes in the hypoxic environment of solid tumors.;In contrast to the enzyme-directed alkylating agents, the pyrimido (4,5-g) quinazoline-5,10-dione and pyrimido (5,4-g) quinazoline-5,10-dione series of compounds were designed to be reductive bisalkylating/intercalating agents whose primary target would be DNA. Also, in an effort to alkylate selectively the A-T rich sequences on DNA in a low reduction potential environment, quinazoline quinones were designed for attachment to the known DNA minor-groove binding peptides distamycin and netropsin. (Abstract shortened by UMI.)...