Synthesis and elucidation of pyrimido (4,5-q) quinazoline derivatives

Abstract

Pyrimido[4,5-g]quinazoline quinone derivatives were synthesized as anthranone-like reductive alkylating agents. Like many naturally-occurring antibiotics, these quinone derivatives are designed to afford an alkylating quinone methide species upon reduction and leaving group elimination. Kinetic studies of pyrimido[4,5-g]quinazoline hydroquinones provided evidence of quinone methide intermediates able to trap nucleophiles (alkylation) and protons. The rate of quinone methide formation is determined by the hydroquinone free energy. Thus, a linear free energy relationship for quinone methide formation was obtained by plotting rates of quinone methide formation, as the log, versus the quinone reduction potential. The pyrimido[4-5-g]quinazoline quinone methides fall on this free energy plot, showing that these species are formed by the same mechanism as the other structurally-diverse quinone methides previously studied in this research group. A drawback of many quinone antibiotics, particularly the anthracyclines, is the formation of toxic oxygen species by quinone/hydroquinone cycling. In the present invention pyrimido[4,5-g]quinazoline hydroquinones are found to be relatively stable toward oxygen, and thus cause little oxygen toxicity. Antitumor screening revealed that the disclosed pyrimido[4,5-g]quinazoline dione derivatives possess excellent inhibitory activity against selected human cancer cell lines. The pyrimido[4,5g]quinazoline-diones have the following structural formulae: ##STR1## wherein: R is H or CH.sub.3 ; and X is Cl or Br.