Controlled stepwise conversion of 2,4,6,8-tetrachloropyrimido[5,4-d]pyrimidine into 2,4,6,8-tetrasubstituted pyrimido[5,4-d]pyrimidines

For the rational synthesis of 2,4,6,8-tetrasubstituted pyrimido[5,4-d]pyrimidines, required as purine mimetics, sequential nucleophilic substitutions of 2,4,6,8-tetrachloropyrimido[5,4-d]pyrimidine have been investigated. Reaction conditions have been devised leading to 2,4,6,8-tetrasubstituted pyrimido[5,4-d]pyrimidines with patterns of substitution denoted as abab (reaction with nucleophile 1 at C-4 and C-8, followed by nucleophile 2 at C-2 and C-6) or abac (reaction with nucleophile 1 at C-4 and C-8, nucleophile 2 at C-2 and nucleophile 3 at C-6) or abcd (reaction with nucleophile 1 at C-4, nucleophile 2 at C-8, nucleophile 3 at C-2 and nucleophile 4 at C-6). The use of low temperature, relatively dilute solution and careful addition of the amine nucleophile can control the critical first step. The third step in the production of the abcd pattern leads to two regioisomers, which have been structurally characterised by 1H NMR and a crystal structure analysis. Selected 2,4,6,8-tetrasubstituted pyrimido[5,4-d]pyrimidines were tested as inhibitors of the cyclin-dependent kinase 1 complex (cyclin B/CDK1), but none of the compounds showed significant activity.