6. Analogues of purine or pyrimidine bases and their derivatives

Among substances with anti-tumor and anti-viral properties, some are artificial molecules obtained by modifying biological molecules and replacing them in metabolic processes. They interfere with essential steps in DNA synthesis and/or transcription, and can exert their action through three often-associated mechanisms:

• competitive inhibition of enzymatic reactions ;

• irreversible inhibition of an enzyme by high-affinity binding ;

• fraudulent incorporation into DNA and RNA nucleic acids.

The first compounds used were structural analogues of purine or pyrimidine bases used in oncology and grouped together under the term antimetabolites. Also of interest were nucleoside analogues with a carbohydrate moiety consisting of various oses other than...