Evidence supporting the activity of 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentafuranosylcytosine as a terminator in enzymatic DNA-chain elongation.

To investigate the stability of 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentafuranosylcytosine 3'-phosphoric acid, its thymidine ester was prepared via the phosphoramidite method using allyl protection for the phosphate function. This ester is stable under acidic conditions but extremely labile under basic conditions, decomposing with a cleavage of the internucleotide bond even at pH 7.3.