Phospho-carboxylic anhydride of a homologated nucleoside leads to primer degradation in the presence of a polymerase.

Starting from thymidine, through a series of key synthetic transformations (e.g., Wittig reaction, hydroboration, Mitsunobu reaction and TEMPO oxidation) a nucleoside homologue bearing a phospho-carboxylic anhydride group at 6' position was synthesized. The potential of polymerases to catalyze amide bond formation was investigated by using a modified primer with an amino group at 3' position and the synthesized phosphoanhydro compound as substrate. Unfortunately, we did not observe the desired product either by gel electrophoresis or mass spectrometry. In contrast, the instability of the phosphoanhydro compound could lead to pyrophosphate formation and thus, to pyrophosphorolysis of the primer rather than to primer extension.