Dideoxy-C (ddC, Figure 1) prevents the DNA polymerase to further extend the nucleotide chain. Therefore, ddC can be effectively used as a chain terminator. For the same purpose, inverted basis, C-spacers, Amino-modifications, and phosphorylation can also be used.
Figure 1. Structure of Dideoxy-C (R = sequence, B = base).
metabion offers ddC as a modification in its DNA portfolio: