3'- spacers are often used as an alternative to 3'-phosphate as blockers; the most common is the C3 spacer. In general, a spacer is incorporated to add a distance between the oligo and a modifier. Spacers can be hydrophilic (e.g., the HEG spacer) or hydrophobic (C3 or C6 spacers).
The C12 spacer (Figure 1) consists of a 12-carbon spacer, useful to introduce a short spacer into an oligonucleotide.
Figure 1. Structure of the C12 spacer (R = sequence, B = base).
metabion offers the C12 spacer in its standard DNA portfolio: