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 C6 spacer consists of a 6-carbon spacer, useful to introduce a short spacer into an oligonucleotide (Figure 1).
Figure 1. Structure of the C6 spacer (R = sequence, B = base).
metabion offers the C6 spacer in its standard DNA portfolio: