α-Tocopherol is a naturally occurring vitamin (vitamin E group). Conjugated to an oligonucleotide it adds a lipophilic character. As tocopherol can be recognised and transported by body specific proteins and carriers, the tocopherol modification may also serve as a means to route delivery of the conjugated oligonucleotide within the organism.

Attachement of small lipophilic molecules to oligonucleotides allows for passage through the cell membrane and thus for the uptake of highly negatively charged DNA or RNA into the cell. Furhtermore, the attachment tocopherol or cholesterol to DNA or RNA molecules may improve the stability and the distribution of the conjugates in the cell.

Literature:
1. Efficient in vivo delivery of siRNA to the liver by conjugation of alpha-tocopherol. Nishina K, Unno T, Uno Y, Kubodera T, Kanouchi T, Mizusawa H, Yokota T; Mol Ther (2008), doi: 10.1038/mt.2008.14
2. Oligonucleotide conjugates for therapeutic applications. Winkler J; Ther Deliv (2013), doi: 10.4155/tde.13.47