Figure 1: Structures of Cholesteryl and Lipophilic Phosphoramidites and Support

(1) Cholesteryl-TEG
(2) 3’-Cholesteryl-TEG CPG
(3) 5’-Cholesteryl-TEG
(4) a-Tocopherol-TEG
(5) 5’- Stearyl


Cholesterol remains one of the most popular forms of labelling of oligonucleotides, especially those destined for use in therapeutics, including antisense and siRNA.1,2 Most oligonucleotides are hydrophilic, so they are constantly challenged in their ability to permeate cell membranes. In order to improve cellular uptake, one strategy is to conjugate oligonucleotides with hydrophobic molecules that are non-toxic and cholesterol is one of the most popular choices.

In 1993, Glen Research introduced Cholesteryl-TEG phosphoramidite (1) and the corresponding CPG support (2). Later, in 2008, we introduced the simplified version 5’-Cholesteryl-TEG phosphoramidite (3), designed solely for 5’ labelling of oligonucleotides.

In those early days, the cholesterol to make these products was sourced from sheep’s wool and the products were perfectly useable for their intended research and development purposes. However, it has become clear that this cholesterol source was unacceptable in situations where product oligonucleotides were required to be certified as being free from BSE/TSE contamination. Bovine spongiform encephalopathy (BSE) is a transmissible spongiform encephalopathy (TSE) that affects cattle. There is also a spongiform encephalopathy associated with sheep, called scrapie, that has been shown to induce BSE in cattle.

We are happy to report that our raw material cholesterol is now from a plant source and our cholesterol products can now be certified as free from BSE/TSE contamination.

Glen Research also offers other hydrophobic labels, 5’-a-Tocopherol-TEG Phosphoramidite (4) and 5’-Stearyl Phosphoramidite (5), to improve the cellular uptake of oligonucleotides.



1. M. Raouane, D. Desmaele, G. Urbinati, L. Massaad-Massade, and P. Couvreur, Bioconjugate Chemistry, 2012, 23, 1091-1104.

2. J. Winkler, Ther Deliv, 2013, 4, 791-809.