Capping

• Suitable for use in the phosphoramidite capping method
• Moisture content has been strictly controlled in both the solution and powder forms
• Available in two types: acetyl-based and phosphoramidite-based capping reagents

Capping reaction using acetic anhydride

Capping Reaction Using EDCP

Issues with Acetyl Capping

In the conventional acetyl capping method using acetic anhydride, impurities originating from adenine and guanine nucleotides are generated. These impurities arise from amide exchange, addition, and substitution reactions mediated by the acylating reagent, and are difficult to remove during purification. In addition, because UnyLinker™ exhibits low reactivity toward the secondary hydroxyl groups, impurities derived from unreacted species are also generated. These by-products are categorized and managed as product-related impurities in nucleic acid therapeutics. Therefore, establishing analytical methods and controlling these impurities remain ongoing challenges.

Generation of Impurities Derived from Adenosine¹⁾

Generation of Impurities Derived from Guanosine²⁾

Generation of Impurities Derived from Unreacted Secondary Hydroxyl Group Associated with UnyLinker™²⁾

To address the issues associated with acetyl capping, various phosphoramidite-type capping reagents have been developed since around 1994 as alternatives to acetic anhydride. Examples of these reagents are shown below. They effectively prevent reductions in purity and reaction yield caused by side reactions commonly observed with acetyl-based capping.

DDP³⁾
(Diethyl N,N-diisopropyl
phosphoramidite)

Lipocap⁴⁾ (X=CH₂)
high lipophilicity
UniCap⁵⁾ (X=O)

Cholesterol phosphoramidite⁶⁾
high lipophilicity

EDCP
(Cyclic phosphoramidite)
high reactivity

1. Rodriguez, A. A. et al. : Bioorg. Med. Chem. Lett., 26, 3268 (2016).
2. Rodriguez, A. A. et al. : Bioorg. Med. Chem. Lett., 24, 3243 (2014).
3. Yu, D. et al. : Tetrahedron Lett., 35, 8565 (1994).
4. Natt, F. and Häner, R. : Tetrahedron, 53, 9629 (1997).
5. Glen Report 17.13. UniCap Phosphoramidite, AN alternative to acetic anhydride capping
6. Ren, Q., Osawa, T. and Obika, S : Tetrahedron., 150, 133774 (2024).