A 'universal' support in the context of oligonucleotide synthesis is a solid support, normally either a controlled-pore glass (CPG) or polystyrene (PS), where no functionality (e.g. nucleobase or modification) of the support is retained at the 3' end of the oligo sequence after cleavage. In this case, the first addition at the 3'-end is determined by the first phosphoramidite used in the synthesis cycle.

There are advantages in using a universal support where there is no nucleobase or modification already present (e.g. when using a plate synthesizer). When preparing wells in plate synthesizers this eliminates the possibility of the incorrect resin being placed in a well. The same rationale applies to column synthesizers. It also enables automated preparation of the plates to stock ready for synthesis. There is also an added benefit in large-scale syntheses, where the supply chain is simplified as only a single support is required.

A universal support can also be applied in situations where a 3'-modification support is not available, using a phosphoramidite modifier as the first addition in the cycle (this will only work with phosphoramidites capable of extending the oligo chain, i.e. not 5' chain-terminating modifiers).

In all cases, the oligo sequence and any modifications incorporated must be compatible with the universal support cleavage and deprotection conditions for the use of a universal support to be viable. This is one reason why a universal support may not always be the optimum choice for synthesis. Typically, a strong base with a high temperature or extended time is required to completely remove the universal linker. Therefore it is inadvisable to use these supports with modifications that may be susceptible to degradation under these conditions. For instance, we would not recommend use with 2’-F RNA chemistry.

We provide customers with several universal support options.

The most widely used and applicable CPG support is UnyLinker™ CPG. We provide this in two pore -sizes – 550 Å and 1000 Å. UnyLinker™ 550 Å CPG has been manufactured using our NextGen process improvements. The product design is a result of our CPG optimization work; it encompasses an optimised combination of pore size, density, surface area and functional loading (what we describe as Surface Area Normalised Loading, SANL) which achieves higher functional loadings without overcrowding the surface of the CPG. This delivers maximum productivity from any given asset, particularly in large-scale therapeutic siRNA applications.* As such, it offers unrivalled performance for a universal CPG. The 1000 Å variant is a more standard specification, potentially useful in longer oligonucleotide synthesis.

For customers whose application may require the use of a polymer support, we now also offer UnyLinker™ Polystyrene as part of our expanding product line. The PS product is a useful alternative to CPG in certain syntheses of uncomplex oligonucleotides at high scale.

As an alternative to the DMT-on / N-Ph structure of UnyLinker, we also provide an analogous DMT-off / N-iPr product. When using DMT-protected universal supports, a slightly extended initial detritylation is employed. This can result in a small percentage of the linker being cleaved off during this step thus reducing the loading and the yield of oligonucleotides. Using a DMT-off product eliminates this scenario if necessary. In addition, the N-iPr version is a more labile linker and hence can be used under milder conditions. In practice, however, this is only important with very sensitive modifications and in the synthesis of routine DNA, for example, there is no real benefit.

Lastly, we offer a product with a DMT-on ribose linker product in different pore sizes (500 Å, 1000 Å and 2000 Å). This variant has no specific advantages, however has been used by customers in some legacy protocols and applications and hence we continue to support it.

When reviewing the options available for your application, our recommendation would be to first consider using a UnyLinker CPG product.

*Customers may note that we offer a number of differently functionalized 500 Å and 600 Å CPGs as our standard products in this pore range; like we have done with UnyLinker™ 550 Å CPG, we will be continuing to introduce further new, improved products with optimised specifications, including pore size, targeted at achieving maximum productivity for different application modalities.

UnyLinker™ is a trademark of Ionis Pharmaceuticals, Inc. and used under license.

The DMT off (N-iPr) Universal Support product is distributed on behalf of AM Chemicals LLC.