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Simple and inexpensive method to link other molecules to DNA sequences with desired functions

The development of new types of drugs based on DNA and RNA is proceeding at a rapid pace. mRNA vaccines against COVID-19 are just one of many examples of DNA/RNA-based drugs on the market. Many are on the way, but producing the necessary modified DNA/RNA is expensive. A research group from Aarhus University has now found an efficient and inexpensive method to produce stable DNA sequences attached to chemical groups that, for example, ensure that drugs are directed to the right cells.

The production of short DNA and RNA sequences, called oligonucleotides, is essential today in the context of diagnosis (COVID-19 test), DNA sequencing, gene synthesis for synthetic biology and gene therapy, as in the CRISPR-Cas9 method.

Oligonucleotide production technology has been advanced since its development in 1981, but the underlying chemistry remains largely unchanged. One is always dependent on phosphoramidites, which are chemical compounds that, unfortunately, are unstable in the production process.

However, Kurt Gothelf and his research group have already shown a more efficient way to produce the building blocks of oligonucleotides by developing a flux-based method to make phosphoramidites immediately before use, thereby avoiding this degradation. You can read more about it in a previous article here: “New method for producing synthetic DNA” (https://inano.au.dk/about/news-events/news/show/artikel/new-method -for-production -DNA-synthetics).

Expensive to acquire DNA sequences with special features

There is a great need for oligonucleotides which have been modified with special functionalities. For example, oligonucleotides modified with certain sugars have been shown to be taken up by the liver. Based on this, several oligonucleotide drugs are used to regulate proteins that are, in fact, produced in the liver and can therefore cure diseases. It is also important to be able to attach dyes to oligonucleotides as this is often used in diagnostics and research.

Usually these functionalities are inserted into the oligonucleotides by the building blocks, the phosphoramidites, being produced with a specific chemical handle or the desired functional group. There are commercial catalogs with several hundred varieties of these modified phosphoramidites. However, such modified phosphoramidites are, in most cases, very expensive to obtain and, as mentioned above, they are unstable in liquids at room temperature.

New easy and inexpensive method for the synthesis of special building blocks

In a scientific article recently published in Nucleic acid researchwhich is the leading journal of oligonucleotides, Angel Santorelli and Kurt Gothelf present a simple and inexpensive method to introduce modifications into oligonucleotides without the need for special phosphoramidites.

For this purpose, they use chemical compounds called sulfonylazides, which can give oligonucleotides many different functionalities during the chemical synthesis of oligonucleotides.

The method is compatible with the previously mentioned automated and flow-based method for oligonucleotide synthesis, where phosphoramidite degradation is avoided. The recently published method for the synthesis of modified phosphoramidites can thus serve as a simple alternative to the unstable and expensive special phosphoramidites currently used in the production of modified oligonucleotides.

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Material provided by Aarhus University. Note: Content may be edited for style and length.