Purification challenges

The key impurities in the crude oligonucleotide, after synthesis, are length-based. The majority of the impurities are shorter than the target product, although longer impurities are also present. Deletions at random locations along the oligonucleotide chain are termed N-x impurities, where N is the full-length oligonucleotide and x the number of deletions. Some "longmers" resulting from the synthesis process and post-synthesis processes can also be found, these are called N+x.

Oligonucleotides will be needed in large quantities and they must be very pure. Typically, after synthesis, the crude 20 mer oligonucleotide is about 70-75% pure. The final purity requirements of therapeutic oligonucleotides usually exceed 95%.