Sequencing of production-scale synthetic oligonucleotides by enriching for coupling failures using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

THERAPEUTIC OLIGONUCLEOTIDES, IMPURITIES, DEGRADANTS, AND THEIR CHARACTERIZATION BY MASS SPECTROMETRY

Oligonucleotides are an emerging class of drugs that are manufactured by solid-phase synthesis. As a chemical class, they have unique product-related impurities and degradants, characterization of which is an essential step in drug development. The synthesis cycle, impurities produced during the synthesis and degradation products are presented and discussed. The use of liquid chromatography combined with mass spectrometry for characterization and quantification of product-related impurities and degradants is reviewed. In addition, sequence determination of oligonucleotides by gas-phase fragmentation and indirect mass spectrometric methods is discussed. © 2019 John Wiley & Sons Ltd. Mass Spec Rev.

Effect of oligonucleotide structural difference on matrix-assisted laser desorption/ionization in-source decay in comparison with collision-induced dissociation fragmentation

RATIONALE

Mass spectrometry (MS) is an effective tool for the structural analysis of oligonucleotides. Currently, various modifications of oligonucleotides have been proposed to increase the efficacy and safety of oligonucleotide therapeutics. For MS-based structural characterization, the fragmentation behavior of modified oligonucleotides by MS must first be determined.

METHODS

The impact of the oligonucleotide structure on the in-source decay (ISD) of matrix-assisted laser desorption/ionization (MALDI) was examined using a new matrix and compared with collision-induced dissociation (CID) fragmentation behavior.

RESULTS

When a part of the oligonucleotide structure was replaced, an impact was observed at the 3' side of the replaced structure. Among the oligonucleotide components considered herein, nucleobases most significantly impacted both ISD and CID fragmentation patterns.

CONCLUSIONS

Compared with CID, ISD was less sensitive to structural differences. Because ISD fragmentation was less affected by various oligonucleotide modifications, MALDI is a useful and applicable method for the structural characterization or identification of various modified oligonucleotide therapeutics.

Nucleobase derivatives induce in-source decay of oligonucleotides as new matrix-assisted laser desorption/ionization matrices

RATIONALE

For quality control of oligonucleotide therapeutics, accurate and efficient structural characterization using mass spectrometry techniques, such as liquid chromatography/mass spectrometry (LC/MS) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), is essential. In MALDI MS analysis, matrix selection is critical and a new matrix could enable more efficient and rapid structural analysis.

METHODS

We hypothesized that nucleobase derivatives could act as matrices more efficiently than the currently used matrices for oligonucleotides because of structural similarity, which leads to close contact with the analyte. To evaluate their suitability as matrices, 16 nucleobase derivatives were selected and tested as matrix candidates for oligonucleotide analysis.

RESULTS

Six of the 16 nucleobase derivatives acted as matrices for oligonucleotides. Particularly, 6-thioguanine (TG) performed well and induced clear in-source decay fragmentation. When TG or 2-amino-6-chloropurine was used as the matrix, oligonucleotides were ionized, and mainly the w and d fragment ions were observed.

CONCLUSIONS

Herein we demonstrate that a 10-mer RNA or DNA sequence can be successfully characterized using TG as matrix and suggest the possibility of using nucleobase derivatives as novel matrices in oligonucleotide sequencing.

Review on investigations of antisense oligonucleotides with the use of mass spectrometry

Antisense oligonucleotides have been investigated as potential drugs for years. They inhibit target gene or protein expression. The present review summarizes their modifications, modes of action, and applications of liquid chromatography coupled with mass spectrometry for qualitative and quantitative analysis of these compounds. The most recent reports on a given topic were given prominence, while some early studies were reviewed in order to provide a theoretical background. The present review covers the issues of using ion-exchange chromatography, ion-pair reversed-phase high performance liquid chromatography and hydrophilic interaction chromatography for the separation of antisense oligonucleotides. The application of mass spectrometry was described with regard to the ionization type used for the determination of these potential therapeutics. Moreover, the current approaches and applications of mass spectrometry for quantitative analysis of antisense oligonucleotides and their metabolites as well as their impurities during in vitro and in vivo studies were discussed. Finally, certain conclusions and perspectives on the determination of therapeutic oligonucleotides in various samples were briefly described.

Sequencing oligonucleotides by enrichment of coupling failures using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A technique for sequencing oligonucleotides using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry is described. Coupling failures are extracted from the full-length 5'-O-DMTr-oligonucleotide in a crude synthesis using C18 purification cartridges. Enhanced signal and resolution of the failure ions are demonstrated during MALDI-TOF analysis. Sequencing information is confirmed by the mass difference between coupling failures to identify a particular base or structural modification. This procedure eliminates difficulties associated with other mass spectrometric techniques, such as interpretation of data, oligonucleotide length, and backbone, sugar or terminal alterations. An example of sequencing a 16-mer composed of deoxyribonucleotides, 2'-O-methylribonucleotides, and a non-nucleosidic linker is reported.

Reversible biotinylation phosphoramidite for 5'-end-labeling, phosphorylation, and affinity purification of synthetic oligonucleotides

A fluoride/amine-cleavable phosphoramidite designed for biotinylation, phosphorylation, and affinity purification of synthetic oligonucleotides was synthesized and coupled efficiently to the 5'-end of DNA on a solid-phase automatic synthesizer. The two hydroxyl groups of diethyl bis(hydroxymethyl)malonate were used to link biotin and the 5'-end of DNA together through a diisopropylsilyl acetal functionality and a phosphate ester group, respectively. The DNA was cleaved from solid support and fully deprotected by treating with a mixture of MeNH(2) ( approximately 40%) and NH(4)OH ( approximately 29%) (1:1, v/v, 65 degrees C, 30 min), and the linkage between biotin and DNA was found completely stable under these conditions. The biotinylated full-length DNA was efficiently attached to NeutrAvidin coated microspheres and failure sequences and other impurities were simply removed by washing with buffer and water. The microspheres were then treated with HF/pyridine/THF (rt, 1 h) and MeNH(2) ( approximately 40%, rt, 15 min) sequentially to yield high quality full-length 5'-end phosphorylated unmodified DNA as revealed by HPLC analysis. It is anticipated that this method will find applications in areas that require efficient isolation of 5'-end phosphorylated DNA from a complex mixture.