Hyperpolarizing DNA Nucleobases via NMR Signal Amplification by Reversible Exchange

• Published in: Molecules (Basel, Switzerland) Switzerland), 2023-01, Vol.28 (3), p.1198
• Main Authors: Kidd, Bryce E, Gemeinhardt, Max E, Mashni, Jamil A, Gesiorski, Jonathan L, Bales, Liana B, Limbach, Miranda N, Shchepin, Roman V, Kovtunov, Kirill V, Koptyug, Igor V, Chekmenev, Eduard Y, Goodson, Boyd M
• Format: Article
• Language: English
• Subjects: Adenine; Bases (nucleic acids); Binding; Catalysts; Cytosine; Deoxyribonucleic acid; Deuteration; DNA; DNA methylation; Epigenetics; Ethanol; Experiments; Hyperpolarization; Imidazole; Imidazoles; Magnetic Resonance Imaging; Magnetic Resonance Spectroscopy; Methods; Nitrogen atoms; Nitrogen isotopes; Nitrogen Isotopes - chemistry; NMR & MRI; Nuclear magnetic resonance; nucleic acids; PHIP; SABRE; Sheaths; Tautomers
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules28031198

The present work investigates the potential for enhancing the NMR signals of DNA nucleobases by parahydrogen-based hyperpolarization. Signal amplification by reversible exchange (SABRE) and SABRE in Shield Enables Alignment Transfer to Heteronuclei (SABRE-SHEATH) of selected DNA nucleobases is demonstrated with the enhancement ( ) of H, N, and/or C spins in 3-methyladenine, cytosine, and 6-O-guanine. Solutions of the standard SABRE homogenous catalyst Ir(1,5-cyclooctadeine)(1,3-bis(2,4,6-trimethylphenyl)imidazolium)Cl ("IrIMes") and a given nucleobase in deuterated ethanol/water solutions yielded low H values (≤10), likely reflecting weak catalyst binding. However, we achieved natural-abundance enhancement of N signals for 3-methyladenine of ~3300 and ~1900 for the imidazole ring nitrogen atoms. H and N 3-methyladenine studies revealed that methylation of adenine affords preferential binding of the imidazole ring over the pyrimidine ring. Interestingly, signal enhancements ( ~240) of both N atoms for doubly labelled cytosine reveal the preferential binding of specific tautomer(s), thus giving insight into the matching of polarization-transfer and tautomerization time scales. C enhancements of up to nearly 50-fold were also obtained for this cytosine isotopomer. These efforts may enable the future investigation of processes underlying cellular function and/or dysfunction, including how DNA nucleobase tautomerization influences mismatching in base-pairing.