Synthetic Approaches for 15N‐Labeled Hyperpolarized Heterocyclic Molecular Imaging Agents for 15N NMR Signal Amplification by Reversible Exchange in Microtesla Magnetic Fields

• Published in: Chemistry : a European journal Vol. 27; no. 38; pp. 9727 - 9736
• Main Authors: Chukanov, Nikita V., Shchepin, Roman V., Joshi, Sameer M., Kabir, Mohammad S. H., Salnikov, Oleg G., Svyatova, Alexandra, Koptyug, Igor V., Gelovani, Juri G., Chekmenev, Eduard Y.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 07-07-2021
• Subjects: Amplification; Biocompatibility; Chemistry; Contrast agents; Contrast media; Hyperpolarization; In vivo methods and tests; Isotopic labeling; Magnetic fields; magnetic resonance imaging; Magnetic resonance spectroscopy; Nitrogen isotopes; NMR; NMR spectroscopy; Nuclear magnetic resonance; Nuclear spin; parahydrogen; Polarization; Polarization (spin alignment); Sensitivity; spectroscopy
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202100212

NMR hyperpolarization techniques enhance nuclear spin polarization by several orders of magnitude resulting in corresponding sensitivity gains. This enormous sensitivity gain enables new applications ranging from studies of small molecules by using high‐resolution NMR spectroscopy to real‐time metabolic imaging in vivo. Several hyperpolarization techniques exist for hyperpolarization of a large repertoire of nuclear spins, although the 13C and 15N sites of biocompatible agents are the key targets due to their widespread use in biochemical pathways. Moreover, their long T1 allows hyperpolarized states to be retained for up to tens of minutes. Signal amplification by reversible exchange (SABRE) is a low‐cost and ultrafast hyperpolarization technique that has been shown to be versatile for the hyperpolarization of 15N nuclei. Although large sensitivity gains are enabled by hyperpolarization, 15N natural abundance is only ∼0.4 %, so isotopic labeling of the molecules to be hyperpolarized is required in order to take full advantage of the hyperpolarized state. Herein, we describe selected advances in the preparation of 15N‐labeled compounds with the primary emphasis on using these compounds for SABRE polarization in microtesla magnetic fields through spontaneous polarization transfer from parahydrogen. Also, these principles can certainly be applied for hyperpolarization of these emerging contrast agents using dynamic nuclear polarization and other techniques.
Getting hyper: This minireview provides a selective overview of 15N‐labeling approaches for the preparation of contrast agents hyperpolarized by using the SABRE‐SHEATH technique. This technique employs parahydrogen as a fast and inexpensive means to produce hyperpolarized biocompatible contrast agents for molecular imaging applications.