Terminal Diazirines Enable Reverse Polarization Transfer from 15 N 2 Singlets

Diazirine moieties are chemically stable and have been incorporated into biomolecules without impediment of biological activity. The N labeled diazirines are appealing motifs for hyperpolarization supporting relaxation protected states with long-lived lifetimes. The (-CH N ) diazirine groups investigated here are analogues to methyl groups, which provides the opportunity to transfer polarization stored on a relaxation protected (-CH N ) moiety to H, thus combining the advantages of long lifetimes of N polarization with superior sensitivity of H detection. Despite the proximity of H to N nuclei in the diazirine moiety, N T times of up to (4.6±0.4) min and singlet lifetimes T of up to (17.5±3.8) min are observed. Furthermore, we found terminal diazirines to support hyperpolarized H singlet states in CH groups of chiral molecules. The singlet lifetime of H singlets is up to (9.2±1.8) min, thus exceeding H T relaxation time (at 8.45 T) by a factor of ≈100.