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Title: Nuclear Spin Hyperpolarization of NH 2 ‐ and CH 3 ‐Substituted Pyridine and Pyrimidine Moieties by SABRE
Abstract

Hyperpolarization of N‐heterocycles with signal amplification by reversible exchange (SABRE) induces NMR sensitivity gains for biological molecules. Substitutions with functional groups, in particular in theortho‐position of the heterocycle, however, result in low polarization using a typical Ir catalyst with a bis‐mesityl N‐heterocyclic carbene ligand for SABRE, presumably due to steric hindrance. With the addition of allylamine or acetonitrile as coligands to the precatalyst chloro(1,5‐cyclooctadiene)[4,5‐dimethyl‐1,3‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene] iridium, the1H signal enhancement increased in several substrates withorthoNH2substitutions. For example, for a proton in 2,4‐diaminopyrimidine, the enhancement factors increased from −7±1 to −210±20 with allylamine or to −160±10 with acetonitrile. CH3substituted molecules yielded maximum signal enhancements of −25±7 with acetonitrile addition, which is considerably less than the corresponding NH2substituted molecules, despite exhibiting similar steric size. With the more electron‐donating NH2substitution resulting in greater enhancement, it is concluded that steric hindrance is not the only dominant factor in determining the polarizability of the CH3substituted compounds. The addition of allylamine increased the signal enhancement for the 290 Da trimethoprim, a molecule with a 2,4‐diaminopyrimidine moiety serving as an antibacterial agent, to −70.

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Award ID(s):
1900406
NSF-PAR ID:
10192748
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
ChemPhysChem
Volume:
21
Issue:
19
ISSN:
1439-4235
Page Range / eLocation ID:
p. 2166-2172
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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