NMR with thermal polarization requires relatively concentrated samples, particularly for nuclei with low abundance and low gyromagnetic ratios, such as ¹⁵N. We expand the substrate scope of SABRE, a recently introduced hyperpolarization method, to allow access to ¹⁵N-enriched Schiff bases. These substrates show fractional ¹⁵N polarization levels of up to 2?% while having only minimal ¹H enhancements.