Hyperpolarized magnetic resonance imaging (MRI) is a powerful technique enabling real-time monitoring of metabolites at concentration levels not accessible by standard MRI techniques. A considerable challenge this technique faces is the T-1 decay of the hyperpolarization upon injection into the system under study. Here we show that A(n)A'nXX' spin systems such as C-13(2)-1,2-diphenylacetylene (C-13(2)-DPA) sustain long-lived polarization for both C-13 and H-1 spins with decay constants of almost 4.5 min at high magnetic fields of up to 16.44 T without spin-locking; the T-1 of proton polarization is only 3.8 s. Therefore, storage of the proton polarization in a C-13(2)-singlet state causes a 69-fold extension of the spin lifetime. Notably, this extension is demonstrated with proton-only pulse sequences, which can be readily implemented on standard clinical scanners.