Toward hyperpolarized molecular imaging of HIV: synthesis and longitudinal relaxation properties of 15N‐Azidothymidine

Previously unreported ¹⁵N labeled Azidothymidine (AZT) was prepared as an equimolar mixture of two isotopomers: 1‐¹⁵N‐AZT and 3‐¹⁵N‐AZT. Polarization decay of ¹⁵N NMR signal was studied in high (9.4 T) and low (~50 mT) magnetic fields. ¹⁵N T₁ values were 45 ± 5 s (1‐¹⁵N‐AZT) and 37 ± 2 s (3‐¹⁵N‐AZT) at 9.4 T, and 140 ± 16 s (3‐¹⁵N‐AZT) at 50 mT. ¹⁵N‐AZT can be potentially ¹⁵N hyperpolarized by several methods. These sufficiently long ¹⁵N‐AZT T₁ values potentially enable hyperpolarized in vivo imaging of ¹⁵N‐AZT, because of the known favorable efficient (i.e., of the time scale shorter than the longest reported here ¹⁵N T₁) kinetics of uptake of injected AZT. Therefore, 3‐¹⁵N‐AZT can be potentially used for HIV molecular imaging using hyperpolarized magnetic resonance imaging.