Facile Removal of Homogeneous SABRE Catalysts for Purifying Hyperpolarized Metronidazole, a Potential Hypoxia Sensor

Abstract

We report a simple and effective method to remove IrIMes homogeneous polarization transfer catalysts from solutions where NMR Signal Amplification By Reversible Exchange (SABRE) has been performed, while leaving intact the substrate’s hyperpolarized state. Following microTesla SABRE hyperpolarization of 15N spins in metronidazole, addition of SiO2 microparticles functionalized with 3-mercaptopropyl or 2-mercaptoethyl ethyl sulfide moieties provides removal of the catalyst from solution well within the hyperpolarization decay time at 0.3 T (T1>3 mins)—and enabling transfer to 9.4 T for detection of enhanced 15N signals in the absence of catalyst within the NMR-detection region. Successful catalyst removal from solution is supported by the inability to “re-hyperpolarize” 15N spins in subsequent attempts, as well as by 1H NMR and ICP-MS. Record-high 15N nuclear polarization of up to ~34% was achieved, corresponding to >100,000-fold enhancement at 9.4 T, and approximately 5/6th of the 15N hyperpolarization is retained after ~20-second-long purification procedure. Taken together, these results help pave the way for future studies involving in vivo molecular imaging using agents hyperpolarized via rapid and inexpensive parahydrogen-based methods.

Hyperpolarizing Concentrated Metronidazole 15NO2 Group over Six Chemical Bonds with More than 15 % Polarization and a 20 Minute Lifetime

“…The 15 Nm agnetization for [ 15 N 3 ]metronidazole is improved by around2 5-fold or more compared with the previously studied molecules [i.e.,c ompared with MZN(n.a.) [36] Moreover,t he 15 Nm agnetization calculated here for [ 15 N 3 ]metronidazole is approximatelys ix-fold greater than that of mono-15 N-labeled [ 15 N]nicotinamide. [36] Moreover,t he 15 Nm agnetization calculated here for [ 15 N 3 ]metronidazole is approximatelys ix-fold greater than that of mono-15 N-labeled [ 15 N]nicotinamide.…”

“…This polarization level is lower (bya round two-fold) than the best P 15N values (ca. [36] This observation can likelyb ee xplained by two effects: First, the labeled compound produces an activec omplex with two 15 Ns ites in the equatorial plane and the polarization is transferredi nt he AA'BB' four-spin system,w hereas in the case of metronidazole with an atural abundance of 15 N, polarization transfer from the pH 2 -derived hydrides to 15 No ccurs in an AA'Bt hree-spin system. [36] This observation can likelyb ee xplained by two effects: First, the labeled compound produces an activec omplex with two 15 Ns ites in the equatorial plane and the polarization is transferredi nt he AA'BB' four-spin system,w hereas in the case of metronidazole with an atural abundance of 15 N, polarization transfer from the pH 2 -derived hydrides to 15 No ccurs in an AA'Bt hree-spin system.…”

“…0.4 mTwith single-exponential fitting.N ote that the buildup of P 15N at the 15 NO 2 and 15 N1 sitesisn ot well describedbym ono-exponentialg rowth due to the complex dynamicsoft he buildup process at multiples ites( the mono-exponentialb uildup curves and time constantsare provided for comparativepurposes (with respectt ot he 15 N3 site) only). [36] 15 Npolarization payload and 15 Nmagnetization 30 mT) usingt he initial conditionsofP 15N3 > P 15N1 > P 15NO2 (the initial points within the dashed box correspondtot hose in (a), denotingthe magnetic field of HP state preparation).…”

“…[26][27][28][29][30][31][32][33] In this work we employed the SABRE in the shield enables alignment transfer to heteronuclei (SABRE-SHEATH) [34,35] variant of SABRE, which relies on simultaneous chemical exchange between parahydrogen (pH 2 )a nd the to-be-hyperpolarizedb iomolecules (without alteringt heir structures) within the ligand sphere of ac atalyst in microtesla (mT) magnetic fields (Figure 1a). [36][37][38] Unlike d-DNP, [12] SABRE-SHEATH requires relatively simple and inexpensive hardware. [36][37][38] Unlike d-DNP, [12] SABRE-SHEATH requires relatively simple and inexpensive hardware.…”

Hyperpolarising Pyruvate through Signal Amplification by Reversible Exchange (SABRE)

“…[6] Molecules hyper-polarised using PHIP have been widely used in NMR spectroscopy,a nd there are examples that feature in vivo imaging. [9] Thechemical identity of pyruvate is unaffected by this process,w hich has already achieved substantial levels of polarisation (63 %in 1 H, [10] 25 %in 13 C, [11] and 43 %in 15 N [12] ) in ar ange of materials that predominantly bind to am etal polarisation transfer catalyst through nitrogen centres. [8] Here though, we hyperpolarise pyruvate based on the non-hydrogenative PHIP derived signal amplification by reversible exchange (SABRE) process,w hich is shown in Figure 1.…”