New hyperpolarized contrast agents for ¹³C-MRI from para-hydrogenation of oligooxyethylenic alkynes

Two alkyne derivatives, which contain one and two oligooxyethylenic chains respectively, showed to be good substrates for para-hydrogenation reactions, yielding the corresponding hyperpolarized alkenes in good yields. A suitable theory has been developed to account for the observed results, fully explaining the different para-H₂ induced effects observed upon the para-hydrogenation of symmetrically and asymmetrically substituted alkynes in ALTADENA and PASADENA modes. The oligooxyethylenic substituent provides good water solubility to the para-hydrogenated symmetrical derivative. ¹³C-MR in vitro images of the latter derivative were obtained both in acetone and in water solutions (130 mM), using the ALTADENA procedure and after application of the field cycling procedure which allows acquisition of an in-phase ¹³C carbonyl resonance. The finding that the hydrogenated product is water-soluble in contrast to the parent alkyne which is not allows for the pursuit of a fast phase-transfer separation from the organic solvent, the unreacted substrate, and the catalyst to obtain a "ready-to-use" water solution suitable for further in vivo MRI applications.