Enhancement of 1H NMR signals of 5-alkyl-6-phenylethynyl-2-pyrone using p-H2.

Abstract

Isotopically labelled C and unlabelled 5-alkyl-6-alkyne-2-pyrone as potential magnetic resonance imaging agents.  The PHIP signal enhancement studies were carried on the addition of p-H2 in the presence of a cationic rhodium catalyst to predominantly afford the semi-hydrogenation product; 6-styryl-5-alkyl-2-pyrone with 92-100% increase in the 1H NMR signals. Moreover, the T1 relaxation rate was found to be 140 seconds when a flow reactor was employed to evaluate the rate of relaxation of these compounds. Meanwhile, the C-isotopically labelled compounds were evaluated for the enhancement of C signals and enhancement of ≥ 30% was obtained. This implies that these compounds could be employed as 1H and 13C NMR imaging agents. Keywords: Hyperpolarization, parahydrogen, SABRE, 2-pyrone, 5-alkyl-6-phenylethynyl-2-pyrone, Sonogashira cross-coupling reactions.