Parahydrogen induced polarization

Mobile single-sided NMR

The theory and practice of hyperpolarization in magnetic resonance using parahydrogen

Enzyme-catalyzed organic synthesis: practical routes to aza sugars and their analogs for use as glycoprocessing inhibitors

Recent developments in NMR hyperpolarization have enabled a wide array of new in vivo molecular imaging modalities, ranging from functional imaging of the lungs to metabolic imaging of cancer. This Concept article explores selected advances in methods for the preparation and use of hyperpolarized contrast agents, many of which are already at or near the phase of their clinical validation in patients.

NMR Hyperpolarization Techniques for Biomedicine

Hydrogenation de composes acetyleniques ou ethyleniques en presence de complexes de rhodium carbonyle ou de palladium

Para hydrogen induced polarization in hydrogenation reactions

INEPT in a chemical way. Polarization transfer from para hydrogen to phosphorus-31 by oxidative addition and dipolar relaxation

electrochemical methods, to furnish 38-52% yields of a blue-green intermediate 6. The optical spectrum [A, 303 (e 15 300), 380 (45 300), 646 (inf; SOOO), 704 nm (9300)] was almost identical with that of the previous intermediate; the greatly simplified proton NMR spectrum showed three methine peaks (6.26, 5.35, 5.00 ppm), two NHs (13.84, 13.22 ppm), nine methyl resonances (2.03-1.77, 1.40 ppm), and an AB quartet [2.98, 2.52 ppm (each d, JAe = 15.3 Hz)] (Figure 3). Insert A in Figure 3 shows the methine protons of the intermediate from the unsymmetrical a,c-biladiene 3 and demonstrates the presence of unequal amounts of two isomeric structures depending upon which of the two terminal methyls in 3 forms the macrocyclic bridging carbon. Irradiation of the methyl singlet in 6 at 1.40 ppm gave a nuclear Overhauser enhancement at the upfield doublet (2.52 ppm) and also at a methyl resonance (1.77 ppm). On the basis of this evidence, we propose structure 6 for the intermediate, with proton NMR assignments as annotated. High resolution FAB mass spectrometryI6 confirmed the expected molecular weight. The mechanism shown in Scheme I is proposed for the decamethyl-apbiladiene 5 electrocyclization; following deprotonationI7 the conjugated tetrapyrrole suffers two-electron oxidation and macrocyclization to give the intermediate 6. Nucleophilic attack,18 presumably by the electrolyte, causes formation of the phlorin 7 which undergoes spontaneous oxidation19 to give porphyrin. Thin-layer spectroelectrochemistry (not shown) indicates that the order of the nucleophilic attack/oxidation steps may be reversed in the electrochemical conversion of 6 into porphyrin.

Thomas C. Eisenschmid

Papers

Para hydrogen induced polarization in hydrogenation reactions

INEPT in a chemical way. Polarization transfer from para hydrogen to phosphorus-31 by oxidative addition and dipolar relaxation

Para hydrogen induced polarization in hydrogenation reactions catalyzed by ruthenium phosphine complexes

Parahydrogen-Induced Polarization and Polarization Transfer in Hydrogenation and Oxidative Addition Reactions

Competitive carbonylation pathways from a dialkyl A-frame complex