Process for the preparation of hyperpolarized carboxylate compounds

1. A para-hydrogenated ester of formula (III)

R—C*(O)—O—R″  (III)

in which:

C* denotes a naturally 13 C enriched or, optionally, 13 C labeled carboxylate carbon atom;

R is a C 1 -C 5 linear or branched alkyl chain which is optionally interrupted by, or substituted with, one or more groups selected from the group consisting of carbonyl (—CO—), hydroxyl (—OH), amino (—NHR 1 ), halogen atom, halo-alkyl group, carbocyclic aliphatic moiety optionally substituted by one or more hydroxyl groups, and aromatic moiety optionally substituted by one or more hydroxyl groups:

R 1 is H or an amino protecting group; and

R″ is a parahydrogenated allyl residue,

or a physiologically acceptable salt thereof.

2. A method for diagnostic MR imaging of a body organ, region, fluid or tissue, or for MR assessment of a biological parameter or metabolic profile of diagnostic interest in an individual patient that comprises:

i) obtaining an unsaturated alkenyl or alkynyl ester of a carboxylate containing molecule of formula (II)

R—C*(O)—O—R′  (II)

in which:

C* denotes the naturally 13 C enriched or, optionally, 13 C labeled carboxylate carbon atom undergoing 13 C hyperpolarization;

R′ is an allyl of formula —CH 2 —CH═CH 2 or a propargyl residue of formula —CH 2 —C≡CH;

R is a C 1 -C 5 linear or branched alkyl chain, which is optionally interrupted by, or substituted with, one or more groups selected from the group consisting of carbonyl (—CO—), hydroxyl (—OH), amino (—NHR 1 ), halogen atom, halo-alkyl group, carbocyclic aliphatic moiety optionally substituted by one or more hydroxyl groups, and aromatic moiety optionally substituted by one or more hydroxyl groups; and

R 1 is H or an amino protecting group,

or a physiologically acceptable salt thereof, and

reacting said unsaturated ester with a molecular para-hydrogen in an aqueous solvent, optionally including an amount from 10% to 30% of an organic solvent selected from short-chain alcohol or acetone, and in the presence of a water soluble hydrogenation catalyst, to produce a para-hydrogenated ester with an [1- 13 C]-carboxylate carbon atom and added polarized hydrogen;

ii) inducing a polarization transfer from the added polarized hydrogen to the [1- 13 C]-carboxylate carbon atom of the para-hydrogenated ester to produce an [1- 13 C]-hyperpolarized ester; and

iii) hydrolyzing the [1- 13 C]-hyperpolarized ester by adding to the aqueous solution of the [1- 13 C]-hyperpolarized ester obtained at step ii) a base promoting its hydrolysis, to give the aqueous solution of the [1- 13 C]-hyperpolarized carboxylate containing molecule of interest, and collecting an aqueous solution of the [1- 13 C]-hyperpolarized carboxylate containing molecule, or of the corresponding [1- 13 C]-hyperpolarized carboxylic acid;

(iv) removing the hydrogenation catalyst and the optional organic solvent from the obtained aqueous solution, to give the aqueous solution of the [1- 13 C]-hyperpolarized carboxylate containing molecule of interest ready for use in an in vivo application;

v) administering the aqueous solution to the individual patient, or contacting the aqueous solution with an ex vivo sample of the body organ, region, fluid or tissue of the individual patient;

vi) exposing the administered individual patient, or the contacted ex vivo sample to a radiation frequency allowing to excite the hyperpolarized [1- 13 C]-carboxylate carbon atom of the [1- 13 C]-hyperpolarized carboxylate containing molecule;

vii) recording a signal intensity generated by the excited [1- 13 C]-carboxylate carbon atom of the [1- 13 C]-hyperpolarized carboxylate containing molecule and/or of a metabolite or catabolite thereof; and

viii) obtaining an image of the individual patient body organ, region, or tissue, or a suitable estimate of the biological parameter or metabolic profile of interest from the signal intensity.

3. A method for diagnostic MR imaging of a body organ, region, fluid, or tissue, or for MR assessment of a biological parameter or metabolic profile of diagnostic interest in an individual patient comprising:

i) obtaining an unsaturated alkenyl or alkynyl ester of a carboxylate containing molecule of formula (II)

R—C*(O)—O—R′  (II)

in which:

C* denotes the naturally 13 C enriched or, optionally, 13 C labeled carboxylate carbon atom undergoing 13 C hyperpolarization;

R′ is an allyl of formula —CH 2 —CH═CH 2 or a propargyl residue of formula —CH 2 —C≡CH;

R is a C 1 -C 5 linear or branched alkyl chain, which is optionally interrupted by, or substituted with, one or more groups selected from the group consisting of carbonyl (—CO—), hydroxyl (—OH), amino (—NHR 1 ), halogen atom, halo-alkyl group, carbocyclic aliphatic moiety optionally substituted by one or more hydroxyl groups, and aromatic moiety optionally substituted by one or more hydroxyl groups; and

R 1 is H or an amino protecting group,

or a physiologically acceptable salt thereof, and reacting the unsaturated ester with a molecular para-hydrogen in an organic solvent, or a suitable mixture of organic solvents, and in the presence of a hydrogenation catalyst soluble in the organic solvent and insoluble in an aqueous solvent;

ii) inducing a polarization transfer from the added polarized hydrogen to the [1- 13 C]-carboxylate carbon atom of the para-hydrogenated ester to produce an [1- 13 C]-hyperpolarized ester;

iii) diluting the organic solution of the [1- 13 C]-hyperpolarized ester obtained at step ii) with an aqueous solution promoting the hydrolysis of the ester to the corresponding water soluble [1- 13 C]-hyperpolarized carboxylate containing molecule, or the corresponding carboxylic acid, and then collecting, by phase transfer extraction, the aqueous solution of the [1- 13 C]-hyperpolarized compound of interest, which is ready for use in an in vivo application;

iv) administering the collected aqueous solution to the individual patient, or contacting the aqueous solution with an ex vivo sample of the body organ, fluid, or tissue of the individual patient;

v) exposing the administered individual patient, or the contacted ex vivo sample to a radiation frequency allowing to excite the hyperpolarized [1- 13 C]-carboxylate carbon atom of the [1- 13 C]-hyperpolarized carboxylate containing molecule;

vi) recording a signal intensity generated by the excited hyperpolarized [1- 13 C]-carboxylate carbon atom of the [1- 13 C]-hyperpolarized carboxylate containing molecule and/or of any suitable metabolite or catabolite thereof; and

vii) obtaining an image of the individual patient body, organ, region, or tissue, or a suitable estimate of the biological parameter or metabolic profile of interest from the signal intensity.

4. The ester according to claim 1 , wherein R is a hydroxyethyl residue of formula CH 3 CH(OH)—.