Compounds, reagents, and uses thereof

1. A compound represented by the following formula:

or a salt thereof, wherein the compound is at least 60%, 70%, 80%, 90%, 95%, 99%, 99.5% or 99.9% pure.

2. The compound of claim 1 , wherein the compound is represented by the following formula:

or a salt thereof.

3. The compound of claim 1 , wherein the compound is isotopically labeled.

4. A method of determining the level of a compound represented by the following formula:

or a salt thereof, in a subject comprising:

(1) preparing an analytical sample from a biological sample obtained from the subject;

(2) determining the level of the compound using chromatography, mass spectrometry, enzyme-linked immunosorbent assay (ELISA), antibody linkage, immunoblotting, immunohistochemistry (IHC), other immunochemical methods, or a combination thereof.

5. The method of claim 4 , further comprising comparing the level of the compound in the biological sample obtained from the subject to the level of the compound in a reference sample.

6. The method of claim 4 , wherein the method further comprises using the determined level of the compound in a mathematical model to assess kidney function.

7. The method of claim 4 , wherein the method further comprises analyzing the biological sample to determine the level of one or more additional biomarkers relevant for the assessment of kidney function.

8. The method of claim 7 , wherein the additional biomarkers are selected from the group consisting of pseudouridine, N-acetylthreonine, 2-C-mannopyranosyl tryptophan, N-acetylserine, N-acetylalanine, N6-carbamoylthreonyl adenosine, 4-acetamidobutanoate, erythritol, myo-inositol, erythronate, urea, arabitol, N2,N2-dimethylguanosine, N1-methyladenosine, 3-methylglutarylcarnitine, S-adenosylhomocysteine, N-acetylmethionine, N6-acetyllysine, Kynurenine, arabonate, succinylcarnitine, ribose, xylonate, N-formylmethionine, O-methylcatechol sulfate, 2-methylbutyrylcarnitine, phenylacetylglutamine, N2,N5-diacetylornithine, tryptophan, creatinine, urate, 3-indoxylsulfate and p-cresol sulfate.

9. A The method of claim 4 further comprising calculating the estimated glomerular filtration rate (eGFR) of the subject using an algorithm that utilizes the determined level of the compound.

10. The method of claim 9 , wherein the calculated estimated glomerular filtration rate (eGFR) is used for assessing kidney function in the subject.

11. The method of claim 4 , wherein the compound is represented by the following formula:

or a salt thereof.

12. A kit comprising a compound represented by the following formula:

or a salt thereof, and instructions for measuring the level of the compound in a biological sample.

13. The kit of claim 12 further comprising

one or more instructions selected from the group consisting of assessing or monitoring kidney function in a subject,

determining predisposition to developing reduced kidney function in a subject,

classifying a subject according to level of kidney function,

diagnosing or monitoring chronic kidney disease (CKD) in a subject,

diagnosing or monitoring acute kidney injury (AKI) in a subject, and

calculating estimated glomerular filtration rate (eGFR) in a subject based on the level of the compound detected in a biological sample obtained from the subject.

14. The kit of claim 12 , wherein the compound is represented by the following formula:

or a salt thereof.

15. The kit of claim 12 , wherein the compound is isotopically labeled.

16. The kit of claim 15 , wherein the compound is N,N,N-Trimethyl- 13 C 3 -L-Alanyl-L-Proline.

17. The kit of claim 12 , wherein the kit further comprises one or more additional biomarkers selected from the group consisting of pseudouridine, N-acetylthreonine, 2-C-mannopyranosyl tryptophan, N-acetylserine, N-acetylalanine, N6-carbamoylthreonyl adenosine, 4-acetamidobutanoate, erythritol, myo-inositol, erythronate, urea, arabitol, N2,N2-dimethylguanosine, N1-methyladenosine, 3-methylglutarylcarnitine, S-adenosylhomocysteine, N-acetylmethionine, N6-acetyllysine, kynurenine, arabonate, succinylcarnitine, ribose, xylonate, N-formylmethionine, O-methylcatechol sulfate, 2-methylbutyrylcarnitine, phenylacetylglutamine, N2,N5-diacetylornithine, tryptophan, creatinine, urate, 3-indoxylsulfate and p-cresol sulfate.

18. A method for preparing a compound represented by the following formula:

or a salt thereof, comprising reacting a compound represented by the following formula:

or a salt thereof, with a methylation reagent CH 3 X or (CH 3 ) 2 SO 4 , wherein X is Cl, Br, I or OSO 2 CF 3 .

19. The method of claim 18 , wherein the compound is represented by the following formula:

or a salt thereof, and the method comprises reacting L-alanyl-L-proline with CH 3 X or (CH 3 ) 2 SO 4 .