Compositions and methods for analyzing cysteine

1. An analytical method comprising:

contacting a sample containing D-cysteine, L-cysteine, or a mixture thereof with a probe, wherein said contacting is carried out under conditions effective to result in double ipso-substitution of any cysteine present in the sample; and

determining, based on any double ipso-substituted cysteine that forms, the absolute configuration of D/L-cysteine in the sample, and/or the enantiomeric composition of cysteine in the sample, and/or the concentration of total cysteine in the sample.

2. The analytical method of claim 1 , further comprising: providing the sample; and

providing the probe.

3. The analytical method of claim 1 , wherein the sample is an aqueous solution.

4. The analytical method of claim 1 , wherein the sample is a biological sample from an animal.

5. The analytical method of claim 4 , wherein the animal is a human subject.

6. The analytical method of claim 4 , wherein the animal is a patient having or suspected of having or at risk of having a disorder mediated by free form cysteine.

7. The analytical method of claim 6 , wherein the disorder is selected from the group consisting of neurodegenerative disease, amyotrophic lateral sclerosis, frontotemporal lobar degeneration, Parkinson's disease, Huntington's disease, mild cognitive impairment, Alzheimer's disease, diseases associated with TPD-43 proteinopathy, metabolic syndrome, central adiposity, hyperglycemia, hypertension, dyslipidemia, insulin resistance, diabetes, obstructive sleep apnea, irritable bowel disease/inflammatory bowel disease, diseases associated with skeletal wasting or muscle fatigue, HIV/SIV infection, cancer, major injuries, sepsis, Crohn's disease, ulcerative colitis, and chronic fatigue syndrome.

8. The analytical method of claim 1 , wherein the absolute configuration of D/L-cysteine in the sample is determined.

9. The analytical method of claim 8 , wherein the absolute configuration is determined using circular dichroism spectroscopy, optical rotatory dispersion, or polarimetry.

10. The analytical method of claim 1 , wherein the enantiomeric composition of cysteine in the sample is determined.

11. The analytical method of claim 10 , wherein the enantiomeric composition is determined using circular dichroism spectroscopy, optical rotatory dispersion, or polarimetry.

12. The analytical method of claim 1 , wherein the concentration of total cysteine in the sample is determined.

13. The analytical method of claim 12 , wherein the concentration is determined using UV/Vis spectroscopy, fluorescence spectroscopy, and/or other spectroscopic techniques.

14. The analytical method of claim 1 , wherein the absolute configuration of D/L-cysteine in the sample and the concentration of total cysteine in the sample are determined.

15. The analytical method of claim 1 , wherein the enantiomeric composition of cysteine in the sample and the concentration of total cysteine in the sample are determined.

16. The analytical method of claim 1 , wherein the absolute configuration of D/L-cysteine in the sample, the enantiomeric composition of cysteine in the sample, and the concentration of total cysteine in the sample are all determined.

17. The analytical method of claim 1 , wherein the absolute configuration of D/L-cysteine in the sample, the enantiomeric composition of cysteine in the sample, and the concentration of total cysteine in the sample are all determined concomitantly.

18. The analytical method of claim 1 , wherein the total cysteine is present in the sample in the micromolar range.

19. The analytical method according to claim 1 , wherein the probe is a compound of Formula I:

wherein:

each X is independently C or N;

each E is independently hydrogen or an electron withdrawing group selected from the group consisting of —CF3, —C(O)—Ra, —SO2—Ra, —CN, and —NO2, with the proviso that at least one E is an electron withdrawing group;

LG is a leaving group;

R1 and R2 are each independently absent or selected from the group consisting of —Ra, -cycloalkyl, -heterocycloalkyl, -aryl, and -heteroaryl; or R1 and R2, together with the carbon atoms to which they are attached, form a cycloalkyl, heterocycloalkyl, aryl, or heteroaryl;

R3 is absent or selected from the group consisting of —Ra, -cycloalkyl, -heterocycloalkyl, -aryl, and -heteroaryl; and

each Ra is independently selected from the group consisting of-H, -alkyl, —O— alkyl, —N-alkyl, -alkenyl, —O-alkenyl, —N-alkenyl, -alkynyl, —O-alkynyl, —N— alkynyl, -aryl, —O-aryl, —N-aryl, -heteroaryl, —O-heteroaryl, —N-heteroaryl, -cycloalkyl, —O-cycloalkyl, —N— cycloalkyl, -heterocycloalkyl, —O— heterocycloalkyl, and —N-heterocycloalkyl.

20. The analytical method according to claim 1 , wherein the probe is a compound selected from the group consisting of