Compositions and methods for stabilizing benzothiazole luciferin analogs

1. A composition comprising

(a) a benzothiazole luciferin analog, or salt thereof, wherein the benzothiazole luciferin analog is a compound of formula (II′)

wherein:

is

R 1′ is H, C 1 -C 4 alkyl, —C 2 -C 4 alkylene-OH, —C 2 -C 4 alkylene-OC 1 -C 4 alkyl, C 3 -C 7 cycloalkyl, aryl, benzyl or substituted benzyl, heterocyclyl, heteroaryl, or —(CH 2 ) q —P(Ph) 3 , wherein q is an integer selected from 1, 2, 3, 4, 5, and 6;

R 2′ is hydrogen, halogen, C 1 -C 4 alkyl, or C 1 -C 4 haloalkyl;

R 3′ is hydrogen, halogen, C 1 -C 4 alkyl, or C 1 -C 4 haloalkyl;

R 4′ is —XG or —XG 1 ;

R 5′ is hydrogen, halogen, C 1 -C 4 alkyl, or C 1 -C 4 haloalkyl;

R 10′ , at each occurrence is independently halo, —SO 3 H, C 1 -C 10 alkyl, —OH, —O(C 1 -C 10 alkyl), —NH 2 , —NH(C 1 -C 10 alkyl), or —N(C 1 -C 10 alkyl)(C 1 -C 10 alkyl);

R 11′ is —OH, —O(C 1 -C 10 alkyl), —NH 2 , —NH(C 1 -C 10 alkyl), —N(C 1 -C 10 alkyl)(C 1 -C 10 alkyl), —OG 1 , —NHG 1 , or —N(C 1 -C 10 alkyl)G 1 ;

n is 0 to 5;

X is —O— or —N(G)-;

G, at each occurrence is independently H, C 1 -C 12 alkyl, or together with one of R 3′ or R 5′ forms a 5- to 8-membered monocyclic heterocyclic ring optionally substituted with 1-4 substituents independently selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 haloalkyl, halo, hydroxy, oxo, and —O(C 1 -C 4 alkyl); or two G together with the nitrogen atom to which they are attached form a 4- to 8-membered monocyclic heterocyclic ring optionally substituted with 1-4 substituents independently selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 haloalkyl, halo, hydroxy, oxo, and —O(C 1 -C 4 alkyl);

G 1 comprises an enzyme substrate, wherein biotransformation of the enzyme substrate by an enzyme converts G 1 to H; and

W 1 and W 2 are each independently hydrogen, C 1 -C 4 alkyl, or arylalkyl; or W 1 and W 2 together with the carbon to which they are attached form a C 3 -C 8 cycloalkyl or a 4- to 8-membered heterocycle, the cycloalkyl and heterocycle being optionally substituted with 1-4 substituents independently selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 haloalkyl, halo, hydroxy, oxo, and —O(C 1 -C 4 alkyl); and

(b) an effective amount of a compound of formula (I) or a tautomer thereof,

wherein

R 1 is hydrogen, optionally substituted alkyl, optionally substituted arylalkyl, optionally substituted heteroarylalkyl, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, carboxylic acid, ester, NR a R b , optionally substituted imine, hydroxyl, or oxo;

R 2 is hydrogen, NR a R b , optionally substituted imine, optionally substituted alkyl, or optionally substituted aryl;

R a and R b , at each occurrence, are each independently hydrogen, optionally substituted alkyl, or optionally substituted aryl; and

(c) optionally, a liquid medium

wherein when the liquid medium is absent, the benzothiazole luciferin analog and the compound of formula (I) form a solid mixture;

wherein when the liquid medium is present, and when the compound of formula (I) is 6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one (ATT), the liquid medium is free of dimethyl sulfoxide (DMSO).

2. The composition of claim 1 , wherein W 1 and W 2 are each independently C 1 -C 4 alkyl.

3. The composition of claim 1 , wherein the benzothiazole luciferin analog is a compound of formula (II)

wherein:

is

R 1′ is H, C 1 -C 4 alkyl, —C 2 -C 4 alkylene-OH, —C 2 -C 4 alkylene-OC 1 -C 4 alkyl, C 3 -C 7 cycloalkyl, aryl, benzyl or substituted benzyl, heterocyclyl, heteroaryl, or —(CH 2 ) q —P(Ph) 3 , wherein q is an integer selected from 1, 2, 3, 4, 5, and 6;

R 2′ is hydrogen, halogen, methyl, or trifluoromethyl;

R 3′ is hydrogen, halogen, methyl, or trifluoromethyl;

R 4′ is —XG or —XG 1 ;

R 5′ is hydrogen, halogen, methyl, or trifluoromethyl;

R 10′ , at each occurrence is independently halo, —SO 3 H, C 1 -C 10 alkyl, —OH, —O(C 1 -C 10 alkyl), —NH 2 , —NH(C 1 -C 10 alkyl), or —N(C 1 -C 10 alkyl)(C 1 -C 10 alkyl);

R 11′ is —OH, —O(C 1 -C 10 alkyl), —NH 2 , —NH(C 1 -C 10 alkyl), —N(C 1 -C 10 alkyl)(C 1 -C 10 alkyl), —OG 1 , —NHG 1 , or —N(C 1 -C 10 alkyl)G 1 ;

n is 0 to 5;

X is —O— or —N(G)-;

G, at each occurrence is independently H, C 1 -C 12 alkyl, or together with one of R 3′ or R 5′ forms a 5- to 8-membered monocyclic heterocyclic ring optionally substituted with 1-4 substituents independently selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 haloalkyl, halo, hydroxy, oxo, and —O(C 1 -C 4 alkyl); or two G together with the nitrogen atom to which they are attached form a 4- to 8-membered monocyclic heterocyclic ring optionally substituted with 1-4 substituents independently selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 haloalkyl, halo, hydroxy, oxo, and —O(C 1 -C 4 alkyl); and

G 1 comprises an enzyme substrate, wherein biotransformation of the enzyme substrate by an enzyme converts G 1 to H.

4. The composition of claim 1 , wherein the composition does not contain a luminogenic enzyme.

5. The composition of claim 1 , wherein the benzothiazole luciferin analog is stabilized against decomposition.

6. The composition of claim 1 , wherein R 1′ is H.

7. The composition of claim 1 , wherein R 2′ is H, R 3′ is H, and R 5′ is H.

8. The composition of claim 1 , wherein R 4′ is —OH or —NH 2 .

9. The composition of claim 1 , wherein the effective amount of the compound of formula (I) is greater than 0.1 mM.

10. The composition of claim 1 , wherein the compound of formula (I) is selected from the group consisting of: ATT, ATCA, 3-(4-Amino-5-oxo-3-thioxo-2,3,4,5-tetrahydro-1,2,4-triazin-6-yl)propanoic acid, tetrahydro-2-methyl-3-thioxo-1,2,4-triazine-5,6-dione, 4-((2-furylmethylene)amino)-3-mercapto-6-methyl-1,2,4-triazin-5(4H)-one, 6-benzyl-3-sulfanyl-1,2,4-triazin-5-ol, 4-amino-3-mercapto-6-methyl-1,2,4-triazin-5(4H)-one, 3-(5-oxo-3-thioxo-2,3,4,5-tetrahydro-1,2,4-triazin-6-yl)propanoic acid, (E)-6-methyl-4-((thiophen-2-ylmethylene)amino)-3-thioxo-3,4-dihydro-1,2,4-triazin-5 (2H)-one, (E)-6-methyl-4-((3-nitrobenzylidene)amino)-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one, (E)-4-((4-(diethylamino)benzylidene)amino)-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5 (2H)-one, ATCA ethyl ester, TAK-0014, TAK-0002, TAK-0021, TAK-0020, TAK-0018, TAK-0009, TAK-0007, TAK-0008, TAK-0003, TAK-0004, 3-thioxo-6-(trifluoromethyl)-3,4-dihydro-1,2,4-triazin-5(2H)-one, 6-cyclopropyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one, and 6-(hydroxymethyl)-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one.

11. The composition of claim 1 , wherein the liquid medium is absent.

12. The composition of claim 1 , wherein the liquid medium is present.

13. The composition of claim 12 , wherein the compound of formula (I) is not ATT.

14. The composition of claim 13 , wherein the liquid medium comprises an organic solvent selected from the group consisting of alcohol, propylene glycol, dimethyl sulfoxide (DMSO), acetonitrile, glycerol, and any combination thereof.

15. The composition of claim 12 , wherein the compound of formula (I) is ATT, and wherein the liquid medium comprises an organic solvent selected from the group consisting of alcohol, propylene glycol, acetonitrile, glycerol, and any combination thereof.

16. A method for stabilizing a benzothiazole luciferin analog, the method comprising contacting a benzothiazole luciferin analog, or salt thereof, with an effective amount of a compound of formula (I) or a tautomer thereof, whereby the benzothiazole luciferin analog, or salt thereof, is stabilized against decomposition,

wherein the benzothiazole luciferin analog is a compound of formula (II′)

wherein:

is

R 1′ is H, C 1 -C 4 alkyl, —C 2 -C 4 alkylene-OH, —C 2 -C 4 alkylene-OC 1 -C 4 alkyl, C 3 -C 7 cycloalkyl, aryl, benzyl or substituted benzyl, heterocyclyl, heteroaryl, or —(CH 2 ) q —P(Ph) 3 , wherein q is an integer selected from 1, 2, 3, 4, 5, and 6;

R 2′ is hydrogen, halogen, methyl, or trifluoromethyl;

R 3′ is hydrogen, halogen, methyl, or trifluoromethyl;

R 4′ is —XG or —XG 1 ;

R 5′ is hydrogen, halogen, methyl, or trifluoromethyl;

R 10′ , at each occurrence is independently halo, —SO 3 H, C 1 -C 10 alkyl, —OH, —O(C 1 -C 10 alkyl), —NH 2 , —NH(C 1 -C 10 alkyl), or —N(C 1 -C 10 alkyl)(C 1 -C 10 alkyl);

R 11′ is —OH, —O(C 1 -C 10 alkyl), —NH 2 , —NH(C 1 -C 10 alkyl), —N(C 1 -C 10 alkyl)(C 1 -C 10 alkyl), —OG 1 , —NHG 1 , or —N(C 1 -C 10 alkyl)G 1 ;

n is 0 to 5;

X is —O— or —N(G)-;

G, at each occurrence is independently H, C 1 -C 12 alkyl, or together with one of R 3′ or R 5′ forms a 5- to 8-membered monocyclic heterocyclic ring optionally substituted with 1-4 substituents independently selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 haloalkyl, halo, hydroxy, oxo, and —O(C 1 -C 4 alkyl); or two G together with the nitrogen atom to which they are attached form a 4- to 8-membered monocyclic heterocyclic ring optionally substituted with 1-4 substituents independently selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 haloalkyl, halo, hydroxy, oxo, and —O(C 1 -C 4 alkyl);

G 1 comprises an enzyme substrate, wherein biotransformation of the enzyme substrate by an enzyme converts G 1 to H; and W 1 and W 2 are each independently hydrogen, C 1 -C 4 alkyl, or arylalkyl; or W 1 and W 2 together with the carbon to which they are attached form a C 3 -C 8 cycloalkyl or a 4- to 8-membered heterocycle, the cycloalkyl and heterocycle being optionally substituted with 1-4 substituents independently selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 haloalkyl, halo, hydroxy, oxo, and —O(C 1 -C 4 alkyl); and

wherein the compound of formula (I) is

wherein

R 1 is hydrogen, optionally substituted alkyl, optionally substituted arylalkyl, optionally substituted heteroarylalkyl, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted heteroaryl, carboxylic acid, ester, NR a R b , optionally substituted imine, hydroxyl, or oxo;

R 2 is hydrogen, NR a R b , optionally substituted imine, optionally substituted alkyl, or optionally substituted aryl; and

R a and R b , at each occurrence, are each independently hydrogen, optionally substituted alkyl, or optionally substituted aryl.

17. The method of claim 16 , wherein W 1 and W 2 are each independently C 1 -C 4 alkyl.

18. The method of claim 16 , wherein the benzothiazole luciferin analog is a compound of formula (II)

wherein:

is

R 1′ is H, C 1 -C 4 alkyl, —C 2 -C 4 alkylene-OH, —C 2 -C 4 alkylene-OC 1 -C 4 alkyl, C 3 -C 7 cycloalkyl, aryl, benzyl or substituted benzyl, heterocyclyl, heteroaryl, or —(CH 2 ) q —P(Ph) 3 , wherein q is an integer selected from 1, 2, 3, 4, 5, and 6;

R 2′ is hydrogen, halogen, methyl, or trifluoromethyl;

R 3′ is hydrogen, halogen, methyl, or trifluoromethyl;

R 4′ is —XG or —XG 1 ;

R 5′ is hydrogen, halogen, methyl, or trifluoromethyl;

R 10′ , at each occurrence is independently halo, —SO 3 H, C 1 -C 10 alkyl, —OH, —O(C 1 -C 10 alkyl), —NH 2 , —NH(C 1 -C 10 alkyl), or —N(C 1 -C 10 alkyl)(C 1 -C 10 alkyl);

R 11′ is —OH, —O(C 1 -C 10 alkyl), —NH 2 , —NH(C 1 -C 10 alkyl), —N(C 1 -C 10 alkyl)(C 1 -C 10 alkyl), —OG 1 , —NHG 1 , or —N(C 1 -C 10 alkyl)G 1 ;

n is 0 to 5;

X is —O— or —N(G)-;

G, at each occurrence is independently H, C 1 -C 12 alkyl, or together with one of R 3′ or R 5′ forms a 5- to 8-membered monocyclic heterocyclic ring optionally substituted with 1-4 substituents independently selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 haloalkyl, halo, hydroxy, oxo, and —O(C 1 -C 4 alkyl); or two G together with the nitrogen atom to which they are attached form a 4- to 8-membered monocyclic heterocyclic ring optionally substituted with 1-4 substituents independently selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 haloalkyl, halo, hydroxy, oxo, and —O(C 1 -C 4 alkyl); and

G 1 comprises an enzyme substrate, wherein biotransformation of the enzyme substrate by an enzyme converts G 1 to H.

19. The method of claim 16 , wherein the effective amount of the compound of formula (I) is greater than 0.1 mM.

20. The method of claim 16 , wherein the compound of formula (I) is selected from the group consisting of: ATT, ATCA, 3-(4-Amino-5-oxo-3-thioxo-2,3,4,5-tetrahydro-1,2,4-triazin-6-yl)propanoic acid, tetrahydro-2-methyl-3-thioxo-1,2,4-triazine-5,6-dione, 4-((2-furylmethylene)amino)-3-mercapto-6-methyl-1,2,4-triazin-5(4H)-one, 6-benzyl-3-sulfanyl-1,2,4-triazin-5-ol, 4-amino-3-mercapto-6-methyl-1,2,4-triazin-5(4H)-one, 3-(5-oxo-3-thioxo-2,3,4,5-tetrahydro-1,2,4-triazin-6-yl)propanoic acid, (E)-6-methyl-4-((thiophen-2-ylmethylene)amino)-3-thioxo-3,4-dihydro-1,2,4-triazin-5 (2H)-one, (E)-6-methyl-4-((3-nitrobenzylidene)amino)-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one, (E)-4-((4-(diethylamino)benzylidene)amino)-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5 (2H)-one, ATCA ethyl ester, TAK-0014, TAK-0002, TAK-0021, TAK-0020, TAK-0018, TAK-0009, TAK-0007, TAK-0008, TAK-0003, TAK-0004, 3-thioxo-6-(trifluoromethyl)-3,4-dihydro-1,2,4-triazin-5(2H)-one, 6-cyclopropyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one, and 6-(hydroxymethyl)-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one.

21. The method of claim 16 , wherein the benzothiazole luciferin analog is stabilized against decomposition in the presence of light.

22. The method of claim 16 , wherein the benzothiazole luciferin analog is stabilized against decomposition in the absence of light.

23. The method of claim 16 , wherein the luciferin analog is stabilized against decomposition at temperatures from −80° C. to 60° C.

24. The method of claim 16 , wherein R 1′ is H, R 2′ is H, R 3′ is H, and R 5′ is H.

25. The method of claim 16 , wherein R 4′ is —OH or —NH 2 .

26. The method of claim 16 , wherein the contacting occurs in a solid mixture of the benzothiazole luciferin analog and the compound of formula (I).

27. The method of claim 16 , wherein the contacting occurs in a liquid medium.

28. The method of claim 27 , wherein the compound of formula (I) is not ATT.

29. The method of claim 28 , wherein the liquid medium comprises an organic solvent selected from the group consisting of alcohol, propylene glycol, dimethyl sulfoxide (DMSO), acetonitrile, glycerol, and any combination thereof.

30. The method of claim 27 wherein the compound of formula (I) is ATT, and wherein the liquid medium comprises an organic solvent selected from the group consisting of alcohol, propylene glycol, acetonitrile, glycerol, and any combination thereof.

31. A kit comprising the composition of claim 1 in a single container, wherein the compound of formula (I) stabilizes the benzothiazole luciferin analog.