Dual protected pro-coelenterazine substrates

1. A compound of formula (I)

or a tautomer, or a salt thereof, wherein

Ar 1 , Ar 2 , and Ar 3 are each independently selected from the group consisting of aryl and heteroaryl, wherein Ar 1 , Ar 2 , and Ar 3 are each optionally substituted, provided that one of Ar 1 , Ar 2 , or Ar 3 is substituted by —X-L 2 -R 6 ;

X is O, S, or NR x , wherein R x is hydrogen or C 1 -C 6 -alkyl;

L 1 and L 2 are each independently selected from the group consisting of a bond and a linker of 1 to 50 atoms, wherein L 1 and L 2 are each optionally substituted; and

R 3 and R 6 are each independently selected from the group consisting of a peptide, an amino acid, a saccharide, and a phosphate.

2. The compound of claim 1 , of formula:

3. The compound of claim 1 , wherein Ar 2 is furyl or phenyl.

4. The compound of claim 1 , wherein X is O.

5. The compound of claim 1 , wherein

L 1 and L 2 are each independently a bond, alkylene, or arylenealkylene;

wherein one or more of the —CH 2 — moieties in the alkylene chain portion of alkylene or arylenealkylene are optionally replaced by C═O, C═S, NR x1 , O, S, NO, SO and SO 2 , wherein R x1 at each occurrence is independently selected from the group consisting of hydrogen and C 1 -C 6 -alkyl;

wherein alkylene and arylenealkylene are each independently substituted with 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 substituents independently selected from the group consisting of halogen, cyano, nitro, fluoroalkyl, alkoxyfluoroalkyl, fluoroalkoxy, alkyl, alkenyl, alkynyl, haloalkyl, haloalkoxy, heteroalkyl, cycloalkyl, cycloalkenyl, aryl, heteroaryl, heterocycle, cycloalkylalkyl, heteroarylalkyl, arylalkyl, hydroxy, hydroxyalkyl, alkoxy, alkoxyalkyl, alkylene, aryloxy, phenoxy, benzyloxy, amino, alkylamino, dialkylamino, acylamino, aminoalkyl, arylamino, sulfonylamino, sulfinylamino, sulfonyl, alkylsulfonyl, arylsulfonyl, aminosulfonyl, sulfinyl, —COOH, ketone, amide, carbamate, silyl, substituted silyl, t-butyldimethylsilyl, alkylsulfanyl, sulfanyl, and acyl.

6. The compound of claim 1 , wherein L 1 and L 2 are each independently selected from the group consisting of:

a bond;

wherein R x1 at each occurrence is independently selected from the group consisting of hydrogen and C 1 -C 6 -alkyl; R y is selected from the group consisting of hydrogen, halogen, and nitro; R z at each occurrence is independently selected from the group consisting of hydrogen and C 1 -C 6 -alkyl; and X 1 is selected from the group consisting of NR x2 , O, and S, wherein R x2 is hydrogen or C 1 -C 6 -alkyl.

7. The compound of claim 1 , wherein L 1 and L 2 are each independently selected from the group consisting of:

a bond;

8. The compound of claim 1 , wherein L 1 and L 2 are each a bond.

9. The compound of claim 1 , wherein R 3 and R 6 are each independently selected from the group consisting of:

wherein

R 20a and R 20b are each independently selected from the group consisting of hydrogen, halogen, and C 1 -C 6 -alkyl optionally substituted with 1, 2, 3, or 4 —OR 30 groups and optionally 1 oxo group, wherein R 30 at each occurrence is independently selected from the group consisting of hydrogen, C 1 -C 6 -alkyl, and C(═O)R 31 , wherein R 31 is C 1 -C 6 -alkyl;

R 21a , R 21b , R 22a , R 22b , R 23a , and R 23b at each occurrence are each independently selected from the group consisting of hydrogen, halogen, OR 32 and NR 33 R 34 , wherein R 32 —R 34 at each occurrence are each independently selected from the group consisting of hydrogen, C 1 -C 6 -alkyl, and C(═O)R 35 , wherein R 35 is hydrogen or C 1 -C 6 -alkyl;

R 24 at each occurrence is independently selected from the group consisting of hydrogen and C(═O)R 36 , wherein R 36 is selected from the group consisting of hydrogen, C 1 -C 6 -alkyl, —OH, and —O—C 1 -C 6 -alkyl;

R 25 and R 26 are each independently selected from the group consisting of hydrogen, and C 1 -C 6 -alkyl;

R 27 and R 28 are each independently selected from the group consisting of:

 and

R 29a and R 29b are each independently hydrogen, or R 29a and R 27 together with the atoms to which they are attached can form a five-membered ring.

10. The compound of claim 1 , wherein R 3 and R 6 are each independently selected from the group consisting of:

11. The compound of claim 1 , selected from the group consisting of:

(2S,3R,4S,5S,6R)-2-(4-(8-benzyl-2-(furan-2-ylmethyl)-3-((4-(((2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-2-yl)oxy)benzyl)oxy)imidazo[1,2-a]pyrazin-6-yl)phenoxy)-6-(hydroxymethyl)tetrahydro-2H-pyran-3,4,5-triol;

4-(((8-benzyl-2-(furan-2-ylmethyl)-6-(3-(phosphonooxy)phenyl)imidazo[1,2-a]pyrazin-3-yl)oxy)methyl)phenyl dihydrogen phosphate;

2-(2-aminoacetamido)-N-(3-(3-((4-(2-(2-aminoacetamido)-3-phenylpropanamido)benzyl)oxy)-8-benzyl-2-(furan-2-ylmethyl)imidazo[1,2-a]pyrazin-6-yl) phenyl)-3-phenylpropanamide;

(2S,3R,4S,5S,6R)-2-(4-(8-benzyl-2-(furan-2-ylmethyl)-3-(((2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-2-yl)oxy)imidazo[1,2-a]pyrazin-6-yl)phenoxy)-6-(hydroxymethyl; and

((8-benzyl-2-(furan-2-ylmethyl)-6-(3-(phosphonooxy)phenyl)imidazo[1,2-a]pyrazin-3-yl)oxy)methyl phosphate;

or a tautomer, or a salt thereof.

12. A kit comprising a compound of claim 1 and a buffer reagent.

13. The kit of claim 12 , further comprising a luciferase.

14. A method for detecting luminescence in a sample, the method comprising contacting a sample with a compound of claim 1 ;

adding to the sample with a coelenterazine-utilizing luciferase, if it is not present in the sample; and

detecting luminescence.

15. The method of claim 14 , wherein the sample contains live cells.

16. The method of claim 14 , wherein a coelenterazine-utilizing luciferase was already present in the sample.

17. A method for detecting luminescence in a transgenic animal comprising administering a compound of claim 1 to a transgenic animal; and

detecting luminescence;

wherein the transgenic animal expresses a coelenterazine-utilizing luciferase.

18. The compound of claim 1 , of formula:

19. The compound of claim 1 , of formula:

20. The compound of claim 2 , wherein

Ar 2 is furyl or phenyl;

X is O;

L 1 and L 2 are each independently selected from the group consisting of:

a bond,

 and

R 3 and R 6 are each independently selected from the group consisting of: