Asymmetric cyanine fluorescent dyes

1. A fluorescent dye comprising a compound having the following general structural formula I:

wherein

n is 1, 2 or 3;

X is chosen from: C(CH 3 ) 2 , O, S or Se;

R 1 and R 2 are each independently chosen from H, C 1-18 alkyl, —C 1-6 alkyl-OR 5 or halogen;

R 3 is independently chosen from: H, C 1-18 alkyl, OR 5 , —C 1-6 alkyl-OR 5 , COOR 5 , NO 2 , CN or halogen;

R 4 is C 1-18 alkyl, —C 1-6 alkyl-OR 5 , benzyl or halogen, said benzyl optionally substituted with one or more substituents independently chosen from: halogen, hydroxyl, sulfhydryl, cyano, nitro, alkyl, aryl, alkoxy, heterocyclyl, haloalkyl, amino, alkylamino, amido, or carboxyl;

R 5 is H or C 1-18 alkyl; and

Y − is a counter ion;

or derivatives and conjugates thereof.

2. The fluorescent dye according to claim 1 , wherein R 1 and R 2 are each independently selected from H, C 1-18 alkyl or halogen.

3. The fluorescent dye according to claim 1 , wherein R 1 and R 2 are both H.

4. The fluorescent dye according to claim 1 , wherein R 3 is independently chosen from: H, C 1-18 alkyl, OR 5 , COOR 5 or halogen.

5. The fluorescent dye according to claim 1 , wherein R 3 is independently chosen from: H, C 1-6 alkyl, OR 5 , COOR 5 or halogen.

6. The fluorescent dye according to claim 1 , wherein R 4 is C 1-18 alkyl, benzyl or halogen, said benzyl optionally substituted with one or more substituents selected from the group consisting of halogen, hydroxyl, sulfhydryl, cyano, nitro, alkyl, aryl, alkoxy, heterocyclyl, haloalkyl, amino, alkylamino, amido, or carboxyl.

7. The fluorescent dye according to claim 1 , wherein R 4 is C 1-6 alkyl or benzyl, said benzyl is optionally substituted with halogen, hydroxyl, sulfhydryl, cyano, nitro or amino.

8. The fluorescent dye according to claim 1 , wherein R 5 is H or C 1-12 alkyl.

9. The fluorescent dye according to claim 1 , wherein R 5 is H or C 1-6 alkyl.

10. The fluorescent dye according to claim 1 , wherein X is C(CH 3 ) 2 , O or S.

11. The fluorescent dye according to claim 1 , wherein X is C(CH 3 ) 2 or S.

12. The fluorescent dye according to claim 1 , wherein n is 1 or 2.

13. The fluorescent dye according to claim 1 , wherein Y − is chosen from:

halogen ions, ClO 4 − , PF 6 − , CF 3 SO 3 − , BF 4 − , acetate or p-toluenesulfonate anions.

14. The fluorescent dye according to claim 1 , wherein said compound is chosen from:

or derivatives and conjugates thereof.

15. A method for synthesizing the compound of formula I according to claim 1 , the method comprising:

i) reacting unsubstituted or substituted 2-methylbenzothiazole, unsubstituted or substituted 2-methylbenzooxazole or unsubstituted or substituted 2,3,3-trimethyl-3H-indoline with substituted or unsubstituted benzylhalide to obtain a quaternary ammonium salt intermediate according to formula II:

ii) condensing the resulting quaternary ammonium salt intermediate of formula II with N,N′-diphenylformamidine or higher homologues thereof to obtain a compound of formula III:

iii) obtaining substituted or unsubstituted 4-methylquinoline quaternary ammonium salt intermediates; and

iv) refluxing the 4-methylquinoline quaternary ammonium salt intermediate obtained in iii) with compounds of formula III to afford compounds of formula I;

wherein X, n, R 1 , R 2 , R 3 , R 4 , R 5 and Y − are as defined in claim 1 .

16. A composition used in staining biological samples, wherein said composition comprises the compound of formula I, according to claim 1 .

17. The composition according to claim 16 , wherein said compound is chosen from:

or derivatives and conjugates thereof.

18. A method for staining biological samples, the method comprising contacting the compound of formula 1, according to claim 1 , with biological samples.

19. The method according to claim 18 , wherein said compound is chosen from:

or derivatives and conjugates thereof.