Fluorescent red emitting functionalizable calcium indicators

1. A compound of formula I

or a salt thereof, wherein

Z represents H, alkyl, CH 2 —OAc, Na + or K + ;

R 1 , R 2 , R 3 and R 4 represent each independently H, halo, alkyl, COR 11 , OR 11 , SR 11 or NR 11 R 12 , wherein R 11 and R 12 represent each independently H, alkyl or aryl;

m represents 0, 3 or 4;

W represents O, NR 9 , S or CR 9 R 10 , wherein R 9 and R 10 represent each independently H or alkyl;

L represents a single bond or a linker selected from the group comprising alkyl, aryl, alkylaryl, arylalkyl, polyethylene glycol (PEG), polypropylene glycol (PPG), peptide, aminocarbonyl, alkylaminocarbonyl, aminothiocarbonyl or a combination thereof; optionally additionally comprising a residue of a reactive group through which L is bounded to Y selected from carbonyl group or triazolo group;

Y represents

a reactive function selected from the group comprising N 3 , amino, alkylamino, COOH, amide, maleimide, alkyne, SH, OH, ester, N-hydroxysuccinimide ester, N-hydroxyglutarimide ester, maleimide ester, acid anhydride, acid halide, halo, nitro, nitrile, isonitriles, acrylamide, aldehyde, ketone, acetals, ketals, anhydride, glutaric anhydride, succinic anhydride, maleic anhydride, thiocyanate, isothiocyanate, isocyanate, hydrazide, hydrazines, hydrazones, ethers, oxides, cyanates, diazo, diazonium, sulfides, disulfides, sulfoxides, sulfones, sulfonic acids, sulfinic acids, sulfates, sulfenic acids, amidines, imides, imidates, nitrones, hydroxylamines, oximes, hydroxamic acids thiohydroxamic acids, allenes, ortho esters, sulfites, enamines, ynamines, ureas, pseudoureas, semicarbazides, carbodiimides, carbamates and imines; or

a bioactive group selected from amino acid, peptide, protein, antibody, enzyme, polysaccharide, dextran, benzylguanine, lipid, lipid assembly, fatty acid, nucleoside, nucleotide, oligonucleotide, hapten, aptamer, biotin, avidin, synthetic polymer, polymeric microparticle, nanoparticle, fluorophore, chromophore, radioisotope, macrocyclic complexes of radioisotope, and combinations thereof;

R 5 and R 6 each independently represent H, alkyl or halo; R 7 and R 8 each independently represent H, alkyl; or R 5 and R 7 are linked together in a single alkyl moiety to form a ring with adjacent carbon and nitrogen atoms; or R 6 and R 8 are linked together in a single alkyl moiety to form a ring with adjacent carbon and nitrogen atoms; and

X represents O, NR 9 , S, CR 9 R 10 , Se or Si, wherein R 9 and R 10 represent each independently H or alkyl.

2. The compounds according to claim 1 , wherein, when R 5 and R 7 , or R 6 and R 8 , are linked together in a single alkyl moiety, the single alkyl moiety is propyl.

3. The compound according to claim 1 , of formula Ia

or a salt thereof, wherein W, L, Y, R 5 , R 6 , R 7 , R 8 and X are as previously defined.

4. The compound according to claim 1 , of formula Ib

or a salt thereof, wherein W, L, Y, R 5 , R 6 , R 7 , R 8 and X are as previously defined.

5. The compound according to claim 1 , selected from the group comprising compounds of formula Ia-1, Ia-2 and Ib-1:

6. Process for manufacturing a compound of formula I according to claim 1 , comprising performing a Vilsmeier-Haack reaction on a compound of formula III

wherein Z, R 1 , R 2 , R 3 , R 4 , m, W, L and Y are as previously defined;

leading to compound of formula II

wherein Z, R 1 , R 2 , R 3 , R 4 , m, W, L and Y are as previously defined;

and further comprising a step of rhodamine formation on the aldehyde function of compound of formula II, to afford compound of formula I.

7. The compound according to claim 2 , of formula Ia

or a salt thereof, wherein W, L, Y, R 5 , R 6 , R 7 , R 8 and X are as previously defined.

8. Method of detecting intracellular calcium comprising:

adding a compound according to claim 1 to a sample containing at least one cell;

incubating the sample for a time sufficient for the compound to be loaded into the cell;

illuminating the sample at an exciting wavelength that generates a fluorescent response from the indicator;

detecting the fluorescent response.

9. Method according to claim 8 , further comprising:

stimulating the cell;

monitoring changes in the intensity of the fluorescent response from the indicator; and

correlating the changes in fluorescence intensity with changes in intracellular calcium levels.

10. Kit for performing a calcium assay, comprising a compound according to claim 1 .