Fluorogenic peptidase substrate

Peptidase substrate of formula (I):

• wherein:
• R0 is a peptidyl or amino acid group bound to the NH group via its carboxy-terminal end,
• n is 0 or 1,
• R1 is a hydrogen atom or a side chain of an amino acid,
• R5 is a phenoxy derivative, the corresponding phenol derivative of which belongs to the ESIPT class of fluorophores,
• R2, R3 and R4 are defined as follows:
• R2 is a (C1-C4)alkyl group or a hydrogen atom, R3 is a (C1-C4)alkyl group, and R4 is a (C1-C4)alkyl group;
• or else
• R2 is a (C1-C4)alkyl group or a hydrogen atom and R3 and R4 are bound together and form with the carbon and nitrogen atoms to which they are bound an aliphatic heterocycle, this heterocycle may be substituted with a group, of the ammonium, carboxylate or sulfonate type allowing an increase in water-solubility of the substrate;
• or else
• R4 is a (C1-C4)alkyl group and R2 and R3 are bound together and form with the carbon atom to which they are bound an aliphatic carbocyl, as a mixture of optical isomers or diastereoisomers in any proportions, or as a form enriched with an optical isomer or with a diastereoisomer.