Fluorescent probe for detecting carboxypeptidase activity

A compound represented by the following general formula (I) or a salt thereof:

• wherein
• R1 represents a hydrogen atom or one to three monovalent substituent groups present on a benzene ring, which are the same or different;
• R2 represents a monovalent substituent group present on a benzene ring;
• R3 and R4 are, each independently, a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a halogen atom;
• R5 and R6 are, each independently, a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a halogen atom;
• L represents an amino acid residue;
• X is selected from an oxygen atom, Si(Ra)(Rb), C(Ra)(Rb), Ge(Ra)(Rb), P(═O)Rc or Se
• where:
• Ra and Rb are, each independently, an alkyl group having 1 to 6 carbon atoms or an aryl group optionally being substituted, and Rc is an alkyl group having 1 to 6 carbon atoms or a phenyl group optionally being substituted;
• Y and Z are selected from a pair of (O, OH), (NR7R8, NR9R10), and (O, NR9R10) where:
• R7 and R8 are, each independently, a hydrogen atom or an alkyl group having 1 to 3 carbon atoms;
• R7 and R8 together optionally form a 4-7 membered heterocyclyl containing a nitrogen atom to which R7 and R8 are bonded;
• R7 or R8, or both R7 and R8, together with R3 and/or R5, respectively, optionally form a 5-7 membered heterocyclyl or heteroaryl containing a nitrogen atom to which R7 and/or R8 are bonded, and optionally contain from one to three heteroatoms selected from the group consisting of an oxygen atom, nitrogen atom, and sulfur atom as ring-constituting members, and the heterocyclyl or heteroaryl is optionally substituted by alkyl having 1 to 6 carbon atoms, alkenyl having 2 to 6 carbon atoms, alkynyl having 2 to 6 carbon atoms, aralkyl group having 6 to 10 carbon atoms, or alkyl-substituted alkenyl group having 6 to 10 carbon atoms;
• R9 and R10 are, each independently, a hydrogen atom or an alkyl group having 1 to 3 carbon atoms;
• R9 and R10 together optionally form a 4-7 membered heterocyclyl containing a nitrogen atom to which R9 and R10 are bonded;
• R9 or R10, or both R9 and R10, together with R4 and/or R6, respectively, optionally form a 5-7 membered heterocyclyl or heteroaryl containing a nitrogen atom to which R9 and/or R10 are bonded, and optionally contain from one to three heteroatoms selected from the group consisting of an oxygen atom, nitrogen atom, and sulfur atom as ring-constituting members, and the heterocyclyl or heteroaryl is optionally substituted by alkyl having 1 to 6 carbon atoms, alkenyl having 2 to 6 carbon atoms, alkynyl having 2 to 6 carbon atoms, aralkyl group having 6 to 10 carbon atoms, or alkyl-substituted alkenyl group having 6 to 10 carbon atoms;
• and
• when Y and Z are O and OH, respectively, and when a monovalent substituent group present on a benzene ring of R2 is a carboxyl group, Y and Z are optionally acetylated.