Fluorescent probe for detection of ENPP activity

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

• wherein
• R1 is one or two monovalent substituents present on a benzene ring, which are electron donating groups independently selected from hydroxyl group, alkoxy group having 1 to 10 carbon atoms, amino group and alkylamino group having 1 to 10 carbon atoms;
• R2 is one or two monovalent substituents independently selected from the group consisting of a sulfonic acid group and a phosphoric acid group;
• 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 an alkyl group having 1 to 6 carbon atoms, or an aryl group, wherein the aryl group is selected from a monocyclic aromatic group or a condensed aromatic group, wherein the aryl ring may contain one or more ring forming hetero atoms selected from nitrogen atom, oxygen atom or sulfur atom;
• R7 and R8 are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a halogen atom;
• X is a silicon atom, a phosphorus atom, or a germanium atom;
• Z is an oxygen atom or N+R9R10,
• where R9 and R10 are each independently a hydrogen atom, or an alkyl group having 1 to 10 carbon atoms,
• R9 and R10 are optionally linked together to form a four- to seven-membered heterocyclyl containing a nitrogen atom bonded to R9 and R10, and
• R9 or R10, or each of both R9 and R10 is optionally linked with R3 or R7 to form a five- to seven-membered heterocyclyl or heteroaryl containing a nitrogen atom bonded to R9 or R10, or optionally contains one to three additional hetero atoms selected from the group consisting of an oxygen atom, a nitrogen atom and a sulfur atom as ring forming members, and the heterocyclyl or heteroaryl is optionally substituted with an alkyl having 1 to 6 carbon atoms, an alkenyl having 2 to 6 carbon atoms, an alkynyl having 2 to 6 carbon atoms, an aralkyl group having 6 to 10 carbon atoms, or an alkyl-substituted alkenyl group having 6 to 10 carbon atoms;
• Y is a single bond, —O—(CH2)n1—, —O—(CH2)n2—Ar1—, —NH—(CH2)n3— or —NH—(CH2)n4—Ar2—,
• where n1, n2, n3 and n4 are each independently an integer of 1 to 10, and
• Ar1 and Ar2 are each independently a substituted or unsubstituted arylene group having 6 to 14 carbon atoms, wherein the substituents are selected from halogen atoms and alkyl groups having 1 to 10 carbon atoms;
• and
• is represented by R—S—
• where R is an organic base selected from the group consisting of a nucleic acid base, (CH3)3N+—C2H4—, (CH3CH2)2N—, and R′2N—, wherein the two R′ groups are independently selected from the group consisting of a hydrogen atom, and an alkyl group having 1 to 10 carbon atoms, and
• S is a sugar selected from ribose, deoxyribose, or a single bond.