Fluorescent probe for detecting calpain activity

Abstract

[Problem] To provide a fluorescent probe that detects calpain activity in cells at high sensitivity. [Solution] A compound represented by the following general formula (I) or a salt thereof.

The invention claimed is: 
     
       1. A compound of the following general formula (I): 
       
         
           
           
               
               
           
         
         wherein R 1  is a hydrogen atom or from one to four of the same or different substituents that bond to the benzene ring; 
         R 2 , R 3 , R 4 , R 5 , R 6 , and R 7  are, each independently, a hydrogen atom, hydroxyl group, alkyl group, or halogen atom; 
         R 8  and R 9  are, each independently, a hydrogen atom or alkyl group; 
         X is a C 1 -C 3  alkylene group; 
         R 10  is selected from the following formula (1) or (2); 
       
       
         
           
           
               
               
           
         
       
       a monovalent substituent cleaved by contact with calpain, and said monovalent substituent consists of an oligopeptide residue having a sequence of Leu-Leu-Tyr or Leu-Met (the amino acid at the right end of the sequence bonds directly to the NH group bonded to the xanthene skeleton), the N end of said oligopeptide residue may be protected;  
       or a salt thereof. 
     
     
       2. A compound of the following formula (3) or a salt thereof 
       
         
           
           
               
               
           
         
       
     
     
       3. A compound of the following formula (4) or a salt thereof 
       
         
           
           
               
               
           
         
       
     
     
       4. A fluorescent probe containing a compound according to  claim 1  or a salt thereof. 
     
     
       5. A method for measuring calpain, comprising the following steps: (a) a step for bringing a compound according to  claim 1  or a salt thereof and calpain into contact and (b) a step for measuring the fluorescence intensity of the compound produced in step (a) after contact with calpain. 
     
     
       6. A diagnostic for retinal disease containing a compound according to  claim 1  or a salt thereof. 
     
     
       7. The diagnostic according to  claim 6  wherein the retinal disease is glaucoma, retinitis pigmentosa, age-related macular degeneration, retinal neuropathy or retinal vascular occlusive disease associated with diabetes. 
     
     
       8. The diagnostic according to  claim 7  wherein the glaucoma is normotensive glaucoma. 
     
     
       9. The compound of claim 1, wherein R 10  is selected from the following formula (1) or (2);