Cysteine derivatives
The present invention provides (1) a compound of the formula (I) ##STR2## wherein R 1  and R 2  are lower alkanoyl, benzoyl, lower alkyl or lower alkyl substituted by carboxy; either R 1  or R 2  may be hydrogen; and a physiologically acceptable salt thereof, (2) a composition comprising a compound of the formula (I) and/or a physiologically acceptable salt thereof and a pharmaceutically acceptable excipient, (3) a method for suppressing liver disorders in a mammal comprising administering an effective dose of a compound of the formula (I) or a physiologically acceptable salt thereof, and (4) a process for producing a compound of the formula (I). Above mentioned lower alkanoyl and lower alkyl contain 1 to 6 carbon atoms. 
     Compounds of the formula (I) of the present invention are useful as a medicine for suppressing liver disorders due to their effect of removing free radicals. 
     Among cysteine derivatives of the formula (I), although compounds having hydrogen atoms in both R 1  and R 2  in the formula are well known as sputum resolvents, derivatives which have the substituted groups in R 1  and R 2  in the formula are novel compounds and their effects of suppressing liver disorders and their antirheumatic effects are newly found facts. 
     Methods for producing compounds of the formula (I) are generally classified into the following two methods (i) and (ii): Method (i): ##STR3## 
     The compounds of the present invention can be obtained by reacting the compound of formula (II) and either carboxylic acids or halide of the formula, R 3  -Y (III), (wherein R 3  is the same as for R 1  or R 2  in the formula (I) and the Y is hydroxyl or halogen) in such common methods as the Schotten-Baumann reaction where they are reacted in water, organic solvents, or mixed solvents of the former two, or the mixed acid anhydride method. 
     Method (ii): 
     The compounds of the present invention can be obtained by reacting a compound of the formula ##STR4## wherein R 1  or Y is the same as in the formula (I) or (III), respectively and cysteine in a similar way as in the case of method (i). 
     The compounds (I) obtained in the aforementioned methods (i) and (ii) are reacted with desired bases to form salts of the compounds (I) which can be approved as medicines can be obtained. Such bases are sodium hydroxide, sodium carbonate, potassium hydroxide, ammonium hydroxide, calcium carbonate, triethylamine, benzylamine, triethanolamine, N,N-dimethylethylenediamine, piperidine, N-ethylpiperidine, morpholine, N-ethylmorpholine, etc. 
     Since the compounds (I) of the present invention have one asymmetric carbon atom, there are stereoisomers. All of them are included in the category of the compounds of the present invention. The following examples illustrate the methods of producing the compounds (I), but are not intended to limit the invention. 
     EXAMPLE 1 
     S-Acetyl-N-(S-acetyl-2-mercapto-2-methylpropanoyl)-L-cysteine 
     N-(2-Mercapto-2-methylpropanoyl)-L-cysteine (11.2 g, 0.05 mol) is dissolved in 1 M potassium carbonate (250 ml) and acetyl chloride (15.7 g, 0.2 mol) is added dropwise while stirring under a nitrogen atmosphere at 0° C. After the addition, the mixture is stirred for 1 hour at room temperature and acidified with 6 N hydrochloric acid. The produced oil is extracted with ethyl acetate. The ethyl acetate layer is washed with water, dried and concentrated to dryness in vacuo to yield 10.7 (69.6%) of S-acetyl-N-(S-acetyl-2-mercapto-2-methylpropanoyl)-L-cysteine. 
     m.p. 131°-132° C. (benzene). [α] D   27  -30.3° (c=1.3, methanol). 
     EXAMPLE 2 
     S-Benzoyl-N-(S-benzoyl-2-mercapto-2-methylpropanoyl)-L-cysteine 
     N-(2-Mercapto-2-methylpropanoyl)-L-cysteine (11.2 g, 0.05 mol) is dissolved in 1 M potassium carbonate (200 ml) and benzoyl chloride (21.1 g, 0.15 mol) is added slowly dropwise at 0° C. with stirring under a nitrogen atmosphere. After the addition, the mixture is stirred for 1 hour at room temperature and acidified with 6 N hydrochloric acid. The produced oil is extracted with ethyl acetate. The ethyl acetate layer is washed with water, dried and concentrated to dryness under reduced pressure to yield 9.7 g (45%) of S-benzoyl-N-(S-benzoyl-2-mercapro-2-methylpropanoyl)-L-cysteine. 
     m.p. 127.5°-128.5° C. (ethyl acetate). [α] D   28  -31.3° (c=1.4, methanol). 
     Analysis for C 21  H 21  NO 5  S 2  ; Calculated: C, 58.45; H, 4.90; N, 3.25; Found: C, 58.28; H, 4.85; N, 3.24. 
     IR (nujol, cm -1 ): 3260, 1730, 1659, 1622, 907, 894. 
     EXAMPLE 3 
     S-Pivaloyl-N-(S-pivaloyl-2-mercapto-2-methylpropanoyl)-L-cysteine 
     N-(2-Mercapto-2-methylpropanoyl)-L-cysteine (11.2 g, 0.05 mol) is dissolved in N sodium hydroxide (50 ml) and pivaloyl chloride (17.0 g, 0.13 mol) and aqueous N sodium hydroxide (150 ml) are added dropwise at 0° C. with stirring under a nitrogen atmosphere. After the addition, the mixture is stirred for 1 hour at room temperature and acidified with 6 N hydrochloric acid. The produced oil is extracted with ethyl acetate and the organic layer is washed with water, dried and concentrated to dryness under reduced pressure to yield 3.2 g (16.4%) of S-pivaloyl-N-(S-pivaloyl-2-mercapto-2-methylpropanoyl)-L-cysteine. 
     m.p. 140°-141° C. (ethyl acetate-petroleum benzine). [α] D   27  -30.0° (c=1.4, methanol). 
     Analysis for C 17  H 29  NO 5  S 2  ; Calculated: C, 52.15; H, 7.47; N, 3,58; Found: C, 52.23; H, 7.55; N, 3.57. 
     IR (nujol, cm -1 ): 3370, 1732, 1685, 1648, 941. 
     EXAMPLE 4 
     S-Pivaloyl-N-(2-mercapto-2-methylpropanoyl)-L-cysteine 
     N-(2-Mercapto-2-methylpropanoyl)-L-cysteine (11.2 g, 0.05 mol) is dissolved in N sodium hydroxide (50 ml) and then pivaloyl chloride (6.6 g, 0.055 mol) and N sodium hydroxide (60 ml) are added dropwise while stirring under a nitrogen atmosphere at 0° C. After the addition, the mixture is stirred for 1 hour at room temperature and acidified with 6 N hydrochloric acid. The produced oil is extracted with ethyl acetate. The organic layer is washed with water, dried and concentrated to dryness to yield 11.5 g (75.0%) S-pivaloyl-N-(2-mercapto-2-methylpropanoyl)-L-cysteine. 
     m.p. 115°-117° C. (benzene). [α] D   27  -25.7° (c=1.1, methanol). 
     Analysis for C 12  H 21  NO 4  S 2  ; Calculated: C, 46.88; H, 6.88; N, 4.56; Found: C, 46.54; H, 6.93; N, 4.49. 
     IR (nujol cm -1 ): 3335, 1743, 1687, 1625. 
     EXAMPLE 5 
     S-Carboxymethyl-N-(2-carboxymethylthio-2-methylpropanoyl)-L-cysteine 
     N-(2-Mercapto-2-methylpropanoyl)-L-cysteine (11.2 g, 0.05 mol) is dissolved in 1 M potassium carbonate and monochloroacetic acid (11.3 g, 0.12 mol) and potassium iodide (1.0 g) are added. The mixture is stirred overnight at room temperature under a nitrogen atmosphere and acidified with 6 N hydrochloric acid. Sodium chloride is added and the mixture is extracted with ethyl acetate. The organic layer is washed with saturated sodium chloride solution, dried and concentrated to dryness to yield 16.5 g (97.2%) of S-carboxymethyl-N-(2-carboxymethylthio-2-methylpropanoyl)-L-cysteine. 
     [α] D   25  -39.5° (c=2.0, methanol). 
     IR (neat, cm -1 ): 1720, 1630, 1260, 1180. 
     EXAMPLE 6 
     S-Methyl-N-[2-methyl-2-(methylthio)propanoyl]-L-cysteine 
     N-(2-Mercapto-2-methylpropanoyl)-L-cysteine (11.2 g) is dissolved in 75 ml of 2 M potassium carbonate and methyl iodide (17.0 g) is added with stirring. The mixture is stirred for 1 hour at room temperature and then acidified with hydrochloric acid. The obtained crystals are separated by filtration and dried to yield 9.44 g (75.1%) of S-methyl-N-[2-methyl-2-(methylthio)propanoyl]-L-cysteine. 
     m.p. 120.5°-121° C. (ethanol-n-hexane). [α] D   19  -19.3° (c=0.7, methanol). 
     IR (nujol, cm -1 ): 3335, 1735, 1725, 1620. 
     NMR (CDCl 3 , ppm): 1.53 (6H, s), 2.10 (3H, s), 2.15 (3H, s), 3.02 (2H, d, J=6 H z ), 4.55-4.90 (1H, m), 7.87 (1H, d, J=8H z ), 11.15 (1H, s). 
     EXAMPLE 7 
     N-[2-Methyl-2-(methylthio)propanoyl]-L-cysteine 
     L-Cysteine (7.1 g) is dissolved in 88 ml of 2 M potassium carbonate and 7.5 g of 2-methyl-2-(methylthio)propanoyl chloride [b.p. 78° C. (37 mmHg)] is added dropwise while stirring under a nitrogen atmosphere at 0° C. After the addition, the mixture is stirred overnight at room temperature. The mixture is acidified with hydrochloric acid and the obtained crystals are separated by filtration and dried to yield 10.4 g (89.8%) of the titled compound. 
     m.p. 110.5°-112° C. (ethyl acetate). [α] D   19  +7.4° (c=1.1, methanol). 
     IR (nujol, cm -1 ): 3350, 1730, 1620. 
     NMR (CDCl 3 , ppm): 1.46 (1H, t, J=9H z ), 1.53 (6H, s), 2.10 (3H, s), 2.93-3.20 (2H, m), 4.66-4.95 (1H, m), 7.93 (1H, d, J=8 H z ), 10.40 (1H, s). 
     Suppressive effects of the compounds on liver disorders can be surveyed by administering drugs causative of liver disorders to animals and examining the suppressive effects of the compounds on the experimentally induced liver disorders. Among them, the drugs which induce experimental liver disorders are carbon tetrachloride, thioacetamide, bromobenzene, paracetamol, D-galactosamine, etc. It is particularly believed that, in liver disorders induced by carbon tetrachloride, cytochrome P-450 breaks carbon-chlorine bond producing free radicals (CCl 3 ) of strong toxicity which bring about disorders combining with thiol groups of proteins of the liver cell membrane or promoting the lipid peroxidation reaction of the membrane [Biochem. Pharmacol., 21, 49 (1972); 25, 2163 (1976)]. 
     In the present invention, in order to investigate suppressive effects on liver disorders, carbon tetrachloride was employed as a drug which brings about experimental liver disorders and the suppressive effects of the compounds of the present invention on liver disorders were examined using serum transaminase (s-GOT and s-GPT) as an indicator. 
     Compounds employed in the experiments are as follows: 
     Compound A: S-Acetyl-N-(S-acetyl-2-mercapto-2-methylpropanoyl)-L-cysteine 
     Compound B: S-Pivaloyl-N-(S-pivaloyl-2-mercapto-2-methylpropanoyl)-L-cysteine 
     Compound C: S-Benzoyl-N-(S-benzoyl-2-mercapto-2-methylpropanoyl)-L-cysteine 
     PHARMACOLOGICAL TESTS 
     Male Wistar-strain rats of 170-200 g body weight, consisting of 5 rats each in one group, were kept without food for 16 hours and then used for experiments. 100 mg of the comounds A to C were orally administered per 1 kg of body weight. 0.25 ml of carbon tetrachloride was intraperitoneally administered per 1 kg of body weight (5 ml per 1 kg of body weight as an olive oil solution) 30 minutes after the administration of each compound. To the control, 5 ml of olive oil was intraperitoneally administered per 1 kg of body weight. Serum transaminase was determined 24 hours after the administration of carbon tetrachloride. 
     TABLE 
     Effect of the compound are on serum transmainase 
     
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       Serum transaminase                                                 
       Serum GOT     Serum GPT                                            
Compound Karmen unit/ml                                                   
                     Ratio   Karmen unit/ml                               
                                       Ratio                              
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None     10428 ± 3118                                                  
                     (100)   2025 ± 650                                
                                       (100)                              
(Control)                                                                 
Compound A                                                                
         6236 ± 234                                                    
                     (59.8)  1656 ± 423                                
                                       (80.9)                             
Compound B                                                                
         7320 ± 822                                                    
                     (70.2)  1825 ± 171                                
                                       (90.1)                             
Compound C                                                                
         5806 ± 1152                                                   
                     (55.7)  1445 ± 207                                
                                       (70.6)                             
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 Each value represents the means ± S.D. for 5 rats.                    
 
    
     As shown in the table, it was found that serum transaminase was suppressed by the administration of the compounds A to C. 
     As clear from the above pharmacological test, the compound (I) of the present invention are useful as a medicine for suppressing liver disorders and are also expected to be an antirheumatic. When used for antirheumatic purpose, the compounds can be combined with thiol compounds depending on the cases as generally used at present. The compounds of the present invention are effective when administered in either manner of oral or parenteral administration and can be prescribed in either form of medicinal compositions for oral or parenteral administration depending on the need. 
     For oral administration, they can be prescribed as tablets, capsules, granules, etc. and are prepared pharmaceutically by mixing the compounds with at least one of such excipients as lactose, starch, sucrose, etc. Further, in preparing these medicine forms, other additives than the aforementioned excipients, such as disintegrators and covering materials as well as lubricants (magnesium stearate, etc.) and binders (dextrin) can usually be employed. 
     Medicines to be parenterally administered can be either in the form of sterilized aqueous or non-aqueous isotonic solution. In these medicines isotonicity adjuvants, such as preservatives, solubilizers and stabilizers can be added. 
     Although contents of the compounds of the present invention in any composition can be appropriately changed, they should be fixed to produce a suitable dosage. Dosage varies depending on the desired therapeutic effects, administration routes, subjects to be administered, duration of treatment, etc. Generally, to achieve desired effects, it is desirable to orally administer 0.2-20 mg of dosage level of the compounds of the present invention per 1 kg of body weight of patients a day. In the case of grown-ups, this can be attained by administering united medicine forms containing 50-30 mg of the compounds of the invention 1-3 times a day. 
    
    
     The following examples illustrate the description of medicines containing the compounds of the present invention as an effective ingredient. It is to be understood that said examples are not intended to limit the invention. 
     
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(a)      Tablet form                                                      
         Compound B          100 mg                                       
         lactose             100 mg                                       
         crystalline cellulose                                            
                             40 mg                                        
         carboxymethyl cellulose                                          
                             7 mg                                         
         magnesium stearate  3 mg                                         
         Total               250 mg                                       
(b)      Granular form                                                    
         Compound A          100 mg                                       
         polyvinylpyrrolidone                                             
                             25 mg                                        
         lactose             305 mg                                       
         hydroxypropyl cellulose                                          
                             50 mg                                        
         talc                10 mg                                        
         Total               490 mg                                       
(c)      Powder form                                                      
         Compound C          300 mg                                       
         lactose             230 mg                                       
         starch              440 mg                                       
         colloidal silica    30 mg                                        
         Total               1000 mg                                      
(d)      Capsul form                                                      
         Compound A          50 mg                                        
         lactose             82 mg                                        
         crystalline cellulose                                            
                             56 mg                                        
         coloidal silica     2 mg                                         
         Total               190 mg                                       
(e)      Injection form                                                   
       1 to 100 mg of the compound A in the form of the                   
       sodium salt is contained in 1 ml of an aqueous                     
       solution of pH 5.0-7.0.                                            
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