1,4-Dihydropyridine-3,5-dicarboxylic acid ester derivatives
DETAILED DESCRIPTION OF THE INVENTION 
     This invention relates to 1,4-dihydropyridine-3,5-dicarboxylic acid ester derivatives shown by the general formula ##STR2## wherein R represents a lower alkyl group and R&#39; represents a hydrogen atom, a lower alkyl group or an aralkyl group, or the therapeutically non-toxic salts thereof and also the invention further relates to a process of producing these compounds. 
     As the lower alkyl group in the above formula, there are, for example, methyl group, ethyl group, propyl group, butyl group, isobutyl group, etc., and as the aralkyl group, there are, for example, benzyl group, phenethyl group, etc. 
     Hitherto, various 1,4-dihydropyridine-3,5-dicarboxylic acid ester derivatives are known and the compound shown by the following formula is practically used for the treatment of angina pectoris; ##STR3## 
     Also, as the 1,4-dihydropyridine derivatives wherein the ester moiety is basic, the following compounds are known. ##STR4## In particular, the first compound (U.S. Pat. No. 3,985,758) is now under investigation for use as medicaments. 
     The compounds of this invention are novel 1,4-dihydropyridine derivatives having different chemical structures from those of the afore-mentioned known 1,4-dihydropyridine derivatives and useful as medicaments. 
     The compounds of formula I provided by this invention possess a vasodilative activity and an antihypertensitve activity and thus are useful as antihypertensive agents, vasodilators, in particular, coronary vasodilators, and cerebral vascular dilators. Particularly, the characteristics of the compounds of this invention are that they have low toxicity, form easily water-soluble salts thereof, and exhibit a therapeutic effect when administered even in small doses since they are slowly metabolized in vivo. 
     The compounds of this invention shown by formula I are usually prepared by reacting the acetoacetic acid ester shown by formula II 1   
     
         CH.sub.3 COCH.sub.2 COOR                                   II.sub.1 
    
     wherein R has the same significance as in formula I, with nitrobenzaldehyde shown by formula III ##STR5## and the compound shown by formula IV 1  ##STR6## wherein R&#39; has the same significance as in formula I or by reacting the acetoacetic acid ester shown by formula II 2  ##STR7## wherein R&#39; has the same significance as in formula I with nitrobenzaldehyde shown by formula III ##STR8## and the compound shown by formula IV 2  ##STR9## wherein R has the same significance as in formula I. 
     The reaction for producing the compounds of this invention is performed by mixing the afore-mentioned compound of formula II 1  or II 2  with an almost equimolar amount of the compound of formula III and an almost equimolar amount of the compound of formula IV 1  or IV 2  and heating the mixture. In this reaction, a reaction solvent may be or may not be used but when a solvent is used, suitable solvents include alcohols, dioxane, dimethylformamide, dimethylsulfoxide, acetonitrile, water, etc. 
     In addition, the compound of formula IV 1  or IV 2  can be obtained by reacting beforehand a compound of formula II 2  or II 1  with ammonia. A compound of formula IV 1  or IV 2  thus obtained is reacted, with or without being isolated, with a compound of formula II 1  or II 2  and a compound of formula III to provide the desired compound of formula I. 
     Furthermore, the compounds of the following formula obtained by reacting beforehand the compound of II 1  or II 2  with the compound of formula III ##STR10## can also provide the desired compounds of formula I by reacting, with or without being isolated, with the compound of formula IV 1  or IV 2 . 
     The desired compounds of this invention shown by formula I obtained in any of the afore-mentioned processes can be isolated and purified by conventional methods such as column chromatography, etc. 
     The compounds of general formula I can be desirably converted into the therapeutically non-toxic salts thereof, for example, mineral acid salts such as hydrochlorides, sulfates, phosphates, etc., or organic acid salts such as acetates, fumarates, maleates, tartarates, etc. 
     The salts of the compounds of formula I are suitable for liquid pharmaceutical preparations (especially injection) since these salts are highly soluble in water without using solubilizing agents. 
     The appropriate dose of the compound of this invention for human beings is 0.1-1.0 mg per single dose in intravenous administration and 5-20 mg per single dose in oral administration, two or three times a day being appropriate. 
     The excellent antihypertensive activity of the compounds of this invention is proved by the following tests in the comparison with a 1,4-dihydropyridine derivative having a basic ester moiety, 2,6-dimethyl-4-(3&#39;-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid 3-methyl ester-5-β-(N-benzyl-N-methylamino)ethyl ester hydrochloride (Compound B, U.S. Pat. No. 3,985,758): 
     (I) Procedures: 
     Male, conscious spontaneously hypertensive rats, Okamoto and Aoki strain were used in the study. Systolic blood pressure and heart rate were determined by tail plethysmographic methods employing a Narco electrosphygmomanometer (PE-300). The drug suspended in 0.5% methyl celullose were administered orally in a dosage volume of 5 ml/Kg. 
     (II) Results and conclusion: 
     As shown in Table 1, the compound of this invention caused hypotensive activity about 5 times more potent than Compound B when orally administered to spontaneously hypertensive rats. These results indicate that hypotensive effect of the compound of this invention was more potent than that of Compound B by oral administration. Since the anti-hypertensive agent was usually administered by oral route, these results may prove that the compound of this invention is suitable for treatment of hypertensive subjects. 
     
                                           Table 1                                 
__________________________________________________________________________
Effects on systolic blood pressure and heart rate in conscious            
spontaneously hypertensive rat.                                           
        Dose                                                              
            No.               Changes in systolic blood pressure          
                              (.increment.mmHg)                           
        mg/kg                                                             
            of          Initial                                           
                              and heart rate (.increment.beats/min) at    
                              stated time (hr)                            
Compound                                                                  
        p.o.                                                              
            animals                                                       
                Parameters                                                
                        value 1      2      4      6                      
__________________________________________________________________________
Compound B                                                                
        10  10  Blood pressure                                            
                        196 ± 11.8                                     
                              -41 ± 6.7                                
                                     -39 ± 8.3                         
                                            -28 ± 7.8                  
                                                   -25 ± 8.2           
(known          Heart rate                                                
                        380 ± 12.5                                     
                              21 ± 31.4                                
                                     36 ± 27.5                         
                                             -9 ± 22.7                 
                                                   -27 ± 20.6          
compound)                                                                 
        30  10  Blood pressure                                            
                        190 ± 12.1                                     
                              -82 ± 11.7                               
                                     -71 ± 18.9                        
                                            -78 ± 16.1                 
                                                   -62 ± 17.0          
                Heart rate                                                
                        363 ± 17.5                                     
                              93 ± 18.4                                
                                     63 ± 22.7                         
                                             41 ± 25.9                 
                                                    -8 ± 22.7          
         3  10  Blood pressure                                            
                        213 ± 16.8                                     
                              -61 ± 14.6                               
                                     -49 ±0 11.7                       
                                            -34 ± 8.3                  
                                                   -43 ± 11.4          
Compound A      Heart rate                                                
                        388 ± 12.6                                     
                              23 ± 21.9                                
                                      9 ± 15.5                         
                                            -22 ± 21.4                 
                                                   -22 ± 19.2          
(hydrochloride                                                            
of compound                                                               
        10   9  Blood pressure                                            
                        204 ± 17.3                                     
                              -99 ± 14.8                               
                                     -83 ± 13.3                        
                                            -79 ± 15.1                 
                                                   -81 ± 15.7          
of Ex. 1)       Heart rate                                                
                        377 ± 16.8                                     
                              68 ± 12.9                                
                                     60 ± 13.0                         
                                             37 ± 17.4                 
                                                    -± 15.7            
__________________________________________________________________________
 
    
    
    
     The process for producing the desired compounds of this invention is illustrated by the following examples. 
     EXAMPLE 1 ##STR11## 
     In 5 ml of isopropyl alcohol were dissolved 1.5 g (0.01 mole) of 3-nitrobenzaldehyde, 2.6 g (0.01 mole) of 1-benzyl-3-acetoacetyloxypyrrolidine, and 1.3 g (0.01 mole) of β-aminocrotonic acid methyl ester and then the solution was refluxed for 8 hours. The solvent was distilled off under reduced pressure, the residue obtained was dissolved in a small amount of chloroform, and the solution was applied to silica gel column chromatography (column diameter 1.5 cm, height 20 cm, and about 200 ml of chloroform was used as the eluant). The eluates were collected and concentrated to give 3.4 g of oily 2,6-dimethyl-4-(3&#39;-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid-3-(1-benzylpyrrolidin-3-yl)ester-5-methyl ester. 
     Elemental analysis for C 27  H 29  N 3  O 6  : 
     
         ______________________________________                                    
          C        H          N                                           
______________________________________                                    
Calculated: 65.98%     5.95%      8.55%                                   
Found:      65.69%     5.83%      8.47%                                   
______________________________________                                    
 
    
     Nuclear magnetic resonance spectra (CDCl 3 ): 
     
         ______________________________________                                    
δ:                                                                  
    1.24-3.0                                                              
              ##STR12##                                                   
    2.33                                                                  
              ##STR13##                                                   
    3.60                                                                  
              ##STR14##                                                   
    3.64     (CH.sub.3COO, s, 3H)                                         
    5.09                                                                  
              ##STR15##                                                   
    6.46                                                                  
              ##STR16##                                                   
    7.28                                                                  
              ##STR17##                                                   
    7.64                                                                  
              ##STR18##                                                   
    8.0                                                                   
              ##STR19##                                                   
    8.12                                                                  
              ##STR20##                                                   
______________________________________                                    
 
    
     In addition, 1-benzyl-3-acetoacetyloxypyrrolidine used in this example was prepared by the following manner. 
     That is, to 8.8 g (0.05 mole) of 1-benzyl-3-hydroxypyrrolidine was added a catalytic amount (0.1 g) of sodium acetate and after stirring the mixture well, 5.0 g (0.06 mole) of diketene was gradually added dropwise to the mixture. Thereafter, the resultant mixture was stirred at 80° C. for 3 hours. After cooling the reaction mixture, it was distilled under reduced pressure to provide 10.3 g of product having a boiling point of 130°-135° C./0.1 mmHg. 
     Elemental analysis for C 15  H 19  NO 3  : 
     
         ______________________________________                                    
          C        H          N                                           
______________________________________                                    
Calculated: 68.94%     7.33%      5.36%                                   
Found:      68.81%     7.20%      5.05%                                   
______________________________________                                    
 
    
     Nuclear magnetic resonance spectra (CDCl 3 ): 
     
         ______________________________________                                    
δ:                                                                  
        1.6-3.0                                                           
                    ##STR21##                                             
        2.2        (CH.sub.3COO, s, 3H)                                   
        3.38       (COCH.sub.2COO, s, 2H)                                 
        3.60                                                              
                    ##STR22##                                             
        5.22                                                              
                    ##STR23##                                             
        7.6                                                               
                    ##STR24##                                             
 
    
     EXAMPLE 2 
     A sterile aqueous solution for injection, containing in 1 ml. 1 mg. of 2,6-dimethyl-4-(3&#39;-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid-3-(1-benzylpyrrolidin-3-yl) ester-5-methyl ester hydrochloride (Compound A) was prepared from the following formulation. 
     Compound A: 100 mg. 
     Glucose: 5000 mg. 
     Water for injection up to 100 ml. 
     Compound A was dissolved in about 80 ml. of water, then the resultant solution was filled up to 100 ml. by the addition of water and sterilized by filtration. The sterile solution was filled in 100 light intercepting ampoules and the ampoules sealed. 
     EXAMPLE 3 
     A tablet containing in 1 tablet 10 mg. of 2,6-dimethyl-4-(3&#39;-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid-3-(1-benzylpyrrolidin-3-yl) ester-5-methyl ester hydrochloride (Compound A) was prepared from the following formulation. 
     Compound A: 10 g. 
     Lactose: 80 g. 
     Starch: 29 g. 
     Magnesium Stearate: 1 g.