Pyrimidine derivatives and anti-viral agent containing the same as active ingredient thereof

Abstract

The disclosure concerns pyrimidine derivatives represented by the following general formulas [I] and [I'] and having antiviral activity, particularly antiretroviral activity such as anti-HIV activity:and pharmaceutical compositions having antiviral activity and comprising the above-described derivative(s) as an active ingredient.

What is claimed is:  
     
       1. A pyrimidine derivative represented by the following formula (I):                    
       wherein 
       R 1  represents C 1  to C 5  alkyl; C 3  to C 8  cycloalkyl; C 2  to C 5  alkenyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2 to C 6  alkoxycarbonyl and carbamoyl groups; C 2  to C 5  alkynyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 2  to C 5  alkylcarbonyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 7  to C 13  arylcarbonyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 8  to C 14  arylcarbonylalkyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 6  to C 12  arylthio optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 7  to C 13  arylcarbonyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 8  to C 14  arylcarbonylalkyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 6  to C 12  arylthio optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; or C 7  to C 17  aralkyl group optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups,  
       R 2  represents C 6  to C 10  arylthio optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano, and C 2  to C 7  acyl groups; C 1  to C 5  alkylthio optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 3  to C 10  cycloalkylthio optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 6  to C 12  arylsulfinyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 1  to C 5  alkylsulfinyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 3  to C 10  cycloalkylsulfinyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 2  to C 5  alkenyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 2  to C 5  alkynyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 7  to C 11  aralkyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 7  to C 13  arylcarbonyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 8  to C 14  arylcarbonylalkyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; or C 6  to C 12  aryloxy group optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  and C 7  acyl groups;  
       R 3  represents ethyl; C 3  to C 10  branched alkyl; or —CH 2 —Z(CH 2 ) n —R 5  group where R 5  represents a hydrogen atom; halogen atom; hydroxyl; nicotinoyloxy; formyloxy; C 2  to C 11  alkylcarbonyloxy; C 4  to C 11  cycloalkylcarbonyloxy; C 8  to C 12  aralkylcarbonyloxy; C 7  to C 13  arylcarbonyloxy; azido; C 2  to C 11  alkoxycarbonyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 2  to C 11  N-alkylcarbamoyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 7  to C 13  N-arylcarbamoyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 2  to C 11  N-alkylthiocarbamoyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 7  to C 13  N-arylthiocarbamoyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 1  to C 10  alkoxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 7  to C 13  aralkyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 3  to C 10  branched alkyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 3  to C 10  cycloalkyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; or C 6  to C 12  aryl group optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups, Z represents an oxygen atom, sulfur atom or methylene group, and n represents 0 or an integer of 1 to 5,  
       R 4  represents a hydrogen atom;  
       X and Y independently represent an oxygen or sulfur atom; provided that when R 4  represents a hydrogen atom and Z represents an oxygen atom or methylene group, R 5  does not represent hydroxyl group, or a pharmaceutically acceptable salt thereof.  
     
     
       2. A pyrimidine derivative represented by the following formula (I′):                    
       wherein: 
       R 1  represents C 1  to C 5  alkyl; C 3  to C 8  cycloalkyl; C 2  to C 5  alkenyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 2  to C 5  alkynyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 2  to C 5  alkylcarbonyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 7  to C 13  arylcarbonyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 8  to C 14  arylcarbonylalkyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 6  to C 12  arylthio optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; or C 7  to C 17  aralkyl group optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups,  
       R 2  represents C 6  to C 10  arylthio optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano, and C 2  to C 7  acyl groups; C 1  to C 5  alkylthio optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 3  to C 10  cycloalkylthio optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 6  to C 12  arylsulfinyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 1  to C 5  alkylsulfinyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 3  to C 10  cycloalkylsulfinyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 2  to C 5  alkenyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 2  to C 5  alkynyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 7  to C 11  aralkyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 7  to C 13  arylcarbonyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 8  to C 14  arylcarbonylalkyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; or C 6  to C 12  aryloxy group optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups;  
       R 3  represents ethyl; C 3  to C 10  branched alkyl; or —CH 2 —Z(CH 2 ) n —R 5  group where R 5  represents a hydrogen atom; halogen atom; hydroxyl; nicotinoyloxy; formyloxy; C 2  to C 11  alkylcarbonyloxy; C 4  to C 11  cycloalkylcarbonyloxy; C 8  to C 12  aralkylcarbonyloxy; C 7  to C 13  arylcarbonyloxy; azido; C 2  to C 11  alkoxycarbonyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 2  to C 11  N-alkylcarbamoyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 7  to C 13  N-arylcarbamoyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 2  to C 11  N-alkylthiocarbamoyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 7  to C 13  N-arylthiocarbamoyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 1  to C 10  alkoxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 7  to C 13  aralkyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 3  to C 10  branched alkyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 3  to C 10  cycloalkyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; or C 6  to C 12  aryl group optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups, Z represents an oxygen atom, sulfur atom or methylene group, and n represents 0 or an integer of 1 to 5, and Y represents an oxygen or sulfur atom, or a pharmaceutically acceptable salt thereof.  
     
     
       3. A compounds  pyrimidine derivative according to  claim 1  or  2 , wherein: 
       R 1  represents C 1  to C 5  alkyl; C 3  to C 8  cycloalkyl; C 2  to C 5  alkenyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 2  to C 5  alkynyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups; C 2  to C 5  alkylcarbonyl; C 7  to C 13  arylcarbonyl; C 9  to C 14  arylcarbonylalkyl; C 6  to C 12  arylthio; or C 7  to C 17  aralkyl group,  
       R 2  represents C 6  to C 10  arylthio optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 1  to C 5  alkylthio; C 3  to C 10  cycloalkylthio optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 6  to C 12  arylsulfinyl; C 1  to C 5  arylsulfinyl; C 3  to C 10  cycloalkylsulfinyl; C 2  to C 5  alkenyl; C 2  to C 5  alkynyl; C 7  to C 11  aralkyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 7  to C 13  arylcarbonyl; C 8  to C 14  arylcarbonylalkyl; or C 6  to C 12  aryloxy,  
       R 3  represents ethyl; or —CH 2 —Z—(CH 2 ) n —R 5  group where R 5  represents a hydrogen atom; halogen atom; hydroxyl; nicotinoyloxy; formyloxy; C 2  to C 11  alkylcarbonyloxy; C 4  to C 11  cycloalkylcarbonyloxy; C 8  to C 12  aralkylcarbonyloxy; C 7  to C 13  arylcarbonyloxy; azido; C 2  to C 11  alkoxycarbonyloxy; C 2  to C 8  N-alkylcarbamoyloxy; C 7  to C 13  N-arylcarbamoyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 2  to C 8  N-alkylthiocarbamoyloxy; C 7  to C 13  N-arylthiocarbamoyloxy optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 1  to C 10  alkoxy; C 7  to C 13  aralkyloxy optionally substituted by one or more substituents selected by the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups; C 3  to C 5  branched alkyl; C 5  to C 7  cycloalkyl; or C 6  to C 12  aryl group optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups, Z represents an oxygen atom, sulfur atom or methylene group, and n represents 0 or an integer of 1 to 5;  
       
         or a pharmaceutically acceptable salt thereof.  
       
     
     
       4. A compound  pyrimidine derivative according to  claim 3 , wherein: 
       R 1  represents C 1  to C 5  alkyl; C 3  to C 8  cycloalkyl; or C 2  to C 5  alkenyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, phenyl, cyano, C 2  to C 6  alkoxycarbonyl and carbamoyl groups,  
       R 2  represents C 6  to C 10  arylthio optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; C 3  to C 10  cycloalkylthio optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups; or C 7  to C 11  aralkyl optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 1  to C 5  alkyl, C 1  to C 5  halogenated alkyl, C 1  to C 5  alkoxy, phenyl, hydroxyl, nitro, amino, cyano and C 2  to C 7  acyl groups,  
       R 3  represents ethyl; or —CH 2 —Z—(CH 2 ) n —R 5  group where R 5  represents a hydrogen atom; halogen atom; hydroxyl; nicotinoyloxy; formyloxy; C 2  to C 11  alkylcarbonyloxy; C 4  to C 11  cycloalkylcarbonyloxy; C 8  to C 12  aralkylcarbonyloxy; C 7  to C 13  arylcarbonyloxy; azido; C 2  to C 11  alkoxycarbonyloxy; C 2  to C 8  N-alkylcarbamoyloxy; C 7  to C 13  N-arylcarbamoyloxy; C 2  to C 8  N-alkylthiocarbamoyloxy; C 7  to C 13  N-arylthiocarbamoyloxy; C 1  to C 10  alkoxy; C 7  to C 13  aralkyloxy; C 3  to C 5  branched alkyl; C 5  to C 7  cycloalkyl; or C 6  to C 12  aryl group optionally substituted by one or more substituents selected from the group consisting of a halogen atom, C 6  to C 12  aryl, C 1  to C 5  alkyl, C 1  to C 5  alkoxy and C 1  to C 5  halogenated alkyl groups, Z represents an oxygen, sulfur or methylene group, and n represents 0 or an integer of 1 to 5;  
       
         or a pharmaceutically acceptable salt thereof.  
       
     
     
       5. A compound  pyrimidine derivative according to  claim 4 , wherein: 
       R 1  represents C 1  to C 5  alkyl,  
       R 2  represents a phenylthio group optionally substituted by a C 1  to C 3  alkyl or halogen atom; or a benzyl group optionally substituted by a C 1  to C 3  alkyl or halogen atom,  
       R 3  represents a —CH 2 —Z—(CH 2 ) n —R 5  group where R 5  represents a hydrogen atom; or a phenyl group optionally substituted by a  1  to  3  alkyl or a halogen atom, Z represents an oxygen atom, and n represents an integer of 1 to 3,  
       R 4  represents a hydrogen atom,  
       X represents an oxygen atom, and  
       Y represents an oxygen atom or sulfur atom;  
       
         or a pharmaceutically acceptable salt thereof.  
       
     
     
       6. A compound  pyrimidine derivative according to  claim 5 , wherein: 
       R 1  represents an ethyl or isopropyl group,  
       R 2  represents a phenylthio group optionally substituted by a C 1  to C 3  alkyl or halogen atom;  
       R 3  represents a —CH 2 —Z—(CH 2 ) n —R 5  group where R 5  represents a hydrogen atom; Z represents an oxygen atom, and n represents an integer of 1 to 3,  
       R 4  represents a hydrogen atom,  
       X represents an oxygen atom, and  
       Y represents an oxygen or sulfur atom;  
       
         or a pharmaceutically acceptable salt thereof.  
       
     
     
       7. A compound  pyrimidine derivative according to claim  6   5 , wherein: 
       R 1  represents an ethyl or isopropyl group,  
       R 2  represents a benzyl group optionally substituted by a a C 1  to C 3  alkyl or halogen atom,  
       R 3  represents a —CH 2 —Z—(CH 2 ) n —R 5  group where R 5  represents a hydrogen atom; Z represents an oxygen atom, and n represents an integer of 1 to 3,  
       R 4  represents a hydrogen atom,  
       X represents an oxygen atom, and  
       Y represents an oxygen atom or sulfur atom;  
       
         or a pharmaceutically acceptable salt thereof.  
       
     
     
       8. A pharmaceutical composition containing a 6-substituted acyclopyrimidine nucleoside  pyrimidine derivative or a pharmaceutically acceptable salt thereof according to any one of claims  1 - 7   claim 1 , in admixture with a pharmaceutical vehicle. 
     
     
       9. A pharmaceutical composition according to  claim 8 , which has effective antiviral activity. 
     
     
       10. A pharmaceutical composition according to  claim 8 , which has effective antiretroviral activity. 
     
     
       11. The pharmaceutical composition of  claim 8 , which is used to treat a vital  viral infection which is susceptible to treatment. 
     
     
       12. A pyrimidine derivative having the following structure:                    
       
         or a pharmaceutically acceptable salt thereof. 
       
     
     
       13. A pharmaceutical composition containing the pyrimidine derivative of  claim 12  in combination with a pharmaceutically acceptable carrier. 
     
     
       14. A method of treating an HIV infection in a host, comprising administering to the host an effective treatment amount of the pyrimidine derivative of  claim 12 . 
     
     
       15. A pharmaceutical composition containing a pyrimidine derivative or a pharmaceutically acceptable salt thereof according to  claim 2 , in admixture with a pharmaceutical vehicle.