A compound of formula (I), wherein R 1 is C 1-6 alkyl; R 2 is benzyl, said benzyl being unsubstituted or substituted by one, two or three substituents independently selected from halogen and C 1-6 alkyl; R 3 is -NR 4 R 5 , wherein R 4 is C 1-6 alkyl or C 1-6 alkoxyC 1-6 alkyl; R 5 is (C 1-6 alkyl) 2 NCOOC 1-6 alkyl, C 1-6 alkoxyC 1-6 alkyl, C 1-6 alkoxycarbonyl(C 1-6 alkyl)aminoC 1-6 alkyl, C 1-6 alkoxycarbonyl(phenyl)C 1-6 alkyl, C 1-6 alkoxycarbonylC 1-6 alkyl, C 1-6 alkoxycarbonyloxyC 1-6 alkyl, C 1-6 alkyl, C 1-6 alkylcarbonyl(C 1-6 alkyl)aminoC 1-6 alkyl or pyrrolidinylcarbamoyloxyC 1-6 alkyl; or R 4 and R 5 together with the nitrogen they are attached to form a heterocyclyl; or pharmaceutically acceptable salt, enantiomer or diastereomer thereof; with the proviso that 6-amino-9-benzyl-2-(propylsulfonimidoyl)-7-(pyrrolidine-1-carbonyl)purin-8-one; 6-amino-9-benzyl-7-(piperidine-1-carbonyl)-2-(propylsulfonimidoyl)purin-8-one; 6-amino-9-benzyl-7-(morpholine-4-carbonyl)-2-(propylsulfonimidoyl)purin-8-one; 6-amino-9-benzyl-7-(3,3-dimethylpyrrolidine-1-carbonyl)-2-(propylsulfonimidoyl)purin-8-one; ethyl 1-[6-amino-9-benzyl-8-oxo-2-(propylsulfonimidoyl)purine-7-carbonyl]pyrrolidine-2-carboxylate; 6-amino-7-(2-azaspiro[3.3]heptane-2-carbonyl)-9-benzyl-2-(propylsulfonimidoyl)purin-8-one; 6-amino-9-benzyl-7-(2-oxa-6-azaspiro[3.3]heptane-6-carbonyl)-2-(propylsulfonimidoyl)purin-8-one; 6-amino-9-benzyl-7-(3,3-difluoropyrrolidine-1-carbonyl)-2-(propylsulfonimidoyl)purin-8-one; 6-amino-9-benzyl-7-(3-fluoro-3-methyl-pyrrolidine-1-carbonyl)-2-(propylsulfonimidoyl)purin-8-one; and their enantiomers or diastereomers are excluded. R 1 is C 1-6 alkyl; R 2 is benzyl, said benzyl being unsubstituted or substituted by one, two or three substituents independently selected from halogen and C 1-6 alkyl; R 3 is -NR 4 R 5 , wherein R 4 is C 1-6 alkyl or C 1-6 alkoxyC 1-6 alkyl; R 5 is (C 1-6 alkyl) 2 NCOOC 1-6 alkyl, C 1-6 alkoxyC 1-6 alkyl, C 1-6 alkoxycarbonyl(C 1-6 alkyl)aminoC 1-6 alkyl, C 1-6 alkoxycarbonyl(phenyl)C 1-6 alkyl, C 1-6 alkoxycarbonylC 1-6 alkyl, C 1-6 alkoxycarbonyloxyC 1-6 alkyl, C 1-6 alkyl, C 1-6 alkylcarbonyl(C 1-6 alkyl)aminoC 1-6 alkyl or pyrrolidinylcarbamoyloxyC 1-6 alkyl; or R 4 and R 5 together with the nitrogen they are attached to form a heterocyclyl; or pharmaceutically acceptable salt, enantiomer or diastereomer thereof; with the proviso that 6-amino-9-benzyl-2-(propylsulfonimidoyl)-7-(pyrrolidine-1-carbonyl)purin-8-one; 6-amino-9-benzyl-7-(piperidine-1-carbonyl)-2-(propylsulfonimidoyl)purin-8-one; 6-amino-9-benzyl-7-(morpholine-4-carbonyl)-2-(propylsulfonimidoyl)purin-8-one; 6-amino-9-benzyl-7-(3,3-dimethylpyrrolidine-1-carbonyl)-2-(propylsulfonimidoyl)purin-8-one; ethyl 1-[6-amino-9-benzyl-8-oxo-2-(propylsulfonimidoyl)purine-7-carbonyl]pyrrolidine-2-carboxylate; 6-amino-7-(2-azaspiro[3.3]heptane-2-carbonyl)-9-benzyl-2-(propylsulfonimidoyl)purin-8-one; 6-amino-9-benzyl-7-(2-oxa-6-azaspiro[3.3]heptane-6-carbonyl)-2-(propylsulfonimidoyl)purin-8-one; 6-amino-9-benzyl-7-(3,3-difluoropyrrolidine-1-carbonyl)-2-(propylsulfonimidoyl)purin-8-one; 6-amino-9-benzyl-7-(3-fluoro-3-methyl-pyrrolidine-1-carbonyl)-2-(propylsulfonimidoyl)purin-8-one; R 4 is C 1-6 alkyl or C 1-6 alkoxyC 1-6 alkyl; R 5 is (C 1-6 alkyl) 2 NCOOC 1-6 alkyl, C 1-6 alkoxyC 1-6 alkyl, C 1-6 alkoxycarbonyl(C 1-6 alkyl)aminoC 1-6 alkyl, C 1-6 alkoxycarbonyl(phenyl)C 1-6 alkyl, C 1-6 alkoxycarbonylC 1-6 alkyl, C 1-6 alkoxycarbonyloxyC 1-6 alkyl, C 1-6 alkyl, C 1-6 alkylcarbonyl(C 1-6 alkyl)aminoC 1-6 alkyl or pyrrolidinylcarbamoyloxyC 1-6 alkyl; or R 4 and R 5 together with the nitrogen they are attached to form a heterocyclyl; <EOS>