Intermediates useful for preparing 4,6-diaminopyrido[5,4-d]pyrimidines

1. A 2-Chloro-4,6-diamino-7,8-dihydropyrimido[5,4d]-pyrimidine of the formula II

wherein

R 1 denotes a hydrogen atom or a C 1 -C 6 alkyl group,

R 2 denotes an optionally substituted C 6 -C 10 aryl group,

R 3 denotes a hydrogen atom or a C 1 -C 6 alkyl group, and

R 4 denotes a hydrogen atom or an optionally substituted C 1 -C 6 alkyl, C 3 -C 6 alkenyl, C 3 -C 8 cycloalkyl or a 4- to 7-membered, nitrogen-containing heterocyclyl group, or

R 3 and R 4 together with the nitrogen atom linked to them denote an optionally substituted heterocyclyl group, and

PG 1 denotes a C 1-6 alkanoyl group.

2. A compound according to claim 1 , wherein R 1 denotes hydrogen or methyl.

3. A compound according to claim 1 , wherein R 2 denotes phenyl which may be substituted by one or two halogen atoms.

4. A compound according to claim 3 , wherein R 2 denotes 3-chloro-4-fluorophonyl.

5. A compound according to claim 1 , wherein R 3 denotes hydrogen or methyl.

6. A compound according to claim 1 , wherein R 4 denotes a 5- or 6-membered, nitrogen-containing heterocycle which may be substituted by one or two C 1-3 -alkyl groups.

7. A compound according to claim 6 , wherein R 4 denotes 1-methylpiperid-4-yl.

8. A compound according to claim 1 , wherein R 3 and R 4 together with the enclosed nitrogen atom form a 5- or 6-membered, nitrogen-containing heterocycle which may be substituted by one or two groups selected from among amino, C 1-3 -alkyl and di-(C 1-3 -alkyl)-amino-C 1-3 -alkyl.

9. A compound according to claim 8 , wherein R 3 and R 4 together with the enclosed nitrogen atom form a 5- or 6-membered, nitrogen-containing heterocycle which is substituted by an amino, methyl or diethylaminomethyl group.

10. A compound according to claim 8 , wherein R 3 and R 4 together with the enclosed nitrogen atom form a 4-amino-4-methylpiperid-1-yl group.

11. A compound according to claim 1 , wherein PG 1 denotes acetyl.

12. A 4-amino-2,6-dichloro-7,8-dihydropyrimido[5,4-d]pyrimidine of the formula III

wherein

R 1 denotes a hydrogen atom or a C 1 -C 6 alkyl group, and

R 2 denotes an optionally substituted C 6 -C 10 aryl group, and

PG 1 denotes a C 1-6 alkanoyl group.

13. A compound according to claim 12 , wherein R 1 denotes hydrogen or methyl.

14. A compound according to claim 12 , wherein R 2 denotes phenyl which may be substituted by one or two halogen atoms.

15. A compound according to claim 12 , wherein R 2 denotes 3-chloro-4-fluorophenyl.

16. A 4-amino-2,6-dichloro-7,8-dihydropyrimido[5,4-d]pyrimidine of the formula V,

wherein

R 1 denotes a hydrogen atom or a C 1 -C 6 alkyl group, and

R 2 denotes an optionally substituted C 6 -C 10 aryl group.

17. A compound according to claim 16 , wherein R 1 denotes hydrogen or methyl.

18. A compound according to claim 16 , wherein R 2 denotes phenyl which may be substituted by one or two halogen atoms.

19. A compound according to claim 16 , wherein R 2 denotes 3-chloro-4-fluorophenyl.

20. A 4-amino-2,6,8-trichloropyrimido[5,4-d]pyrimidine of the formula VI,

wherein

R 1 denotes a hydrogen atom or a C 1 -C 6 alkyl group, and

R 2 denotes an optionally substituted C 6 -C 10 aryl group.

21. A compound according to claim 20 , wherein R 1 denotes hydrogen or methyl.

22. A compound according to claim 20 , wherein R 2 denotes phenyl which may be substituted by one or two halogen atoms.

23. A compound according to claim 20 , wherein R 2 denotes 3-chloro-4-fluorophenyl.