Process for preparing n-protected 4-ketoproline derivatives
The present invention is concerned with a process for preparing compounds of the general formula (I). These compounds can preferably be used to prepare bioactive agents. The reaction of the invention starts from the corresponding hydroxy compounds which are oxidized, with Ru catalysis, in a one-phase aqueous system.
1. A process for preparing N-protected 4-ketoproline compounds of formula (I):
in which
X is an acid, ester or amide function,
PG is an N-protective group which comprises a carbonyl function and is bonded via this function to the nitrogen,
said process comprising oxidizing a 4-hydroxyproline compound with an oxidizing agent in the presence of catalytically active ruthenium compounds,
wherein the oxidation is carried out in an aqueous one-phase system, and the oxidation product (I) is induced to crystallize out during the addition of said oxidizing agent.
2. The process of claim 1 , wherein said hydroxyproline compound is a compound of formula (III):
in which
R 1 is CO—R 3 or fluorenylmethoxycarbonyl,
R 2 is NH 2 , or OR 4 ,
R 3 is (H), (C 1 -C 8 )-alkyl, phenyl, benzyl, benzyloxy, NH 2 , NO 2 -phenyloxy, NO 2 -benzyloxy, (C 1 -C 8 )-alkoxy or phenyloxy,
R 4 is H, (C 1 -C 8 )-alkyl, benzyl, phenyl, NO 2 -benzyl, or NO 2 -phenyl.
3. The process of claim 1 , wherein the temperature during the oxidation is kept at ≦30° C.
4. The process of claim 1 , wherein the temperature during the oxidation is kept at ≦15° C.
5. The process of claim 1 , wherein said oxidizing agent is a hypohalite, halate or perhalate salt.
6. The process of claim 5 , wherein said hydroxyproline compound is a compound of formula (III):
in which
R 1 is CO—R 3 or fluorenylmethoxycarbonyl,
R 2 is NH 2 , or OR 4 ,
R 3 is (H), (C 1 -C 8 )-alkyl, phenyl, benzyl, benzyloxy, NH 2 , NO 2 -phenyloxy, NO 2 -benzyloxy, (C 1 -C 8 )-alkoxy or phenyloxy,
R 4 is H, (C 1 -C 8 )-alkyl, benzyl, phenyl, NO 2 -benzyl, or NO 2 -phenyl.
7. The process of claim 5 , wherein the temperature during the oxidation is kept at ≦30° C.
8. The process of claim 5 , wherein the temperature during the oxidation is kept at ≦15° C.
9. The process of claim 1 , wherein seed crystals are added to the reaction mixture after addition of 50% of said oxidizing agent.
10. The process of claim 9 , wherein said hydroxyproline compound is a compound of formula (III):
in which
R 1 is CO—R 3 or fluorenylmethoxycarbonyl,
R 2 is NH 2 , or OR 4 ,
R 3 is (H), (C 1 -C 8 )-alkyl, phenyl, benzyl, benzyloxy, NH 2 , NO 2 -phenyloxy, NO 2 -benzyloxy, (C 1 -C 8 )-alkoxy or phenyloxy,
R 4 is H, (C 1 -C 8 )-alkyl, benzyl, phenyl, NO 2 -benzyl, or NO 2 -phenyl.
11. The process of claim 9 , wherein the temperature during the oxidation is kept at ≦30° C.
12. The process of claim 9 , wherein the temperature during the oxidation is kept at ≦15° C.
13. The process of claim 9 , wherein said oxidizing agent is a hypohalite, halate or perhalate salt.
14. The process of claim 13 , wherein the temperature during the oxidation is kept at ≦30° C.
15. The process of claim 13 , wherein the temperature during the oxidation is kept at ≦20° C.
16. The process of claim 13 , wherein the temperature during the oxidation is kept at ≦15° C.
17. The process of claim 1 , wherein said oxidizing agent is sodium periodate and wherein the temperature during the oxidation is kept at ≦30° C.
18. The process of claim 1 , wherein the oxidation takes place in a purely aqueous solvent and the temperature during the oxidation is kept at ≦30° C.
19. The process of claim 1 , wherein said aqueous solvent also includes a water-soluble organic solvent and the temperature during the oxidation is kept at ≦30° C.
20. The process of claim 19 , wherein said oxidizing agent is sodium periodate.