Methods for the preparation of charged crosslinkers

1. A process for the preparation of a compound of formula (3):

or a salt thereof, comprising the step of:

a) reacting a lactone of formula (4):

with a sulfonating agent to form a compound of formula (5):

or a salt thereof;

b) reacting the compound of formula (5) or a salt thereof with a sulfur-bearing nucleophile, optionally followed by deprotection, to form a compound of formula (6):

or a salt thereof;

c) reacting the compound of formula (6) or a salt thereof with a disulfide compound to form the compound of formula (3), wherein:

Q′ is a linear, branched or cyclic alkyl having 1 to 10 carbon atoms, phenyl, ortho or para-nitrophenyl, dinitrophenyl, pyridyl or nitropyridyl; and

R a , R b , R c , R d and R e , each independently, is H or a linear, branched or cyclic alkyl having 1 to 10 carbon atoms.

2. The process of claim 1 , wherein the sulfonating agent is selected from chlorosulfonic acid or sulfur trioxide.

3. The process of claim 1 , wherein the sulfonating agent is chlorosulfonic acid.

4. The process of claim 1 , wherein the sulfur-bearing nucleophile is selected from hydrogen sulfide or a salt thereof, thiourea, thioacetic acid or 2-(tirmethylsilyl)ethanethiol.

5. The process of claim 4 , wherein the sulfur-bearing nucleophile is thiourea or thioacetic acid.

6. The process of claim 5 , wherein the reaction between the compound of formula (5) and a sulfur-bearing nucleophile is carried out in the presence of a base and/or a Lewis acid.

7. The process of claim 6 , wherein the deprotection of step b) is catalyzed by a base.

8. The process of claim 7 , wherein the disulfide compound is selected from the group consisting of 2,2′-dithiodipyridine, 4,4′-dithiodipyridine, 2,2-dithiobis(5-pyridine), 4-nitrophenyldisulfide, S-methyl methanethiosulfonate and dimethyl disulfide.

9. The process of claim 8 , wherein the disulfide compound is 2,2′-dithiodipyridine.

10. A process for the preparation of a compound of formula (Ia):

or a salt thereof, comprising the steps of:

a) reacting a lactone of formula (4):

with a sulfonating agent to form a compound of formula (5):

or a salt thereof;

b) reacting the compound of formula (5) or a salt thereof with a sulfur-bearing nucleophile, optionally followed by deprotection, to form a compound of formula (6):

or a salt thereof;

c) reacting the compound of formula (6) or a salt thereof with a disulfide compound to form a compound of formula (3)

or a salt thereof

d) reacting the compound of formula (3) with a hydroxy or mercapto compound to form the compound of formula (Ia), wherein:

Q′ is a linear, branched or cyclic alkyl having 1 to 10 carbon atoms, phenyl, ortho or para-nitrophenyl, dinitrophenyl, pyridyl or nitropyridyl;

R a , R b , R c , R d and R e , each independently, is H or a linear, branched or cyclic alkyl having 1 to 10 carbon atoms; and

C(═O)L is a reactive ester or thioester group.

11. The process of claim 10 , wherein the sulfonating agent is selected from chlorosulfonic acid or sulfur trioxide.

12. The process of claim 10 , wherein the sulfonating agent is chlorosulfonic acid.

13. The process of claim 10 , wherein the sulfur-bearing nucleophile is selected from hydrogen sulfide or a salt thereof, thiourea, thioacetic acid or 2-(tirmethylsilyl)ethanethiol.

14. The process of claim 13 , wherein the sulfur-bearing nucleophile is thiourea or thioacetic acid.

15. The process of claim 14 , wherein the reaction between the compound of formula (5) and a sulfur-bearing nucleophile is carried out in the presence of a base and/or a Lewis acid.

16. The process of claim 15 , wherein the deprotection of step b) is carried out in the presence of a base.

17. The process of claim 16 , wherein the disulfide compound is selected from the group consisting of 2,2′-dithiodipyridine, 4,4′-dithiodipyridine, 2,2-dithiobis(5-pyridine), 4-nitrophenyldisulfide, S-methyl methanethiosulfonate and dimethyl disulfide.

18. The process of claim 17 , wherein the disulfide compound is 2,2′-dithiodipyridine.

19. The process of claim 18 , wherein the hydroxy or mercapto compound is selected from the group consisting of N-hydroxysuccinimide, N-hydroxy sulfo-succinimide, tetrafluorophenol, nitrophenol, dinitrophenol and thiopyridine.

20. The process of claim 19 , wherein the hydroxyl or mercapto compound is N-hydroxysuccinimide.

21. The process of claim 20 , wherein the reaction between the compound of formula (3) and the hydroxy or mercapto compound is carried out in the presence of a coupling agent.

22. The process of claim 21 , wherein the coupling agent is selected from N,N′-dicyclohexylcarbodiimide (DCC), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), N,N′-diisopropyl carbodiimide (DIC) and 1-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ).

23. The process of claim 22 , wherein the coupling agent is EDC.

24. The process of claim 23 , wherein R a , R b , R c , R d and R e are all H.

25. A process for the preparation of a compound of formula (3):

or a salt thereof, comprising the step of:

a) reacting a thiolactone of formula (7):

with a sulfonating agent to form a compound of formula (8):

or a salt thereof;

b) hydrolyzing the compound of formula (8) or a salt thereof to a compound of formula (6)

or a salt thereof;

c) reacting the compound of formula (6) or a salt thereof with a disulfide compound to form the compound of formula (3), wherein:

Q′ is a linear, branched or cyclic alkyl having 1 to 10 carbon atoms, phenyl, ortho or para-nitrophenyl, dinitrophenyl, pyridyl or nitropyridyl; and

R a , R b , R c , R d and R e , each independently, is H or a linear, branched or cyclic alkyl having 1 to 10 carbon atoms.

26. The process of claim 25 , wherein the sulfonating agent is selected from chlorosulfonic acid or sulfur trioxide.

27. The process of claim 25 , wherein the sulfonating agent is sulfur trioxide.

28. The process of claim 25 , wherein the hydrolysis reaction of step b) is carried out in the presence of a base.

29. The process of claim 28 , wherein the disulfide compound is selected from the group consisting of 2,2′-dithiodipyridine, 4,4′-dithiodipyridine, 2,2-dithiobis(5-pyridine), 4-nitrophenyldisulfide, S-methyl methanethiosulfonate and dimethyl disulfide.

30. The process of claim 29 , wherein the disulfide compound is 2,2′-dithiodipyridine.

31. A process for the preparation of a compound of formula (Ia):

or a salt thereof, comprising the steps of:

a) reacting a thiolactone of formula (7):

with a sulfonating agent to form a compound of formula (8):

or a salt thereof;

b) hydrolyzing the compound of formula (8) or a salt thereof to a compound of formula (6)

or a salt thereof;

c) reacting the compound of formula (6) or a salt thereof with a disulfide compound to form a compound of formula (3),

or a salt thereof,

d) reacting the compound of formula (3) with a hydroxy or mercapto compound to form the compound of formula (Ia) or a salt thereof, wherein:

Q′ is a linear, branched or cyclic alkyl having 1 to 10 carbon atoms, phenyl, ortho or para-nitrophenyl, dinitrophenyl, pyridyl or nitropyridyl;

R a , R b , R c , R d and R e , each independently, is H or a linear, branched or cyclic alkyl having 1 to 10 carbon atoms; and

C(═O)L is a reactive ester or thioester group.

32. The process of claim 31 , wherein the sulfonating agent is selected from chlorosulfonic acid or sulfur trioxide.

33. The process of claim 32 , wherein the sulfonating agent is sulfur trioxide.

34. The process of claim 33 , wherein the hydrolysis reaction of step b) is carried out in the presence of a base.

35. The process of claim 34 , wherein the disulfide compound is selected from the group consisting of 2,2′-dithiodipyridine, 4,4′-dithiodipyridine, 2,2-dithiobis(5-pyridine), 4-nitrophenyldisulfide, S-methyl methanethiosulfonate and dimethyl disulfide.

36. The process of claim 35 , wherein the disulfide compound is 2,2′-dithiodipyridine.

37. The process of claim 36 , wherein the hydroxy or mercapto compound is selected from N-hydroxysuccinimide, N-hydroxy sulfo-succinimide, tetrafluorophenol, nitrophenol, dinitrophenol and thiopyridine.

38. The process of claim 37 , wherein the hydroxyl or mercapto compound is N-hydroxysuccinimide.

39. The process of claim 38 , wherein the reaction between the compound of formula (3) and the hydroxy or mercapto compound is carried out in the presence of a coupling agent.

40. The process of claim 39 , wherein the coupling agent is selected from N,N′-dicyclohexylcarbodiimide (DCC), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), N,N′-diisopropyl carbodiimide (DIC) and 1-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ).

41. The process of claim 39 , wherein the coupling agent is EDC.

42. The process of claim 41 , wherein R a , R b , R c , R d and R e are all H.