Process for the synthesis of 4,5,6,7-tetrachloro-3′,6′-dihydroxy-2′, 4′, 5′7′-tetraiodo-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one (Rose Bengal) and related xanthenes
View Patent ↗A new process for the manufacture of iodinated xanthenes in high purity includes a cyclization step followed by an iodination step. No extraction, chromatographic or solvent concentration steps are required, and the intermediate as well as final compounds are isolated via filtration or similar means. The process requires a single organic solvent, and the steps are completed at temperatures below 100° C. The exclusion of chloride ions, of chloride free-radicals, hypochlorite ions, or hypochlorous acid as reagents or from reagents that may generate these species in situ in the presence of oxidants, prevents undesirable impurity formation. Several new compounds have been conceived and isolated using these methods. These new compounds are also formed into new medicaments.
1. A process for the preparation of a compound of Formula 4:
wherein R 1 is independently Cl or Br, R 2 , R 3 , R 4 and R 5 are I, R 6 is H, and R 11 and R 12 are independently H or a counter-ion capable of forming a pharmaceutically acceptable salt, comprising:
a) combining a compound of Formula 1a,
wherein R 1 is independently Cl or Br, with about two equivalents of a compound of Formula 2,
wherein R 7 , R 8 , R 9 and R 10 are H, in an acidic solution substantially free of chloride ions and substantially free of chloride-ion producing impurities, to form an intermediate compound of Formula 3a,
wherein R 1 is independently Cl or Br and R 2 , R 3 , R 4 , R 5 and R 6 are H;
b) combining the intermediate compound of Formula 3a with at least 4 equivalents of iodine in a solution substantially free of chloride ions and substantially free of chloride-producing impurities to form the compound of Formula 4 substantially free of transhalogenated impurities of the compound of Formula 4 wherein R 1 is independently Cl or Br; at least one of R 2 , R 3 , R 4 and R 5 is Cl and the remainder are I; R 6 is H; and R 11 and R 12 are independently H, Na, K, Li, or a counter-ion capable of forming a pharmaceutically acceptable salt.
2. The process of claim 1 wherein a transhalogenated impurity of the compound of Formula 4 comprises less than 0.15 percent by weight.
3. The process of claim 1 wherein the transhalogenated impurities comprise at least one compound selected from the group consisting of:
2′,4,5,6,7-pentachloro-3′,6′-dihydroxy-4′,5′,7′-triiodo-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one; 4,4′,5,6,7-pentachloro-3′,6′-dihydroxy-2′,5′,7′-triiodo-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one; 2′,4,5,6,7,7′-hexachloro-3′,6′-dihydroxy-4′,5′-diiodo-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one; 4,4′,5,5′,6,7-hexachloro-3′,6′-dihydroxy-2′,7′-diiodo-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one; 2′,4,5,5′,6,7-hexachloro-3′,6′-dihydroxy-4′,7′-diiodo-3H-Spiro[isobenzofuran-1,9′-xanthen]-3-one;
an isomeric quinoid thereof; and mixtures thereof.
4. The process of claim 1 wherein the acidic solution comprises less than 1500 ppm chloride.
5. The process of claim 1 wherein the acidic solution comprises at least one acid selected from the group consisting of an alkyl sulfonic acid or aryl sulfonic acid with a melting point of less than 250° C., an alkyl carboxylic acid or aryl carboxylic acid with a melting point of less than 250° C., a non-chloride Br{acute over (ø)}nsted acid, a non-chloride Lewis Acid, a polymer bound preparation thereof, a salt thereof, an aqueous solution thereof, and mixtures thereof, alone or in combination with methanesulfonic acid.
6. The process of claim 1 wherein the acidic solution comprises at least one acid selected from the group consisting of p-toluenesulfonic acid, benzenesulfonic acid, sulfuric acid, trifluoromethanesulfonic acid, ethanesulfonic acid, acetic acid, propionic acid, trifluoroacetic acid, camphorsulfonic acid, a polymer bound preparation thereof, a salt thereof, an aqueous solution thereof, and mixtures thereof, alone or in combination with methanesulfonic acid.
7. The process of claim 1 wherein the acidic solution comprises methanesulfonic acid.
8. The process of claim 1 wherein the compounds of Formula 2 and Formula 1a are combined in a ratio in the range of 2.5:1 to 3.2:1.
9. The process of claim 1 further comprising heating the compounds of Formula 1a and Formula 2 in the acidic solution at a temperature in the range of 85° C. to 95° C. for a time period of 1 to 16 hours.
10. The process of claim 1 wherein the compound of Formula 1a is in a mixture with Formula 1
and the mixture is combined with two equivalents of the compound of Formula 2.
11. The process of claim 1 further comprising isolating the intermediate compound of Formula 3a.
12. The process of claim 11 wherein the isolating comprises suspension of the intermediate compound of Formula 3a, collection of the intermediate compound of Formula 3a, and rinsing the intermediate compound of Formula 3a with a substantially chloride-ion-free solvent.
13. The process of claim 12 wherein the solvent comprises a mixture of acetone and water heated to 60° C.
14. The process of claim 1 wherein the solution containing the intermediate compound of Formula 3a and iodine comprises less than 1500 ppm chloride.
15. The process of claim 1 further comprising heating the combined intermediate compound of Formula 3a and iodine in basic solution at a temperature in the range of 20° C. to 100° C. for a time period in the range of 1 to 24 hours.
16. The process of claim 15 further comprising heating the combined intermediate compound of Formula 3a and iodine in solution at a temperature in the range of 70° C. to 95° C. for a time period in the range of 1 to 24 hours.
17. The process of claim 1 wherein the solution comprises at least one base selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium bicarbonate, potassium bicarbonate, and mixtures thereof.
18. The process of claim 1 wherein the solution comprises sodium hydroxide at a concentration of 0.4 to 1.0 M.
19. The process of claim 1 further comprising adding at least one iodine-solubilizing agent to the solution comprising the intermediate compound of Formula 3a and iodine wherein the iodine-solubilizing agent is selected from the group consisting of potassium iodide, lithium iodide, sodium iodide, and mixtures thereof.
20. The process of claim 19 wherein the iodine-solubilizing agent comprises 1 to 2.5 equivalents of sodium iodide.
21. The process of claim 1 wherein iodine is generated in situ by adding to the solution an oxidizing agent and an iodide salt wherein the solution is substantially free of chloride ions, chloride-ion free radicals, hypochlorite, hypochlorous acid or mixtures thereof.
22. The process of claim 1 further comprising adding an iodine scavenger to the solution subsequent to the formation of the compound of Formula 4, wherein the scavenger is selected from the group consisting of sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate, potassium sulfite, sodium sulfite and mixtures thereof.
23. The process of claim 22 wherein the iodine scavenger is sodium sulfite.
24. The process of claim 23 wherein the addition of the iodine scavenger is performed at a temperature of 10° C. or lower.
25. The process of claim 1 wherein R 11 and R 12 are sodium.
26. A process for the preparation of a compound of Formula 3
wherein R 1 is independently Cl or Br, R 2 , R 3 , R 4 and R 5 are I and R 6 is H, comprising:
a) combining a compound of Formula 1a,
wherein R 1 is independently Cl or Br, with two equivalents of a compound of Formula 2,
wherein R 7 , R 8 , R 9 and R 10 are H, in an acidic solution at a temperature in the range of 20° C. to 250° C. to form a compound of Formula 3a;
b) isolating the intermediate compound of Formula 3a,
wherein R 1 is independently Cl or Br and R 2 , R 3 , R 4 , R 5 and R 6 are H;
c) combining the intermediate compound of Formula 3a with 4 equivalents of iodine in a solution substantially free of chloride ions and substantially free of chloride-ion-producing impurities at a temperature in the range of 20° C. to 100° C. to form the compound of Formula 3;
d) adding an iodine scavenger to the compound of Formula 3;
e) acidifying the compound of Formula 3 to a pH of less than 5 and cooling to a temperature of less than 10° C.; and
f) isolating the compound of Formula 3 substantially free of transhalogenated impurities wherein R 1 is independently Cl or Br, at least one of R 2 , R 3 , R 4 and R 5 is Cl and the remainder are I, and R 6 is H.
27. The process of claim 26 wherein a transhalogenated impurity of the compound of Formula 3 comprises less than 0.15 percent by weight.
28. The process of claim 26 wherein the transhalogenated impurities comprise at least one compound selected from the group consisting of:
2′,4,5,6,7-pentachloro-3′,6′-dihydroxy-4′,5′,7′-triiodo-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one; 4,4′,5,6,7-pentachloro-3′,6′-dihydroxy-2′,5′,7′-triiodo-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one; 2′,4,5,6,7,7′-hexachloro-3′,6′-dihydroxy-4′,5′-diiodo-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one; 4,4′,5,5′,6,7-hexachloro-3′,6′-dihydroxy-2′,7′-diiodo-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one; 2′,4,5,5′,6,7-hexachloro-3′,6′-dihydroxy-4′,7′-diiodo-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one;
an isomeric quinoid thereof; and mixtures thereof.
29. The process of claim 26 wherein the acidic solution comprises less than 1500 ppm chloride.
30. The process of claim 26 wherein the acidic solution comprises at least one acid selected from the group consisting of an alkyl sulfonic acid or aryl sulfonic acid with a melting point of less than 250° C., an alkyl carboxylic acid or aryl carboxylic acid with a melting point of less than 250° C., a non-chloride Br{acute over (ø)}nsted acid, a non-chloride Lewis Acid, a polymer bound preparation thereof, a salt thereof, an aqueous solution thereof, and mixtures thereof, alone or in combination with methanesulfonic acid.
31. The process of claim 26 wherein the acidic solution comprises at least one acid selected from the group consisting of p-toluenesulfonic acid, benzenesulfonic acid, sulfuric acid, trifluoromethanesulfonic acid, ethanesulfonic acid, acetic acid, propionic acid, trifluoroacetic acid, camphorsulfonic acid, a polymer bound preparation thereof, a salt thereof, an aqueous solution thereof, and mixtures thereof, alone or in combination with methanesulfonic acid.
32. The process of claim 26 wherein the acidic solution comprises methanesulfonic acid.
33. The process of claim 26 wherein the compounds of Formula 2 and Formula 1a are combined in a ratio in the range of 2.5:1 to 3.2:1.
34. The process of claim 26 further comprising heating the compounds of Formula 1a and Formula 2 in the acidic solution at a temperature in the range of 85° C. to 95° C. for a time period of 1 to 16 hours.
35. The process of claim 34 wherein the compound of Formula 1a is in a mixture with Formula 1
and the mixture is combined with two equivalents of the compound of Formula 2.
36. The process of claim 26 further comprising isolating the intermediate compound of Formula 3a.
37. The process of claim 36 wherein the isolating comprises suspension of the intermediate compound of Formula 3a, collection of the intermediate compound of Formula 3a, and rinsing the intermediate compound of Formula 3a with a substantially chloride-ion-free solvent.
38. The process of claim 37 wherein the solvent comprises a mixture of acetone and water heated to 60° C.
39. The process of claim 26 wherein the solution containing the intermediate compound of Formula 3a comprises less than 1500 ppm chloride.
40. The process of claim 26 further comprising heating the combined intermediate compound of Formula 3a and iodine in basic solution at a temperature in the range of 20° C. to 100° C. for a time period in the range of 1 to 24 hours.
41. The process of claim 40 further comprising heating the intermediate compound of Formula 3a and iodine in solution at a temperature in the range of 70° C. to 95° C. for a time period in the range of 1 to 24 hours.
42. The process of claim 26 wherein the solution of combined intermediate compound of Formula 3a and iodine comprises at least one base selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium bicarbonate, potassium bicarbonate, and mixtures thereof.
43. The process of claim 26 wherein the solution comprises sodium hydroxide at a concentration of 0.4 to 1.0 M.
44. The process of claim 26 further comprising adding at least one iodine-solubilizing agent to the solution comprising the combined intermediate compound of Formula 3a and iodine wherein the iodine-solubilizing agent is selected from the group consisting of potassium iodide, lithium iodide, sodium iodide, and mixtures thereof.
45. The process of claim 44 wherein the iodine-solubilizing agent comprises 1 to 2.5 equivalents of sodium iodide.
46. The process of claim 26 wherein iodine is generated in situ by adding to the solution containing the intermediate compound of Formula 3a an oxidizing agent and an iodide salt wherein the solution is substantially free of chloride ions, chloride-ion free radicals, hypochlorite, hypochlorous acid or mixtures thereof.
47. The process of claim 26 further comprising adding an iodine scavenger to the solution subsequent to the formation of the compound of Formula 3, wherein the scavenger is selected from the group consisting of sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate, potassium sulfite, sodium sulfite and mixtures thereof.
48. The process of claim 47 wherein the iodine scavenger is sodium sulfite.
49. The process of claim 48 wherein the addition of iodine scavenger is performed at a temperature of 10° C. or lower.
50. The process of claim 26 wherein acidifying comprises adding a chloride-ion-free acid to the solution containing Formula 3.
51. The process of claim 50 wherein the chloride-ion-free acid comprises sulfuric acid at a concentration of 1 percent to 5 percent, and where this sulfuric acid is added in sufficient quantity to adjust pH of the solution to be in the range of pH 2 to pH 5.
52. The process of claim 51 wherein the pH is adjusted to approximately 3.
53. The process of claim 26 wherein the isolating comprises suspending the compound of Formula 3 in a solvent selected from the group consisting of water, dimethylformamide, acetone and mixtures thereof; vacuum filtration; and rinsing the resultant filter cake with a solvent selected from the group consisting of water, dimethylformamide, acetone and mixtures thereof.
54. The process of claim 26 wherein said compound of Formula 3, in which R 1 is independently Cl or Br, R 2 , R 3 , R 4 , R 5 are I and R 6 is H, is converted to the quinoid form of Formula 4, wherein R 11 and R 12 are independently H or a counter-ion capable of forming a pharmaceutically acceptable salt
55. The process of claim 54 wherein R 11 and R 12 are sodium.