Process for preparing diaminophenothiazinium compounds

1. A process for preparing a compound corresponding to formula (I) below:

in which each of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 and R 10 is chosen, independently of the others, from the group constituted of:

a hydrogen atom,

saturated or unsaturated, linear or branched C 1 -C 6 alkyl groups, or C 3 -C 6 cycloalkyl groups, optionally substituted with one or more functions chosen from a halogen atom, and a C 1 -C 6 alkoxy, C 1 -C 6 alkoxycarbonyl or —CONH 2 function,

aryl groups optionally substituted with one or more functions chosen from: a C 1 -C 4 alkyl, a halogen atom, and a C 1 -C 6 alkoxy, C 1 -C 6 alkyloxycarbonyl or —CONH 2 function,

X − represents an organic or inorganic anion,

wherein the process comprises at least one step during which a compound of formula (II):

in which R represents a group chosen from:

a phenyl or benzyl group, optionally substituted with one or more functions chosen from: a C 1 -C 4 alkyl, a halogen atom, a C 1 -C 4 haloalkyl and a nitro group,

a phenyloxy or benzyloxy group optionally substituted on the aromatic nucleus with one or more functions chosen from: a C 1 -C 4 alkyl, a halogen atom, a C 1 -C 4 haloalkyl and a nitro group,

Z represents an atom chosen from O and S,

is subjected to a purification step, and thereafter reacting that compound of formula (II) with a quinone to produce the compound of formula (I), and wherein the reaction of compound (II) with a quinone to produce compound (I) is achieved in a one-pot process step.

2. The process as claimed in claim 1 , in which R 1 , R 2 , R 3 , R 4 , R 5 and R 6 , which may be identical or different, are chosen from a hydrogen atom and a C 1 -C 4 alkyl.

3. The process as claimed in claim 1 , in which one or more of the following requirements are met:

R 5 , R 8 , R 9 and R 10 represent H,

X represents Cl or OH,

R 1 , R 2 , R 3 and R 4 , which may be identical or different, are chosen from a hydrogen atom and methyl,

R 6 represents a hydrogen atom,

R 7 represents a hydrogen atom,

Z represents O.

4. The process as claimed in claim 1 , in which the compound of formula (I) is tetramethylthionine chloride.

5. The process as claimed in claim 1 , in which the compound of formula (I) is chosen from:

dimethylthionine chloride or Azure A,

trimethylthionine chloride or Azure B,

monomethylthionine chloride or Azure C.

6. The process as claimed in claim 1 , in which the purification step comprises at least one filtration through a support capable of retaining metal compounds.

7. The process as claimed in claim 6 , in which the filtration support is chosen from: a silica gel, a neutral, basic or acidic alumina gel, an optionally modified diatomite, celite, a microporous membrane, a resin grafted with metal-capturing groups, and fibers grafted with metal-capturing groups.

8. The process as claimed in claim 6 , in which, for the filtration, the compound of formula (II) is solubilized in a solvent chosen from chlorinated solvents, alcohols, acetonitrile, ethyl acetate or tetrahydrofuran, or a mixture of these solvents.

9. The process as claimed in claim 1 , wherein the quinone is 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.

10. The process as claimed in claim 1 , which also comprises a step for ion exchange, by treatment with HCl.