U.S. patent application number 16/884107 was filed with the patent office on 2020-09-10 for process for preparing indigo carmine.
This patent application is currently assigned to PROVEPHARM LIFE SOLUTIONS. The applicant listed for this patent is PROVEPHARM LIFE SOLUTIONS. Invention is credited to Michel FERAUD, Nicolas LOPEZ, Stephane QUERU, Babak SAYAH.
Application Number | 20200283632 16/884107 |
Document ID | / |
Family ID | 1000004856886 |
Filed Date | 2020-09-10 |
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United States Patent
Application |
20200283632 |
Kind Code |
A1 |
SAYAH; Babak ; et
al. |
September 10, 2020 |
PROCESS FOR PREPARING INDIGO CARMINE
Abstract
Process for preparing disodium 5,5'-indigosulfonate, the
feedstock being indigo, this process including the following steps:
i) the indigo is subjected to a sulfonation treatment resulting in
a mixture that contains 5,5'-indigosulfonic acid, this process
including: ii) a reduction treatment is applied to the mixture
obtained in step i), and optionally a purification step, so as to
obtain a composition including leuco-5,5'-indigosulfonic acid, iii)
the leuco-5,5'-indigosulfonic acid is isolated from the composition
resulting from step ii), iv) the leuco-5,5'-indigosulfonic acid
resulting from step iii) is oxidized to give disodium
5,5'-indigosulfonate.
Inventors: |
SAYAH; Babak; (Marseille,
FR) ; QUERU; Stephane; (Marseille, FR) ;
FERAUD; Michel; (Marseille, FR) ; LOPEZ; Nicolas;
(Marseille, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PROVEPHARM LIFE SOLUTIONS |
Marseille |
|
FR |
|
|
Assignee: |
PROVEPHARM LIFE SOLUTIONS
Marseille
FR
|
Family ID: |
1000004856886 |
Appl. No.: |
16/884107 |
Filed: |
May 27, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16465040 |
May 29, 2019 |
|
|
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PCT/FR2017/053260 |
Nov 27, 2017 |
|
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16884107 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09B 7/02 20130101; A23V
2002/00 20130101; A61K 47/22 20130101; A23L 5/47 20160801; C09B
67/0096 20130101 |
International
Class: |
C09B 7/02 20060101
C09B007/02; A23L 5/47 20060101 A23L005/47; A61K 47/22 20060101
A61K047/22; C09B 67/54 20060101 C09B067/54 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 2016 |
FR |
1661784 |
Claims
1. A composition comprising at least 99.5% of disodium
5,5'-indigosulfonate, the percentage being measured by
high-pressure liquid chromatography with detection at 290 nm.
2. The composition as claimed in claim 1 comprising at least 99.7%
of disodium 5,5'-indigosulfonate, the percentage being measured by
high-pressure liquid chromatography with detection at 290 nm.
3. The composition as claimed in claim 1 in which no impurity is
present in an amount of greater than 0.10%, the percentage being
measured by high-pressure liquid chromatography with detection at
290 nm.
4. The composition as claimed in claim 3 in which no impurity is
present in an amount of greater than 0.05%, the percentage being
measured by high-pressure liquid chromatography with detection at
290 nm.
5. A medicament or a diagnostic product comprising the composition
as claimed in claim 1 and a pharmaceutically acceptable
support.
6. The medicament or diagnostic product as claimed in claim 5,
which is in the form of a tablet or a gel capsule comprising from 1
to 1000 mg of the disodium 5,5'-indigosulfonate.
7. The medicament or diagnostic product as claimed in claim 5,
which is in the form of an aqueous solution comprising the disodium
5,5'-indigosulfonate in a concentration ranging from 0.1% to 10% by
mass.
8. A food composition comprising the composition as claimed in
claim 1 and a support that is compatible with a food
application.
9. The food composition as claimed in claim 8, which is in powder
form.
10. The food composition as claimed in claim 8, which is in aqueous
solution form.
11. The composition as claimed in claim 1, wherein the disodium
5,5'-indigosulfonate is obtained by a process comprising the
following steps, the starting material being indigo: i) indigo is
subjected to a sulfonation treatment leading to a mixture which
contains 5,5'-indigosulfonic acid, ii) the mixture obtained in step
i) is subjected to a reduction treatment, and optionally a
purification step, so as to obtain a composition comprising
leuco-5,5'-indigosulfonic acid, iii) the leuco-5,5'-indigosulfonic
acid is isolated from the composition derived from step ii), and
iv) the leuco-5,5'-indigosulfonic acid obtained from step iii) is
oxidized to disodium 5,5'-indigosulfonate.
12. The composition as claimed in claim 11, in which the reduction
treatment of step ii) is performed using sodium dithionite in
aqueous medium.
13. The composition as claimed in claim 11, in which the
leuco-5,5'-indigosulfonic acid precipitates in the reaction medium
on conclusion of step ii).
14. The composition as claimed in claim 11, in which step iii)
includes the steps of: iiia) filtration of the composition obtained
from step ii), and iiib) recovery of the solid retained on the
filter.
15. The composition as claimed in claim 14, in which step iii) also
includes, after step iiib), at least one step iiic) consisting of
washing the solid with an aqueous medium.
16. The composition as claimed in claim 15, in which step iiic) is
applied from one to five times.
17. The composition as claimed in claim 11, in which the
composition obtained on conclusion of step iii) includes at least
90 mol % of leuco-5,5'-indigosulfonic acid relative to the total
number of moles of the composition.
18. The composition as claimed in claim 11, in which step iv)
includes at least one step iva) consisting of a treatment with a
base in alcoholic medium in the presence of an oxidizing agent.
19. The composition as claimed in claim 18, in which step iva)
consists of a treatment with sodium ethoxide in ethanol, in the
presence of an oxidizing agent.
20. The composition as claimed in claim 18, in which the oxidizing
agent is gaseous oxygen.
21. The composition as claimed in claim 18, which also includes,
after step iva), at least one step ivb) consisting of one or more
washes with one or more alcoholic and/or aqueous-alcoholic
solvents.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a Continuation of application Ser. No. 16/465,040
filed May 29, 2019, which in turn is a national stage entry of
PCT/FR2017/053260 filed Nov. 27, 2017, which claims priority to FR
1661784 filed Dec. 1, 2016. The disclosure of the prior
applications is hereby incorporated by reference herein in its
entirety.
[0002] The present invention relates to a novel process for
preparing the indigo carmine molecule, this process making it
possible to achieve a high degree of purity, while at the same time
being very simple to perform and having high yields.
PRIOR ART
[0003] Indigo carmine, also known under the names disodium
5,5'-indigosulfonate and disodium
3,3'-dioxo-2,2'-bis(indolidene)-5,5'-disulfonate (CAS number
860-22-0), is known for its uses as a dye, in the food,
pharmaceutical and cosmetics fields, but also in the fields of
printing and photography (R. W. Sabnis, Handbook of Biological Dyes
and Stains, 2010, Wiley and Sons, page 239). In the food sector,
indigo carmine is the subject of specifications which are reported
in EFSA Journal 2014; 12(7): 3768. In the pharmaceutical sector, it
is used notably for dying tissues, for the detection of certain
tumoral cells. Disodium 5,5'-indigosulfonate is generally obtained
from indigo or
2-(1,3-dihydro-3-oxo-2H-indol-2-ylidene)-1,2-dihydro-3H-indol-3-one
(CAS number: 482-89-3), according to a reaction summarized in
scheme 1 below:
##STR00001##
[0004] However, in the course of this reaction, other compounds are
usually formed that are mono-, di-, tri- or tetrasulfonated,
predominantly in positions 5, 5', 7, 7'.
##STR00002##
Disodium 5,5'-indigosulfonate
[0005] The disulfonated isomers are present in large amounts, and
their physicochemical properties are very similar to those of
indigo carmine. The structural similarity of the disulfonated
molecules makes them difficult to separate. The presence of
disulfonated isomers has the drawback, for medical or diagnostic
applications, of introducing undesired contaminants into the
patient's body. Sung-Hoon Kim et al., Korean J. Anesthesiol. 2011
November; 61(5): 435-438 have described cases of hypotension in the
case of patients to whom an indigo carmine containing impurities
had been administered. These side effects were attributed to the
impurities.
[0006] The object of the invention was thus to develop a process
for preparing disodium 5,5'-indigosulfonate that is substantially
free of impurities, and notably of disulfonated impurities. It was
sought to develop a process which gives access to a disodium
5,5'-indigosulfonate which complies with the EFSA requirements in
the food sector and with the standard ICH in the pharmaceutical
sector (International conference on harmonisation of technical
requirements for registration of pharmaceuticals for human use; ICH
harmonised tripartite guideline--Impurities in new drug
substances--Q3A(R2); Step 4 version; 25 Oct. 2006). The ICH
standard specifies that an active principle should not contain
unidentified impurities in a content of greater than or equal to
0.10% relative to the active principle. It was sought to develop a
process that is rapid, inexpensive, efficient, with high yields,
and readily extrapolable to the industrial scale.
SUMMARY OF THE INVENTION
[0007] The invention relates to a process for preparing disodium
5,5'-indigosulfonate, the starting material being indigo, this
process comprising the following steps:
[0008] i) indigo is subjected to a sulfonation treatment leading to
a mixture which contains 5,5'-indigosulfonic acid,
[0009] this process being characterized in that:
[0010] ii) the mixture obtained in step i) is subjected to a
reduction treatment, and optionally a purification step, so as to
obtain a composition comprising leuco-5,5'-indigosulfonic acid,
[0011] iii) the leuco-5,5'-indigosulfonic acid is isolated from the
composition derived from step ii),
[0012] iv) the leuco-5,5'-indigosulfonic acid derived from step
iii) is oxidized to disodium 5,5'-indigosulfonate.
[0013] According to a preferred embodiment, the reduction treatment
of step i) is performed using sodium dithionite in aqueous
medium.
[0014] According to a preferred embodiment, the
leuco-5,5'-indigosulfonic acid precipitates from the reaction
medium on conclusion of step ii).
[0015] According to a preferred embodiment, step iii) includes at
least one step consisting in:
[0016] iiia) filtration of the composition derived from step
ii),
[0017] iiib) recovery of the solid retained on the filter.
[0018] Advantageously, step iii) also includes, after step iiib),
at least one step iiic) consisting in washing the solid with an
aqueous medium.
[0019] More advantageously, step iiic) is applied from one to five
times.
[0020] According to a preferred embodiment, the composition
obtained on conclusion of step iii) includes at least 90 mol % of
leuco-5,5'-indigosulfonic acid relative to the total number of
moles of the composition.
[0021] According to a preferred embodiment, step iv) includes at
least one step iva) consisting of a treatment with a base in
alcoholic medium in the presence of an oxidizing agent.
[0022] Advantageously, step iva) consists of a treatment with
sodium ethoxide in ethanol, in the presence of an oxidizing
agent.
[0023] Advantageously, the oxidizing agent is gaseous oxygen.
[0024] According to a preferred embodiment, the process also
includes, after step iva), at least one step ivb) consisting of one
or more washes with one or more alcoholic and/or aqueous-alcoholic
solvents.
[0025] The invention also relates to the use of the process defined
above for producing a composition comprising at least 99.5% of
disodium 5,5'-indigosulfonate, the percentage being measured by
high-pressure liquid chromatography with detection at 290 nm.
[0026] The invention also relates to the use of the process as
defined above for producing a composition in which no impurity is
present in an amount of greater than 0.10%, the percentage being
measured by high-pressure liquid chromatography with detection at
290 nm.
[0027] The invention also relates to a process for manufacturing a
medicament or a diagnostic product comprising disodium
5,5'-indigosulfonate, this process comprising the manufacture of
disodium 5,5'-indigosulfonate via the process described above and
detailed below, and the introduction of the disodium
5,5'-indigosulfonate into a pharmaceutically acceptable
support.
[0028] The invention also relates to a process for manufacturing a
food composition comprising disodium 5,5'-indigosulfonate, this
process comprising the manufacture of disodium 5,5'-indigosulfonate
via the process described above and detailed below, and the
introduction of the disodium 5,5'-indigosulfonate into a support
that is compatible with a food application.
[0029] For example, the latter process may concern the manufacture
of a food coloring composition, or of a colored food
composition.
[0030] The inventors have observed, surprisingly, that
leuco-5,5'-indigosulfonic acid could be readily separated from its
disulfonated isomers, obtained by sulfonation of indigo and
application of a reduction treatment, whereas mixtures of
5,5'-indigosulfonic acid and its disulfonated isomers, in acid form
or in disodium salt form, are difficult to separate.
##STR00003##
[0031] Specifically, the reduction was performed in a reaction
medium in which leuco-5,5'-indigosulfonic acid is sparingly
soluble, whereas its contaminants, notably its disulfonated
isomers, are soluble in this medium.
[0032] Proceeding via these intermediate products in reduced form
thus allows efficient separation, with high yields.
Leuco-5,5'-indigosulfonic acid is thus recovered. The isolated
product may then be subjected to an oxidation treatment so as to
form a disodium 5,5'-indigosulfonate having a high level of
purity.
DETAILED DESCRIPTION
Step i): Sulfonation of Indigo
[0033] The starting material is indigo or
2-(1,3-dihydro-3-oxo-2H-indole-2-ylidene)-1,2-dihydro-3H-indole-3-one
(CAS: 482-89-3). Indigo is subjected to a sulfonation treatment
according to scheme 2 below:
##STR00004##
[0034] This known reaction is usually performed by treatment with
sulfuric acid. Reference may be made, for example, to the following
publications: US-647280; Tudora Baltac et al., Revista de Chimie
(Bucharest, Romania) (2012), 63(6), 618-620; Iqbal T. Shadi et al.,
Chemical Communications (Cambridge, United Kingdom) (2004), (12),
1436-1437; Capron, F. (1863), Blues and carmines of indigo: a
practical treatise on the fabrication of every commercial product
derived from indigo; Philadelphia: H. C. Baird
(https://catalog.hathitrust.org/Record/006218585); Vanessa Bianda
et al., Bulgarian Journal of Science Education, Volume 22, Number
1, 2013; Charles E. Carraher et al., Journal of Macromolecular
Science, Volume 15, Issue 5 1981, pages 773-785; R. W. Sabnis,
Handbook of Biological Dyes and Stains, 2010, Wiley and Sons, page
239.
[0035] However, the process of the invention is not limited to the
product of this reaction and can be applied to any composition
comprising 5,5'-indigosulfonic acid and disulfonated isomers of
5,5'-indigosulfonic acid, irrespective of the process for obtaining
them.
[0036] When the starting composition is derived from the
sulfonation of indigo, it may also comprise, in addition to
5,5'-indigosulfonic acid and disulfonated isomers: indigo,
monosulfonated, trisulfonated, tetrasulfonated derivatives, and
also side products of this reaction. However, usually, these other
derivatives are removed by means of a known method, for instance
high-pressure liquid chromatography (HPLC).
[0037] When the starting composition is derived from the
sulfonation of indigo, it comprises approximately from 60% to 95%
of 5,5'-indigosulfonic acid and from 5 to 40% of disulfonated
isomers, preferably from 75 to 80% of 5,5'-indigosulfonic acid and
from 20 to 25% of disulfonated isomers, the percentages being given
as number of moles relative to the sum of the numbers of moles of
all of the disulfonated molecules. However, the process of the
invention may be applied to a composition comprising a mixture of
isomers in all proportions.
[0038] Advantageously, for implementation in the process of the
invention, use is made of a starting composition in which
5,5'-indigosulfonic acid and its disulfonated isomers represent at
least 90 mol % relative to the total number of moles of the
starting composition, even more advantageously at least 95%, and
better still at least 98%.
[0039] The term "disulfonated isomers" of 5,5'-indigosulfonic acid
means any molecule having the structure of indigo, or
2-(1,3-dihydro-3-oxo-2H-indol-2-ylidene)-1,2-dihydro-3H-indol-3-one,
bearing a substitution with a sulfonic acid or sulfonate function
on each of the indole groups. 5,7'-indigosulfonic acid is an
example of a disulfonated isomer of 5,5'-indigosulfonic acid.
Step ii): Reduction of the Mixture Derived from Step i)
[0040] In a first step, the mixture derived from step i) comprising
5,5'-indigosulfonic acid is subjected to a reduction treatment
leading to a mixture of leuco-5,5'-indigosulfonic acid and other
compounds.
[0041] Advantageously, this reduction treatment is performed using
sodium dithionite as reducing reagent. Alternatively, use may be
made of one or other of the following reducing agents: a mixture of
arsenic sesquisulfide and of sodium hydrogen sulfite, iron(II)
sulfate, zinc, or a reduction by electrolysis may be performed.
[0042] Preferably, the reduction treatment is performed in aqueous
medium.
[0043] Advantageously, the reduction treatment is performed by
applying heating at a temperature ranging from 40 to 60.degree. C.,
advantageously from 45 to 55.degree. C.
[0044] Preferably, the total duration of the treatment is from 30
minutes to 6 hours, advantageously from 1 hour to 4 hours.
[0045] Preferably, after the reduction treatment, the composition
obtained is purified under conditions making it possible to
increase the content of leuco-5,5'-indigosulfonic acid. Notably,
the medium is extracted with an organic solvent so as to remove
certain contaminants, for instance the reduced indigo. The
extraction may be performed with ethyl acetate, or with any other
solvent that is suitable for extracting non-sulfonated
components.
Step iii): Separation of the leuco-5,5'-indigosulfonic Acid
[0046] In a second step, the leuco-5,5'-indigosulfonic acid is
separated from the reaction medium. Advantageously, the
leuco-5,5'-indigosulfonic acid is separated from the reaction
medium by precipitation of the leuco-5,5'-indigosulfonic acid,
followed by filtration and recovery of the solid.
[0047] Preferably, step ii) was performed in a solvent in which the
isomer leuco-5,5'-indigosulfonic acid precipitates. Preferably, the
isomer leuco-5,5'-indigosulfonic acid is separated from an aqueous
composition comprising it. Advantageously, the separation is
performed directly in the reaction medium derived from step ii),
optionally after a first purification, for instance extraction
using an organic solvent. Preferably, the leuco-5,5'-indigosulfonic
acid precipitates in the reaction medium on conclusion of step
ii).
[0048] Alternatively, if the reaction of step ii) was performed in
a medium in which leuco-5,5'-indigosulfonic acid is soluble, an
addition of water to the reaction medium, or a solvent exchange,
may then be performed so as to precipitate the
leuco-5,5'-indigosulfonic acid.
[0049] Preferably, the separation is performed by passing the
reaction medium derived from step ii) through a filtration support.
For example, the reaction medium derived from step ii) may be
filtered through a filter such as a porosity 3 filter funnel or a
multifilament polypropylene filtering gauze. Advantageously, the
reaction medium derived from step ii) is hot-filtered, preferably
at a temperature ranging from 40 to 60.degree. C., advantageously
from 45 to 55.degree. C.
[0050] Under these conditions, the isomer leuco-5,5'-indigosulfonic
acid, which is solid, is retained by the filter, whereas the other
components of the reaction medium, which are soluble in the
reaction medium from step ii), are entrained in the aqueous phase
during the filtration.
[0051] Advantageously, this filtration may be completed with a
treatment consisting in slurrying the solid in an organic solvent,
for example THF, and filtering the paste thus formed. This
slurrying makes it possible to improve the degree of purity of the
leuco-5,5'-indigosulfonic acid.
[0052] According to the invention, it is advantageously envisaged
to complete the leuco-5,5'-indigosulfonic acid separation step by
an additional purification such as washing with water, for example
by taking up the solid phase comprising the
leuco-5,5'-indigosulfonic acid in water, which is brought to a
temperature ranging from 40 to 60.degree. C., advantageously from
45 to 55.degree. C., and then filtering the suspension thus
prepared. The solid recovered on the filter is
leuco-5,5'-indigosulfonic acid. Its degree of purity is improved by
this additional purification step.
[0053] Advantageously, the operation of washing with water of the
leuco-5,5'-indigosulfonic acid is applied from one to five times,
even more advantageously from two to four times.
[0054] Advantageously, this washing may be completed with a
treatment consisting in slurrying the solid in an organic solvent,
for instance THF, and filtering the slurry thus formed. This
slurrying makes it possible to improve the degree of purity of the
leuco-5,5'-indigosulfonic acid.
[0055] Advantageously, the purification treatments are repeated
until a leuco-5,5'-indigosulfonic acid is obtained which has the
expected level of purity. Preferably, the purification treatments
are repeated until a composition comprising at least 99 mol % of
leuco-5,5'-indigosulfonic acid is obtained, relative to the number
of moles of the composition.
[0056] Leuco-5,5'-indigosulfonic acid is an essential intermediate
in performing the process of the invention.
[0057] Use may be made of other techniques, for instance
high-pressure liquid chromatography (HPLC), to separate the
leuco-5,5'-indigosulfonic acid from the reaction medium derived
from step ii). However, filtration has the advantage of being a
practical, efficient method that is very readily extrapolable to
the industrial scale.
Step iv): Oxidation of leuco-5,5'-indigosulfonic Acid
[0058] In a fourth step, leuco-5,5'-indigosulfonic acid is
transformed into disodium 5,5'-indigosulfonate via a suitable
oxidation treatment, according to scheme 3 below:
##STR00005##
[0059] Advantageously, this treatment consists of a treatment with
a base in alcoholic medium in the presence of an oxidizing agent.
Preferably, the leuco-5,5'-indigosulfonic acid is treated with
sodium alkoxide in alcohol medium and in the presence of an
oxidizing agent.
[0060] Preferably, the leuco-5,5'-indigosulfonic acid is treated
with sodium ethoxide in ethanol medium in the presence of an
oxidizing agent. Preferably, the treatment is performed hot,
advantageously at a temperature ranging from 40 to 60.degree. C.,
even more advantageously from 45 to 55.degree. C. Preferably, the
leuco-5,5'-indigosulfonic acid is treated with 0.5 to 2.5 molar
equivalents of sodium alkoxide, preferably 0.8 to 1.5 molar
equivalents of sodium alkoxide, in the presence of an oxidizing
agent. Even more preferentially, the leuco-5,5'-indigosulfonic acid
is treated with 0.5 to 2.5 molar equivalents of sodium ethoxide,
preferably 0.8 to 1.5 molar equivalents of sodium ethoxide, in the
presence of an oxidizing agent. Advantageously, the oxidizing agent
is chosen from O.sub.2, H.sub.2O.sub.2, KHSO.sub.5, FeCl.sub.3.
[0061] Preferably, the oxidizing agent is gaseous oxygen, which may
be used pure or as a mixture with other gases, for instance
atmospheric oxygen. Preferably, the duration of the treatment is
from 30 minutes to 10 hours, even more preferentially from 1 hour
to 8 hours and advantageously from 2 hours to 6 hours.
[0062] Preferably, the treatment of step iv) is followed by one or
more washes with one or more organic solvents. Preferably, the
treatment of step iv) is followed by one or more washes with one or
more alcoholic and/or aqueous-alcoholic solvents, notably washing
with ethanol and/or washing with methanol and/or washing with a
mixture of water and methanol and/or washing with a mixture of
water and ethanol.
[0063] Uses:
[0064] A subject of the invention is also the use of the process
described above for producing an indigo carmine or disodium
5,5'-indigosulfonate with a high level of purity. In particular,
the invention relates to the use of the process described above for
producing a composition comprising at least 99.5%, better still at
least 99.7%, of indigo carmine or disodium 5,5'-indigosulfonate.
For the evaluation of the amount of indigo carmine in the material
composition, the % is measured by high-pressure liquid
chromatography (HPLC) with detection at 290 nm, on a 150.times.4.6
5 .mu.m C18 column, eluting with a gradient of 10 mM sodium
phosphate buffer (pH 3.0)+1 mM TBACl/MeOH (70/30.fwdarw.10/90).
[0065] The invention relates to the use of the process described
above for producing a composition in which no impurity is present
in an amount of greater than 0.10%, better still no impurity is
present in an amount of greater than 0.05%. The evaluation of the
amount of impurities is performed by means of the same method as
that used for the evaluation of the amount of indigo carmine.
[0066] A subject of the invention is also the use of the process
described above for producing a medicament or a diagnostic product
comprising indigo carmine or disodium 5,5'-indigosulfonate. Said
medicament or diagnostic product may be in any form that is
suitable for its use in these applications. In particular, mention
may be made of: in the form of a tablet or a gel capsule comprising
from 1 to 1000 mg of indigo carmine; in the form of an aqueous
solution comprising indigo carmine in a concentration ranging from
0.1% to 10% by mass. Such compositions comprise, besides indigo
carmine, excipients that are well known to those skilled in the
art, for instance citric acid and/or citrates, a phosphate buffer,
polymers, cellulose derivatives, lipids. Formulations comprising
indigo carmine are illustrated notably in WO 2011/107945 and in WO
2010/018723. In the medical and diagnostic applications, the indigo
carmine obtained via the process of the invention has the advantage
of high purity, which avoids the introduction into the body of
materials that are not useful for the application.
[0067] A subject of the invention is also the use of the process
described above for producing a food coloring comprising indigo
carmine or disodium 5,5'-indigosulfonate. Said food coloring may be
in any form that is suitable for its use in these applications,
notably in powder or aqueous solution form. The high level of
purity of the indigo carmine obtained via the process of the
invention makes it possible to ensure its harmlessness.
[0068] The efficiency of the process of the invention affords
access to a product with reduced costs.
EXPERIMENTAL SECTION
I--Materials and Methods
1--Starting Materials and Equipment
[0069] Indigo was purchased from the company Fisher Scientific
under the commercial reference 21213. Purity: 94.8% according to
the supplier's specifications.
[0070] Gauze (filtration): commercial reference V-05-6-475 K
available from the company SEFAR.
[0071] Nutsche filter: 280 mm diameter, 35 L, available from the
company BUCHI.
2--Analytical Methods
[0072] Machine: Agilent 1100.RTM.
[0073] Column: KROMASIL C18.RTM. 150.times.4.6-5 .mu.m
[0074] Detection: at 290 nm
[0075] Concentration of the sample: 1000 ppm
[0076] Solvent for dissolving the sample: 90/10 H.sub.2O/MeOH
[0077] Elution solvent: 10 mM sodium phosphate buffer (pH 3.0)+1 mM
TBACl/MeOH
II--Protocols
1--Transformation of Indigo into 5,5'-indigosulfonic Acid
[0078] 1.5 kg of indigo (5.72 mol) are placed in a 10 liter
reactor, to which are added, with stirring, and at room
temperature, 6 liters of aqueous H.sub.2SO.sub.4 solution of 96%
concentration. The mixture is maintained at 70.degree. C. for 3
hours, with continued stirring. The mixture is then cooled to
5.degree. C. The mixture is added slowly to a 60 liter reactor
containing 15 liters of water cooled to 5.degree. C. The addition
of the mixture is performed over 1 hour 15 minutes. 90 ml of
octanol are added to the mixture and the resulting mixture is
brought to 50.degree. C. A solid in suspension in the reaction
medium is obtained, which is a mixture comprising
5,5'-indigosulfonic acid.
2--Reduction of the Mixture Comprising 5,5'-indigosulfonic Acid
[0079] An aqueous sodium dithionite solution is prepared from 15
liters of water and 3.51 kg of 85% sodium dithionite solution. The
aqueous solution thus prepared is placed in a dropping funnel under
nitrogen. The aqueous sodium dithionite solution is added to the
reaction mixture obtained from step 1-, with stirring, while
maintaining the medium at 50.degree. C. The addition of the aqueous
sodium dithionite solution is performed over 1 hour. The mixture is
then kept stirring at 50.degree. C. for about 1 hour. 7.5 liters of
ethyl acetate are then added to the mixture, and the resulting
mixture is stirred at 50.degree. C. for 20 minutes. The medium is
still in the form of a suspension comprising
leuco-5,5'-indigosulfonic acid.
3--Separation of the leuco-5,5'-indigosulfonic Acid
[0080] The reaction medium derived from step 2--is then filtered
through a Nutsche filter, equipped with a V-05-6-475 K gauze.
[0081] The solid remaining on the filter is slurried with 4.5
liters of tetrahydrofuran (THF) and the liquid is then
filtered.
4--Washing of the leuco-5,5'-indigosulfonic Acid
[0082] The product remaining on the filter on conclusion of step
3--is taken up in 30 liters of water, in a 60 liter reactor. The
whole is heated at 50.degree. C. for 30 minutes and then filtered
through the Nutsche filter, equipped with a V-05-6-475 K gauze.
[0083] The solid remaining on the filter is slurried with 4.5
liters of tetrahydrofuran (THF) and the liquid is then
filtered.
[0084] This washing is repeated so as to arrive at a total of three
washes under the same conditions. 1.8 kg of a wet product are
obtained. Estimated dry mass: 1.3 kg.
5--Transformation of the Disodium leuco-5,5'-indigosulfonate Acid
into Disodium 5,5'-indigosulfonate
[0085] The 1.8 kg of product obtained in step 4--are suspended in
26 liters of ethanol in a 60 liter reactor. 1143 ml of a solution
containing 21% by mass of sodium ethoxide (NaOEt) in ethanol are
added. The mixture is brought to 50.degree. C. and air is sparged
into the reaction medium over 4 hours, while maintaining it at
50.degree. C.
[0086] At the end of this period, the reaction medium is filtered
through a sinter funnel, the filtration being followed by washing
with 5.2 liters of ethanol.
6--Washing of the Disodium 5,5'-indigosulfonate
[0087] The wet solid is taken up in 26 liters of methanol, the
whole is heated for 30 minutes at 40.degree. C. and then filtered
through a sinter funnel, the filtration being followed by washing
with 5.2 liters of methanol.
[0088] This washing is repeated once.
[0089] Next, the wet solid is taken up in a mixture of 13 liters of
water and 13 liters of methanol, the whole is heated for 30 minutes
at 60.degree. C. and then filtered through a sinter funnel, the
filtration being followed by washing with 3.9 liters of
methanol.
[0090] The solid is dried in a ventilated oven.
[0091] 1.05 kg of disodium 5,5'-indigosulfonate are obtained, the
yield is 39% relative to the total amount of indigo engaged in the
process.
III--Results
[0092] The product obtained is analyzed by HPLC by means of the
method described above. The purity is evaluated as being from
99.85% to 99.95%, as a function of the tests (three tests
performed).
[0093] It is found that the process of the invention makes it
possible to obtain a product of high purity, with good yields, by
applying a simple, inexpensive protocol that is easily extrapolable
to large scale, and with results that are reproducible from the
point of view of the quality (purity) of the product obtained.
* * * * *
References