NOVEL METHOD OF EXTRACTION OF 6-O-PROTECTED TRICHLOROGALACTOSE FROM THE CHLORINATED MASS

NOUVEAU PROCEDE D'EXTRACTION DE TRICHLOROGALACTOSE 6-O-PROTEGE DE LA MASSE CHLOREE

English Abstract

A process is described for extraction of 6- acyl - 4,1~, 6~
trichlorogalactosucrose abbreviated as TGS-6-ester from a process stream
containing one or more of TGS-6-ester and impurities including DMF, requiring
DMF removal, comprising neutralization of the process stream, adjustment of pH
thereafter to acidic side, preferably between 5 to 7, followed by extraction
with a partially miscible or immiscible organic solvent, optional
concentration of the organic solvent extract, extraction of the organic
solvent extracts with saturated aqueous salt solution to remove
dimethylformamide (DMF) and isolation of TGS-6-acetate in a pure fraction
which can be subjected to deacylation at alkaline pH to form TGS.

French Abstract

La présente invention concerne un processus d'extraction de 6- acyle - 4,1', 6' trichlorogalactosaccharose, abrégé en ester TGS-6 d'un flux de processus contenant un ou plusieurs esters TGS-6 et des impuretés comprenant DMF, nécessitant l'élimination du DMF. Ce processus comprend la neutralisation de ce flux de processus, le réglage du pH ensuite au côté acide, de préférence entre 5 et 7, suivi de l'extraction avec un solvant organique non miscible ou partiellement miscible, éventuellement la concentration de l'extrait de solvant organique, l'extraction des extraits de solvant organique avec une solution de sel aqueuse saturée destinée à éliminer le diméthylformamide (DMF) et l'isolation d'acétate TGS-6 dans une fraction pure qui peut être soumise à une désacylation à un pH alcalin pour former le TGS.

Claims

CLAIMS
1. A process of production of 1'-6'-Dichloro-1'-6'-DIDEOXY-.beta.-
Fructofuranasyl-4-chloro-4-deoxy-galactopyranoside abbreviated
as TGS, or 6- acyl - 4,1', 6' trichlorogalactosucrose abbreviated as
TGS-6-ester comprising a process stream containing one or more
of TGS-6-ester, DMF, one or more of an inorganic salt, one or
more of an organic salt, one or more of a caramelization product,
one or more of an enzyme and the like, wherein isolation of TGS-
6-ester is achieved comprising one or more of a step of:
a. adjustment of pH of the said process stream after
neutralization to acidic side, preferably between 5 to 7,
b. extraction of the process stream of step (a.) of this claim with
a partially miscible or immiscible organic solvent comprising
one or more of ethyl acetate, butyl acetate, methyl ethyl
ketone, dichloromethane, toluene, cyclohexane, chloroform,
and the like,
c. optional concentration of the organic solvent extract of step
(b.) of this claim,
d. extraction, for one or more number of times, of the organic
solvent extract of step (b) or (c.) of this claim with saturated
aqueous salt solution to remove dimethylformamide (DMF)
until content of residual DMF in the said organic solvent
extract reduces appreciably, preferably to 0.5% or less,
e. subjecting the organic solvent extract at the end of step (d.)
of this claim for isolation of TGS-6-acetate, or subjecting
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TGS-6-acetate formed, after or before isolation and
purification, to deacylation at alkaline pH to form TGS.
2. A process of step I wherein
a. the ester group of the said TGS-6-ester comprises an alkyl
or an aryl group, preferably an acetate or a benzoate,
b. the said organic solvent used for extraction of the said
process stream is ethyl acetate.
3. A process of claim 1 or 2 wherein the said process stream is a
neutralized chlorination reaction mixture produced by steps
comprising:
a. preparing a Vilsmeier Reagent of general formula
HCIC=N+ R₂ ]Cl^- where R represents an alkyl
group, typically a methyl or ethyl group, by one or more of a
method of its preparation by reacting a tertiary amide,
preferably DMF, with an acid chloride or
[Bis(trichloromethyl) carbonate] (C3O3Cl6) or carbonyl
chloride (COCl2) or thionyl chloride (SOCl2) including a
method of reacting DMF with Phosphorus Pentachloride or
ethanedioyl chloride with DMF, or
b. preparing a Vilsmeier Reagent of formula
[HPOCl₂.O.C.sup+=N.sup+.R₂] Cl^- where R
represents an alkyl group, typically a methyl or ethyl group-
by one or more of a method of its preparation by reacting a
tertiary amide, preferably DMF, with phosphorus oxychloride,
c. reacting sucrose-6-ester solution, preferably a sucrose-6-
acetate or sucrose-6-benzoate solution, made preferably in
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DMF, with the said Vilsmeier reagent of the step (a.) or (b.)
of this claim,
d. heating the reaction mass to around 85°C, and maintaining
the same for a period of time, preferably for about 60
minutes,
e. then further heating to around 100°C, and maintaining the
same for a period of time, preferably for about 5 hours, and
f. then further heating to around 115°C and maintaining the
same for a period of time, preferably for around 90 minutes,
g. cooling the chlorinated mass to lower temperature,
preferably around 60°C,
h. neutralizing the said cooled chlorinated mass with an alkali,
preferably by calcium hydroxide slurry in water, to around pH
7Ø

Description

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TITLE
NOVEL METHOD OF EXTRACTION OF 6-0-PROTECTED
TRICHLOROGALAC-TOSE FROM THE CHLORINATED MASS
TECHNICAL FIELD
The present invention relates to a novel process and a novel strategy for
purification of the sucrose-6-ester free from amide such as
dimethylformamide (DMF) by direct extraction from the reaction mixture in
process for production of chlorinated compounds including sucrose, 1'-6'-
Dich(oro-1'-6'-D I D EOXY-(i-Fructofuranasyl-4-ch Ioro-4-deoxy-
galactopyranoside.
BACKGROUND OF THE INVENTION
Prior art literature describes the synthetic scheme to produce the 1'-6'-
Dichloro-1'-6'-DI DEOXY-P-Fructofuranasyl-4-chloro-4-deoxy-
galactopyranoside i.e. 4,1', 6' trichlorogalactosucrose (abbreviated as
TGS), starting from sucrose. In one of the embodiments one could protect
the 6t" position of the sucrose molecule before submitting it to the
chlorination reaction. Chlorination of the sucrose-6-acetate, or any other
equivalent sucrose-6-ester, could be carried out using any of the
conventional Vilsmeier reagents prepared from phosphorus oxychloride,
phosphorus pentachloride, phosgene or [Bis(trichioromethyl) carbonate]
and solvents like DMF or dimethylacetamide. The difficulty in these
reactions is the isolation of the product in the protected or deprotected
form free from the solvent such as DMF used during the reaction. Various
methods are reported in the patent literature wherein the reaction mixture
is first quenched in an aqueous alkali solution, which could be either
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subjected to steam stripping to remove only the DMF (Navia et al US
patent nos. 5530106 and 5498709) or by removing all the water and the
solvent in a suitable drier [Ratnam et al (2005)a (WO/2005/090374 i.e.
PCT/IN2004/000142 and Ratnam et al (2005)b (WO/2005/090376) i.e.
PCT/IN20041000064). Both the methods have one drawback that during
the de-protection process where the pH of the quenched mass goes up to
9 to 11, there is considerable loss in the DMF. Also if the DMF is not
totally removed from the reaction mass it is carried over till the
crystallization stage and hinders the crystallization process.
The present invention relates to a novel process and a novel strategy for
isolation of the 6-protected trichlorogalactosucrose derivatives from the
reaction mixtures obtained from the chlorination of the 6-acyl sucrose. The
acyl group could be an aromatic acyl group like benzoyl, substituted
aromatic acyl group such as paramethoxy benzoyl group or alkyl acyl
group namely acetyl group. The 6-protected-trichlorogalactosucrose
derivative could be deprotected by conventional alkaline hydrolysis to
produce the desired trichlorogalactosucrose.
SUMMARY OF THE INVENTION
One embodiment of this invention relates to protecting DMF as well as
TGS-6-ester from destruction by adjusting the pH of the neutralized
chlorinated reaction mixture to pH 5 to 7, then extracting the same by
immiscible or partially immiscible organic solvents, washing the organic
solvent extract with saturated aqueous salt solution to achieve removal of
DMF and recovery of the extracted organic ingredients from the organic
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solvent extract by applying appropriate method of purification including but
not limited to solvent extraction, column chromatography and the like.
The TGS-6-ester isolated either in crude or pure form is de-esterified at
alkaline pH and TGS formed is isolated by applying one or more of a
purification process.
DETAILED DESCRIPTION OF THE INVENTION
In the present embodiment a process has been developed wherein after
the chlorination reaction the pH of reaction mass is adjusted to about 5 to
7 by hydroxides or carbonates of alkali, alkaline earth metals or even with
alkoxides of alkali or alkaline earth metals. The neutralized mass is
analyzed by TLC and it was seen that there was practically no
deacetylation observed from 6-acetyl TGS (TGS-6-acetate) to TGS. The
mass is then extracted with water immiscible or sparingly miscible
solvents such as ethyl acetate, methyl ethyl ketone, dichloromethane, etc.
All the 6-acyl trichlorogalactosucrose (TGS-6-ester) along with other
chlorinated sucrose derivatives comes into the organic solvent layer.
The organic extract is concentrated to 50 % of its initial volume and is
washed with saturated sodium chloride aqueous solution in order to
remove DMF extracted in the organic layer. The ratio of saturated sodium
chloride solution to organic extract is maintained between 1:5 to 1:7 The
washing was repeated for 5 to 10 cycles It has been seen that the DMF,
which is more water soluble, is retained back into the aqueous layer. Thus
this methodology also gives an innovative process to remove the DMF
from the reaction mixture, which is rather difficult to get rid off.
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The crude TGS-6-acetate could be isolated from ethyl acetate extract. It
is then purified by either extractive purification using solvents or purifying
the product by column chromatography using silanized silica gel. The
purified could be isolated and deactylated either in an aqueous alkaline
solution or in alcoholic alkoxide solution to give the desired
trichlorogalactosucrose.
In an another strategy after the solvent extraction of the neutralized
reaction mass, concentration and saturated sodium chloride washings, the
impure TGS-6-ester could be deacetylated first to afford the crude
trichlorogalactosucrose which is subsequently purified by either extractive
purification method or by column chromatography using silanized silica
gel.
Once the pure TGS is obtained from either extractive or chromatographic
purification, it is crystallized by using solvent mixtures like ethyl acetate
/
dichloromethane, methanol / ethyl acetate, butyl acetate /
dichloromethane or methanol / butyl acetate.
The examples given below are only illustrations of preferred embodiment
of this invention. They shall in no way be construed to limit the scope of
the invention by the actual chemicals used, by the actual reaction
conditions used and the like. This invention is applicable to one or more
of a process of production of TGS-6-acetate or TGS wherein DMF is a
component of the process stream / Reaction Mixture and is required to
be removed for making next process step possible more efficiently. Any
adaptation or modification of the embodiments described here or new
embodiments that are within the scope of the claims, that are obvious to
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a person skilled in the art, are considered as within the scope of this
specification. Similarly, any mention of singular is also meant to cover
its pleural also unless the context does not permit so. If the said singular
word refers to a generic term / name, it also encompasses ail the
specific examples of that kind, uniess the context does not permit so.
Thus, "a solvent" covers use of all known solvents, of one or more of
them, either singly, or in combination as a mixture or as used
successively and "a process of purification" encompasses one or more
or all the known processes applicable in the context.
Further, mention of any ester group in general, including "acyl" or in
specific including "acetyl" or "acetate" shafl be construed to include every
chemical equivalent to that group.
Example 1
Tertiary amide removal from extracted neutralized mass by NaCI
washings and subsequent purification by extractive purification
80 kg of sucrose-6-acetate was chlorinated by the Vilsmeier reagent
generated by PC15 (252.8 kg) and DMF (480 kg). After chlorination, the
reaction mass was neutralized in water and calcium hydroxide slurry was
used for adjusting the pH to 6.8. The total volume after neutralization was
3500 L. After neutralization the pH was then adjusted to 5.0 using dilute
HCI.
The neutralized mass was filtered through the filter press to remove
extraneous solids in the solution. Then the solution was subjected to
Packed column Liquid-Liquid extraction using 1:3.5 times of ethyl acetate.
The layers were separated and the respective layers were analyzed for
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TGS-6-acetate content by HPLC and DMF content by GC. It was found
that 93% of the 6-0-acetyl TGS was extracted into the organic layer and
DMF content was found to be 1.87%.
The organic layer was then concentrated to 50% and was treated with
1:0.1 times of saturated NaCI solution. The layers were separated and
five such washings were carried out. The DMF in the extract was reduced
to less than 0.5%. The organic layer was then further concentrated for
complete removal of ethyl acetate.
The syrup obtained was diluted to 1:2 times with water and then the pH
] 0 was adjusted to 9.0 using sodium hydroxide. The Deacetylation was
monitored by TLC and after stirring for 4-5 hrs, the deacetylation was
completed.
.The mass was filtered and neutralized with 30% Hydrochloric acid to a pH
of 7.0 - 7.5.
The deacetylated aqueous layer was taken for extractive purification for
removal of polar and non polar impurities. Partial extraction of the
neutralized mass was performed with 1: 0.25 v/v of 1:1 mixture of ethyl
acetate and cyclohexane so as to remove the majority of the non-polar
impurities. The aqueous layer was saturated with sodium chloride and the
TGS was extracted back in to ethyl acetate.
The ethyl acetate extract was concentrated under vacuum to thick syrupy
mass to which three times its volume of methanol was added.. Then the
TGS was precipitated by addition of 1:3 times of ethyl acetate and slow
removal of inethanoi by distillation. The crystallized product was 98.9%
pure and the yield obtained was 45% from the chlorination stage.
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Example 2
Tertiary amide removal from extracted neutralized mass by NaCI
washings and subsequent. purification by column chromatography
80 kg of sucrose-6-acetate was chlorinated by the Vilsmeier reagent
generated by PCI5. (252.8 kg) and DMF (480 kg). After chlorination, the
reaction mass was neutralized using 30% sodium hydroxide solution and
then the pH was again brought back to 5.0 by addition of dilute HCI. The
total volume of the filtered solution was found to be 3200L. Then the
solution was filtered to remove extraneous solids and was subjected to
Packed column Liquid-Liquid extraction using 1:3.5 times of ethyl acetate.
The organic layer was then concentrated to 50% and was treated with
1:0.1 times of saturated NaCI solution. The layers were separated and
five such washings were carried out. The DMF in the extract was reduced
to less than 0.5%. The organic layer was then further concentrated for
complete removal of ethyl acetate.
The aqueous concentrate syrup obtained was loaded on to a SS column
packed with Silanized hydrophobic silica. The quantity of silanized silica
gel taken was 10 times the quantity of the aqueous concentrate taken for
separation. The mobile phase used to separate the TGS from other
chlorinated sucrose derivatives was aqueous buffer at pH 11Ø
The pure product fractions collected from the column chromatographic
process were pooled together and concentrated by reverse osmosis
membrane system up to a level of 30% concentration of TGS solution.
Then the syrupy solution was extracted into ethyl acetate and was
subjected to vacuum concentration and crystallization.
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